Masayoshi Morioka

Keywords: clinical narrative approach, listening process, self-talk, lived story, non-linearity

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Introduction

The storytelling mind is always at work [START_REF] Varela | The Embodied Mind: Cognitive Science and Human Experience[END_REF].

The aim of the present study was to refine listening to a personal life history as a method for psychosocial support from the viewpoint of a narrative-based approach. We particularly discuss the clinical listening process following the narrative approach as presented by [START_REF] Bruner | Acts of Meaning[END_REF].

The narrative approach in practice is located at the crossroads of clinical practice and human science. However, it is necessary to investigate how the practice of listening to a personal life history is to be meaningful, genetic and useful for psychosocial practice on the recovery of the sense of self and the link between elder and future generations.

The theory of narrative approach has been elaborated in its theoretical frame of reference in terms of speech acts and reality construction. Nevertheless, the orientation of the narrative approach has not yet been clarified in psychological clinical practice except for the school of narrative therapy [START_REF] White | Narrative Means and Therapeutic Ends[END_REF].

Recently, there has been a tendency for narrative-based practice to shift from psychotherapeutic practices to a social practice of ethics that involves co-authoring a concrete description of the story of the other's suffering (Kleinman, 1997;[START_REF] Charon | Narrative Medicine: Honoring the Stories of Illness[END_REF].

The fundamental form of narrative

According to [START_REF] Bruner | Acts of Meaning[END_REF], "One of the most ubiquitous and powerful discourse forms in human communication is narrative." Bruner (1990, pp. 77-78) presents four crucial grammatical constituents in the form of Narrative.

The first constituent states that if narrative can be effectively carried out, it requires a means for emphasizing human action or agentivity -action goals controlled by agents. According to the second, narrative requires a sequential order to be established and maintained -events and states must be "linearized" in a standard way.

The grammatical subject-verb-object (SVO) order is mastered first in most cases.

Children start early on mastering the grammatical and lexical forms of these sequences.

The third constituent is sensitivity to what is canonical and what violates canonicality in human interaction. Early readiness is to mark the unusual and to leave the usual unmarked to concentrate attention and information processing on the offbeat. The very act of speaking is an act of marking the unusual from the usual. The fourth constituent is the narrator's perspective: it cannot be, in the jargon of narratology, "voiceless;" voice or perspective must be included. Thus, the narrative approaches the perspective of the subject. Any story inevitably has a narrative voice that causes events to be seen through a particular set of personal prisms.

These four grammatical/lexical/prosodic features provide the child with narrative tools. From the genetic viewpoint, they are concerned with early infant behavior principally indicated by crying and other affective expression, and also by stress levels and similar prosodic features in early speech.

An additional remark on the unique point of narrative is that subjunctive stories are easier to enter into, easier to identify with. Bruner (1990, p. 55) states that narrative is located in the domain midway between the real and the imaginary, and that humankind will go "meta" on received versions of reality.

The basic form of narrative is useful for description in complex fields of practice such as medicine and clinical psychology. According to the narrative form, we are able to obtain another viewpoint on a person's illness or disability as that person's own lived experience. It is easier to live with alternative versions of a story than with a scientific account. Narrative is a frame of reference that can connect even contradictory heterogeneous items. The function of the story is to find an intentional state that mitigates or at least makes comprehensible any deviation from a canonical cultural pattern (Bruner, 1990, p. 49).

A unique person's knowing: first-person knowledge

The narrative approach is to be clearly based on the particularity of the act of personal meaning making. The ground of the narrative approach is that the believability of a story is derived from the concreteness and truth included in the unique life history of the individual.

The author focuses on his or her life history as the basis of clinical narrative practice, and the particularity of narrative appears in the personal theme of this life history. A life history is authored by a unique person who has his or her own proper name. The discourse of a life history is made not only in the third person but also in the first person. The first-person description is thus potentially available as the basis for a concrete research method of human science.

In medical practice, the medical staff first traces back the cause of the patient's sickness; this causal point of view is universal in medical practice. However, there are many differences in how people experience their own sickness because each person experiences his or her own illness through his or her own life context [START_REF] Kleinman | The Illness Narratives[END_REF].

The therapist tries to listen to the illness narrative to determine how it can explain the patient's lived experience. The disease has a significant meaning in the patient's life history, but will emerge with various meanings in the patient's life.

The clinical listening process

Let us now consider a case vignette. Ms. A is a 22-year-old office worker who had injured herself with wrist cutting until she was in high school. She had many scars from her left wrist to the elbow. She also cut her side and thigh, and sometimes knocked her head against a wall. Her temper is often uneasy. She carried a set of goods for treatment in her bag. It was hard for her to express her own conflict.

Her adaptation in the workplace has been reasonably good and her co-workers have a good impression of her. In the therapeutic interview, she said she could not express her true feelings.

Unbearable affect and self-injury

Ms. A's mal affect states are seized at the moment following the action, but gradually feelings of regret become strong. Unbearable affect arises both before and after cutting. The action of self-injury does not regulate affect. Sometimes she experiences emotional distress when she tries to phone a close friend before cutting, but such a state does not continue.

Affect regulation is the central task in treatment for self-injury. Most patients describe distress before self-injury. Anxiety regulation in particular is an essential part of treatment. An uncertain sense of self is latent in almost all those who self-harm.

Anxiety evokes tension, which then leads to self-injury. Thus, the therapist must begin affect regulation to help the patient recover a subjective appropriation of his or her experience.

First, we listen for events around the beginning and end of the self-injury. Is there any particular pattern to what happens before self-harm? Ms. A usually said she could not remember the act of self-injury clearly. The therapist tried to listen for how changes in Ms. A's affect and consciousness arose and for how she experienced her own body. She might feel boredom, for example. The therapist tried to deal with such uncertain negative emotions through conversation.

Uncomfortable tension and excitation of the body cannot be treated well by the patient alone in the beginning. It is an essential theme of human existence that one cannot deal well with tension and excitation alone. A neighbor, friend or other significant person who cares about the patient and will talk to him or her must help the patient gain control over his or her tension.

Self-talk

Through the important work of self-talk, self-regulation of affect can be achieved. In the present case, the therapist encouraged Ms. A to accept her vague uncertain affect.

Ms. A began to talk about her affect experience. The fluctuation of self-states arose in the conversation: Ms. A said, "There are two of me, one is an unsettled and restless self, the other self is calm and stands still. The restless self tries to cut the calm one." Ms. A said, "I am always slow to decide things. Sometimes I am on one polar side and other times I am extremely to the opposite side. There is no grey area for me.

Gradually, Ms. A arrived at a more reflective viewpoint.

In another session, the therapist asked her, "Is there anyone who knows about your cutting behavior?" Ms. A said that nobody had noticed her cutting except one of her high school friends: Ms. A.: I remember that my friend discovered that I had repeatedly self-harmed. She asked me to stop it, but I could not stop.

Therapist: "What do you think about it now?" Ms. A: I think no one will pay much attention to me except this friend. I regret that I worried her so much.

Creative conversation between I and me

Ms. A was able to gradually create another person in her mind that served as a double for her. She said, "I tried to show myself a better image than the actual figure.

There are two people in my mind: one is cold and tries to cut herself, and the other, who gets cut, is weak and does not wish to live. I have two of me, one who walks around actively and one who stops because of anxiety about something. I always worry about my work, even on holiday." Her self-talk was transformed into actual conversation with her therapist. She learned to feel real feelings in the process of dissolving her tension. This experience lays the ground for warm and full acceptance of oneself. Additionally, the actual conversation transformed into her new self-talk. Gradually Ms. A grew warmer toward herself.

In this internal conversation, a new narrative was generated. The confused and fragmented events in Ms. A's life history were connected in the new narrative.

Reworking the word of other

The therapist takes the position of reworking the words of the other. In the case of Ms. A, her father image had gradually changed in therapeutic conversation. The therapist and Ms. A mutually elaborated the words of the response, and mutually explored words that could regulate her negative affect derived from her interpersonal relationships.

The awareness of one's sense of self, "I am," emerges in a specific mode of relationship and in a particular context of conversation. The client can recover her subjective appropriation through co-experience in which her sense of agency is supported.

In another session, Ms. A said "But I guess my fluctuation is affected by my father's constraint. I feel strong constraint from my father." She gradually came to express natural affect such as anger. I asked her how she usually expressed herself when she got angry. She said nobody knew she had gotten so angry. Ms. A's grandfather was a gardener who was an alcoholic and was severely violent with his sons. Ms. A's father worked patiently with the gardeners and did well in school.

After he graduated from college, he established a company. At first his company grew, but then it gradually declined due to economic fluctuation. He is now deep in debt. He also had some lovers and didn't usually return home. He borrowed money from A's salary, but never paid her back.

In a later session there arose a moment in which she was able to say that she was an independent enough person. The addressee of her utterance is dual in this conversation, that is, one addressee is the therapist and the other is her internal other (the figure of her father). There emerges an alternative narrative in the space between the two sides of the dual conversation. Gradually she can take confrontation honestly to the weak part of herself.

Such conversation can activate the distorted internal figures of the patient's interpersonal relationships (in Ms. A's case, her father). The client's condensed affect can be shared with the therapist through self-narrative.

Ms. A reported a new habit of narrating to herself in her mind. She made up stories that included some of the events of each day. She remembered some scenes of the day and tried to create new conversations with the characters she had met that day. This secret work of retelling was her practice at night before she fell asleep. It was important for her emotional regulation and acted as a kind of catharsis. This space of fantasy relieved her unusual affective experience. A narrative can coordinate the internal mind scape where one can accept his/her compound experience.

Discussion

We are usually aware in the field of psychosocial support that the human power of recovery is quite astonishing. People seem to have the basic power of connecting difficult experiences such as traumatic disaster to their own life history. We try to learn from past experience without denying. This action creates certain images for our future.

Narrative has the basic function of connecting divided items such as mind and body, I and the other, life and death. These include hard conflict and split that are not easy to resolve. The function of narrative is to link the past to the future.

Let us consider the clinical listening process according to the narrative approach on the basis of its form as presented by [START_REF] Bruner | Acts of Meaning[END_REF].

The meaning of the event is co-constructed

The experience of illness includes something not yet completed. It is a necessary point of view that we grasp the action as relational and historical. Self-injury or self-mutilation is treated as a challenge to the limitations of human conduct. People always become anxious when faced with this action.

We must try to determine certain aspects of the 'action' of a self-injury. The action always has some meaning; self-injury is not only an impulsive behavior. Any action may have an intention toward an object. The action of self-injury also has an aim, even if that aim is not always certain. There are typically some realizations concerning the aims gained by the act of self-injury. But how can we read the intention of the action? Under a superficial understanding, it seems to be an incredible action.

The action is self-destructive but also seems to be a defense against some deeper destruction of the mind and body. Ms. A had hidden her action from the eye of her family but on another side she seemed to gain a certain awareness from her family. The action is thus ambiguous.

The action of self-injury itself may express her epitomized life story. The experience of illness includes something not yet completed. The action has meaning in one's life history, particularly as a negative experience concerning the theme of attachment of a family relationship. In the case of Ms. A., she had a negative father image. She said she could not have an intimate relationship with her father. Her father has lovers and sometimes lives in the home of one or another of his lovers. Ms. A's mother usually makes negative comment about her conduct. Sometimes she tried to run away from home, but she always returned. If one has been affected by repeated negative feedback from one's family and affection was not accompanied by good acceptance, one's sense of self may be uncertain and one's sensitivity of affect may be ambiguous. Consequently one's feeling of being oneself will be uncertain. This uncertainty is latent in the action of self-injury.

On living a connected sequence of events (plot)

In the fundamental form of the narrative, sequential order is established and maintained; that is, events and states are linearized in a standard way.

We are able to listen, using clinical materials along with the plot, which consists of the client's main complaint. Many clients seem to be at a turning point in their life. Ms.

A was also at a deadlock in her life course. The psychotherapist paid attention to how Ms. A selected events and in what context they were given meaning. Why are the particular events selected and arranged in sequential order and why are other events latent?

If we try to recollect the sequence of events, with one event leading to the next in as lively a manner as possible, we are evoking the images of the scene constructed by the events. However, we cannot evoke the link of sequence itself using the same method of stringing together unique events. The connecting sequence itself, that is, the plot, must be re-created and lived at the moment of recollecting. This living plot is not manifest in the text, which is a non-scribed space during the events and for connecting one event to the next. This space is held in the act of storytelling and the process of co-constructing the story.

The Japanese call this invisible space "ma." The complex cultural concept of ma indicates a chronotope in which meaning is generated [START_REF] Morioka | Creating dialogical space in psychotherapy: meaning-generating chronotope of ma[END_REF]. It is the boundary zone, A<>non-A field, where meaning is constructed and re-constructed [START_REF] Valsiner | Forms of dialogical relations and semiotic autoregulation within the self[END_REF]. Some events are selected and re-authored according to the psychotherapeutic context. In this context, the therapist and the client can collaboratively explore the hidden sense of values. Telling and listening are inseparable. The therapist and client cooperate in order to discover the client's own stories that make his or her life comprehensible. In turning the problem context into a therapeutic context, the hidden power relationship will become overt for the client.

In the present case, two events, Ms. A's latent angry feelings and her father's action, are at first not connected consciously. At a certain point, Ms. A began to talk about her father's story spontaneously, and the therapist was able to see that her father's life history was superimposed on her narrative of self-injury. In this instance, the told story became a lived story. The therapist can listen to the client's life history as a method of reading the structure of anticipating a personal image of his or her future.

Transforming the told story into a lived story; linearity and non-linearity

The author focuses on the transformation of the story, turning from told stories to lived stories. From the point of view of the basic form of narrative, this theme is concerned with the property of narrative; the narrative includes voice or perspective.

There is a distinction between lived story and told story. According to the form of linearity of narrative, one can change one's own affect into a regulative one. Together with the basic form of narrative, in which a sequential order is established and maintained, the client's inexplicable affect experience can be transformed into a shareable one. The other person, that is, the psychotherapist, can understand the client's experience by listening to the told story. The form of sequential order is significant in that events and states are "linearized" in a standard way.

Next we transform the told story into a lived story through the listening process.

What kind of story is the lived story? "When we dream at night we find ourselves inhabiting a dream reality that exhibits its own coherence and order, its own 'way things are' and 'what's happening'. This lived reality, the ongoing story, unfolds with a vitality that no subsequent telling can wholly capture." [START_REF] Petranker | The when of knowing[END_REF]. In a dream we simply inhabit the story and live it forward.

It is exactly a lived story.

The dynamic transformation from told story to lived story occurs in the narrative as performance level. In the therapeutic conversation, the therapist and the client collaborate to discover words suitable to the meaning of the experience of the event. Not only the content level of the narrative but also the performance level of the narrative will be communicative in the work of co-constructing the meaning.

One's own personal characteristics usually appear in the narrative as performance level. If one could listen to the lived story, the characters of the story could be re-envoiced and could recover their vitality. The characters in the narrated story are actively imaged and form clear figures in the deep listening relationship. There is a fluid and realistic interchange between characters of narrative organization. These characters have their own voices, and any character might be re-envoiced in the therapeutic situation. In Ms. A's case, her father gradually got a clearer character with a strong voice in the story. Ms. A tried to make a conversation in the present moment of the therapy session.

"Perhaps time was a contributory factor to the happiness that reached right down to the innermost depths of my soul. There was, however, no element in my present condition that had to follow the course of time and develop successively from one stage to another. My happiness was not due to the fact that one event arrived as another left, and was in turn followed by a third whose eventual departure heralded the birth of number four. It was derived from the atmosphere that pervaded my surroundings: an atmosphere of unvarying intensity that had remained with me there in that one place from the beginning" (Sōseki, (1906) This has always been a radical theme of aesthetics and literature. Artistic expression such as painting seems to be better than language for expressing non-linear emotional states. These states have simultaneous features such as graduation, ambivalence, and contradiction. They may involve representations of spatial arrangements, as painting does. Language has the basic trait of linearity and successive logic at its essence.

Let us consider the following quotation: "Personal knowing in psychotherapy has logic but it is not discursive, not set out in a straight line" [START_REF] Hobson | Forms of Feeling: The Heart of Psychotherapy[END_REF]. It can be understood that many psychotherapeutic methods have been developed in terms of the solution to the limits of the client's linear understanding. We may say that the turning point of personal narrative has no linearity. Paradoxically, it is a gap in consciousness or in the language of linearity [START_REF] Morioka | The Cosmology of Inner Speech: Jung and Vygotsky[END_REF].

It is a valid assumption that dialogical conversation in itself can transcend this limit. The position of the two persons in the dialogue collaborates in creating a story through dialogue. The dialogical reality or space people spontaneously construct in their joint actions is experienced (sensed) as a "third realm of activity" [START_REF] Katz | Hearing the patient's voice: toward a 'social poetics' in diagnostic interviews[END_REF]. Third-realm activities occur in those moments when, as living beings, we approach or encounter another or otherness. A responsive other is necessary for narrative knowing. The therapist tries to enter the client's emotional experience fully while simultaneously offering distance from it.

Supporting the person as the agent

Telling and listening to ones' own story is in itself a self-formative activity. It is remarkable that the personal narrative must be heard as a lived story. Narrative is the frame of the subject's experience. The subject of the act of meaning is constructed and shaped through his or her narrative. This subject is generated through the telling of the story, which connects events to other events. This is a retrospective act that generates the teller's future. The past is constructed through the action of telling about it, and events obtain new meanings in connection with the events that follow. From this point of view, uncompleted events have some potentiality for the subject.

The knowing of a lived story is that of the immediacy of a present experience, and knowing in the present has potentiality: it creates the dynamic time and space known as ma in Japanese. In ma, the past and the future may intercross. Although the past can never be reversible, the meaning of past experience can be variable. There is a latent resource in one's own life history for transforming negative experiences into positive ones.

One can transform past events by giving them new meaning with the support of a carefully listening other in the present moment. The other appreciates the images and emotional experiences evoked by the story and listens deeply to the uniqueness of the story. In this process, the internal listener is generated in telling one's story and takes a position as an internal audience.

When the client talks about different parts of his or her self, the therapist listens as openly as possible to all the different parts, meanings and conflicts gradually unveiled by the client. At first, the different parts of herself were unfamiliar to Ms. A. She said, "There are two of me: one is unsettled and restless, and the other is calm and still."

Her conflict was acted out in the unusual event of self-injury, but some of those parts gradually became familiar to her and might even have been given independent positions in her self-talk. The fluctuation of self-states arises through conversation.

The therapist posed some questions in order to expand the conversational space in her mindscape. For example "What might be different parts within yourself? What do they say?" "What were the parts of you at earlier times in your life? What did they say then?" Ms. A tried to connect the different parts of herself guided by questions like "How do/did these different parts relate to each other?" Through such guided conversation, a third part of the self transforms into a self-as-agent that can contain and regulate conflict without driving affect.

Listening to a life history helps to create a linear sequence of events, which is the basic form of narrative. The very act of speaking is an act of marking the unusual from the usual. Ms. A's story was full of unusual events, but she said "I want to speak with him 'naturally'," which indicates a desire for the usual. The function of the story is to find an intentional state that mitigates or at least makes comprehensible a deviation from a canonical cultural pattern (Bruner, 1990, pp. 49-50). In the clinical listening process, the client's story is co-constructed with the therapist by incorporating usual events into unusual ones. The therapist can support the client's sense of agency through this process.

Conclusion

In this paper, the author investigates the meaning-making function of narrative in the clinical listening process. The four fundamental characteristics of form of narrative according to [START_REF] Bruner | Acts of Meaning[END_REF] are examined in the process of psychotherapy in a case of self-injury.

We can see the therapeutic effect and function of narrative from this example. First, narrative frames the subject's experience. The act of storytelling is a retrospective act but generates the teller's future. Second, narrative is useful for affect regulation and can be effective in cases of severe self-injury based on dissociative states. Third, the subject of the act of meaning is constructed and shaped through his or her narrative. This subject is generated through the act of telling, which connects events.

A history of illness is a patient history in which both the therapist and the patient/client are involved collaboratively. The therapist can accept the person's life through the act of listening to his or her story. The complaint or disease of the client includes his or her internal life theme. The therapist can read the client's latent and yet unrealized theme by listening carefully to his or her story. This stance may be significant in psychotherapeutic practice.

The therapist must remain open to contact with the uncertain parts of a person in order to encounter an uncompleted event, and must be able to help the client deal with the uncertainty of the personal narrative in order to re-organize the client's narrative of life.

  Therapist: Now then … From whom does your angry feeling stem? Ms. A: My father constraint hardly about my job change. And I finally changed his mind. I have been controlled by him. Therapist: If possible, can you tell me more about your father's history? Ms. A began to talk about her father's life history. The summarized history was follows.

  Ms. A: I want to speak with him 'naturally.' I talk with my father frankly after I confronted him. I try to tell him what I am thinking.Therapist: Your image of your father is becoming clearer to me.

  p. 93; italics added) Sōseki compared the two modes of artistic representation of language and of painting. Condensed elements are necessarily included simultaneously in our emotional experience. Emotional experience does not necessarily have to be consistent with linear thinking over the course of time. How can we represent something that has remained with us in one place from the beginning?


domain: spi chim

text:
J A Mbey
email: mbey25@yahoo.fr

Ngally Sabouang

Cyrill Joël

AN INSIGHT ON THE WEAKENING OF THE INTERLAYER BONDS IN A CAMEROONIAN KAOLINITE THROUGH DMSO INTERCALATION

Keywords: Kaolinite, Intercalation, Weakening, Interlayer bond, Composite

In this study, intercalation of dimethylsulphoxide (DMSO) in a cameroonian kaolinite is used to achieve weakening of the interlayer hydrogen bonds, in the perspective of dispersion or even exfoliation of the clay within polymer composite materials. Displacement of intercalated DMSO by ethyl acetate and ammonium acetate is studied in order to simulate the interactions with the polymer matrix. The exfoliation of the kaolinite is well evidenced by X-ray diffraction and SEM observations. The disruption of the interlayer bonds is shown by the displacement of the FT-IR vibration modes of both Al-OH and Si-O functions, and by the decrease of the dehydroxylation temperature recorded by Controlled Rate Thermal Analysis.

Complete displacement of DMSO by ethyl acetate is achieved and the crystalline structure is deeply disordered as a result of interlayer bonds weakening. The displacement of DMSO by ammonium acetate leads to a ternary composite of DMSO/ammonium acetate with respective intercalation ratio of 62.4 % and 57.7 %.

INTRODUCTION

Clays are growingly used in the industry as mineral fillers in polymers composite materials, due to their high aspect ratio and high specific area that determine the intensity of the claypolymer interactions [START_REF] Luo | Characterization and modeling of mechanical behavior of polymer/clay nanocomposites[END_REF]. It has been demonstrated for more than two decades that many properties of polymer materials, such as the mechanical or thermal properties, or water and gas barrier effect, can be improved by incorporation of clay particles in the polymer [START_REF] Arora | Review: nanocomposites in food packaging[END_REF][START_REF] Pavlidou | A review on polymer-layered silicate nanocomposites[END_REF][START_REF] Ray | Biodegradable polymers and their layered silicate nanocomposites: In greening the 21 st century materials world[END_REF][START_REF] Alexandre | Polymer-layered silicate nanocomposites: preparation, properties and uses of a new class of materials[END_REF].The key factor to achieve such improvements is the dispersion of the clay particles within the polymer matrix. Therefore montmorillonite is most commonly used in polymer-clay composites because of its high surface area and expansible nature of its crystallites which allows complete delamination in aqueous medium [START_REF] Cabedo | Development of EVOH-kaolinite nanocomposites[END_REF].

Kaolinite is widely used in the paper industry as a glossy surface agent in coated papers, diluting agent of titanium dioxide, white pigment, paint extender, or rubber filler [START_REF] Murray | Traditional and new applications of kaolin, smectite, and palygorskite: a general overview[END_REF]Conceicao et al., 2005). Conversely, its use in polymer-clay composites is by far less common (de [START_REF] Carvalho | A first insight on composites of thermoplastic starch and Kaolin[END_REF]Whilhem et al., 2003;[START_REF] Chen | Thermoplastic starch-clay nanocomposites and their characteristics[END_REF]. However, kaolinite is the most ubiquitous clay. Natural kaolinite deposits are sometimes of such purity level that there is not much additional purification required prior to industrial use, since only little contamination with illite/muscovite, quartz, rutile, ilmenite, or feldspar is observed [START_REF] Murray | Kaolin Minerals: their genesis and occurrences[END_REF]. In Africa, the occurrence of kaolinite clay was recently evaluated, and it appears that the exploitation of the occurrences is still to be improved, which offers both investment and research opportunities [START_REF] Ekosse | Kaolin deposits and occurrences in Africa: Geology, mineralogy and utilization[END_REF]. The use of kaolinite as reinforcing filler in the production of polymer-clay (nano)composite is one of the potential applications of interest, and represents the general aim of the present work.

The asymmetrical structure due to the superposition of the tetrahedral and the octahedral sheet in the kaolinite layer induces strong superposed dipoles, which, in conjunction with hydrogen bonds between the silicone oxide ring and the aluminol surface result in strong cohesive energy of the mineral [START_REF] Cabedo | Development of EVOH-kaolinite nanocomposites[END_REF][START_REF] Giese | Kaolin Minerals: Structures and Stabilities[END_REF]. In addition, the crystalline network of kaolinite is practically devoid of isomorphic substitutions, and does not require charge compensation of hydrated interlayer cations. These characteristics cause kaolinite to occur as non-expandable, large particles of low anisotropy, which explains the lack of interest up to now for its use as mineral filler in polymer-clay composites.

For a convenient use of kaolinite in exfoliated state, one must use a route that ensures weakening of the interlayer bonding between the kaolinite layers, prior to its dispersion within a polymer matrix. There are few organic molecules that can be directly intercalated within the kaolinite. This is the case for dimethylsulfoxide (DMSO), N-methylformamide, acetamide, formamide, potassium acetate; ammonium acetate [START_REF] Frost | Vibrational spectroscopy of intercalated kaolinites[END_REF][START_REF] Frost | The effect of machanochemical activation upon the intercalation of a high-defect kaolinite with formamide[END_REF][START_REF] Itagaki | Synthesis of a kaolinite-poly(βalanine) intercalation compound[END_REF][START_REF] Frost | Intercalation of kaolinite with acetamide[END_REF][START_REF] Olejnik | The intercalation of polar organic compound into kaolinite[END_REF][START_REF] Olejnik | Infrared Spectra of Kaolin Mineral-Dimethyl Sulfoxide Complexes[END_REF]). These molecules are divided into three types: (i) compounds such as urea or formamide which contain two distinct groups to accept and donate hydrogen; (ii) compounds with a high dipole moment, such as dimethyl-sulfoxyde (DMSO); (iii) ammonium, potassium, rubidium and caesium salts of short-chain fatty acids (acetate, propionate) [START_REF] Lagaly | Nanohybrid materials from the intercalation of imidazolium ionic liquids in kaolinites[END_REF]Oleijnik et al., 1970). The displacement of the guest molecule from an intercalated kaolinite is often used to promote intercalation of other molecules [START_REF] Lagaly | Nanohybrid materials from the intercalation of imidazolium ionic liquids in kaolinites[END_REF][START_REF] Cabedo | Development of EVOH-kaolinite nanocomposites[END_REF][START_REF] Itagaki | Synthesis of a kaolinite-poly(βalanine) intercalation compound[END_REF][START_REF] Komori | Direct intercalation of poly(vinylpyrrolidone) into kaolinite by a refined guest displacement method[END_REF]. Also, the rate at which the displacement takes place is determined by the weakening of the interlayer interactions in the clay. Another interesting factor to consider is the time lasting of the intercalated molecule which, to the knowledge of the authors, was not yet evaluated in the literature, although it is evident that this factor may be of interest in the prospect of the production of a readily usable intermediate product.

This paper aims at evaluating the benefit of DMSO intercalation as a pathway toward dispersion of a cameroonian kaolinite to be used within a polymer matrix for composite materials preparation. The rationale is that initial disordering of the kaolinite will determine the dispersion of the particles within the polymer matrix. For this purpose the displacement of the intercalated DMSO by the polymer matrix was simulated in low polarity and ionic medium, respectively ethyl acetate and ammonium acetate, since the polarity of the medium may have consequences on the displacement rate and hence influence the clay structure. X Ray diffraction, infrared spectroscopy and thermal behaviour of the intercalated and raw kaolinite is used as a tool to evaluate the weakening of the layer-layer interactions and stability of the intercalated product.

MATERIAL AND METHODS

A kaolinite from the Mayouom deposit located at the bottom of a mylonitic cliff in western Cameroon is used in this study. The genesis of this kaolin has been established by [START_REF] Njoya | Genesis of Mayouom kaolin deposit (western Cameroon)[END_REF] as a result of a hydrothermal process. This clay has been thoroughly described in the frame of its possible use in ceramic products [START_REF] Djangang | Sintering behaviour of porous ceramic kaolin-corundum composites: Phase evolution and densification[END_REF][START_REF] Njoya | Microstructural characterization and influence of manufacturing parameters on technological properties of vitreous ceramic materials[END_REF][START_REF] Nkoumbou | Kaolin from Mayouom (Western Cameroon): Industrial suitability evaluation[END_REF][START_REF] Djangang | Refractory ceramics from clays of Mayouom and Mvan in Cameroon[END_REF][START_REF] Kamseu | Characterisation of porcelain compositions using two china clays from Cameroon[END_REF].

The sample used in the present study was taken at 3 m depth. The fraction < 40 µm, labelled K3, was collected by means of wet sieving. Using major elemental composition of the sample obtained by inductive coupled plasma by atomic emission spectrometry (ICP-AES), an approximation of the structural formula of the kaolinite phase was found to be (Al 1.94 Fe 0.06 )(Si 1.98 Fe 0.02 )O 5 (OH) 4 (Mg 0.02 Ca 0.002 ). The mineralogical composition of the clay sample, estimated from the chemical composition (table I), the structural formula of the kaolinite phase and from the mineral composition determined by powder X ray diffraction (figure 1), is as follows: Kaolinite 83.3%; Illite 10.4 %; Titanium oxide 3.4 %. DMSO intercalated kaolinite (labelled K3-D) was prepared using the method described by [START_REF] Gardolinski | Layered polymer-kaolinite nanocomposites[END_REF], excepted that the preparation was performed at room temperature and lasted for 20 days, instead of short stirring at 60 °C followed by a lasting period of 10 days. Typically, 9g of kaolinite were mixed with 60 mL of DMSO and 5.5 mL of demineralised water and left for a 20 days stay. The time-lasting of DMSO intercalation in the clay was tested after 3-years conservation of the dried intercalated samples.

Displacement of the DMSO from the kaolinite was performed using ethyl acetate and ammonium acetate by Prolabo. The respective products are labelled K3-EA and K3-AA. For the K3-AA product, 1 g of K3-D was left to stay at room temperature for 72 hours in 20 mL of a saturated aqueous solution of ammonium acetate. For the K3-AE product, 2 g of K3-D were heated under stirring at 60 °C in 15 mL of ethyl acetate during 5 minutes and left for a 48 hours stay. For both preparations, the collected clay cake after gravimetric filtration on a 8 µm filter (Whatman grade 40) was left to dry at ambient temperature.

X-Ray powder diffraction patterns were recorded using a D8 Advance Bruker diffractometer equipped with a Co Kα radiation ( = 1.7890 Å) operating at 35 kV and 45 mA. The diffraction patterns were obtained from 1.5° to 32° at a scanning rate of 1° min -1 .

Infrared spectra were recorded in diffuse reflection mode using a Bruker IFS 55 spectrometer.

The spectra, recorded from 4000 cm -1 to 600 cm -1 with a resolution of 4 cm -1 , are accumulation of 200 scans.

Scanning Electron Microscopy (SEM) was performed on a Hitachi S-4800 using a YAG (Yttrium Aluminium Garnet) backscatter secondary electron detector for morphological observation on the raw and DMSO-intercalated kaolinite.

Thermal analysis was performed on a home made Control Rate Thermal Analysis (CRTA) apparatus equipped with a mass spectrometer. In CRTA, the temperature increase is not imposed but in controlled by the reaction rate through pressure measurement. The sample is placed under dynamic vacuum through a micro leak that is calibrated so that the emitted gases can be quantified. The limiting pressure is fixed at 2 Pa, which ensures a linear weight loss with time. The emitted gases are analysed by a Balzers (QMS, QMA and QME 200 Pfeiffer Vacuum) mass spectrometer [START_REF] Feylessoufi | Water Environment and Nanostructural Network in a Reactive Powder Concrete[END_REF].

RESULTS AND DISCUSSION

Intercalation and displacement of the DMSO molecules

The X-ray diffraction patterns (figure 1a) show a complete shift of the characteristic d 001 peak of kaolinite from 7.19 Å to 11.26 Å. This shift is in accordance with a full monolayer intercalation of DMSO giving rise to a 4.06 Å increase of the basal spacing [START_REF] Fang | Intercalation of dimethyl sulphoxide in kaolinite: Molecular dynamics simulation study[END_REF].

The presence of interlayer DMSO is evidenced on the FT-IR spectrum (figure 2a) by the S=O stretching at 1095 cm -1 and by the modification of the external inner surface OH stretching mode at 3693, 3668 and 3651 cm -1 (figure 2b) due to interactions of the sulfonyl group in DMSO with the surface Al-OH groups of the clay. The decrease of the band at 3693 cm -1 is related to the interaction of the external inner surface hydroxyl with the sulfonyl group in the DMSO molecule. The bands at 3540 cm -1 and 3498 cm -1 account for the hydrogen bond of the DMSO molecules to some inner surface hydroxyl group of the kaolinite layer [START_REF] Johnston | Vibrational spectroscopic study of the interlamellar kaolinite-dimethyl sulfoxide complex[END_REF][START_REF] Olejnik | Infrared Spectra of Kaolin Mineral-Dimethyl Sulfoxide Complexes[END_REF]. The C-S-C symmetric and asymmetric stretching at 659 cm -1 and 700 cm -1 (figure 2a) in the pure liquid DMSO are observable in the intercalated kaolinite at 661 cm -1 and 719 cm -1 (figure 2c).

The bending mode of the Al-OH (figure 2 d) is shifted to higher wavelength, due to interaction with DMSO. The Si-O, in plane vibrations at 1020 and 1112 cm -1 (figure 2e) are shifted to lower wavelengths. These shifts are evidences for the inner surface oxygen atom interactions with DMSO. Given that, interlayer bonds in kaolinite are due to Al-OH and Si-O interactions, the interactions of these functions with DMSO, necessarily results in weakening of the layer-layer interactions and therefore of the crystallite cohesion.

The weakening of the inter-layer interactions is further shown by the dehydroxylation temperature recorded by CRTA (figure 3a and3b). The dehydroxylation of the kaolinite is completed at 408°C for the raw kaolinite, and at 275 °C for the DMSO-intercalated kaolinite.

The changes in pressure are used to detect the dehydroxylation temperature. Mass spectrometry measurements (figure 4a) support this observation. The ion current due to water fragments is plotted as a function of time. The trend of this curves reveal three temperatures of water release (figure 4a) assigned respectively to hydration water (64 -90 °C) and to structural water of the kaolinite (408 °C in the raw kaolinite and 273 °C in the DMSOintercalated kaolinite). The degradation of the intercalated DMSO is observed at 186 °C and the ion currents of both the S=O fragment (m/z = 48) and the CH 3 -S-CH 3 fragment (m/z = 62) are consistent (figure 4a) with the degradation of DMSO at 186 °C. The lowering of the dehydroxylation temperature is consistent with lower energy for the interlayer bonds within the clay, in accordance with the conclusion drawn from FT-IR spectra, (figure 2d, and2g).

The time lasting of the DMSO intercalation in kaolinite was clearly shown by X-ray pattern as well as FTIR spectroscopy that remain unchanged after three years conservation of the sample in a polyethylene bag under ambient temperature. The presented figure 3 and4 from CRTA as well as the SEM images (figure 6) were obtained using a three years old sample.

The comparison with a one month age sample (figure 3b), further confirms the time lasting of DMSO intercalation within the kaolinite. For the one month old sample, the dehydroxylation of the kaolinite is observed at 240 °C. The difference between the dehydroxylation temperatures for the one month and the three year old samples is possibly due to an increase stability of the DMSO-Kaolinite interactions with time as a consequence of the attendant release of co-intercalated water molecules.

Contact with ethyl-acetate leads to almost complete displacement of the DMSO as shown by the disappearance of the peak at 11.26 Å from XRD (figure 1b), which is characteristic of DMSO intercalation. This complete displacement is also evidenced by the O-H stretching modes (figure 5b), which are almost the same for K3-AE and the raw K3, and by the absence of the S=O stretching due to DMSO at 1099 cm -1 (figure 5c). The FT IR spectrum for the K3-AE product does not show the carbonyl vibration mode (figure 5e) and the Al-OH bending returns to 916 cm -1 as observed in the raw kaolinite (figure 5f). All these observations indicate that the ethyl acetate is not intercalated. However, the stretching and bending bands of C-H on the FTIR spectrum of K3-AE (figure 5a), indicate traces of remaining DMSO within the kaolinite and this presence is evidenced by mass spectroscopy during CRTA (figure 4c) through the ion current of the fragments m/z = 48 (for S=O) and m/z = 62 (for CH 3 -S-CH 3 ). The fact that ethyl acetate does not replace DMSO is probably due to the low polarity of this molecule (dipole moment 1.88) because high dipole moment is a requirement for intercalation in kaolinite [START_REF] Lagaly | Nanohybrid materials from the intercalation of imidazolium ionic liquids in kaolinites[END_REF]. Hence hydrogen bonds of interest are not formed between this compound and the hydroxyl groups within the kaolinite.

The use of ammonium acetate also leads to DMSO displacement as shown by the presence of the characteristic basal peak of kaolinite at 7.15 Å (figure 1b). Unlike ethyl acetate, ammonium acetate partially replaces DMSO between the clay sheets. The partial displacement of DMSO is evidenced by X-ray patterns, since the peak at 11.26 Å due to DMSO intercalation is still observable (figure 1b). Also, the IR vibrations mode of S=O from DMSO at 1095 cm -1 are detected on the IR spectrum (Figure 5c). The 14.38 Å XRD peak, although weak, is consistent with that described by [START_REF] Itagaki | Synthesis of a kaolinite-poly(βalanine) intercalation compound[END_REF] and [START_REF] Sugahara | Evidence for the formation of interlayer Polyacrylonitrile in kaolinite[END_REF] for ammonium acetate intercalated kaolinite. It is then suggested that intercalation of ammonium acetate occur in K3-AA. The FT-IR spectra clearly show the presence of ammonium ions within the clay through the bending mode of NH 4 + that are observed at 1419 cm -1 (figure 5b) and the carbonyl stretching mode at 1598 cm -1 (Figure 5e). The replacement of DMSO by ammonium acetate is associated to the formation of interactions of greater energy than DMSO interactions with the kaolinite hydroxyl groups and this is well confirmed by the bending modes of Al-OH on figure 5f, where the Al-OH bending mode are moved to higher energy compared to the displacement due to DMSO intercalation.

The ion current due to water release during CRTA (figure 4b), clearly shows that the K3-AE and K3-AA have lower dehydroxylation temperatures as proof of the weakening of interlayer bonds. On figure 4b, three dehydroxylation temperatures (90 °C, 362 °C, 417 °C) for K3-AA and two (90 °C and 392 °C) for K3-AE are observed. The dehydroxylation at 362 °C is associated to the part of kaolinite co-intercalated with ammonium acetate and DMSO and at 417 °C we have the dehydroxylation of the recovered kaolinite due to DMSO displacement.

The evidence for the dehydroxylation of kaolinite co-intercalated with ammonium acetate and DMSO, is given by the ion current of the fragment of m/z = 14 (related to nitrogen in ammonium acetate) and the fragment of m/z = 48 (related to S=O from DMSO) (figure 4b).

At 392 °C the dehydroxylation of the kaolinite recovered from the displacement of DMSO by ethyl acetate is observed and at 90 °C for both K3-AA and K3-AE, the release of the hydration water is observed. The thermal stability of the kaolinite is decreased by the intercalation. Gabor et al (1995) reported the same conclusion in their study of Hydrazine and potassium acetate intercalated kaolinite. The thermal stability, of the kaolinite phase obtain after DMSO displacement, is significantly different and this is due to the induced disordering upon DMSO displacement.

Because the dehydroxylation of the recovered kaolinite after DMSO displacement with acetate ammonium is higher for the recovered kaolinite using ethyl acetate for DMSO displacement, then, one can conclude that, the kaolinite recovered by DMSO displacement with ammonium acetate is less disordered. This observation suggest a high disordering by displacement with ethyl acetate in comparison to displacement by ammonium acetate. The displacement rate may be the cause of this difference. The thermal treatment in the synthesis protocol for the K3-AE is probably the cause of this high displacement rate.

Effect of the DMSO intercalation and displacement on the kaolinite structure

The DMSO intercalation does not modify the initial kaolinite structure, since the number of layers per crystallite, determined from the coherent domain thickness after the Scherrer equation, remains constant (table II). The SEM micrographs (figure 6) show the morphological evolution due to intercalation. On this image, one can clearly observe that clay stacks appear to be thinner in the intercalated kaolinite than in the raw clay. The intercalation of the kaolinite is evidenced and the conservation of the layer ordering is also observable.

The subsequent displacement of DMSO, strongly affects the kaolinite crystalline structure as shown by the broadening and almost vanishing of the d 001 peaks on the X-ray patterns (figure 1b). The displacement using ethyl acetate dramatically disorders the kaolinite crystallites.

Heller-Kallai and al. (1991) also reported crystallinity reduction in kaolinite samples after DMSO displacement by heating or washing in water. In this study, the drastic change in the crystallinity is probably due to the displacement rate which induce an important disordering particularly for the K3-AE product.

The calculated thickness of the coherent domain in K3-EA shows an increase compared to the pristine kaolinite (from 169 Å to 451 Å) (table II) given a number of layers per crystallite twice as much as in the raw kaolinite (from 25 to 62). In addition, the basal distance for the d 001 peak is substantially different from that of the pristine kaolinite (7.29 Å in K3-EA against 7.19 Å in the raw material). The explanation of these differences is that high disordering takes place which result in a value for the coherent domain thickness which is not associated to the number of layer per crystallite but rather evidenced the random orientation of clay sheet upon DMSO displacement. Consequently, the number of sheets per crystallite calculated is aberrant. The displacement of DMSO using ethyl acetate does not allow the clay sheets to fall down following a path close or identical to the DMSO intercalation path. In the case of ammonium acetate, the return path of the clay sheets is almost identical to the initial route of DMSO intercalation. The number of layer in kaolinite pseudo-crystal after DMSO displacement is 25 layers per crystallite (against 24 in the raw kaolinite) and the basal distance is 7.15 Å (7.19 in the raw kaolinite). All of which indicates that the kaolinite phase recovered after the DMSO displacement is structurally very close to initial kaolinite. The dehydroxylation temperature from CRTA also supports this conclusion.

The ammonium acetate intercalation gives rise to a ternary composite and makes it evident that the DMSO displacement is a route for composite preparation. The intercalation ratios (or degree of reaction) within this ternary composite was calculated using the equation below.

One must keeps in mind that this equation does not consider the influence of lorentz and polarization factors, the interstratification and layer shape (distortion for example). Hence the relationship is used, assuming, for both expanded and unexpanded phase, the same degree of particles orientation [START_REF] Lagaly | Nanohybrid materials from the intercalation of imidazolium ionic liquids in kaolinites[END_REF][START_REF] Wang | The influence of intercalation rate and degree of substitution on the electrorheological activity of a novel ternary intercalated nanocomposite[END_REF][START_REF] Olejnik | Infrared Spectra of Kaolin Mineral-Dimethyl Sulfoxide Complexes[END_REF].

I.R = I 001intercalate / (I 001intercalate + I 001Kaolinite )

where I 001intercalate is the d 001 peak intensity due to intercalation; I 001Kaolinite is the residual intensity of kaolinite basal peak in the intercalated product and I.R is the intercalation ratio.

The calculated intercalation ratios are 57.7 % and 62.4 % respectively for ammonium acetate and DMSO intercalation. The preparation conditions probably determines the intercalation ratios and one can imagine that setting the preparation conditions, for DMSO displacement, will help designing the desired composite. In addition, the structural differences in the recovered kaolinite after DMSO displacement are due to the displacement rate. Ethyl acetate leads to a rapid displacement of DMSO which contributed to higher disordering in the recovered kaolinite whereas ammonium acetate displacement is less rapid and allows the sheets to almost return to their initial position. This conclusion is corroborated by the results from CRTA. Hence depending on the purpose, the use of DMSO displacement as a route for composite preparation may either need a rapid or low rate for the displacement of the intercalated molecule. In particular, for clay dispersion in a polymer matrix, a rapid and efficient displacement may be needed.

CONCLUSION

This study shows the weakening effect of DMSO intercalation in kaolinite and point out the benefits that could be derived from DMSO displacement as a pathway for composite making.

The evidence of the intercalation is clearly observed on X-ray patterns and FT-IR spectra. The Hence, if conevenient and adapted conditions are set, the displacement of DMSO from DMSO intercalated kaolinite could be used as a route for composite preparation. In particular, for polymer-clay composite, a rapid displacement may help to obtain optimal dispersion and distribution of the kaolinite as filler within the polymer matrix. The present conclusions have served as basis for the preparation of cassava starch-kaolinite composite films. The evaluation of the films properties changes confirms that the use of DMSO-intercalated kaolinite is advantageous and the results are subject of a companion paper [START_REF] Mbey | Cassava-starch kaolinite composite film. Effect of clay content and clay modification on film properties[END_REF].

  interlayer interactions are weakened, as revealed by the IR bending modes of Al-OH and the in plane vibrations of Si-O in the kaolinite. This is further confirmed by the dehydroxylation temperature observed in CRTA. The DMSO intercalation is a time lasting modification of the kaolinite. The total displacement of the intercalated DMSO is achieved in hot ethyl acetate medium leading to a random orientation of the clay sheets in the recovered kaolinite due to a great disturbance of the clay sheets interactions. The disordered kaolinite obtained is a consequence of a rapid displacement of the intercalated DMSO. Displacement of DMSO by ammonium actetate follows a path which is similar to that of DMSO intercalation, and a ternatry composite, ammmonium acetate/DMSO/kaolinite is formed.

Figure 2 :

 2 Figures and Captions

Acknowledgement

University of Yaounde I (Cameroon) for laboratory facilities for the synthesis of the kaolinite derivatives.

INPL Nancy (France) for a Doctorate research grant.