Cécile Mclaughlin¹

Petra Pelletier¹٫²

Magali Boespflug

Storytelling of a Virus: A Focus on COVID-19 Narratives of Older Adults

Keywords: COVID-19, virus, older adults, storytelling, narratives, meaning, emotions, spatio-temporal mapping

The global COVID-19 Coronavirus outbreak overwhelmed the world in 2020. The unprecedent pandemic situation, elicited by the invisible virus SARS-CoV-2, shattered people's usual benchmarks and representations of reality. Storytelling proliferates in times of crisis because this universal phenomenon allows people to structure the shapeless reality via meaning-making processes, and therefore to cope with the collective upheaval that represents the COVID-19 outbreak. The current research aims to investigate the storytelling underpinning the social construction of the invisible virus, conveyed by written and oral narratives of older adults. The automatized qualitative data analyses of older adults' written narratives (N = 144) demonstrated that the virus represents serious danger of sickness which arouses negative emotional reactions and the duality of life and death. The analyses of older adults' oral narratives (N = 26) demonstrated that their storytelling tends to anchor the biological functioning of the virus, which remains a mystery and a source of various fears, fantasies and fascinations. Furthermore, the "war metaphor" and martial rhetoric that emerged in the storytelling of older adults indicate a shared pool of knowledge that resonates in line with the COVID-19 mass media and political storytelling in France. Indeed, older adults' storytelling is anchored within specific spatio-temporal dimensions, as every extreme situation occurs within a particular time and space. Thus, the storytelling of a virus, that should be apprehended as a journey of meaning, demonstrates a hidden coherence and a collectively shared base of COVID-19 narratives.

INTRODUCTION

The global COVID-19 Coronavirus pandemic that overwhelmed the world in 2020 represents one of the major largescale societal threats of the 21 st century. Such an unprecedent pandemic situation has shattered people's usual benchmarks and representations of reality. The invisible and intangible SARS-CoV-2 virus that is at the origin of COVID-19 Coronavirus disease became an enemy we have to fight with at the individual and collective levels. The invisible virus remains constantly an object of storytelling that allows people to elaborate meaning and to construct the representation of this invisible enemy [START_REF] Pelletier | COVID-19: From Biological Reality to the Social Construction of a Virus[END_REF]. Indeed, meaning-making and social construction processes help people to achieve goals and overcome obstacles in order to cope with the psychologically challenging situation that represents the global COVID-19 breakdown [START_REF] De | From shattered goals to meaning in life: life crafting in times of the COVID-19 pandemic[END_REF]. Further, various forms of short-term storytelling allow people to decrease the overall feeling of anxiety and uncertainty [START_REF] Rosnow | Inside rumor: A personal journey[END_REF] in order to cope with threatening situations [START_REF] Difonzo | Rumor psychology: Social and organizational approaches[END_REF].

Storytelling as a Universal Activity

Storytelling represents a universal activity that has a central role in the transmission of memories and various cultural elements between individuals [START_REF] Brown | Human universals[END_REF]. The interactive conversational activity between individuals that drives the transmission of relevant information by various narratives has also a central role in meaning-making of uncertain, novel and dangerous situations [START_REF] Boyd | A different kind of animal[END_REF]. Indeed, narratives are complex cognitive processes that allow to acquire survival relevant information and that are consistent across different cultures [START_REF] Sugiyama | Food, foragers, and folklore: The role of narrative in human subsistence[END_REF][START_REF] Scalise Sugiyama | Oral storytelling as of pedagogy in forager societies[END_REF]. Therefore, storytelling takes important part in the context of the COVID-19 Coronavirus pandemic that is conveyed by mass media, authorities and interpersonal conversations. Storytelling has important function in people's adaptation to the extraordinary situation by contracting its meaning and sharing feelings that contribute to overcome the collective trauma [START_REF] Di Napoli | Italian Community Psychology in the COVID-19 Pandemic: Shared Feelings and Thoughts in the Storytelling of University Students[END_REF][START_REF] Pelletier | Meaning-Making and Rumour-Mongering in the Shadow of Terrorism: The Case of the Charlie Hebdo Attack in Paris[END_REF]. According to some scholars, storytelling has important adaptive function primarily as a collective meaning-making in short-term daily situations, such as various gossips, rumors, legends and conspiracy theories, and also over long-term periods, such as various cultural narratives that are transmitted over generations and anchored in collective history [START_REF] Bietti | Storytelling as adaptive collective sensemaking[END_REF].

Indeed, storytelling has several prominent functions for human beings. Firstly, individuals transmit narratives to provide audiences with relevant information that might be particularly persuasive and that allow the audience to construct representations of the unknown object or situation [START_REF] Brown | Human universals[END_REF][START_REF] Jodelet | Uses and misuses of threats in the public sphere[END_REF][START_REF] Moscovici | La psychanalyse, son image et son publique[END_REF]. Although, narratives are also used by storytellers to manipulate the audience's representations about the physical and/or social environment to fit his or her fitness-enhancing aims [START_REF] Scalise Sugiyama | On the origins of Narrative: Storyteller Bias as a Fitness-Enhancing Strategy[END_REF][START_REF] Sugiyama | Food, foragers, and folklore: The role of narrative in human subsistence[END_REF]. Thus, private and institutional storytelling is highly transformative and powerful process of transmission and co-creation of common reality [START_REF] Barkow | Are the new mass media subverting cultural transmission?[END_REF]. Secondly, storytelling has important evolutionary function which is to transmit a survival-relevant information. Thus, some narratives allow group members to avoid physical and social dangers and to approach benefits in order to ensure their survival [START_REF] Boyd | A different kind of animal[END_REF][START_REF] Sugiyama | Food, foragers, and folklore: The role of narrative in human subsistence[END_REF][START_REF] Scalise Sugiyama | Oral storytelling as of pedagogy in forager societies[END_REF]. Thirdly, one of the most important functions of narratives is the facilitation of social cohesion between individuals. In particular, narratives tend to create and strengthen social bonds between individuals, thereby facilitating and fostering social cohesion and cooperation that is primordial for species' survival [START_REF] Bowles | A Cooperative Species: Human Reciprocity and Its Evolution[END_REF][START_REF] Mellmann | Is Storytelling a biological adaptation?[END_REF].

Storytelling in Times of Crisis

Storytelling is proliferating in crises that are inherent to the human condition. Since the dawn of time, various forms of storytelling proliferate in the context of dangerous, threatening and unusual situations, such as wars, riots or natural and man-made disasters [START_REF] Allport | The psychology of rumor[END_REF][START_REF] Bhavnani | Rumor dynamics in ethnic violence[END_REF][START_REF] Knapp | A psychology of rumor[END_REF][START_REF] Prasad | The psychology of rumor: A study relating to the great Indian earthquake of 1934[END_REF][START_REF] Rouquette | La théorie des rumeurs et théorie des problèmes[END_REF][START_REF] Roux-Dufort | Rumors and crises: A case study in the banking industry[END_REF]. Indeed, literary studies have paid great attention to storytelling as a fictional form of a story. In particular, Marc Marti [START_REF] Marti | Le récit : de l'objet littéraire au discours scientifique[END_REF] provides an enlightening synthesis on the evolution of various theoretical approaches. Marti's [START_REF] Marti | Le récit : de l'objet littéraire au discours scientifique[END_REF] seminal work identifies four main approaches. Firstly, the Structuralist approach, analyzes the story from the logic of an action, by proposing a proper grammar of the story: one event leads to another, in a causal logic of an intrigue. Secondly, the Genettian approach distinguishes history (cf., the statement) and the discourse (cf., the way of telling the event). The third approach presents the story as a space presenting incompleteness that the reader will fill in with his or her own subjectivity. This approach has been defended in particular by writers, such as Italian writer and semiotician Umberto Eco in his emblematic work Lector in Fabula [START_REF] Eco | Lector in Fabula[END_REF]. Finally, the fourth approach positions the story as a product of a social and cultural context. Thus, the production of a story is intrinsically related to a particular situation that will be either cultural or generic, depending on a type of the story.

Actually, the theoretical approaches concerning the story abound and very often confine the story to a fiction. Although, the recent fundamental and applied research highlights the contamination of the concept of a story in other spheres than literary and analyze what is currently agreed to be named as "storytelling". Thus, the art of telling stories and related theoretical approaches is spreading across various fields, such as political communication and even marketing, notably with the narrative approach to branding [START_REF] Anderson | Storytelling[END_REF]. Since the 1990s, storytelling seemed to invade multiple fields, such as law, marketing, business management, politics, therapy, etc. We are witnessing a veritable "narrative revolution" [START_REF] Marti | Le récit : de l'objet littéraire au discours scientifique[END_REF], according to some scholars, we are at the entry of the "narrative age" [START_REF] Van Laer | The Extended Transportation-Imagery Model: A Meta-Analysis of the Antecedents and Consequences of Consumers' Narrative Transportation[END_REF] which has as many followers as detractors [START_REF] Salmon | Looking back on narrative research: An exchange[END_REF].

Indeed, the storytelling approach is constructed around antagonistic viewpoints. According to the very critical approach of Salmon [START_REF] Salmon | Storytelling : la machine à fabriquer des histoires et à formater les esprits[END_REF], the use of storytelling in politics tilts politics into the field of the emotional, thus deactivating the reflexive logic of citizens. Although, such a justified critical reading obscures an essential fact, which the French philosopher, literary critic and semiologist, Roland Barthes largely defends: a story, a narration is a universal device that constructs meaning. Every narrative is the bearer of a value, unifying narratives are carriers of collective values. Therefore, "the narrative is present at all times, in all places, in all societies; the history of the narrative begins with the history of mankind; there does not exist, and never have existed a people without narratives; all classes, all social groups have their narratives and very often the taste for these narratives is shared by men of different, even opposing cultures. The narrative scores division into categories of good and bad literature: transcending national, historical, cultural barriers, the narrative is there where life is" [START_REF] Barthes | Introduction to the structural analysis of the narrative[END_REF].

Therefore, the universal phenomenon of storytelling makes possible to structure shapeless worlds, to give meaning, and participates in a better understanding of the world. As we know, the sanitary crisis due to the presence of the invisible COVID-19 virus has completely shattered our lifestyles, our spatio-temporal benchmarks, our relationship to others. While facing such upheavals, a feeling of incomprehension, even a feeling of chaos, has greatly developed in the population. In a crisis, "people suddenly and deeply feel that the universe is no longer a rational, orderly system" [START_REF] Weick | The collapse of Sense making in Organizations: The Mann Gulch Disaster[END_REF]. While facing such an upheaval, two scenarios for returning to balance are possible: the first one consists of activating scientific knowledge in an attempt to find evidence and facts that will render possible to understand the situation; and or the second one that consists in activating the structuring function of narratives that allow to seize a priori insane events [START_REF] Fisher | Human Communication as Narration: Toward a Philosophy of Reason, Value and Action[END_REF].

The trial and error of science is forced to react immediately to the COVID-19 Coronavirus outbreak elicited by the SARS-CoV-2 virus, coupled with the mass media cacophony related to the diffusion of simplified scientific discourses. These circumstances leave a large place for the narration and narrativization of the crisis by the civilian populations, but also by politicians and certain scientists themselves. This profusion of storytelling has necessarily an impact on our understandings of the world; these narratives sometimes contradict each other, but are also woven together, therefore constructing an intertextual mode that offers sometimes even more confusing reading grid of the sanitary crisis. The purpose of these narrative production processes is not to offer a true explanation of the world, but rather to offer plausible avenues for reading the world that allow us to face chaos.

Storytelling During the COVID-19 Outbreak

Thus, since the beginning of the COVID-19 crisis, research from the field of social sciences and humanities attempt to shed light on the situation we are currently living [START_REF] Lanssens | La pandémie de Covid-19 sous le microscope des sciences sociales. Premières analyses. [The Covid-19 pandemic under the microscope of social sciences. First analyses[END_REF]. Storytelling has transformational potential that is a particularly powerful process that triggers change. Specifically, COVID-19 narratives are often spreading fear that is supposed to motive or to curb a change and that is an object of worldwide digitalization [START_REF] Essebo | Storying COVID-19: fear, digitalisation, and the transformational potential of storytelling[END_REF]. For example, Pedersen [START_REF] Pedersen | A Pandemic of Narratives[END_REF] investigated the pandemic of narratives that emerged simultaneously between the beginning and the end of the COVID-19 lockdown in Scandinavian countries. Furthermore, the political scientist Postel-Vinay [START_REF] Postel-Vinay | Les récits de l'incertitude planétaire. Discordance ou pluralism? [The stories of planetary uncertainty. Discordance or pluralism[END_REF] affirms the absolute necessity of storytelling of this chaotic event, while pointing out "the chronic deficit of European narrative power". Additionally, other research perspectives have focused on political narratives, in order to define their symbolic repertoire, such as martial rhetoric on the French side, and medical rhetoric on the Italian side [START_REF] Boussaguet | Comment mobiliser les populations ? La réponse symbolique des exécutifs français, italien et britannique[END_REF].

The aim of the current research was to investigate the storytelling underpinning the construction of representations of the invisible COVID-19 virus conveyed by written and oral narratives of older adults, in the ex-Limousin region (currently Nouvelle-Aquitaine region) in France. The storytelling produced by older adults have the particularity of not being "manufactured" consciously and in a conative logic (e.g., such as to make people join, to make vote, or to make buy) as it can be the case of political storytelling or the brand speech. The individuals' storytelling emanates spontaneously, nourished by mass media storytelling and interpersonal conversations about the COVID-19 crisis. Indeed, storytelling manifests, by its very existence, a narrative mechanism that is spontaneously activated to trigger a process of signification and meaning-making in the face of a situation that escapes us.

METHOD Participants

The current research was based on written and oral narratives produced by older participants aged 60 years and older, inhabitants of ex-Limousin region (currently Nouvelle-Aquitaine region) in France. The participants were recruited by snowball sampling procedure during the COVID-19 pandemic outbreak, during the first half of the year 2021 in France.

Gathering of Written Narratives

Specifically, the written narratives of this research were collected by an online questionnaire. The participants of the current research were inhabitants of ex-Limousin region (currently Nouvelle-Aquitaine region) in France. In particular, participants were requested to write spontaneously their most important ideas and feelings while thinking specifically about the COVID-19 virus during the COVID-19 pandemic lockdown in France. The instructions specified that their answers are anonymous and confidential and that the free association task without any constraint of production aims to investigate their perception of the COVID-19 virus. The sample of older participants (N = 144) that answered the online questionnaire was aged from 60 to 84 years (M = 70.22, SD = 5.63). The sample was composed equally of 50.00% males and 50.00% females, and 59.00% of participants declared that someone from their family or friends has been already infected with the COVID-19 Coronavirus disease. The older participants' written narratives were collected, coded and analyzed afterwards.

Gathering of Oral Narratives

Additionally, semi-directive research interviews were conducted afterwards, when the sanitary situation in France allowed to conduct face-to-face interviews. The semi-structured face-to-face interviews were conducted by three investigators with a sample of older participants (N = 26), inhabitants of ex-Limousin region (currently Nouvelle-Aquitaine region) in France, aged from 63 to 84 years. The totality of participants signed a consent to participate in the interview and an agreement to record the audio of their interview. The semi-structured research interviews were based on an interview guide, composed of several main parts, that aimed to gather laypeople's feelings and ideas about various aspects of the COVID-19 pandemic. Specifically, the interview guide aimed to investigate the participants' knowledge, representations and emotions elicited by the COVID-19 virus and the specificities of the COVID-19, compared to other viruses. Moreover, the interview guide aimed to explore how participants were living the COVID-19 pandemic lockdown and the overall impact of the COVID-19 pandemic on various aspects of their lives, and their perception of mass media and biological images of SARS-CoV-2 virus. The totality interviews were recorded and analyzed afterwards.

RESULTS

Automatized Qualitative Data Analyses of Written Narratives

The written narratives of older participants were analyzed by automatized qualitative data analyses that were conducted with the software IRaMuTeQ version 0.7 alpha 2 [START_REF] Ratinaud | IRaMuTeq version 0.7 alpha 2 2020[END_REF][START_REF] Ratinaud | IRAMUTEQ : Interface de R pour les Analyses Multidimensionnelles de Textes et de Questionnaires[END_REF]. The software IRaMuTeQ, which is an interface of the quantitative software R version 4.1.0.for Windows, allows to conduct multidimensional analyses of text datasets. The principle of these multidimensional analyses is based on similar principles to social network analyses that allow to quantify and represent existing relationships between specific research units [START_REF] Wasserman | Social Network Analysis: Methods and Applications[END_REF].

The main analysis of written narratives of older participants is represented in Figure 1. The participants (N = 144) produced 694 text forms that are structured in several specific clusters, represented in different colors in Figure 1. The Figure 1 represents the graph of similarity analysis with the size of verbatims proportional to their frequency in the text dataset. The 694 text forms are structured in 9 main clusters, where the main cluster, represented in the dark blue color in the center of the graph is structured around the noun "Sickness" (maladie) which is "serious" (grave), and to which "vaccination" (vaccination) offers a solution. Older participants have apprehended the virus as danger that might cause important "sequels" (séquelles) to their "health" (santé) that make important to respect the "restrictions" (restrictions) imposed by public policies, represented below in the green cluster.

Moreover, older participants expressed the values of "solidarity" (solidarité) and "freedom" (liberté) during the COVID-19 pandemic outbreak, represented in the red cluster. Further, participants expressed their worries related to the "risk" (risque) of "contamination" (contamination) during the "pandemic" (pandémie) that elicits the feeling of "stress" (stress) and "anxiety" (angoisse) and the need for "protection" (protection), represented in the light green cluster. The COVID-19 virus represents for the older participants the duality of "life" (vie) and "death" (mort), represented in the dark green cluster. Participants pointed out the "social isolation" (isolement social) as a source of "worry" (inquiétude) and also as a source of "concerns" (concerner) about the "population" (population), represented in the purple cluster.

Additionally, older participants expressed also the fact that the sanitary "containment" (confinement) that represents "danger" (danger) for family life (familial) and elicits the feeling of "solitude" (solitude) and "sadness" (tristesse), represented in the light blue cluster on the right side of the graph. Further, participants indicated that they "think" (penser) about their "loved ones" (entourage) due to the "contamination" (contamination) and about "economic consequences" (économique), and they expressed their hope that the "society" (société) will "exit" (sortie) the "crisis" (crise), represented in the brown cluster.

Crisis Storytelling: Analyses of Oral Narratives

Every story is part of a temporality and a sequencing. Crisis situations, whatever the nature of the crisis, fit into the following generic sequencing: the initial situation where everything is relatively "calm", an imbalance which acts like a temporal rupture in the routines and which makes enter the populations in a collective test, and the time after the crisis, the "world after". Within this narrative framework, one must consider the narrative sequence which concerns precisely the period of testing which makes from the populations a collective actor in a conflict with the virus. In the oral narratives of older participants, we can firstly observe a first essential point: they do not just describe the virus, as an object; they integrate the virus into a succession of events. It is not the virus that matters in the end -or by necessity, since this virus is invisible, its static description is replaced by a logic of an action, but more exactly virus' modes of action on humans. Where there is no implication of human interest (where the reported events are neither produced by agents nor undergone by anthropomorphic patients), there can be no narrative, because it is only in relation to a human project that events take on a meaning and organize themselves into a structured time series [START_REF] Bremond | La logique des possibles narratifs. [The logic of possible narratives[END_REF]. Thus, we observe in the narratives produced by older participants recurring narrative programs that focus in particular on the biological functioning of the virus:

• "It has to hold on with its peaks, it goes through the body, it goes looking for cells to feed itself, it destroys the cells, it grows bigger, it has to come out and infect other people in the clusters." (Female, 72 years) [« Il doit se cramponner avec ses pics, il passe dans l'organisme, il va chercher les cellules pour se nourrir, il détruit les cellules, il grossit, il doit ressortir et contaminer d'autres personnes dans les clusters. » (Femme, 72 ans)]

The accumulation of action verbs and their sequencing very clearly signal the temporal and action logic of the storytelling and the beginning of a plot. The plot is based on a conflicting knot: the virulence of the virus is brought to light and seems to be confronted with the force of inertia. The power of the virus is such that it does not allow its target to form adversaries who would fight against it. Thus, we subscribe, in the narratives of older participants, what Bremond [START_REF] Wasserman | Social Network Analysis: Methods and Applications[END_REF] calls the narrative logic of aggression. According to him, two sequences govern the structuring events of a narrative: the improvement to be obtained and the foreseeable degradation. It is in this first principle of dichotomous classification that he approaches the logic of aggression. The interest of this logic, is first of all, to allow a double point of view: that of the aggressor and that of the aggressed. From the perspective of the victimized, the process of aggression constitutes a peril to be avoided, setting in motion a protective process which will or will not fail. From the perspective of the virus-aggressor (the subject-virus), the goal of eliminating the adversary (the anti-subject-population) entails the damage to be inflicted, the aggressive process and the damage inflicted. In the verbatim quoted above, this is exactly what is described with the additional feeling that the sequence of the aggression is not terminative: the virus "emerges", it "infects" other people ... as in infinite. Faced with such a rapidity of the virus and the generalized uncertainty, the actants which logically should be positioned as adjuvants, no longer appear to be the authority:

• "We wanted to know if we were going to get to the end of the problem quickly, but even the doctors didn't know.

They are powerless, whether it is politics, medicine, no one knows where we are going". (Female, 72 years)

[« On aurait voulu savoir si on allait rapidement arriver au bout du problème, mais même les médecins n'en savent rien. Ils sont impuissants, que ce soit les politiques, le médical, personne ne sait où on va. » (Femme, 72 ans)]

• "In medical broadcasts, we saw them unarmed. Some have said things and they have retracted. It's unhealthy". (Female, 78 years).

[« Dans les émissions médicales, on les voyait désarmés. Y en a qui ont dit des choses et ils se sont rétractés. C'est malsain. » (Femme, 78 ans)]

Thus, the adversaries appear disarmed and no reinforcement seems operational. A fight with unequal arms seems to animate the very heart of the stories produced by the older participants. While the subject, anti-subject, potential adjuvant actants are clearly identified, the question of the identity of the sponsor remains a complete mystery. Indeed, the question of the origin of the virus is at the origin of the ordeal. We are experiencing, raising questions and referring to a classic lever in narratology which is the level of a "mystery". Thus, we can identify in the following narratives elements characterizing the mystery, a mystery which is the source of all fantasies and fears.

• "I can't believe it happened like this. It comes China. We have been told about pangolin. Is this a lab leak?

There are too many people on the planet, it would be a will of the powers. A war with a virus and not with weapons." (Female, 78 years).

[« J'ai du mal à croire que ce soit venu comme ça. Ça vient de Chine. On nous a parlé de pangolin. Est-ce une fuite d'un labo ? Il y a trop de monde sur la planète, ce serait une volonté des puissances. Une guerre avec un virus et pas avec des armes. » (Femme, 78 ans)]

• "It comes from China: somebody made a mistake in the labs, he had to not speak and he is dead." (Female, 75 years).

[« Ça vient de Chine : y a quelqu'un qui a fait une erreur dans les labos, il ne fallait pas qu'il parle et il est mort.

» (Female, 75 ans)]

Is the virus of natural origin? Or was it a creation, a result of a laboratory manipulation error? Is it a bacteriological weapon used by China to go to war against the Western powers? Is it a punitive reaction from the planet which wants to put an end to disrespectful human behavior and overpopulation?

In all these questions that have been raised by older adults, we try to understand the origin, the root cause; the actant who wishes and triggers the quest for the subject -here the subject-virus -because there is a problem to be solved: the problem identified by older adults is either ecological or political. Once again, in the production and genesis of the story, we observe a shift in the process of meaning. With the stabilized characterization of the invisible, unpredictable virus escaping older citizens, we move back up the chain trying to grasp the force that is at the origin of its existence, by tapping into universes of stable references. Thus, depending on the positioning of the discourse with regard to the determination of this force, we find ourselves faced with different types of narratives which implement sets of tensions which summon various actants: tensions; tensions between countries and world powers; tensions between planet and humankind.

Therefore, the narratives produced by older participants place the virus in a space of mysterious and sometimes paradoxical tensions: on the one hand, it is scary but on the other, we want to know. Fear and fascination intertwine in a classic process during the COVID-19 pandemic. On one hand, the virus is what we would like to be able to escape, and on the other hand, the virus arouses a form of desire and transforms, through the logic of verbalization, into a character endowed with intentionality and act of performing:

• "He is clever, he goes fast, "he knows where he strikes", he is an "octopus which suffocates with its tentacles" (Female, 67 years); "clever, when he cannot achieve his goals, he mutates" (Female, 72 years); who "enters quietly, by breaking and entering" (Male, 78 years).

[« Il est malin, il va vite, « il sait où il frappe », il est une « pieuvre qui étouffe avec ses tentacules » (Femme, 67 ans) ;« malin, quand il ne peut pas arriver à ses fins, il mute. » (Femme, 72 ans) ; qui « entre sans faire de bruit, par effraction » (Homme, 78 ans)].

Finally, the accounts of the older participants call forth imaginaries that are directly linked to the characteristics of the crisis: an invisible enemy that is spreading, circulating among the population, with a willingness of contagion. It is a contagious disease "vector of the dissolution of certain social forms, an agent of decomposition and re-composition" [START_REF] Fabre | Épidémies et Contagions : L'imaginaire du mal en Occident[END_REF]. Thus, in the participants' storytelling, a profound dialectical process operates: between order and disorder, a dialectic which characterizes the imaginations of contagious disease. We note this dialectical process in particular, in the verbatims that are based on the planet-humankind tensions with the idea of a punitive sanction for humankind, as a necessary act of regulation that is going through a phase of chaos. This dialectic that is specific to epidemics is manifested in the narratives by metaphorical networks and precisely by the "war metaphor". Indeed, the narrative logic of the crisis storytelling hinges on an intrigue and a conflict between different actants. These narratives translate, from a figurative point of view, into the production, in the discourse of semantic fields, that are directly related to martial rhetoric. Older adults are storytelling the COVID-19 crisis, as they would tell a story of a war. The influence of martial rhetoric widely used by the French mass media and political authorities is certainly not for nothing in this convocation of imaginary warriors [START_REF] Postel-Vinay | Les récits de l'incertitude planétaire. Discordance ou pluralism? [The stories of planetary uncertainty. Discordance or pluralism[END_REF]. During the semi-structured research interviews, the researchers wanted to confront older participants to the image of the COVID-19 virus that mass media disseminate. The mass media image of a round virus surrounded by peaks generates fear and spreads the idea of dangerousness, in particular through the symbolism of a war:

• "It makes you think of a missile, it's the bomb that will explode, like in the 7th company, it's scary" (Female,67 years).

[« ça fait penser à un missile, c'est la bombe qui va exploser, comme dans la 7ème compagnie, ça fait peur » (Femme, 67 ans)]

• "An underwater mine. When you touch it, it explodes "(Male, 78 years).

[« Une mine sous-marine. Quand on la touche, ça explose. (Homme, 78 years)]

Storytelling Takes Place in Time and Space

The results of the similarity analysis, presented above in Figure 1, indicate different clusters of heterogeneous narrative categories: freedom, protection, death, health, disease, public action, confinement, future life (economic, social and health). Specifically, the multivariate technique of factorial correspondence analysis, represented above in Table 1, demonstrated three broad categories that will be analyzes on a basis of two specific axes: intrinsic (disease) and extrinsic (fear speech); personal consequences (illness, cases, risks, etc.) and social consequences (isolation, health policies, etc.).

The qualitative analysis of older participants' storytelling indicates a logic of an action, temporal aspects in the construction of the COVID-19 storytelling (cf., origin, causes, consequences for me and others), and symbolic aspects that are present in the narrative construction (i.e., martial, geopolitical, animal, historical, spiritual references as well as the scapegoat or the snake…) in order to give a base, and therefore a meaning to this invisible and intangible viral enemy. The narratives present also intrinsic and extrinsic aspects, a self-centered vision of the pandemic or rather a collective vision. Thus, the construction of the older adults' storytelling seems to be developed in line with spatial and temporal dimensions, which leads us to propose the following spatio-temporal mapping and therefore the typology of the COVID-19 discourse. Furthermore, the COVID-19 crisis storytelling is fed and emerges from the human beings' emotions. Ultimately, these different analyses highlight the temporal dimension and the individual versus collective aspects, represented in Figure 2.

In fact, as argued by Lewin [43] every change presents three main stages: (1) unfreezing, (2) change process and (3) refreezing, and every social group or society evolves at different rates. But these past 20 years demonstrated that the original 3-Stage Model has attracted major criticisms. The original model tends to ignore organizational power and politics, as such the model was essentially top-down and the original model operates mainly in a stable environment [START_REF] Burnes | Managing change: A strategic approach to organisational dynamics[END_REF]. Although, rhythms of adaptation are more variable for every single individual in times of crisis. These rhythms depend rather on the seven phases of concerns [START_REF] Burnes | Managing change: A strategic approach to organisational dynamics[END_REF] related to the sudden and unpredictable change generated by the COVID-19 pandemic. Therefore, temporality represents a main dimension that allows to analyse the COVID-19 crisis related change.

Foremost, first phases of concerns [START_REF] Bareil | Modèle diagnostique des phases de préoccupations : une approche utile dans la gestion du changement. [Diagnostic Model of the Concerns Phases: A Useful Approach in Managing Change[END_REF] are centred on the individual (i.e., personal security, questioning the seriousness of government decisions and seeking the COVID-19 related information), when this change takes place, the individual can open up to a more collective view of the change elicited by the COVID-19 pandemic. Additionally, the analysis of emotions that are activated by older participants' storytelling shows an individual predominance that is marked by withdraws into oneself, into his or her fears and anxiety, that are afterwards projected towards the collective predominance, expressing primarily sadness and anger. Therefore, the storytelling dimension is also spatial, referring to the social space: self towards others (individual predominance versus collective predominance). The Figure 2, represented below, synthesizes these two main storytelling dimensions with the "Spatio-Temporal Mapping of COVID-19 Narratives of Older Adults".

DISCUSSION & CONCLUSION

The storytelling represents a universal activity of meaning-making that allows people to construct representations of the unprecedent situation, and therefore to cope with the collective upheaval that represents the COVID-19 outbreak. Indeed, human beings strive towards spontaneous construction of meaning because "our minds protest against chaos" [START_REF] Allport | The psychology of rumor[END_REF]. Thus, the aim of the current research was to investigate the storytelling underpinning the construction of representations of the invisible COVID-19 virus, conveyed by written and oral narratives of older adults, in the ex-Limousin region (currently Nouvelle-Aquitaine) in France. The current research deployed different methods in order to offer a thorough investigation of older adults' storytelling. The main results demonstrate that older adults 'storytelling is anchored within specific spatiotemporal dimensions, since every extreme situation occurs within a particular time and space [START_REF] Weick | The collapse of Sense making in Organizations: The Mann Gulch Disaster[END_REF][START_REF] Weick | Managing the unexpected: Sustained performance in a complex world[END_REF]. Furthermore, the multidimensional analysis of participants' written narratives demonstrated that older adults tend to apprehend the invisible virus in terms of serious sickness that has individual and collective consequences on people's lives. Also, the COVID-19 virus represents for older adults an object of duality that is situated between life and death. Indeed, the invisible virus SARS-CoV-2 that represents a major threat to people's life tends to activate thoughts of death and mortality, and related humans' defenses that drive the need to construct a meaning, personal values, and the need for social relationships [START_REF] Pyszczynski | Terror management theory and the COVID-19 pandemic[END_REF]. Obviously, the invisible virus elicits negative emotional reactions, such as anxiety, sadness and stress that drive people's attitudes and behaviors during the COVID-19 crisis situation. Although, the older adults' storytelling is also embedded in a collective memory that is the reconstruction of the past within a specific social and temporal context [START_REF] Halbwachs | Les cadres sociaux de la mémoire[END_REF]. Indeed, the "war metaphor" and martial rhetoric that emerged in the storytelling of older adults indicate a shared pool of knowledge that resonates in line with the COVID-19 mass media and political storytelling in France.

Therefore, the storytelling appears as a cultural form that people activate in order to grasp an object, a context, an event, the contours of which they seek to limit, to put into shape. Indeed, the narrativization of an event is a good lever for initiating the process of signification, for structuring, through the temporal and causal arrangements, a situation which at first glance escapes common understandings. Similarly, to the logic of journalism that aims to seize an object in order to relate it, storytelling aims to structure the shapeless COVID-19 reality. Although, to limit and to put into shape is also the logic of any thought process, named "effort after meaning" [START_REF] Bartlett | Remembering[END_REF], while confronted with an object that tends to escape the common cognitive schemes of understanding. The storytelling that should be apprehended as a journey of meaning, constructed through analysis, allows us to understand that beyond the abundant and dissociating narratives, whether they are conveyed by mass media or political communications, or a simple product of interpersonal conversations, there is a hidden coherence and shared, deep and stable knowledge base.

Figure 1 :

 1 Figure 1: Graph of Similarity Analysis of Older Adults' Written Narratives Represented with Specific Color per Cluster. The multidimensional analysis has been completed by the multivariate technique of factorial correspondence analysis that demonstrates three main discourse classes. The detailed results are represented in Table 1. These results indicate that Class 1 (34.55%) refers primarily to personal consequences of the COVID-19 virus on participants' life; Class 2 (30.91%) refers mainly to social consequences of the COVID-19 virus; and Class 3 (34.55%) indicates older participants' fear of the serious sickness elicited by the COVID-19 virus.

Figure 2 :

 2 Figure 2: Spatio-Temporal Mapping of COVID-19 Narratives of Older Adults

Table 1 :

 1 Classes obtained with the Multivariate Technique of Factorial Correspondence Analysis of Older Adults'

		Written Narratives
	Classes	Main Verbatims	p
		Life (Vie)	<0.0001
		Vaccine (Vaccin)	0.00035
	Class 1	Mask (Masque)	0.00124
	34.55%	Go (Aller)	0.00124
		Feel (Sentir)	0.01420
		To lack (Manquer)	0.02497
		Social (Social)	0.02497

Acknowledgements

This research was conducted as a part of the research program CoviZion "Storytelling of a Virus: Representations, Images and Imaginations. Represent and Understand in Order to Act Better and Live with it", funded by AMI FLASH Research and Innovations COVID of Nouvelle-Aquitaine, France.

The authors declare to have no financial or non-financial conflicts of interest with regard to this research.


Rémi Busselez

Ronan Lefort

Mohammed Guendouz

Bernhard Frick

Odile Merdrignac-Conanec

Denis Morineau
email: denis.morineau@uniuv-rennes1.fr

Molecular dynamics of glycerol and glycerol-trehalose bioprotectant solutions nanoconfined in porous silicon

come     Molecular dynamics of glycerol and glycerol-trehalose bioprotectant solutions nanoconfined in porous silicon.

Introduction

The glass transition and the molecular dynamics of fluids can be markedly different under confinement in mesoporous materials. Although this fact is revealed by a large amount of experimental and numerical data, 1,2 these data also reveal numerous contradictory expressions of nanoconfinement effects. For instance the glass transition temperature (T g ) usually decreases in confinement but may also remains constant or increases. 1,3,4,5,6,7,8 Non-monotonic variations of T g as a function of the pore size of a series of mesostructured porous silicates have also been reported. 9,10 In some cases, confinement also leads to the observation of two distinct glass transition temperatures. 11,12,13,14 Although no conciliating viewpoint on these results has been reached yet, it is recognized that the nature of the confining medium, of the interaction between fluid and matrix as well as intermolecular interactions are essential issues.

Key-parameters of interest include the topology of the confinement in terms of pore connectivity and dimensionality (isolated channels, spherical cavities, fractal or bi-continuous disordered structures), the nature of the porous matrix (smooth or hard confinement), 15 the chemical nature (hydrophilic, silanized) and the shape of the interface (rough or smooth). 1,2 Beyond the simple determination of the glass transition temperature, a variety of experimental spectroscopies (quasielastic neutron scattering, dielectric spectroscopy, depolarized dynamic light scattering) and molecular simulation techniques have been used to investigate confinement effects on the molecular dynamics and especially the structural relaxation processes related to the glass transition. 5,10,11,12,13,16,17,18,19,20,21 They provide an extended accessible timescale (from a few picoseconds to the macroscopic limit of about a thousand seconds), which allows following the signatures of confinement as a function of temperature from the liquid phase down to the glass transition. Despite the persisting disparity of the observations (slowing down or speeding up of the relaxation dynamics), these results emphasize an apparently general feature of confined fluids: nanoconfinement magnifies the non-Debye character of the structural relaxation process. This feature is commonly related to dynamical heterogeneities for bulk glass-forming system. 22 In confinement, molecular dynamics simulations provide a microscopic insight into the molecular dynamics, which allows attributing the additional broadening of the distribution of relaxation times to a spatially highly inhomogeneous dynamics in the pore. 21 Despite the number of interpretations proposed in literature, the problem of the molecular dynamics of nanoconfined fluids is still an open question. It certainly stresses the existence of many competing effects, the relative contributions of which depend on the characteristics of the system. Surface effects have been generally invoked and can be crucial according to the large surface-to-volume ratio of mesoporous materials. It is based on the introduction of a boundary condition, which is experienced by the molecules at the surface of the pore. This interfacial condition depends on the fluid-wall interaction and the roughness of the interface.

It could either concern only the population of molecules localized at the interface (two-states situation) or propagate to the inner pore via a mechanism mediated by the extension of regions of dynamically correlated molecules. 11,12,13,16,21 Another major issue concerns the thermodynamic state of the confined phase, which may differ from the bulk one in terms of structure or density. 9,23 The structure of H-bonding fluids is likely to be more sensitive to confinement since they develop interfacial and intermediate range orders. 24,25 Differences in density can be induced by surface tension and also because the timescale for density equilibration through a liquid flow within the porous material exceeds the experimental one at low temperature. 5,9,26 Finally, finite size is expected to prevent the extension of any correlation length beyond the pore size. This potential effect is pertinent to supercooled liquids since the glassy dynamics is commonly associated to the growth of nanometric cooperative rearrangement regions or frustration limited domains. 27,28 However, a definite signature of such intrinsic geometrical confinement effects seems elusive because of the complex entanglement with the above mentioned dominant effects.

Although there is still a lot of discussion even in the case of pure low-molecular weight simple glass-forming liquids, we are convinced that it is timely to extend the problem of nanoconfinement to more complex fluids. The latter are more relevant to different domains of technological or biological interest and also they can pose new questions for fundamental research. One example concerns mesogenic fluids, the phase transition and glass-like dynamics of which have been shown to be sensitive to confinement induced quenched disorder effects and low dimensionality. 29,30,31 Another example of such fluids is bioprotectant solutions, 32,33 which are used to prevent proteins and biological membranes from irreversible damage under drastic stress environmental conditions (e.g. drying or freezing conditions).

They are often binary systems with strong and selective H-bond interactions (like sugar-water or sugar-polyalcohol solutions), which can lead to an unusual behavior under nanoconfinement. For instance, concentration fluctuations can be amplified by a possible asymmetric affinity of one particular constituent with the pore surface. In the case of glassforming constituents with very different T g , the relaxation dynamics of the mixture in the liquid phase is expected to cover a very broad range of characteristic times. As an indirect sign, the scrutiny of the resulting T g of the bulk solution versus concentration can reveal its non regularity (departure from the Gordon-Taylor law). 34,35 Here again, these effects are expected to be strongly affected by nanoconfinement.

The aim of this paper is indeed to identify some generic features related to confinement and interfacial effects on the molecular dynamics of bioprotectant solutions. This investigation is performed in controlled model conditions by using porous silicon material as a confinement matrix. It has been shown to provide unique experimental conditions to study nanoconfined complex fluids due to the low dimensionality of its macroscopically oriented pores. 30 Glycerol/Trehalose binary solutions are chosen as a model bioprotective fluid. These solutions are formed with two glass-forming liquids with very different glass transition temperatures, as measured by differential scanning calorimetry for the two pure components trehalose T g =393 K 36,37 and glycerol T g =190 K. 7 The addition of 20 % (Wt) trehalose to glycerol leads to an upward shift of Tg of about 13 K, which is almost twice smaller than what is predicted by assuming a regular solution model. 34,38 Such a discrepancy probably reflects effects of non-idealities, which have been already reported for binary systems with different molecular size and specific H-bond interactions. 39,40 They have been recently

highlighted by experiments and simulations for their optimal biopreservation properties. 41,42 Incoherent quasielastic backscattering experiments are performed on fully hydrogenated pure glycerol and a glycerol-trehalose binary solution (80%:20% Wt) both in bulk and confined in nanoporous silicon layers. The effects of adding trehalose and confinement effects on the structural relaxation dynamics in the liquid state are discussed from the analysis of the dynamic structure factor. The consequences on the dynamical arrest of the relaxation dynamics on approaching the glass transition are revealed by the analysis of elastic fixed window temperature scans on cooling.

Experimental procedure

Samples

Porous silicon matrices were made from a crystalline silicon substrate using an electrochemical anodization process in a HF electrolyte solution. The conditions of this process control properties such as porosity, thickness and pore size. Anodization of heavily pdoped (100) oriented silicon leads to highly anisotropic pores running perpendicular to the surface wafer (called columnar form of the PSi). These samples were electrochemically etched with a current density of 50 mA.cm -2 in a solution composed of HF, H 2 O and ethanol (2:1:2) according to previous studies. 43 Scanning electron microscopy (SEM) measurements provide interesting information about the shape of the porosity. It forms a parallel arrangement of not-connected channels of length 200 μm as shown in Fig. 1. A noticeable feature of PSi, which is at variance to other unidirectional pores such as MCM-41 or SBA-15, is the rough dendritic structure of the inner pore surface. 44,45 The latter has been recently shown to introduce strong disorder effects, which influence phase transitions such as capillary condensation or nematic to smectic transition. 30,46 SEM has shown to provide a rather poor estimation of the pore size. It can be explained by the low spatial resolution of this technique, which is even deteriorated by the low conductivity of PSi, and by the fact that only the pore opening is checked and not the inside porous layer. Therefore, nitrogen adsorption isotherms have been preferred to characterize the pore size.

The analysis of the onset of capillary condensation in the nitrogen adsorption/desorption curves with a model based on the Kelvin equation provides an average value of the pore diameter of 8 nm, as shown in Fig. 2.

FIG. 2:

Adsorption/desorption isotherms of nitrogen at 77 K in porous silicon films.

The strongly hydrophobic character of the inner surface of freshly prepared PSi was minimized by treating the sample with hydrogen peroxide (H 2 O 2 ). H 2 O 2 leads to a slow oxidation of the proximity of the inner pore surfaces. 47 A droplet of H 2 O 2 was spread on the porous surface and the sample was placed in a vacuum chamber. Capillary impregnation of H 2 O 2 in the entire porosity was achieved under primary vacuum at 293 K. Atmospheric pressure was then restored in the chamber and the sample maintained for 15 minutes for the oxidation to proceed. PSi wafers were dried under vacuum (4. 10 -2 mbar) at 373 K for 24 h and stored in the vacuum chamber until used.

Fully hydrogenated glycerol (C 3 O 3 H 8 , 99%) and anhydrous trehalose (C 12 H 22 O 11, 99%) were purchased from Sigma-Aldrich and Merck, respectively. A glycerol-trehalose binary solution (80%:20% Wt) was prepared by adding the appropriate mass of crystalline trehalose to glycerol. The mixture was maintained in a hermetically closed flask, then heated up to 333 of full dissolution of trehalose. Just before the execution of neutron scattering experiments, pure glycerol and trehalose-glycerol were filled in PSi samples by capillary impregnation from the liquid phase in a vacuum chamber. The complete loading was achieved under vapor pressure and at a temperature of 333 K. The filled porous membranes were taken out from the vacuum chamber, the excess of liquid was removed from the wafer surface by wiping the samples with filtration papers and the samples were placed immediately in hermetically closed neutron scattering aluminum cells.

Quasielastic neutron scattering

Quasielastic neutron scattering experiments were carried out with fully hydrogenated samples using the high resolution back scattering spectrometer (BS) IN16 at the Institut Laue Langevin (Grenoble). 48 For the two molecular fluids, the contribution from the incoherent cross section corresponds to more than 93% of their total scattering cross section. It means that, after appropriate subtraction of the intensity arising from the sample environment and PSi, the contribution to the measured scattering intensity from coherent scattering can be neglected within a good approximation for the four samples. Moreover, 85% of the incoherent scattering of the glycerol-trehalose binary solution is arising from glycerol molecules. This means that despite a predominant contribution from glycerol to the incoherent scattering, results obtained for the mixture are composite functions, which reflect the dynamics of both constituents of the solution. A standard configuration of the IN16 spectrometer was chosen with Si(111) monochromator and analyzers in backscattering geometry, which corresponds to an incident wavelength of 6.271 Å and results in an energy resolution (FWHM) of 0.9 μeV.

The energy range was 15 μeV with a range of transfer of momentum Q between 0.2 Å -1 and 1.9 Å -1 .

PSi layers were placed in cylindrical aluminium cells. The selected orientation of the cell leads to a pore axis angle with respect to the incident neutron beam of about ω=45°.

Anisotropic dynamics is not expected for this system. The choice of this angle of incidence essentially guarantees that self-attenuation effects, which occur in the direction parallel to the PSi wafer surface, are significant only for an angle of diffraction of about 2θ ≈135°. Such large values are outside our range of interest. A cryofurnace was used in order to regulate the sample temperature in a range from 10 K to 350 K.

Elastic fixed window scans (EFWSs, i.e. with Doppler device stopped) were carried out in a temperature range from 10 K to 350 K. EFWSs have been performed both on cooling with typical ramps of 0.5 K.min -1 from 350 K down to 130 K and with 2 K.min -1 below. Data accumulation was performed during the continuous temperature scan integrating over intervals of 1 to 2 K. Quasielastic scattering functions S(Q,ω) were acquired at 310 K for the four different samples. The spectrometer resolution function R(Q,ω) was measured on each sample at 10 K. Standard data corrections were applied to EFWSs and scattering functions using conventional programs provided at ILL (sqw). The intensity was corrected for the contribution arising from the empty sample (empty cell and empty PSi) and thereafter normalized to the lowest temperature intensity. These background contributions appeared as purely elastic signals on IN16. There were extremely small for the bulk samples. For the confined systems, the contribution arising for the silicon wafers accounted for 25% to 35% of the maximum intensity at the highest intensity. The fitting of scattering functions S(Q,ω) in the frequency domain was carried out using the programs provided by the LLB (quensh). [START_REF] Is | Laboratory Léon Brillouin[END_REF]

Results and discussion

Molecular dynamics in the high temperature liquid phase.

Quasielastic neutron scattering experiments have been used to investigate confinement effects on the molecular dynamics on a typical timescale from 0.1 to 2 nanoseconds. The scattering intensity from the fully hydrogenated molecules essentially corresponds to the incoherent scattering function S inc (Q,ω), which allows to probe the self-correlation of the hydrogen motion. This function is commonly approximated by Eq. 1 :

( ) ( ) [ ] ω ω δ ω , ) ( 1 ) ( ) ( 3 exp ) , ( 2 2 Q S Q A Q A Q u Q S quasi inc - + ⎟ ⎟ ⎟ ⎠ ⎞ ⎜ ⎜ ⎜ ⎝ ⎛ - = (1)
In this expression, A(Q) stands for the elastic incoherent structure factor coming from restricted motions, S quasi (Q,ω) is the quasielastic response of slow molecular relaxations, and the contribution of the fast vibrational modes is approximated by the Debye-Waller factor expressed as an overall intensity loss expressed by the vibrational mean square displacement 2 u . [START_REF] Bée | Quasielastic Neutron Scattering[END_REF] The incoherent scattering function has been measured for the four systems at T=310 K, in order to characterize the liquid dynamics above the glass transition temperature, as shown in Fig. 3. The incoherent scattering function appears essentially as a quasielastic line, which is broader than the elastic resolution (A(Q)=0, S inc (Q,ω) ∝ S quasi (Q,ω)). The absence of any pure elastic contribution proves the loss of correlation of the protons motion on the time scale of the experiment. [START_REF] Bée | Quasielastic Neutron Scattering[END_REF] This non-localized character of the motion of the molecules most probably implies that translational diffusion processes occur on the time and length scales of the experiment. Comparing the line width of the scattering functions, one can also deduce the qualitative conclusion that the relaxation dynamics of the pure glycerol samples is faster at 310 K than for the binary solution samples. Nevertheless, a more quantitative analysis of the shape of the quasielastic lines is required to draw more detailed conclusions. ( )

) ( exp ) ( ) ( ) , ( Q b Q t FT R Q f Q S k K quasi + ⎪ ⎭ ⎪ ⎬ ⎫ ⎪ ⎩ ⎪ ⎨ ⎧ ⎟ ⎟ ⎠ ⎞ ⎜ ⎜ ⎝ ⎛ ⎟ ⎟ ⎠ ⎞ ⎜ ⎜ ⎝ ⎛ - ⊗ = β τ ω ω (2)
This stretched-exponential law is recognized as a convenient empirical way to reproduce the relaxation functions of glass-forming materials. This single function usually better reproduces the experimental data than a discrete combination of different modes (translation, rotation…), which are most probably coupled in the case of glass-forming liquids. [START_REF] Wuttke | [END_REF]52 τ K stands for the characteristic relaxation time, whereas β K reflects the non-Debye character of the relaxation function and the average relaxation time is

⎟ ⎟ ⎠ ⎞ ⎜ ⎜ ⎝ ⎛ Γ = K K K β β τ τ 1 .
This procedure provides good fits of the data for the four systems as shown as solid lines in Fig. 3. In a first step, both τ K and β K values were fitted for each Q values. Since no significant and systematic Q dependence of the β K exponents were observed, in a second step, they have been fixed for each sample to an average value and only τ K (Q) values were refined.

The value of β K exponents for pure glycerol is about 0.6. Different values for the β K exponent have been reported for pure glycerol. As reported in ref. 53, the shape of the relaxation function may depend on the experimental method used to probe the liquid dynamics. In fact, the value in our study is in full agreement with previous quasielastic neutron scattering experiments performed on a larger temperature range and using timetemperature superposition principle (0.58±0.02). [START_REF] Wuttke | [END_REF]54 Interestingly, β K differs significantly for the binary solution (β K = 0.5 for the bulk binary solution) and is also reduced by confinement, being equal to β K =0.5 and β K =0.4 for the pure confined glycerol and the confined binary solution, respectively. The exact values of β K should be taken with some care, since they result from a fit at different Q-values but at a unique temperature and covering a limited frequency (or time) scale of about one decade only. However, the difference between the β K exponents for the different samples is so large, that uncertainties coming for the fitting procedure could not affect the qualitative conclusions concerning trehalose and confinement effects on the dynamics.

It is well-known that the stretched exponential relaxation function may be expressed within two different scenarios, corresponding to the limiting cases of heterogeneous and homogeneous dynamics. 22 The homogeneous scenario assumes that the relaxation process is intrinsically of non-Debye type. On the contrary, the heterogeneous scenario relates stretching to the existence of dynamical heterogeneities of given typical size and life-time. Each individual heterogeneity may relax according to a simple Debye mode, with a different relaxation time, leading on average to a broadening of the distribution of relaxation times.

The marked decrease of the β K exponent in the binary system as compared to pure glycerol is most probably a direct consequence of a more heterogeneous dynamics. The bulk solution is composed of two glass-forming molecules with very different glass transition temperatures.

The calorimetric glass transition of the solution depends strongly on the concentration. 38 The local molecular dynamics can be affected likewise by the existence of concentration fluctuations at the nanometer scale, which are inherent to binary solutions. Moreover, this tendency to form spatial heterogeneities is amplified by the H-bonding character of the two molecules, which usually favors the formation of transient networks and clusters of mesoscopic size. 55 Indeed, trehalose and homologous dissacharide aqueous solutions are known to develop structural inhomogeneities, in terms of clusters and transient H-bond networks. 56 They are probably responsible for the major part of the broadening of the distribution of times of the structural relaxation with respect to neat glycerol.

Confinement also leads to a reduction of the β K exponent. This observation is in agreement with previous QENS experiments and molecular dynamics simulations of other nanoconfined glass-forming liquids. 19,21 This increase of the non-Debye character of the relaxation is likely to be attributed to the formation of spatial heterogeneities within the pore, which dynamical parameters depend on the distance to the pore surface. There are indeed an increasing number of experimental and numerical evidences that the dynamics of a confined fluid is spatially heterogeneous. 16,19,21,57,58,59 The case of the confined trehalose-glycerol solution is very striking, leading to a very small β K exponent (β K =0.4). For a binary glass-forming liquid, it is not excluded that dynamical heterogeneities can be amplified by non-homogeneous concentration distribution profile across the pore diameter.

Figure 4 shows the Q-dependence of the average relaxation rate 1/<τ>. This quantity is preferred to τ K , since it is much less sensitive to statistical uncertainties induced by numerical correlations between τ K and β K in the fitting procedure. Power law fits of τ give In the case of pure glycerol a departure from this single power law is observed at low Q (Q<1 Å -1 ), leading to a steeper Q-dependence. This feature has already been reported for bulk glycerol and more usually in glass-forming polymers. 54,61,62 A dispersion relation with ν=2 in the case of a stretching exponent β K smaller than 1 means that the Gaussian approximation of the shape of the van Hove self correlation function does not hold anymore. In fact, our observation supports the idea of a possible non-Gaussian to Gaussian cross-over around the location of the main diffraction peak, as already discussed for pure glycerol. 54,62 It highlights the coupling of the self-diffusion to the structural relaxation on the time and length scales probed by QENS. The analysis of this feature, including the case of a binary mixture and confined systems goes beyond the scope of the present paper, but will be discussed in a future study combining ongoing molecular dynamics simulations. 38 In order to address the influence of confinement on the molecular dynamics of the investigated liquids, we have compared the slopes of the dispersion curves in the Q-range where the Q -2 power law holds (Q>1 Å -1 ). The incoherent intermediate scattering function relaxes mainly via the translational diffusion of the protons, with a reduced amplitude due to fast relaxation and vibrational processes. Assuming a model based on an inhomogeneous distribution of normal diffusion processes, it can be expressed as follows: 63 ( ) ( )

k t Q D Q f t Q S w quasi β 2 exp ) ( ) , ( - = (3).
From the dispersion curve, one can obtain an average diffusion coefficient <D>=1/(<τ>Q 2 ), as already described for other liquids, such as confined water. 64 The values of <D> at the temperature T=310 K are reported for the four samples in Table 1. The value obtained for bulk glycerol is <D>=5.10 -8 cm 2 .s -1 , in quantitative agreement with a recent NMR study. 65 The addition of 20 percents trehalose considerably reduces the average diffusion coefficient of the solution, which is ten times smaller than for pure glycerol.

Moreover, the diffusion coefficients under confinement are systematically about 1.5 larger than for the bulk liquids (see Table 1 and also Fig. 4) both for the pure and the binary solution. This result demonstrates that the microscopic molecular dynamics is already affected by confinement in the normal liquid phase above the melting point.

Variable temperature fixed window scans

In order to monitor the molecular dynamics from the liquid to the glassy state, elastic fixed window scans (EFWS) have been acquired during cooling from 350 K to 10 K, as shown in A comparison between the EFWS displayed in Fig. 5 for the four different systems reveals some distinct effects on the relaxation dynamics of glycerol solutions on the nanosecond timescale of both confinement and of the addition of trehalose. The elastic intensity of the bulk trehalose-glycerol solution qualitatively resembles the bulk glycerol one, except for an overall shift to higher temperature of about 20 K, when measured at half the maximum elastic intensity. This overall slowing down of the relaxation dynamics of the binary solution on increasing the amount of trehalose is mostly related to the change in the glass transition temperature. Experiments with specifically H/D labeled binary systems could partly disentangle the different processes involving glycerol and trehalose molecules, which contribute to the overall slowdown of the relaxation decay probed for fully hydrogenated solutions.

Conversely, confinement leads to an apparent shift to lower temperature of the elastic intensity of about ΔT= -7 ±2 K when measured a half maximum intensity. Interestingly, the confinement effect cannot be described by a simple temperature shift. Indeed, the slope of the elastic intensity as a function of temperature is smaller in confinement than in bulk in the temperature region where the time scale of quasielastic relaxation processes crosses the instrumental resolution (i.e. between 300 K and 250 K for glycerol and between 330 K and 270 K for the binary solution). This feature is observed for pure glycerol and for binary solution. As a consequence, the difference of the elastic intensity between bulk and confined pure glycerol keeps increasing on decreasing temperature from about 300 K to 250 K and approaching the glass transition. The situation of the trehalose-glycerol solution is even more striking, since the two elastic intensities cross at about 325 K. This observation is of central interest to understand confinement effect. A broadening of the transition region could reflect a broader distribution of relaxation times related to a higher degree of heterogeneity of the dynamics in confinement. In addition, it may arise from an increasing deviation between the dynamics of the bulk and confined liquid during cooling on approaching the glass transition.

It is also remarkable that the elastic intensity vanishes or is very small at 350 K for the two confined fluids (i.e. 50-60 K above T g of bulk glycerol). This differs from previous neutron spin echo and neutron backscattering experiments on confined liquids, which show a remaining elastic intensity well above the glass transition: more than 20% of elastic intensity 150 K above T g for the glass-former OTP in 7 nm SBA-15 porous silicates and 20% of elastic intensity 30 K above the clarification point for a mesogenic liquid 8CB in PSi. 20,31 This remaining apparent elastic contribution is commonly attributed to a fraction of the confined liquid, most probably located near the solid interface, which is immobile on the time scale of the experiment. Such surface induced blocking effect on the molecular dynamics is obviously of smaller importance in our case, probably because of a smaller surface to volume ratio or a different nature of the surface interaction.

Low temperature mean square displacement

At low temperature, the quasielastic lines due to relaxation processes are not broad enough to be discriminated from a true elastic peak within the experimental resolution. Vibrational modes lead to an inelastic contribution, which is outside the energy range covered by BS.

They also lead to a reduction of the elastic intensity, which allows one to measure the mean square displacement (MSD) <u²> of vibrational modes from a linear regression of the logarithm of the elastic intensity as a function of Q 2 on a Q-range from 0.7 Å -1 to 1.9 Å -1 according to 66 This is at variance to some polymeric systems, which MSD exhibit well-defined low temperature modes related to side group dynamics and decoupled from the alpha relaxation. 67 The rise of the MSD shows up in a temperature region around the calorimetric glass transition temperature (T g =190 K), as already observed for many other glass-forming molecular systems. These findings suggest that the fast dynamics probed by the MSD also senses the glass transition as other quantities such as enthalpy and specific volume, as discussed in ref. 68. In the case of the bulk binary solution, a similar behavior is observed but the deviation from the harmonic behavior occurs at higher temperature (about 210 K), in agreement with previously discussed EFWS. A similar cross-over is observed for the two confined systems, which suggest that the glass transition is also probed in confinement from the variation of MSD. Similar signatures of the glass transition are usually reported for confined molecular liquids and polymers, 67 although this upturn is not universally related to Tg as shown by the work of Soles, et al. on nanoconfined polycarbonate thin films. 69 For both pure glycerol and the trehalose-glycerol solution, confinement results in an increase of the MSD in the glassy and liquid states. In the low temperature region, this suggests a weaker stiffness for the confined vitreous phase whereas in the high temperature region, the larger amplitude movements mostly result from the lower glass transition temperature of the confined phase as compared to the bulk. Here again, such a behavior does not seem to be universal to confined glassforming systems, and reductions of the MSD have been also reported for polymer thin films in the glassy state. 69

⎟ ⎟ ⎟ ⎠ ⎞ ⎜ ⎜ ⎜ ⎝ ⎛ - = 3
) ( exp ) ( ) 10 , , ( / ) , , ( 2 2 Q T u K Q S T Q S inc inc ω δ ω ω . ( 4

Summary and conclusions

We have investigated the dynamics of pure glycerol and a trehalose-glycerol binary solution in bulk and confined situations. The incoherent dynamic structure factor measured by QENS has provided information on the proton self-motion in the liquid phase well above Tg (at T=310 K), corresponding to a typical time window of about 0.1 to 2 ns, which also corresponds to the liquid structural relaxation timescale at this temperature. EFWS have allowed measuring the molecular relaxation dynamics on a temperature range corresponding to the liquid and supercooled liquid. The vibrational and sub-nanosecond fast relaxation dynamics have been described by the mean square displacement <u²> in the glass (below 200 K) and in the region of the glass transition temperature.

It is noteworthy that the overall measurements provide a same qualitative depiction of trehalose and confinement effects on the dynamics of the glycerol solution. This is also in agreement with ongoing NMR and dielectric spectroscopy studies on the same materials. Erreur ! Signet non défini., [START_REF] Ulbrig | Diploma arbeit from the University of Saarbrücken[END_REF] Trehalose significantly slows down the dynamics of the glycerol solution. At T=310 K in the liquid phase, it corresponds to a decrease of the average self diffusion coefficient by a factor of ten. This effect persists on decreasing temperature and affects the glassy dynamics, as reflected by a significant shift to high temperature of the EFWS (ΔT g ≈20 K). This confirms the so-called 'switching-off' effect of trehalose, which has been related to its exceptional biopreservative efficiency. 32,33,41,42 The second observation is a smearing out of the relaxation steps. It is characterized by an increased non-Debye character of the incoherent intermediate scattering function in the liquid phase. It supports the idea that trehalose in glycerol promotes dynamical inhomogeneities. This is generally awaited for a binary system composed by molecules, which have different characteristic relaxation modes and most specifically for disaccharides bioprotectant solutions, which are known to develop structural inhomogeneities, in terms of clusters and transient H-bond networks. 56 In addition, we have investigated the same two liquids under confinement using PSi nanochannels. At T = 310 K, in the liquid phase, we have observed a slight modification of the incoherent quasielastic neutron scattering functions, which are broader and more stretched as compared to the same bulk systems (β K stretching exponent as small as β K = 0.4 for the confined binary solution). These effects have been quantified assuming a model of an inhomogeneous distribution of diffusion coefficients, which are coupled to the structural relaxation in the time and lengthscale of this study. The average diffusion coefficient is found systematically larger in confinement by a factor of 1.5 as compared to bulk value.

On decreasing temperature, fixed window scans confirm a deviation of the relaxation dynamics of the confined systems from the bulk one, which seems to increase on approaching the glass transition. It results in a substantial shift (estimated to about ΔT = -7 K) of the temperature where the MSD <u 2 > departs from its essentially vibrational behavior in the glassy state.

The broadening of the intermediate scattering function at T = 310 K in the liquid state proves that confinement amplified the inhomogeneous character of the liquid dynamics. This is an evidence for the existence of non-equivalent dynamical environments within the pore.

We note that this feature is likely to be amplified for a multi-constituent system with nonsymmetric fluid-wall interactions.

These overall results (e.g. change of the average relaxation time and broadening of the relaxation distribution) agree with ongoing solid-state NMR and dielectric experiments on the same systems. 22,[START_REF] Ulbrig | Diploma arbeit from the University of Saarbrücken[END_REF] Such features have been frequently reported for other systems and often discussed with respect to some predictions about finite size effects. However, we note that these observations are not systematic among different systems and a unifying picture is certainly missing. 1,2,4,6,7 It is also possible that the observed confinement effects on the glassy dynamics result from a modification of some other physical properties of the confined liquid (such as density, rheology or H-bonds induced intermediated range order), which indirectly affects the structural relaxation. 5,9,26 Very recently, there has been a growing number of evidences of long-lived mesoscopic dynamical heterogeneities in bulk liquid glycerol and long-time long-range relaxation processes in glycerol-aerosils dispersions well above T g , which suggest that confinement may lead the confined glass-forming liquid to a frustrated state with different physical (static or dynamical) properties. [START_REF] Zondervan | Proc. Natl. Acad. Sci. USA[END_REF][START_REF] Zondervan | Proc. Natl. Acad. Sci[END_REF][START_REF] Sharma | [END_REF] For pure glycerol, our results emphasize significant confinement effects on the structural relaxation deep in the liquid phase as well as on the glassy dynamics on cooling, which relation to bulk mesoscopic dynamical heterogeneities is to be unraveled. We have also reported unprecedented manifestation of an amplified non-Debye character of the relaxation function for the binary bioprotectant solution that goes beyond the case of pure glycerol.

Molecular simulations are required in order to scrutinize potential mesoscopic inhomogeneities related to concentration fluctuations and specific interfacial interactions.

Table 1

Average diffusion coefficient and Kohlrausch stretching exponent obtained from the incoherent quasielastic neutron backscattering function at a temperature T = 310 K.

FIG. 1 :

 1 FIG. 1: Scanning electron micrographs of the porous silicon film. (a) top view at low magnification showing the 30 μm thick porous layer attached to the silicon substrate and (b) side view at higher magnification.

FIG. 3 :

 3 FIG. 3: Incoherent quasielastic spectra of glycerol and the glycerol-trehalose solution in bulk and confined in porous silicon layers measured at T=310 K on the high resolution backscattering spectrometer IN16. The intensity is corrected for empty sample contribution and normalised to maximum intensity. The displayed curves have been scaled to one at the maximum intensity for clarity. The resolution function of the apparatus is displayed as a filled gray shape. The solid lines are best fits of the data using a stretched exponential (see text). The graphs correspond to three different values of the transfer of momentum, (a) Q=0.54 Å -1 , (b) Q=0.96 Å -1 and (c) Q=1.33 Å -1 .

60 FIG. 4 :

 604 FIG. 4: Average relaxation time τ as a function of the transfer of momentum Q obtained from the incoherent quasielastic spectra at T =310 K for pure glycerol and the glyceroltrehalose solution in bulk and confined in porous silicon. Dashed lines superimposed on bulk glycerol data emphasize the cross-over between two different power law variations.

Fig. 5 .FIG. 5 :

 55 Fig. 5. In a EFWS, the measured intensity is in principle S inc (Q,ω=0) (see equation 1). It

)FIG. 6 :

 6 FIG. 6: Mean square displacement of glycerol and the glycerol-trehalose solution in bulk and confined in porous silicon layer obtained from incoherent neutron backscattering on cooling. Inset : magnification of the temperature region of the glass transition.

Figure 6

 6 Figure 6 shows the measured mean-square displacement as a function of temperature. The

FIG. 1 :FIG. 2 :FIG. 3 :FIG. 4 :FIG. 5 :FIG. 6 :

 123456 FIGURE CAPTIONS

Figure 3

 3 Figure 3

Figure 4 Molecular 38 Figure 5

 4385 Figure 4 Molecular dynamics of glycerol and glycerol-trehalose bioprotectant solution nanoconfined in porous silicon. R. Busselez et al.

Table 1

 1 Average diffusion coefficient and Kohlrausch stretching exponent obtained from the incoherent quasielastic neutron backscattering function at a temperature T = 310 K.

		Bulk glycerol	Confined	Bulk trehalose-	Confined
			glycerol	glycerol	trehalose-
	β Κ	0.6	0.5	0.5	glycerol 0.4
	<D>	5.0	7.6	0.52	0.77
	(10 -8 cm 2 .s -1 )

Acknowledgements

We thank R. Pelster and P. Huber from the University of Saarbrücken for fruitful discussions and J. M. Zanotti from LLB Saclay for making available the software package quensh for neutron data modeling. R. B. has benefitted from a doctoral research grant from the Brittany Region. Financial supports from the Centre de Compétence C'Nano Nord-Ouest and Rennes Metropole are expressly acknowledged.