Note publique d'information : LA REFLECTOMETRIE LASER A ANGLE FIXE A CONSTITUE LA PRINCIPALE TECHNIQUE EMPLOYEE
DANS CETTE ETUDE AFIN D'ANALYSER LA CROISSANCE DES FILMS MULTICOUCHES. CETTE TECHNIQUE
OPTIQUE PERMET DE SUIVRE LES VARIATIONS DES PROPRIETES DE REFLEXION D'UN FAISCEAU
DE LUMIERE LASER POLARISEE A L'INTERFACE SOLIDE/SOLUTION OU L'ON GENERE LE FILM MULTICOUCHE.
LA REFLECTOMETRIE LASER SE REVELE AINSI TRES UTILE POUR L'ETUDE DE L'EFFET DES CONDITIONS
EXPERIMENTALES SUR LA CROISSANCE D'UNE MULTICOUCHE DE POLYMERES. NOUS NOUS SOMMES
INTERESSES A LA CONVERSION DU SIGNAL REFLECTOMETRIQUE EN QUANTITE DE POLYMERE ADSORBE.
EN EFFET, EN COMPARANT LES RESULTATS OBTENUS PAR REFLECTOMETRIE ET PAR MICROBALANCE
A QUARTZ EN MILIEU LIQUIDE, L'ABSENCE D'UNE RELATION LINEAIRE ENTRE CES DEUX PARAMETRES
A ETE MISE EN EVIDENCE. NOUS AVONS ALORS DEVELOPPE DEUX NOUVELLES METHODES PERMETTANT
DE QUANTIFIER L'EPAISSEUR ET L'INDICE DE REFRACTION MOYENS DE LA MULTICOUCHE (METHODE
DES EPAISSEURS OU DES REFLECTIVITES). DANS LA DEUXIEME PARTIE DU TRAVAIL, EN COMBINANT
LES ANALYSES PAR REFLECTOMETRIE ET PAR MICROSCOPIE A FORCE ATOMIQUE (AFM), NOUS AVONS
MONTRE L'EFFET PREPONDERANT DE LA NATURE DU SUBSTRAT SUR LA CROISSANCE ET LA MORPHOLOGIE
DES FILMS DE MADQUAT/PAA. ENFIN, L'INFLUENCE DES PRINCIPAUX PARAMETRES PHYSICO-CHIMIQUES
(FORCE IONIQUE, TYPE DE SEL, PH) A ETE ETUDIEE. AFIN D'INTERPRETER LES RESULTATS EXPERIMENTAUX,
NOUS AVONS PROPOSE UN MECANISME MONTRANT QUALITATIVEMENT COMMENT LE DEPOT INITIAL
D'ILOTS DE POLYMERES, DETERMINE PAR LES INTERACTIONS ELECTROSTATIQUES, CONDUISAIT
A UNE CROISSANCE HETEROGENE ET DE TYPE EXPONENTIEL DU FILM TELLE QUE NOUS L'AVONS
OBSERVEE DANS CETTE ETUDE.
Note publique d'information : THE IN-SITU LAYER-BY-LAYER DEPOSITION (LBL) OF POLYELECTROLYTES WAS STUDIED BY OPTICAL
REFLECTOMETRY. THIS METHOD WAS BASED ON THE MEASUREMENT OF THE RELATIVE CHANGE OF
INTENSITIES OF A POLARIZED LASER BEAM ON A PLANAR SUBSTRATE WHERE THE FILM WAS FORMED.
OPTICAL REFLECTOMETRY IS A POWERFUL TOOL TO STUDY IN-SITU THE EFFECT OF EXPERIMENTAL
VARIABLES ON THE LBL DEPOSITION. IN THE FIRST PART WE FOCUSED ON THE CONVERSION OF
THE REFLECTOMETRIC SIGNAL IN POLYMER UPTAKE. COMPARISON BETWEEN REFLECTOMETRIC OUTPUT
AND LIQUID QUARTZ CRYSTAL MICROBALANCE MEASUREMENTS SHOWED INDEED NO LINEAR RELATIONSHIP.
TWO NEW ROUTES WERE THEREFORE DESIGNED TO QUANTIFY INDEPENDENTLY THE MEAN THICKNESS
AND THE REFRACTIVE INDEX OF THE LAYER (FUTHER CALLED THICKNESS METHOD AND REFLECTIVITY
METHOD). IN THE SECOND PART OF THE STUDY WE SHOWED THE DETERMINING INFLUENCE OF THE
NATURE OF THE SUBSTRATE ON THE GROWTH AND MORPHOLOGY OF THE MADQUAT/PAA FILM, OWING
TO THE COMBINATION OF REFLECTOMETRIC MEASUREMENTS AND ATOMIC FORCE MICROSCOPY IMAGING
(AFM). FINALLY, THE EFFECT OF THE PRINCIPAL PHYSICO-CHEMICAL PARAMETERS (IONIC STRENGTH,
NATURE OF THE SALT, PH) ON THE FILM FORMATION WAS STUDIED. AIMING AT RATIONALIZING
THE EXPERIMENTAL RESULTS A GROWING MECHANISM WAS PROPOSED WHERE, DUE TO THE HIGH CHARGE
DENSITY OF THE POLYELECTROLYTE,THE FIRST BILAYER IS ACTUALLY A DISTRIBUTION OF DISTANT
ISLANDS ON THE SUBSTRATE, CAUSING INITIALLY AN HETEROGENEOUS GROWTH THAT LEADS TO
THE FORMATION OF PEAKS AND HOLES AS SEEN WITH AFM. THE LATER MECHANISM MAY ALSO
EXPLAIN THAT WE HAVE OBSERVED RATHER AN EXPONENTIAL THAN A LINEAR GROWTH RATE VERSUS
DEPOSITION STEP NUMBERS.
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