The behavior of the system consisted by mixture of two different molecular weight hyaluronates and surfactant was investigated. Mixtures were 17 kDa hyaluronate with 1,46 MDa, 73 kDa with 1,46 MDa, 300 kDa with 1,46 MDa, 806 kDa with 1,46 MDa and 1800 kDa with 1,46 MDa. These compounds were always mixed in the weight ratios 70:30, 50:50 and 30:70. As the surfactant cetrimonium bromide and TWEEN 20 were used. Interactions were studied in aqueous solution with different ionic strength. Sudan red was used as hydrophobic dye. In all experimental series with cetrimonium bromide was observed phenomenon of discontinuous separated phases, described as pearls. Samples containing pearls were tested on stability, were dried and rehydrated back, as were also heated in solution. Subsequently, the particle size was measured in the remaining sample after pearls were filtrated. Mixtures of hyaluronate were characterized by measuring the viscosity using rheology microrheology. It was found that these compounds are heterogeneous and each sample point is not the same viscosity.

Ces travaux de thèse présentent une étude expérimentale des fluctuations d'une particule Brownienne soumise à deux différentes conditions hors-équilibre dans un fluide . Le but est de comprendre d'une manière générale la relation entre les fluctuations spontanées, la fonction de réponse linéaire et la production totale d'entropie des processus loin de l'équilibre thermique. La première partie est consacrée à l'étude du mouvement d'une particule colloïdale dans un état stationnaire périodique hors-équilibre induit par une force non-conservative et à sa réponse à une perturbation externe. Nous analysons la dynamique du système dans le contexte des différentes approches généralisées de fluctuation-dissipation. Nous montrons que ces relations théoriques sont satisfaites par les données expérimentales quand on prend en compte le rôle du courant du à la rupture du bilan détaillé. Dans une deuxième partie nous étudions les fluctuations et la réponse d'une particule Brownienne dans deux types de bains vieillissants qui relaxent vers l'équilibre thermique: un verre colloïdal de Laponite et une solution aqueuse de gélatine. Dans ce cas-là nous montrons que le flux de chaleur de la particule vers le bain pendant sa relaxation représente une correction hors-équilibre du théorème de fluctuation-dissipation. Donc, le flux de chaleur joue le même rôle que le courant dans un état stationnaire. En conséquence, les résultats de la thèse mettent en évidence l'importance générale de la production totale d'entropie pour quantifier les relations de fluctuation-dissipation généralisées dans les systèmes hors-équilibre. / This thesis describes an experimental study on fluctuations of a Brownian particle immersed in a fluid, confined by optical tweezers and subject to two different kinds of non-equilibrium conditions. We aim to gain a rather general understanding of the relation between spontaneous fluctuations, linear response and total entropy production for processes away from thermal equilibrium. The first part addresses the motion of a colloidal particle driven into a periodic non-equilibrium steady state by a nonconservative force and its response to an external perturbation. The dynamics of the system is analyzed in the context of several generalized fluctuation-dissipation relations derived from different theoretical approaches. We show that, when taking into account the role of currents due to the broken detailed balance, the theoretical relations are verified by the experimental data. The second part deals with fluctuations and response of a Brownian particle in two different aging baths relaxing towards thermal equilibrium: a Laponite colloidal glass and an aqueous gelatin solution. The experimental results show that heat fluxes from the particle to the bath during the relaxation process play the same role of steady state currents as a non-equilibrium correction of the fluctuation-dissipation theorem. Then, the present thesis provides evidence that the total entropy production constitutes a unifying concept which links the statistical properties of fluctuations and the linear response function for non-equilibrium systems either in stationary or non stationary states.

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Les méthodes d'imagerie et de vélocimétrie ultrasonores ont prouvé leur efficacité pour étudier des matériaux divers. À haute intensité, il est connu que les ultrasons exercent des forces stationnaires dans les fluides newtoniens, par le biais d'effets non linéaires comme la pression de radiation acoustique. Néanmoins, ces effets n'ont encore jamais été exploités d'un point de vue fondamental dans le contexte de la physique des matériaux mous. L'objet de cette thèse est d'exploiter l'interaction d'ultrasons de puissance avec des matériaux bloqués afin de sonder activement, voire d'influencer leurs propriétés mécaniques. Nous proposons tout d'abord une méthode de microrhéologie active : la « mésorhéologie acoustique ». En analysant le mouvement d'un intrus sous l'effet de la pression de radiation acoustique, nous caractérisons localement la rhéologie du matériau étudié. Nous mettons cette technique en œuvre avec un fluide à seuil simple : un microgel de carbopol. Nous exploitons les résultats obtenus à la lumière d'une caractérisation rhéologique poussée du comportement de ce matériau en dessous de son seuil d'écoulement et proposons diverses pistes d'amélioration du dispositif.Ensuite, nous décrivons la mise en écoulement d'un empilement granulaire immergé par des ultrasons intenses focalisés et comparons les observations aux résultats de simulations de dynamique moléculaire. La transition de fluidification observée car l'injection d'énergie y est discontinue. Elle est intermittente et hystérétique, propriétés reproduites par des simulations numériques et dont un modèle phénoménologique simple permet de rendre compte.Enfin, en remplaçant le plan d'un rhéomètre classique par un transducteur ultrasonore, nous mesurons l'effet de vibrations à haute fréquence sur les propriétés mécaniques d'un gel colloïdal fragile de noir de carbone. Nous observons un effet significatif et potentiellement irréversible des ultrasons sur le module élastique et sur la mise en écoulement de ce système. Les vibrations semblent favoriser le glissement du gel aux parois mais il semble toutefois qu'elles induisent également des changements en volume dans l'échantillon. / Ultrasonic imaging and velocimetry has been proved to be very efficient methods to study various materials. At high intensity, ultrasonic waves are known to exert steady forces in newtonian fluid through nonlinear effects like the acoustic radiation pressure. However those effects have never been used in fundamental studies of the physics of soft materials. This thesis aims at exploiting the interaction between high intensity ultrasound and soft jammed materials to probe actively and even modify their mechanical properties.We first introduce an alternative technique for active microrheology we called « acoustic mesorheology ». By analyzing the motion of an intruder under the acoustic radiation pressure we characterize locally the rheology of the system under study. We test this technique on a simple yield stress fluid, namely a carbopol microgel. We compare the results with those obtained by standard rheology measurements of the behaviour of this gel under its yield stress.Then we describe the fluidization of an immersed granular packing by high intensity focused ultrasound. We compare our observations with the results of molecular dynamics simulations. The obtained fluidization is original as the injection of energy is discontinuous in time. It is hysteretic and intermittent and those properties are well captures by both simulations and a phenomenological model.Finally, we replace the plane of a standard cone-plate rheometer by an ultrasonic transducer. This allows us to characterize the effect of high frequency vibrations on the rheology of a fragile carbon black gel. We observe a significant and eventually irreversible effect of ultrasound on the elastic modulus and on the yielding of the system. Vibrations are shown to favor wall slip but seem to induce changes in the volume of the sample though.

This thesis describes the study on structure and dynamics of various kinds of molecular membranes in general. We have studied the morphological transition of colloidal as well as biologically relevant membranes and qualitatively argued regarding the interplay between structure and dynamics. Systematic measurements have been performed to address the issue of ambiguous behavior of molecules under stress when its confined at the interface. The structural and dynamical effect on interfacial membranes have been studied for soft colloidal free standing langmuir monolayer as well as for the quasi two dimensional lipid membranes on solid supports. For organic nanoparticle monolayer we have observed a correlation between the nanoparticle raft dynamics and the underlying morphological transition. In this study we have also found a non-monotonic behavior of dynamical heterogeneity with time which is unusual for a colloidal system in common and beyond the prediction of Mode Coupling Theory. In the case of lipid membrane, we have given an experimental evidence of lipid molecular rearrangement process at molecular level when its perturbed by foreign entities. Using sophisticated X-Ray scattering techniques, we were able to capture the subtle changes happening in the assembly of lipid molecules in a planar bilayer structure when it interacts with molecules having biological relevance. In the next level we have used lipid membranes as an active plat-form to study the physical interaction with several kinds of nanoparticles and explored the mechanism of active participation of lipid molecules in self assembly process. Besides with the help of Fluorescence Correlation Spectroscopy, we have also studied the effect of nanoparticles assemblies on the dynamics of lipid molecules itself. In Chapter 1, we have provided the background along with a brief review of the existing literature for understanding the results represented in the subsequent chapters. This includes discussion on the various physical properties of our systems of interest, including dynamic behavior of colloidal particles in different concentration regime and a detailed theoretical understanding regarding the glass transition and jamming transition for a highly dense colloidal packing. In this section we have also discussed the advantages of interfacial microrheology technique over conventional bulk rheology in terms of efficiency and sensitivity. Here we have also pointed out the formulation of the multi-particle tracking method for achieving different parameters which are correlated in space and time for a given system. Followed by that the Dynamical Susceptibility and the anomaly in Van Hove correlation function, for a heterogeneous system has been argued thoroughly. Towards the end we have discussed about the general features of another type of two dimensional membrane i.e. the lipid membrane at interface. Using raft theory we have also tried to give a plausible explanation of the dynamical heterogeneity of the real cell membrane which is mimicked by the model supported lipid membrane. Here we have argued about the structural six fold symmetry of a compact monolayer. Finally in the last part we have summarized the theoretical aspects of the lipid molecule mediated self assembly process and the how the lipid diffusion plays a vital role in it. Chapter 2 deals with the aspect of measuring the morphological transition and its effect on the dynamics for a two dimensional membrane at air/water interface. It starts with the discussion on the synthesis method for various types of organic molecule grafted nanoparticles like Cadmium Selenide(CdSe Quantum Dots) and Gold Nanoparticle(Au NPs) of different size and properties and followed by a preparation method of 2D film at air/water interface and on solid substrate using Langmuir-Blodgett method. In this chapter we have discussed about the basic principles of several experimental tools like Brewster Angle Microscopy(BAM), Laser Scanning Confocal Microscopy(LSCM), Atomic Force Microscopy(AFM), Thermogravimetric Analysis(TGA), X Ray Reflectivity(XRR), Grazing Incidence Diffraction(GID), Fluorescence Correlation Spectroscopy(FCS) etc. Chapter 3 explains the main aspects of the microscopic dynamics in dense amorphous nanoparticle monolayer at the air-water interface. In this study we have found a transition in mechanical properties, tracked down through the systematic variation of isothermal compressibility(�) with increasing two dimensional packing fraction of nanoparticle rafts up to the area fraction of Φ∼0.82 using Laser Scanning Confocal Microscope. Here we have used multi particle tracking method for a close packed gold monolayer with CdSe tracer to estimate different dynamical properties like Mean Square Displacement(MSD), Dynamical Heterogeneity etc. These calculations indeed point out the non-monotonic variation of the amplitude in the four-point dynamic susceptibility (χ4), a signature of spatio-temporal extension of correlated domains. Along with that we have also observed the anomaly in trend for the inherent relaxation time τ∗with increasing area fraction(Φ). Interestingly the variation in χ4exactly follows the systematic we found for the isothermal compressibility( �) with increasing Φ and that indicates the connection between the observed macroscopic transitions in mechanical properties and the microscopic dynamical phase transitions. Finally we have given a possible explanation of these kind of events in terms of the interaction between this sterically stabilized nanoparticle domains with the help of interpenetration of the capping long chain polymers of the neighboring nanoparticle. Chapter 4 opens up the possibilities of probing the hidden features of biomembranes at molecular scale with the help of very precise techniques based on synchrotron X ray diffraction. Here we have studied the rearrangement of the lipid molecules of an artificial membrane on a solid support as an effect of ad-sorption of organic branched molecules. In this work we have used non toxic PETIM dendrimers of two different generations, i.e. G3and G4which differs a lot in terms of size, no of termination groups, molecular weights and protonation states. Our initial measurements shows quantitatively the in-plane and out of plane symmetry breaking of the lipid bilayer as a result of the interaction with these two types of molecules. The molecular adsorption effect was quantified in terms of thickness reduction and the change in the scattering length density(SLD) or the electron density of the top layer in out of plane reflectivity model. Interestingly both the dendrimers showed different behavior and the interaction reflected in terms of membrane penetration was found stronger for higher generation. On the other hand the GID measurement indicates an enhancement of the in plane unit cell dimension and associated parameters of the arrangement of lipid molecules as a result of interaction with dendrimers. The combined XRR and GID measurements indicate a local fluidization of lipid packing as an outcome of charged branched molecules adsorption on the membrane surface. Chapter 5 is summarizes the lipid mediated self assembly process of nanoparticles on a bilayer and how the interaction changes the local properties of the bilayer represented by the molecular diffusivity. In this study we have used particles of wide variety of features in terms of size, charge, functionality, polarity etc and found a quite dramatic effect in the nanoparticle adsorption event on a solid supported Lαphased DMPC lipid bilayer. We have also seen that de-pending on the concentration and amount of surface charge the nanoparticles form two dimensional regular self assembled patterns on the bilayer surface. In FCS measurement, we have also found a second group of dynamics ( distribution of diffusivity) along with the normal bilayer diffusion which has been identified as the diffusion of the lipid molecules where nanoparticles are adsorbed. The inherent increment in diffusivity supports the argument of local fluidization in lipid membrane in presence of charged nanoparticle as we have observed in our XRR and GID data described in chapter 4. Chapter 6 contains the summary and the future perspective of the work presented here.