A une époque où la miniaturisation est l'un des principaux défis de la science, la physique du mouillage aux petites échelles est loin d'être complètement comprise. Le rôle structurant des interfaces, les hétérogénéités du substrat ou l'occurrence d'effets dits de "ligne" commencent à se faire sentir. Le but de la présente thèse, expérimentale, est d'apporter de nouveaux indices permettant le développement des analyses théoriques. Deux systèmes à petite échelle et complexes ont été étudiés : les films minces de cristaux liquides sur substrat liquide et les précurseurs de liquides ioniques sur substrats solides. La description des propriétés de mouillage des cristaux liquides nématiques nécessite deux ingrédients s'ajoutant à ceux des liquides usuels : l'élasticité, qui est source d'interactions à longue portée et l'ancrage qui décrit le rôle spécifique joué par les conditions aux limites. Sur un substrat liquide, les films minces nématiques avec des conditions d'ancrage antagonistes montrent des structures complexes ainsi qu'une coexistence d'épaisseurs. Différents systèmes ont été étudiés au microscope optique dans la gamme de température nématique et aux alentours de la transition nématique / isotrope. Les résultats ont été comparés aux modèles disponibles qui sont basés sur une théorie continue de l'élasticité nématique. Les liquides ioniques sont des sels surfondus à température ambiante. Ils sont devenus omniprésents dans l'industrie, ce qui explique que la compréhension de leur mouillage soit un sujet brûlant. De faibles quantités de liquides ioniques ont été déposées sur différents substrats, lisses ou rugueux. Le paysage que l'on obtient, gouttelettes et films minces, a été imagé par AFM (Atomic Force Microscopy). Les résultats ont été comparés aux modèles disponibles pour les films minces et les gouttes nanoscopiques.

Il est connu depuis 1831 que les fluides vibrés verticalement sont sujets à l'instabilité de Faraday. Au-dessus d'une certaine accélération dite accélération critique, des ondes stationnaires apparaissent à la surface du fluide et forment un motif géométrique caractérisé par une longueur d'onde critique. Dans ce travail nous montrons que la microstructure d'un fluide complexe peut se coupler fortement à l'instabilité et induire différents types de comportements selon le fluide étudié. Dans des solutions semi diluées de micelles géantes, la forte viscosité du fluide engendre des ondes stationnaires dans la hauteur du fluide. Dans des solutions diluées de micelles géantes, le cisaillement engendré par les ondes de surface conduit à un chargement de la microstructure se traduisant par un phénomène de rhéo-épaississement. Enfin, dans des suspensions de bâtonnets rigides, le couplage entre instabilité et microstructure induit un alignement localisé des bâtonnets.

Le mouillage d'un substrat soluble est une situation couramment rencontrée dans la vie de tous les jours les jours. Par exemple, les motivations pratiques de cette étude concernent la préparation de boissons à partir de poudres déshydratées, constituées de substances solubles dans l'eau telles que les glucides. Les modèles hydrodynamiques décrivant le mouillage sur un substrat non soluble ne peuvent pas expliquer les observations expérimentales dans le cas d'un liquide s'étalant sur un substrat soluble. Tay et al.(1) ont émis l'hypothèse que la fraction d'eau à la ligne de contact contrôle la valeur de l'angle de contact et ils ont montré l'importance du processus d'évaporation/condensation du solvant lors du mouillage. Dans cette étude, nous montrons que d'autres transferts de matière doivent être considérés pour améliorer la compréhension du processus de mouillage d'une couche soluble; ainsi la diffusion dans le polymère de l'eau condensée, ou directement depuis la goutte sont des processus qui contribuent à hydrater le substrat et modifier l'angle de contact de la goutte. Nous avons utilisé l'approche suivante pour réaliser cette étude: (i) pour prendre en compte la diffusion dans le substrat, nous avons réalisé des simulations en éléments finis qui permettent de valider nos arguments théoriques, (ii) des expériences d'étalement de goutte sur des couches minces de maltodextrine ont été réalisées afin d'étudier le mouillage et l'hydratation en avant de la ligne de contact. Ce travail nous permet de mettre en avant l'influence de la diffusion dans la couche qui complexifie les profils d'hydratation en avant de la ligne de contact, avec notamment l'apparition d'une région de diffusion où de l'évaporation est observée. Un diagramme de mouillage épaisseur-vitesse (e − U) avec différents régimes est établi. Nous validons ces régimes expérimentalement et plus particulièrement un régime où l'angle de contact est une fonction du produit eU. Par ailleurs, nous montrons l'influence de la transition vitreuse du polymère sur l'angle de contact et l'hydratation. Enfin, une étude préliminaire est réalisée pour comprendre l'influence de la dissolution du polymère lors du mouillage.

Avec l'avènement de la microélectronique et des techniques de miniaturisation, de nouveaux domaines transdisciplinaires sont nés au confluent des sciences de l'ingénieur, de la matière et du vivant. La technologie a désormais investi l'échelle du nanomètre ; elle parvient à sonder, mais aussi surtout à façonner les constituants élémentaires de la matière synthétique et organique, depuis les atomes jusqu'aux complexes macromoléculaires. La nécessité d'isoler des molécules et des assemblages supramoléculaires est motivée par leur découplage du milieu environnant avec lequel ils interagissent. Des stratégies de compartimentation se sont devéloppées pour répondre aux besoins grandissants d'isolement de ces entités, en particulier à travers deux approches classiques en nanotechnologie : top-down et bottom-up. L'approche top-down consiste à "sculpter" la matière pour lui conférer des dimensions compatibles avec les objets à confiner. La lithographie et les techniques de microfabrication en général rentrent typiquement dans cette catégorie. Des stratégies microfluidiques destinées à manipuler spécifiquement des assemblages supramoléculaires ont été ainsi développées soit en vu d'applications pour la microanalyse totale, soit pour des études biophysiques fondamentales. Dans l'approche bottom-up, des molécules de natures différentes sont agencées pour former l'entité qui va confiner les objets d'intérêt. La chimie et le vivant procèdent par cette approche pour synthétiser des assemblages supramoléculaires et des organismes. Dans cette optique, la compaction de polyélectrolytes par des agents lipidiques en particules nanométriques a été étudiée. Cette stratégie permet en particulier de transférer des gènes au sein des cellules. Enfin, toujours dans le cadre d'une approche bottom-up de la compartimentation, nous présentons une méthodologie résolument bio-inspirée qui exploite les propriétés naturelles d'auto-assemblage des virus. Cette autre statégie ouvre la voie à l'encapsulation d'une large variété de molécules et de nano-objets. Elle tire avantage de l'extraordinaire précision moléculaire de l'assemblage d'un virus et vise à tirer profit de ses propriétés circulatoires dans l'organisme. C'est dans cet esprit que se clôt ce mémoire avec une présentation succinte des perspectives à long terme orientées autour de l'assemblage de systèmes viro-inspirés. Les objectifs seront d'élucider les mécanismes moléculaires sur des systèmes de complexité croissante, et en parallèle de maîtriser ces mécanismes via le développement de méthodologies d'auto-assemblage dirigé.

The goal of this thesis is to study the role of single particle elasticity in the overall behavior of particulate systems. For this purpose, we use microgel particles, which are crosslinked polymer networks immersed in a solvent. In these systems, the amount of cross-linker determines their elasticity and ultimately the stiffness of the particle. For a system of hard spheres, the phase behavior is solely determined by the volume fraction occupied by the particles. Based on the volume fraction, liquid, crystal and glassy phases are observed. Interestingly, microgel particles display a richer and fascinating set of different behaviors depending on the particle stiffness. Previous results obtained in our group show that for highly cross-linked microgels, the glass phase disappears and there are only liquid and crystalline phases. By contrast, preliminary measurements indicate that for ultrasoft microgel particles the system does not show any signature of crystalline or glassy phases. The system seems to remain liquid irrespective of volume fractions. In this Thesis, we will address this striking result using light scattering as well as rheology, in order to access both static and dynamic properties in a wide range of length and time scales. In addition, we will also perform additional studies using very stiff microgels and use their swelling capabilities to change the volume fraction. We will use hydrostatic pressure to change the miscibility of the polymer network and thus change the microgel size; the use of this external variable allows fast equilibration times and homogeneous changes throughout the sample. By using neutron scattering techniques, we study the structural and dynamical properties of the system in its different phases involved.

The arrangement of soft materials through solution processing techniques is a topic of profound importance for next generation solar cells; the resulting morphology has a major influence on construction, performance and lifetime. This thesis investigates the connections between the soft matter physics of colloidal systems and solid state dye sensitised (SSDS) and bulk heterojunction (BHJ) solar cells. A study of aqueous titanium dioxide nanoparticulate suspensions was carried out in order to observe how suspension structure can be controlled by altering the inter-colloid potential via pH-induced electrostatic charging. Measurements were performed at volume fractions between 0.025% and 8.2% with the solution pH set to 3.1, 3.5 or 4.5 before mixing. Suspensions with a volume fraction above 4% formed self-supporting gels regardless of the set pre-mix pH. These gels displayed shear thinning behaviour with a power law exponent of 0.8, a yield stress of 11(1) Pa and rheological response consistent with an aggregated fractal network. At lower volume fractions, suspensions exhibited consolidation interpreted as the collapse of a gel of fractal clusters with a fractal dimension of 2.36. The velocity of the suspension/supernatant interface exhibited delayed sedimentation behaviour, as well as further fractal-based power law scalings with volume fraction. Lower volume fraction suspensions were explored using dynamic light scattering. Limited aggregation of ‘stable’ suspensions was observed when compared to primary aggregate radii measured from electron microscopy images. To connect suspension structure and cell manufacture, the behaviour of more concentrated suspensions was observed during the drying of thin films, a process which forms an essential part of a SSDS solar cell. Lowering the pH of the suspension after mixing from 4 to 3 resulted in an ordering of observed crack domains. An increase in film delamination was also observed. Rates of mass loss during drying followed the expected three phase process, although there was an unexpected increase in rate during the initial phase (where rate is usually constant in time). Dynamic light scattering was found to be a useful but demanding technique for studying cluster formation in titanium dioxide suspensions. A non-linear fitting technique utilising the method of moments was thoroughly explored using computer simulated datasets. The algorithm reduced the systematic error in fitted parameters for moderately polydisperse (0:2 < < 0:4) datasets as compared to the commonly applied linear algorithm. The fitting algorithm was also robust to bad initial estimates of parameters. Finally, test solar cells have been built using blends of titanium dioxide and poly-3-hexylthiophene. Device performance was reduced with blend standing time after mixing but could be improved by remixing the blend before spin coating, implicating a reversible process (e.g. aggregation of titanium dioxide or crystallisation of P3HT) in the loss of performance. Addition of a titanium dioxide hole blocking layer before spin coating reduced cell performance. Combining the above studies and these device designs provides a future platform for continuation of this work in the context of real devices.

CAMARÃO, Diego de Lucena. Diffusive properties of soft condensed matter systems under external confinement. 2014. 142 f. Tese (Doutorado em Física) - Programa de Pós-Graduação em Física, Departamento de Física, Centro de Ciências, Universidade Federal do Ceará, Fortaleza, 2014. / Submitted by Edvander Pires (edvanderpires@gmail.com) on 2015-04-09T20:25:36Z No. of bitstreams: 1 2014_tese_dlcamarao.pdf: 4771668 bytes, checksum: 12d4989237a73eeafcc143c607fa30dd (MD5) / Approved for entry into archive by Edvander Pires(edvanderpires@gmail.com) on 2015-04-10T20:52:49Z (GMT) No. of bitstreams: 1 2014_tese_dlcamarao.pdf: 4771668 bytes, checksum: 12d4989237a73eeafcc143c607fa30dd (MD5) / Made available in DSpace on 2015-04-10T20:52:49Z (GMT). No. of bitstreams: 1 2014_tese_dlcamarao.pdf: 4771668 bytes, checksum: 12d4989237a73eeafcc143c607fa30dd (MD5) Previous issue date: 2014 / In this thesis we study the influence of external confinement potentials on the dynamical properties of soft condensed matter systems. We analyze the diffusive properties of two specific systems by means of Langevin and Brownian Dynamics simulations. In Chapter 1, we introduce the subject of soft condensed matter. We show several theoretical and experimental aspects of these type of systems. We make a brief introduction to the topic of diffusion, where we discuss main aspects of Brownian motion. We introduce the single-file diffusion (SFD) problem and discuss it in the context of soft condensed matter systems, both theoretically and experimentally. In Chapter 2, we introduce the computational method used in this thesis. We discuss Molecular Dynamics (MD) and its variants, Langevin and Brownian Dynamics simulations. We also introduce numerical algorithms used in the following chapters. In Chapters 3, 4 and 5, we analyze two different systems, namely (i) a system of interacting Yukawa particles confined in a parabolic quasi-one-dimensional (q1D) channel and (ii) a system of magnetic colloidal particles under the influence of both a parabolic confinement potential and a periodic external modulation along the unconfined direction. In the former, we study the transition from the single-file diffusion (SFD) regime to the two-dimensional (2D) diffusion regime. In the latter, we study the influence of several parameters that characterizes the system, e.g., the strength of an external magnetic field and the periodic modulation along the unconfined direction, on its dynamical properties. Finally, we present the summary of the main findings reported in this thesis and we show some open questions as perspectives for future research in the field of diffusion in soft condensed matter systems. / Nesta tese estudamos a influência de potenciais de confinamento externos nas propriedades dinâmicas de sistemas de matéria condensada mole. Analisamos as propriedades difusivas de dois sistemas específicos utilizando simulações computacionais (Dinâmica Molecular de Langevin e Dinâmica Browniana). No Capítulo 1, introduzimos o tópico sobre matéria condensada mole. Mostramos vários aspectos teóricos e experimentais neste tipo de sistema. Fazemos uma breve introdução ao tópico de difusão, onde discutimos os principais aspectos do movimento Browniano. Introduzimos o problema de difusão em linha (SFD, do inglês "single-file diffusion") e o discutimos, teorica e experimentalmente, no contexto de sistemas de matéria condensada mole. No Capítulo 2, introduzimos os métodos computacionais utilizados nesta tese. Discutimos os métodos de Dinâmica Molecular e suas variantes, o método de Dinâmica de Langevin e Dinâmica Browniana. Também introduzimos algoritmos de integração utilizados nos capítulos posteriores. Nos Caps. 3, 4 e 5, analisamos dois sistemas distintos, (i) um sistema de partículas de Yukawa confinadas em um canal parabólico quasi-unidimensional (q1D) e (ii) um sistema de colóides magnéticos sob a influência de um potencial parabólico e uma modulação periódica externa ao longo da direção não confinada. No primeiro sistema, estudamos a transição do regime de difusão em linha (SFD) para o regime de difusão normal (2D). No segundo sistema, estudamos os efeitos de vários parâmetros que caracterizam o sistema (e.g., a magnitude do campo magnético externo e a presença da modulação periódica externa) em suas propriedades dinâmicas. Finalmente, apresentamos um sumário dos principais resultados obtidos nesta tese e mostramos algumas questões em aberto como perspectivas para pesquisas futuras na área de difusão em sistemas de matéria condensada mole.

CoordenaÃÃo de AperfeiÃoamento de Pessoal de NÃvel Superior / Nesta tese estudamos a influÃncia de potenciais de confinamento externos nas propriedades dinÃmicas de sistemas de matÃria condensada mole. Analisamos as propriedades difusivas de dois sistemas especÃficos utilizando simulaÃÃes computacionais (DinÃmica Molecular de Langevin e DinÃmica Browniana). No CapÃtulo 1, introduzimos o tÃpico sobre matÃria condensada mole. Mostramos vÃrios aspectos teÃricos e experimentais neste tipo de sistema. Fazemos uma breve introduÃÃo ao tÃpico de difusÃo, onde discutimos os principais aspectos do movimento Browniano. Introduzimos o problema de difusÃo em linha (SFD, do inglÃs "single-file diffusion") e o discutimos, teorica e experimentalmente, no contexto de sistemas de matÃria condensada mole. No CapÃtulo 2, introduzimos os mÃtodos computacionais utilizados nesta tese. Discutimos os mÃtodos de DinÃmica Molecular e suas variantes, o mÃtodo de DinÃmica de Langevin e DinÃmica Browniana. TambÃm introduzimos algoritmos de integraÃÃo utilizados nos capÃtulos posteriores. Nos Caps. 3, 4 e 5, analisamos dois sistemas distintos, (i) um sistema de partÃculas de Yukawa confinadas em um canal parabÃlico quasi-unidimensional (q1D) e (ii) um sistema de colÃides magnÃticos sob a influÃncia de um potencial parabÃlico e uma modulaÃÃo periÃdica externa ao longo da direÃÃo nÃo confinada. No primeiro sistema, estudamos a transiÃÃo do regime de difusÃo em linha (SFD) para o regime de difusÃo normal (2D). No segundo sistema, estudamos os efeitos de vÃrios parÃmetros que caracterizam o sistema (e.g., a magnitude do campo magnÃtico externo e a presenÃa da modulaÃÃo periÃdica externa) em suas propriedades dinÃmicas. Finalmente, apresentamos um sumÃrio dos principais resultados obtidos nesta tese e mostramos algumas questÃes em aberto como perspectivas para pesquisas futuras na Ãrea de difusÃo em sistemas de matÃria condensada mole. / In this thesis we study the influence of external confinement potentials on the dynamical properties of soft condensed matter systems. We analyze the diffusive properties of two specific systems by means of Langevin and Brownian Dynamics simulations. In Chapter 1, we introduce the subject of soft condensed matter. We show several theoretical and experimental aspects of these type of systems. We make a brief introduction to the topic of diffusion, where we discuss main aspects of Brownian motion. We introduce the single-file diffusion (SFD) problem and discuss it in the context of soft condensed matter systems, both theoretically and experimentally. In Chapter 2, we introduce the computational method used in this thesis. We discuss Molecular Dynamics (MD) and its variants, Langevin and Brownian Dynamics simulations. We also introduce numerical algorithms used in the following chapters. In Chapters 3, 4 and 5, we analyze two different systems, namely (i) a system of interacting Yukawa particles confined in a parabolic quasi-one-dimensional (q1D) channel and (ii) a system of magnetic colloidal particles under the influence of both a parabolic confinement potential and a periodic external modulation along the unconfined direction. In the former, we study the transition from the single-file diffusion (SFD) regime to the two-dimensional (2D) diffusion regime. In the latter, we study the influence of several parameters that characterizes the system, e.g., the strength of an external magnetic field and the periodic modulation along the unconfined direction, on its dynamical properties. Finally, we present the summary of the main findings reported in this thesis and we show some open questions as perspectives for future research in the field of diffusion in soft condensed matter systems.

Fingering instabilities can be observed when studying many different phenomena and display elegant pattern formation. Adhesion-induced fingering instabilities, discovered in the early 2000s, are instability patterns that arise when elastic films are sandwiched between two rigid surfaces. In this thesis we investigate this adhesion-induced fingering instability in thin elastic films. This work builds upon previous research into this instability. Experiments based on studies in the literature were performed to further examine past results; general scaling rules were confirmed, but discrepancies between current and past data show that there is still much to understand theoretically. We also perform novel experiments to elucidate the effects of strain on the instability pattern. It is found that the pattern aligns with the direction of strain in a thin film. We provide a theoretical model to explain this result. / Thesis / Master of Science (MSc)

Soft condensed matter (SCM) systems are ubiquitous in nature. SCM systems contain mesoscopic structures in the size range 10 nm to 1 am that are held together by weak entropic forces. These materials are therefore easily perturbed by external fields such as shear, gravity and electric and magnetic fields and are novel systems for studying non-equilibrium phenomena. The elastic constants of these materials are ≈ 109 times smaller than conventional atomic fluids and hence it is possible to measure the viscoelastic response of these materials using commercial instruments such as rheometers. The relaxation time in SCM systems are of the order of milliseconds as compared to atomic systems where relaxation times are of the order of picoseconds. It is easy to study the effect of shear on SCM, as the shear rates attainable by commercial rheometers are of the order of the inverse of their relaxation times. The dynamics of SCM systems and their local rheological properties obtained using the method of probe diffusion can be quantified through dynamic light scattering experiments. The structure of SCM systems can be quantified using diffraction techniques such as small angle x-ray scattering. In this thesis we report experimental studies on the linear and nonlinear rheology and the dynamics of surfactant cetyltrimethylammonium tosylate (CTAT), which forms cylindrical wormlike micelles, studied using bulk rheology and dynamic light scattering (DLS) technique, respectively. We have also studied the phase behaviour of the ternary system formed by cetyltrimethylammonium 3-hydroxy-napthalene 2-carboxylate (CTAHN), sodium bromide (NaBr) and water using small angle x-ray scattering (SAXS). In Chapter 1, we discuss why SCM systems are suitable for studying non-equilibrium phenomena such as the effect of shear on the structure and dynamics of condensed matter. This is followed by a discussion on the chemical structure, phase behaviour and self assembling properties of the amphiphilic molecules in water. We then discuss the intermacromolecular forces such as van der Waals interaction, the screened Coulomb repulsion and hydrophobic and hydration forces. The systems that have been the subject of our experimental studies, viz. CTAT and CTAHN/NaBr/water have also been discussed in detail. This is followed by a theoretical background of linear and nonlinear rheology, dynamic light scattering and small angle x-ray scattering techniques. Next we describe the stress relaxation mechanisms in wormlike micelles. This is followed by a discussion on some standard techniques of nonlinear time series analysis, in particular the evaluation of the delay time L, the embedding dimension m, the correlation dimension ν and the Lyapunov exponent λ. We have also mentioned a few examples of experimental systems where chaos has been observed. We have also discussed in detail the various routes to chaos namely, the period-doubling route, the quasiperiodic route and the intermittency route. The concluding part of this chapter summarises the main results of the thesis. Chapter 2 discusses the experimental apparatus used in our studies. We have discussed the different components of the MCR-300 stress-controlled rheometer (Paar Physica, Germany). The rheo-small angle light scattering experiments and the direct visualisation experiments done using a home-made shear cell are also discussed. Next we describe the various experiments that can be done using a commercial rheometer. The frequency response and flow experiments have been discussed with some examples from our own work on entangled, cylindrical micelles. This is followed by a discussion on the various components of our dynamic light scattering (DLS) setup (Brookhaven Instruments, USA). Particle sizing of submicrometer colloidal spheres using our DLS setup has been discussed with an example of an angle-resolved DLS study of 0.05µm polystyrene colloids. Next we describe the various components of the SAXS setup (Hecus M. Braun, Austria). As an example application of SAXS we have quantified the structure of the lamellar phase formed by the surfactant CTAHN/water. We finally describe the sample preparation methods employed by us for the different experiments. Our nonlinear rheology experiments on viscoelastic gels of surfactant CTAT (cCT AT= 2wt%) in the presence of salt sodium chloride (NaCl) at various concentrations has been discussed in Chapter 3. We observe a plateau in the measured flow curve and this is attributed to a mechanical instability of the shear banding type. The slope of this plateau can be tuned by the addition of salt NaCl. This slope is due to a concentration difference between the shear bands arising from a Helfand-Fredrickson mechanism. This is confirmed by the presence of a “Butterfly” light scattering pattern in SALS experiments performed simultaneously with rheological measurements. We have carried out experiments at six different salt concentrations 10mM < cN aCl<1M, which yield plateau slopes (α) ranging from 0.07 < α < 0.4. We find that a minimum slope of 0.12, corresponding to a salt concentration of 25mM NaCl, is essential to see a “Butterfly” pattern indicating the onset of flow-concentration coupling at this α value. After this we turn our attention to stress/shear rate relaxation experiments. The remainder of this chapter is split in four parts. We show in Part-I that the routes to rheochaos in stress relaxation experiments is via Type-II intermittency. Interestingly in shear rate relaxation, the route is via Type-III intermittency. We also show that flow-concentration coupling is essential to see the route to rheochaos. This section also brings out the crucial role played by orientational ordering of the nematics during rheochaos using SALS measurements performed simultaneously with rheological measurements. In part-II, we study the spatio-temporal dynamics of the shear induced band en route to rheochaos. Our direct visualisation experiments show that the complex dynamics observed in stress/shear rate relaxation measurements during the route to rheochaos is a manifestation of the spatio-temporal dynamics of the high shear band. In part-III, we describe the results of our stress/shear rate relaxation measurements at a fixed shear rate/stress with temperature as the control parameter and thereby control the micellar length. We see the Type-II intermittency route to rheochaos in stress relaxation measurements and the Type-III intermittency route to rheochaos in shear rate relaxation measurements. We conclude this section by showing the results of linear rheology measurements carried out at different temperatures. We estimate the mean micellar length ¯L, reptation time τrepand the breaking time τbreak. We show that L¯ increases by ≈ 58%, as the sample goes through the route to rheochaos. In Part-I of this chapter we had only qualitatively discussed the correlations between the measured time series of stress and the VH scattered intensity during the Type-II intermittency route to rheochaos. In part-IV we have attempted to quantify the correlations between the two time series using the technique of linear and nonlinear Granger causality. We have also studied the phase space dynamics of the two time series using the technique of Cross Recurrence Plots. We show that there exists a causal feedback mechanism between the stress and the VH intensity with the latter having a stronger causal effect. We have also shown that the bivariate time series share similar phase space dynamics using the method of Cross Recurrence Plots. In chapter 4, we have studied the dynamics of wormlike micellar gels of surfactant CTAT using the DLS technique. We report an interesting result in the dynamics of these systems: concentration fluctuations in semidilute wormlike-micelle solutions of the cationic surfactant Cetyltrimethylammonium Tosylate (CTAT) at wavenumber q have a mean decay rate α qz, with z -̃1.8, for a wide range of surfactant concentrations just above the overlap value c∗. The process we are seeing is thus superdiffusive, like a L´evy flight, relaxing on a length scale L in a time of order less than L2 . The rheological behaviour of this system is highly non-Maxwellian and indicates that the micelle-recombination kinetics is diffusion-controlled (DC) (micelles recombine with their original partners). With added salt (100mM NaCl) the rheometric behaviour turns Maxwellian, indicating a crossover to a mean-field (MF) regime (micelles can recombine with any other micellar end). The concentration fluctuations, correspondingly, show normal diffusive behaviour. The stress relaxation time, moreover is about twenty times slower without salt than with 100mM NaCl. Towards the end of this chapter, we propose an explanation of these observations based on the idea that stress due to long-lived orientational order enhances concentration fluctuations in DC regime. In the previous chapter we had studied the dynamics of wormlike micellar gels of pure CTAT 2wt% and found superdiffusive relaxation of concentration fluctuations due to a nonlinear coupling of long-lived stress and orientational fluctuations to the con- centration. In chapter 5 we present results from dynamic light scattering experiments to quantify the diffusive motion of polystyrene (PS) colloids in the same system. This chapter is split in two parts. In Part-I, we discuss dynamics of PS particles of radius 115 nm and 60 nm in CTAT 2wt%. The radius of the colloidal spheres is comparable to the mesh size ξ = 80 nm of the wormlike micellar network and hence we are probing the network dynamics. We find that ∆r2(t) is wavevector independent at small and large lag times. However at intermediate times, we find an anomalous wavevector dependence which we believe arises from the rapid restructuring of the gel network. This anomalous wavevector dependence of ∆r2(t) disappears as the temperature is increased. In Part-II we discuss the dynamics of PS particles of radius 25 nm and 10 nm, smaller than ξ, in CTAT 1wt% & 2wt%. We once again find an anomalous wavevector dependence of ∆r2(t) at intermediate times for the 2wt% sample. Surprisingly, at large times the particle motion is not diffusive, rather ∆r2(t) saturates. We do not have a clear understanding of this as yet. Also for the 10 nm particle, the motion at small lag times is superdiffusive. The motion of these particles is probably influenced by the superdiffusion of concentration fluctuations observed in pure CTAT 2wt% system (chapter 4). In chapter 6, we report the observation of an intermediate mesh phase with rhom- bohedral symmetry, corresponding to the space group R¯3m, in the ternary system consisting of CTAHN/NaBr/water. It occurs at lower temperatures between a random mesh phase (LDα ) and a lamellar phase (Lα) on increasing the surfactant concentration φs. The micellar aggregates, both in the intermediate and random mesh phases, are found to be made up of a two-dimensional network of rod-like segments, with three rods meeting at each node. SAXS studies also show the presence of small angle peaks corresponding to ad−spacing of 25 nm. Freeze fracture electron microscopy results shows that this peak may correspond to the presence of nodule like structures with no long-range correlations. The thesis concludes with a summary of main results and a brief discussion of the scope for future work in Chapter 7.