Self-assembled nonionic alkyl glycoside surfactants are of interest for creating functional adsorption and catalytic sites at the surface of mesoporous metal oxides, but they typically impart poor long-range order when used as pore templates. Improved order and control over the functional site density may be achieved by mixing them with a cationic surfactant. To confirm this hypothesis, we investigate the lyotropic liquid crystalline (LLC) phase behavior of aqueous solutions of the functional nonionic surfactant n-dodecyl β-D-maltoside (C12G2) and cationic cetyltrimethylammonium bromide (C16TAB). A ternary phase diagram of the C16TAB-C12G2-water system is developed at 50 °C. By replacing the volume of water in the phase diagram with an equivalent volume of silica, ordered mesoporous materials are prepared by nanocasting with variable C12G2/C16TAB ratios. Metal oxide mesophases can almost always be predicted from the ternary phase diagram, except that silica prepared with high C12G2/C16TAB ratios are very weakly ordered, perhaps due to differences in hydrogen bonding or rate of assembly. Based on the ternary phase diagram of the system, a systematic approach is taken to the incorporation of titania sites via complexation to the maltoside headgroup of C12G2. Complexation to a saccharide is expected not only to guide titanium to the pore surface, but also to prevent uncontrolled hydrolysis and condensation of the (usually quite reactive) titanium precursor. Tetrahedrally coordinated titanium atoms incorporated into a silica network are believed to be the active oxidation sites required for heterogeneous silica-supported titania oxidation catalysts. To promote well-ordered materials and to allow control over titania site density, the mixed C12G2 / C16TAB system is used for pore templating. Series of Si-Ti mixed oxide thin films and bulk materials are synthesized with different amounts of titanium loading by utilizing pre-complexation between C12G2 and titanium isopropoxide. The degrees of homogeneity (indicated by tetracoordinated Ti) in these films are superior to those of films synthesized with the same loading of titanium but without C12G2 or without pre-complexation. Transition metal-carbohydrate complexation provides highly dispersed, tetrahedrally coordinated titanium atoms rather than the octahedral sites found without saccharide complexation.

Rhamnolipid (RL) biosurfactants have been considered "green" alternatives to synthetic surfactants. Here, systematic studies of monorhamnolipids (mRLs) and their synthetic analogues are performed to characterize their interfacial and solution behaviors as surfactants. Chemical structure-surface activity relationships of rhamnolipids were probed using surface tension measurements on RLs and a series of their synthetic analogues designed by "truncation modification." Based on our study on RLs and the rationally-designed RL analogues, the key structural factor responsible for the excellent surface activity performance of rhamnolipids is the presence of the rhamnose moiety in the headgroup. As a result, rhamnopyranosides (RhEs), the simplest surfactants with a rhamnose moiety in the headgroup, show surface activity comparable to the bioproduced mRLs. The purified mixture of mRLs harvested from Pseudomonas aeruginosa ATCC 9027 was mixed with a nonionic surfactant Tween-20 (TW) and studied by surface tension measurements at pH 8. The experimental values of CMC show deviation from the theoretical values predicted by ideal solution theory, which is hypothesized to be due to a shape change from rod-shaped to spherical as the mole fraction of TW is increased. The hypothesis about the shape change is supported by dynamic light scattering results, regular solution theory, and packing parameter theory. Polarization modulated-infrared reflection-absorption spectroscopy (PM-IRRAS) has been used to characterize the orientation of the synthetic rhamnolipid Rha-C18-C18 at the air-water interface. Although rhamnolipids exhibit pH-dependent micellization, their orientation at the air-water interface is not affected by pH. The average tilt angle of their alkyl chains is determined to be ~45° at a surface pressure π = 40 mN/m which decreases to 36° when Pb²⁺ is present in the subphase. Assisted by molecular modeling, the packing of mRLs at the air-water interface is believed to be dominated by the packing of their large hydrophilic headgroups. Finally, the adsorption isotherm of mRLs on hydrophobic polyethylene surfaces was generated by ATR-FTIR from solutions of different pH, which were then fit to a Frumkin adsorption model to yield the thermodynamic adsorption parameters, the adsorption equilibrium constant and the interaction parameter. mRLs strongly adsorb to d-PE, and the adsorption is pH dependent.

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This work addresses fundamental aspects of designing templates and curing conditions for the synthesis of mesoporous metal oxide thin films. The first section addresses selection of cationic-carbohydrate surfactant mixtures to synthesize templated silica thin films for selective adsorption of simple carbohydrates based on molecular imprinting. Nuclear magnetic resonance and fluorescence spectroscopy results suggest a novel structure for mixtures of alkyl glucopyranosides or xylopyranosides with cationic (trimethylammonium) surfactants. Despite thermodynamically favorable mixing, the carbohydrate headgroups in the mixed micelle adopt an inverted configuration with their headgroups in the micelle core, and therefore are inaccessible for molecular imprinting. This orientation occurs even when the alkyl tail length of the carbohydrate surfactant is greater than that of the cationic surfactant, but this limitation can be overcome by introducing a triazole linker to the carbohydrate surfactant. The next section addresses the effects of aging conditions on the structural and chemical evolution of surfactant templated silica thin films. The third section describes the synthesis of carbohydrate/cationic surfactant imprinted silica thin films with orthogonally oriented cylindrical pores by modifying the glass surface with a random copolymer. The last part of the dissertation addresses the effect of pore orientation on the transformation mechanism of block copolymer templated titania thin films during high temperature curing. Mesoporous titania thin films can be used for photochemical and solar cell applications, but doing so requires addressing the tradeoff between loss of mesostructural order and growth of crystallinity during thermal treatment. By using advanced x-ray scattering techniques it has been shown that the titania films with vertically oriented pores can better withstand the anisotropic stress that develops during thermal treatment compare to titania films with mixed pore orientation. For instance, films with parallel or mixed pores can only be heated at 400 °C for a brief time (~10 min) without loss of order, while orthogonally oriented films can be heated at 550 °C or greater for extended time periods (on the order of hours) without significant loss of long-range mesopore structure. Detailed kinetic modeling was applied to enable the comparison of activation energy for mesostructure loss in films as a function of pore orientation and thickness.

‘Soft condensed matter’ is a newly-emerged sub-discipline of physics concerned with the study of systems that are mechanically soft such as colloids, emulsions, surfactants, polymers, liquid crystals, granular media and various biomaterials including DNA and proteins. These materials display a broad range of interesting microstructures and phase behaviours and have a myriad of applications in the materials, food, paint and cosmetic industries as well as medical technologies. Soft condensed matter physics presents new opportunities and challenges for the development of new ideas and concepts in experimental and theoretical physics alike. Because the field overlaps with many different disciplines, the study of soft matter also offers promising developments to other fields of science including chemistry, chemical engineering, materials science, biology, and environmental science. The behaviour of these systems is dominated by one simple fact: they contain mesoscopic structures in the size range 10 nm to 1 µm that are held together by weak entropic forces. The elastic constants of these materials are 109 times smaller than the conventional atomic materials and hence are easily deformable by external stresses, electric or magnetic fields, or even by thermal fluctuations. We have studied two important classes of soft matter systems in this thesis -colloidal suspensions and surfactant systems. The thesis is divided into two main themes: (a) Effects of electric field on the colloidal suspensions, and (b) Effects of shear on surfactant solutions. Motions of colloidal particles under the influence of applied electric field were observed under a microscope and were studied using image analysis and particle tracking. We have also used tracking of thermal fluctuations of colloidal particles embedded in surfactant gels to study microrheology of surfactant solutions. Linear and non-linear rheology of aqueous solutions of cationic cetyltrimethyl ammonium bromide (CTAB) and anionic sodium-3-hydroxynapthalene-2-carboxylate (SHNC) were studied using bulk rheology in a commercial rheometer. Rheological studies of an anionic surfactant sodium dodecyl sulphate (SDS) in the presence of strongly binding counterion p-toluidine hydrochloride (PTHC) has also been done. Chapter 1 starts with a general introduction to soft condensed matter systems and then we proceed to describe two specific class of soft condensed materials which we have studied in this thesis -colloidal suspensions and surfactant/water systems. After describing different types of colloids, we discuss why colloids are suitable as model systems in condensed matter physics. This is followed by a discussion on the chemical structure, phase behaviour and self assembling properties of surfactant molecules in water. We then discuss the inter-macromolecular forces such as van der Waals interaction, the screened Coulomb repulsion, hydrogen bond, hydrophobic and hydration forces and steric repulsion which are the major players in the interaction in soft condensed matter systems. The systems that have been the subject of our experimental studies, viz. polystyrene colloidal suspensions, CTAB+SHNC, SDS+PTHC and CTAT have also been discussed in detail. Then we have given an overview of effects of electric field on the colloidal suspensions. Two types of geometries have been discussed: one in which the field is parallel to the plates and another when the field is perpendicular to the electrodes. Application of colloidal particles in diagnostic tests (Latex Agglutination Tests) has been discussed after this. Some methods used to enhance the sensitivity of LATs have also been reviewed. This is followed by a theoretical background of linear and non-linear rheology. We have also given an introduction to digital video microscopy, its advantages and discussed few quantities like pair correlation function, structure factor which can be extracted using digital video microscopy and particle tracking. The concluding part of this chapter describes the organization of this thesis. Chapter 2 discusses the experimental apparatus and techniques used in our studies. We describe our setup for applying the electric field to the colloidal particles and imaging and tracking their motion. We also discuss the image processing and analyzing methods for extracting the useful quantities from the digitized images. We have described the various components of the MCR-300 stress-controlled rheometer (Paar Physica, Germany) and the AR-1000N stress-controlled rheometer (T. A. Instruments, U. K.) followed by different experimental geometries that we have used for our experiments. Next we have described the various experiments that can be done using a commercial rheometer. Calculation of surface charge of colloidal particles using a conductivity meter has been demonstrated for our colloidal particle suspensions. We also describe the sample preparation methods employed in different experiments. In Chapter 3, we have discussed our study of clustering of colloidal particles under the influence of an ac electric field as a function of frequency. The field was applied in a direction perpendicular to the confining walls. Two regimes are observed, a low frequency regime where the clusters are isotropic with a local triangular order and a new high-frequency regime where the clusters are highly elongated (anisotropic) with no local order. The crossover from one regime to the other occurs at a critical frequency, fc. The formation of elongated clusters seen at high frequencies is explained in terms of rotation of particles due to a phase lag between the polarization of the electric double layer around a particle and the applied electric field that arises because of inhomogeneities of the conducting surface. We have also observed that the threshold field for the cluster formation, Eth, increases with frequency in both the regimes. We did these studies on two different sizes of particles and found that both Eth and fc were lower for the larger particles. Our model based on particle rotation was able to estimate the value of fc correctly for both the sizes of the particles. Chapter 4 describes a method employing an ac electric field applied perpendicular to the confining walls to increase the sensitivity of recognition of ligands by their corresponding receptors grafted on Brownian latex particles. Application of electric field assists the colloidal micro-particles grafted with receptors to come nearer due to electro-hydrodynamic drag. This increase in the local concentration of the latex particles results in improving the chances of ligand-receptor interaction leading to the aggregation of the latex particles. With this technique we have been able to increase the sensitivity of the ligand-receptor recognition by a factor as large as 50. We have demonstrated the utility of our method using streptavidin as the model receptor and biotinylated RNase A as the model ligand. We have also applied our technique to a commercially available kit for rheumatoid factor (RF) with successful results. The same method was also successfully applied for the detection of typhoid whose antibodies were purified and attached to polystyrene particles by our collaborators from DRDE Gwalior. In Chapter 5, we have studied the statics and dynamics of colloidal particles at different applied electric fields from zero to beyond the threshold field. We have taken a series of time-lapsed images and calculated out the pair-correlation function, mean squared displacement, structure factor, non-Gaussian parameter etc. We have studied both mono-dispersed colloidal system and binary colloidal system (mixture of two different sizes of particles). The aggregates formed in the two cases were analysed with the help of Voronoi polygons to quantify the microscopic structure. In mono-dispersed system, the aggregates formed were two-dimensional hexagonal crystals and we have used this system to study the freezing transition in 2-dimension. The properties of the system in the liquid and the crystalline state satisfy various criteria for the 2-d freezing transition. The first maximum of the structure factor at the voltage at which freezing occurs, is 5.5 as has been suggested for the 2-d freezing. This is reflected in the dynamics of the system also, where the ratio D/D0 falls below 10%, in accordance with the LPS (L¨owen, Palberg, Simon) criterion for freezing in 2-d colloidal systems [Phys. Rev. Lett. 70, 1557 (1993)]. However, in the binary colloidal system the clusters formed were not crystalline but more like 2-d dense liquids. A closer inspection of these clusters reveals that the motion of a smaller subset of particles is cooperative and follows string-like paths. The mean square displacement of such a system shows a plateau in the intermediate times which indicates the “caging” of particles by its neighbours. A peak in non-gaussian parameter indicates the presence of dynamical heterogeneities in the system. In Chapter 6, we have described the use of multiple particle tracking to study the microrheology of semidilute solutions of wormlike micelles and compared the results with those from macrorheology experiments done on the same samples. Two concentrations of CTAT (1.3% and 2%) were used. We observed that, in spite of the mesh size being much smaller than the size of the probe particles, the viscoelastic response function calculated using the one-point microrheology does not match with that measured from macrorheology. This can be attributed to the fact that there is another important length scale in the system, the mean micellar length, and it is comparable to the probe particle size. Two-point microrheology was successful in verifying the macrorheology results for CTAT 1.3% but it fails to do so for CTAT 2%. We attribute this to the fact that in a higher viscosity sample (2%), the hydrodynamic force propagate to a lesser distance, thereby limiting the measurable correlation between the particles and precluding the success of two-point microrheology. Chapter 7 describes a rheological study of aqueous solutions of varying concentration of cationic cetyltrimethyl ammonium bromide (CTAB) and anionic sodium-3-hydroxynapthalene-2-carboxylate (SHNC) kept at a fixed molar concentration ratio [CTAB]/[SHNC] = 2. At this molar ratio, the surfactants self-assemble into wormlike micelles which get entangled above the overlap concentration to form viscoelastic gel. The range of the total surfactant concentration φ varies from 1.17% to 5.16% by weight. We found that, plateau modulus, G0, shows a power law dependence on the surfactant concentration, φ, with an exponent 3, which is higher than the expected value of 2.25 observed for the one-component wormlike micelles. Zero shear viscosity, η0, and relaxation time, τR show a maximum at the surfactant concentration, φmax = 1.9% in contrast to a monotonic increase with φ. We propose that this non-monotonic behaviour is due to the unusual dependence of the average micellar length L ¯on φ, showing a maximum in average micellar length L at φmax. This argument provides a strong support to the model of micellar growth in the presence of electrostatic interactions developed by Mackintosh et. al [Europhys. Lett. 12, 697 (1990)]. The presence of electrostatic interactions also appears in the behaviour of the plateau modulus G0 that exhibits a larger φ dependence than in highly screened micelles. In the non-linear flow experiments, a minimum observed in critical shear rate (the shear rate at which shear thinning starts), ˙γc, at φmax strengthens our arguments. In Chapter 8, we describe the phase behaviour and rheology of SDS+PTHC (sodium dodecyl sulphate + p-toluidine hydrochloride) micellar solutions at different molar ratios α=[PTHC]/[SDS]) of the two components. At low values of α, polarizing microscopy observations reveal a transition from an isotropic to a nematic phase of disk-like micelles, whereas a transition to a lamellar phase occurs at higher α values > 0.5, on increasing the surfactant content. Linear rheology of the isotropic micellar solution reveal a viscous behaviour over a large range of surfactant concentrations. Surprisingly, this also extends to the nematic phase of disk-like micelles observed at α =0.2 and φ =0.35. These systems also exhibit a viscoelastic behaviour over a narrow range of surfactant concentration as reported in earlier studies. The extent of the viscoelastic region of the isotropic micellar solution also decreases with increase in α. Frequency sweep curves in this region, scaled on to a master curve is reminiscent of dilute suspensions of hard spheres or rigid Brownian rods. Consistent with the results from oscillatory shear measurements, the f;ow behaviour examined under steady shear is Newtonian over a large range of surfactant content in the isotropic micellar solution. An interesting result in these studies is the non-monotonic behaviour of the viscosity with increase in surfactant concentration. It is likely that the sharp rise in viscosity arises from a jamming effect of the rigid rods. Dynamic light scattering studies suggest that the drop in viscosity is due to the decrease in the length of the micellar aggregates. This is followed by a change in the morphology of the micelles from rods to disks as indicated by the transition to a nematic phase of disk-like micelles or a lamellar phase. A change in the morphology of micellar aggregates with increase in α is expected in mixed surfactant systems with strongly binding counterions. However, the surprising result is the change in morphology of the micellar aggregates with surfactant content. Such a behaviour is seen in mixed surfactant systems for the first time. The thesis concludes with a summary of our main results and a brief discussion of the scope of future work in Chapter 9.

This thesis deals with the non-equilibrium phenomena under shear observed mainly in bilayer forming liquid crystalline phases of mixed surfactant systems, anisotropic colloidal dispersions as well as Langmuir monolayers of membrane peptides. To correlate the structural transitions under shear with the mechanical properties or flow behaviour, the rheological measurements are combined with different techniques such as optical imaging (bright field, polarizing or confocal), small angle light scattering as well as small angle x-ray scattering (Rheo-SAXS) measurements. The bilayer forming phases that have been studied consist of mixed surfactant system formed by a mixture of ionic amphiphiles with strong binding organic counter ions. The propensity of the hydrophobic counterion to modify the spontaneous curvature at the micelle-water interface gives rise to a rich equilibrium phase behaviour consisting of different bilayer forming liquid crystalline mesophases in between the hexagonal and lamellar phases. The liquid crystalline mesophases presently examined under shear are the weakly swollen isotropic and lamellar phases as well as the random and rhombohedral mesh phases. The main motivation of the thesis was to examine the stability of these phases under shear since all the existing studies so far on shear induced structural transitions are mainly confined to highly swollen isotropic sponge phase of interconnecting bilayers that can transform to a lamellar phase consisting of a stack of bilayers with 1D quasi long range order or a dilute lamellar phase is shear transformed to a collapsed surfactant rich lamellar phase coexisting with excess solvent at Peclet Number greater than 1. The present study revealed for the first time a shear reversible crystallization above the equilibrium crystallization temperature in the weakly swollen isotropic and lamellar phases formed in the SDS-PTHC-water system where the structural transition is feasible through a shear induced segregation/microphase separation of the hydrophobic counterions to tune the curvature of the bilayer-water interface. These results incited us to examine the role of shear on another class of mesophases that are structurally similar to lamellar phase but with a non-uniform interfacial curvature of the bilayers identified as the intermediate mesh phases. Mesh phases are formed by a 1D stack of perforated bilayers with quasi-long range order where the water filled pores or curvature defects can have a liquid-like ordering in the plane of the bilayers as in a random mesh phase or the pores can have a square or hexagonal ordering locking into a three dimensional lattice with either tetragonal or rhombohedral symmetry to form Tα or R3m ordered mesh phases. Two characteristic features of the mesh phases that is noteworthy are i) the non-uniform mean curvature for the bilayers formed by 3-coordinated hexagonal mesh or the 4-coordinated square mesh; ii) the elasticity of the bilayers forming the hexagonal or square ordered mesh in R3m or Tα phases as opposed to the fluid-like bilayers with zero surface shear modulus in the random mesh or classical lamellar phases (Lα). Hence the structural similarity as well as differences of the mesh phases with the lamellar phase raises some pertinent questions regarding the stability of surfactant mesh phases under shear. Two striking consequences of shear flow on the random and ordered mesh phases of a cationic-anionic mixed surfactant system were revealed: a shear-induced 3D ordering of the curvature defects in LDα phase as well as a hydrodynamic instability wherein a sequence of structural rearrangements leading to buckling instability gives rise to unstable flows in the R3m phase. These studies on shear induced structural transitions on partially ordered mesophases is juxtaposed with the study on another class of systems that were examined under shear comprising dispersion of anisotropic colloidal rods. We demonstrate that these suspensions shear thicken at low concentrations (≥ 25 %) and origin of shear thickening is formation of stress bearing hydrodynamic clusters rather than order-disorder transition. Finally we also examine the rheological properties of a monolayer of membrane peptide Alamethicin where the coexistence of solid-like domains in a backround of liquid expanded phase at high surface concetrations gives rise to a dense anisotropic suspension in 2D. The rheological properties of these jammed fluid/fluid interfaces formed by membrane proteins is well explained by the soft glassy rheology model proposed earlier in the context of 3D soft glasses, comprising emulsions, foams, colloidal glasses and gels. Chapter 1 starts with a general introduction of soft condensed matter systems and then we proceed to describe surfactant systems, their phase behaviour and self assembly. The formation of liquid crystalline phases in pure surfactant systems and in presence of additives such as salt or counterions are discussed. A brief introduction to colloids is explained further. This is followed by the discussion on the inter-macromolecular forces governing soft matter systems such as van der Waals interaction, the screened Coulomb repulsion, hydrogen bond, depletion, peristaltic, hydrophobic and hydration forces and steric repulsion. We further explain the systems studied and their phase behaviour at different concentrations formed by SDS-PTHC-water, CTAB-SHN-water system in detail. In the next section we describe the characterization of different liquid crystalline phases viz. nematic, hexagonal, isotropic, lamellar, intermediate mesh and ribbon phases using cross polarizing optical microscopy, small angle x-ray and rheology. Then, a theoretical background of linear and nonlinear rheology, optical/confocal microscopy and x-ray scattering techniques are given. This is followed by discussion on flow properties of colloidal suspensions in dilute and semi-dilute regime and finally shear thickening phenomena observed in concentrated suspensions. We discuss shear thickening phenomena observed in anisotropic precipitated calcium carbonate (PCC) colloids. We have also discussed shear induced phase and structural transitions observed in different liquid crystalline phases. Chapter 2 discusses the experimental apparatus and techniques used in our studies. We have discussed the different components of the MCR-300 and 101 stress-controlled rheometer (Paar Physica, Germany). The cross polarizing optical microscopy in transmission and reflection mode using a home-made shear cell and in built set-up respectively, and small angle light scattering set-up are discussed. Next, we discuss in-situ small angle x-ray rheology setup, a home made Couette cell installed at RRI Bangalore, Couette installed at SWING beamline Soleil, Paris, France and parallel plate setup at PETRA III, Germany. This is followed by discussion on sample preparation and synthesis technique of silica colloidal rods and modification of surface potential using a thermo-responsive polymer. Further, we explain the algorithm to track rods and analysis of SAXS 2D diffraction pattern. Flow behaviour of different phases formed in SDS-PTHC-water system are described in Chapter 3. This chapter has been divided into four sections. In section I, we describe the phase behaviour and rheology of micellar solution at different surfactant concentrations (ϕ) and molar ratios (α = [PTHC]/[SDS]) of two components. At ϕ = 0.3, a transition from viscous to visco-elastic behaviour is observed with increasing α from 0 to 0.3. Zero shear viscosity shows a non-monotonic behaviour with increasing α and reveals a maxima at α = 0.15. At low α, we observe a Newtonian behaviour which changes to shear thinning behaviour with increasing α and finally again retains the Newtonian behaviour. Dynamic light scattering studies in conjunction with presence of nematic phase made up of disks (confirmed by cross-polarizing optical microscopy) at higher α > 0.325, suggest that the drop in zero shear viscosity is due to decrease in length of the micelles from rods to disks. A similar behaviour is observed with increasing ϕ at constant α = 0.2, 0.25, 0.6. A change in the morphology of micellar aggregates with increase in α is expected in mixed surfactant systems with strongly binding counterions. However the change in morphology of micellar aggregates with surfactant content in surprising which is witnessed for the first time in mixed surfactant systems. In section II of this chapter we discuss the phase behaviour and rehological properties of different liquid crystalline phases formed in SDS-PTHC-water system at ϕ = 0.4, and varying α from 0 to 0.4. Using deutrium nuclear magnetic resonance (NMR) studies we show that the transition from hexagonal phase at α = 0, to lamellar phase at α = 0.4 occurs through a nemtaic phase of rods at α = 0.05 and nemtaic phase of disks at α = 0.2 through an isotropic phase of rods at α = 0.15. NMR studies reveal a decrease in variation of the quadrupole splitting across the transition from NC to ND. The visco-elastic and flow behaviour of the different phases were examined. A decrease in the steady shear viscosity across the different phases with increasing α suggests a decrease in the aspect ratio of the micellar aggregates. From the transient shear stress response of the NC and ND nematic phases in step shear experiments, they were characterized to be tumbling and flow aligning, respectively. Our studies reveal that by tuning the morphology of the surfactant micelles, strongly binding counterions modify the phase behaviour and rheological properties of concentrated surfactant solutions. In section III, we discuss shear induced phase transition in SDS-PTHC-water system using in-situ rheo-optical imaging and in-situ rheo-SAXS. Bilayer forming liquid crystalline phases namely isotropic (Li - optically isotropic) and lamellar (Lα - optically birefringence) are formed at α = 1.5, ϕ = 0.4 and α = 1, ϕ = 0.5. Both phases co-exist with excess solvent and remain fully swollen at temperature T > 50 oC. We have constructed a dynamic phase diagram in the parameter space of shear rate and temperature which demonstrate a novel shear induced phase transition to a crystalline phase (Lc) above a critical shear rate. At constant shear rate, the increase in viscosity is accompanied by presence of birefringent texture of Lα phase after a waiting time (t) which decreases with increasing shear rate. The Lc phase is stable under shear and melts back to equilibrium Li phase once shear is stopped. At higher temperature a transition from Li → Lα is observed. In-situ small angle x-ray scattering reveals an evolution of additional peaks in small as well as wide angle region which does not evolve any further once the viscosity reaches a maxima. The Lc phase obtained under shear at different shear rates can be indexed to a triclinic lattice with the lattice parameters depending on shear rates. We propose that the possible origin of phase transition is re-distribution of counterions under shear which results in counterion-rich and counterion-poor region. This counterion rich region results in crystalline Lc phase. In addition to revealing a unique class of non-equilibrium phase transition, the present study urges a unique approach toward understanding shear-induced phenomena in concentrated meso-phases of mixed amphiphilic systems In section IV we propose a shear induced nucleation and growth of crystalline phase in metastable bilayer forming Li and Lα phases. Nucleation and growth of crystalline phase ac-celerated by shear exhibits a power law dependence on time. The time of nucleation strongly depends on the shear rate with different exponents for different phase compositions. The crystalline phase formed under the influence of shear is stable and irreversible for tempera-ture < 28 oC. The crystal structure obtained under shear can be indexed to a triclinic unit cell with different lattice parameters depending on the shear rate and concentration probed. In Chapter 4, we discuss shear induced transitions observed in mesh phases formed in cationic surfactant system CTAB in the presence of strongly binding counterions SHN formed at different surfactant concentration (ϕ) and molar ratio (α). Random mesh phase (LDα) formed at ϕ = 0.3, 0.4, 0.5 and α = 1 are identified as stack of bilayers having curvature defects in form of water filled pores in the plane of bilayers . These pores do not have any long range correlation either in-plane or across the plane. A 3D ordered mesh phase (R3m) is formed at α = 1 and ϕ = 0.6, where these pores have in-plane and out of plane positional correlation and locked into a 3D lattice with rhombohedral symmetry. These phases are easily identified from small angle x-ray scattering studies wherein LDα a diffuse peak corresponding to in-plane defect spacing (ddef ) is observed along with lamellar d-spacing (d). However several additional peaks along with lamellar peak are observed for R3m phase revealing a long range correlation of pores. By shearing different LDα phases formed at different ϕ′s, we D phases formed probe the effect of shear far and near to the R3m phase boundary. When Lα at ϕ = 0.3 and 0.4 are sheared at constant shear rate, we observe a structural transition to an onion phase which is accompanied by increase in viscosity at the onset of the transition. D When Lα phase formed near R3m phase at ϕ = 0.5 is sheared, we observe a decrease in viscosity which is accompanied by the presence of a sharp peak near the diffuse peak corresponding to ddef along with several other small as well as wide angle peaks. All these D phase. We propose that peaks can be indexed to R3m phase co-existing with equilibrium Lα the locking of the defects into a 3D lattice occurs when the in-plane correlation length (ddef ) is larger than the bilayer periodicity (d). Prior to appearance of sharp peak near ddef , we observe an a-orientation of lamellae i.e. bilayers align along the shear-gradient plane where shear is likely to increase the length of cylindrical arrays or rods. A shear driven increase in the length of the rods implies a larger radius of this in-plane circle forming the pores, leading to a lower curvature and consequently a lower curvature energy. This increase in average size of the pores under shear favored by the lower curvature energy is expected to increase the in-plane as well as the trans-bilayer correlation length of the defects. The Lα → R3m phase transition is also observed in another system cetylpyridinium chloride (CPCl)-SHN-water. Thus this type of transition is general feature of random mesh phases when sheared near R3m phase in the equilibrium phase diagram. A thixotropic behaviour with yield stress (σy = 500 Pa, is observed when equilibrium R3m phase is sheared. When the shear stress crosses a threshold value of 1000 Pa, we observe an avalanche behaviour with drop in viscosity of more than 4 orders of magnitude. This drop is accompanied by appearance of several sharp peaks which can be indexed to two or three R3m phases. The similar transition is observed under shear in R3m phase formed in CPCl-SHN-water system. We propose that shearing a 3D ordered lattice of defects as in the R3m phase leads to additional structural transitions, though the rhombohedral symmentry is retained. In Chapter 5, we discuss shear thickening observed in colloidal rods. Using rheology combined with microscopy, we demonstrate that origin of shear thickening in colloidal rods is the formation of hydroclusters and not order-disorder transition. We observe continuous (CST) as well as discontinuous shear thickening (DST) at volume fractions of colloidal sus-pension at 25 % and > 30 % respectively. In DST, in controlled stress measurements, flow curve exhibits an S-shaped flow curve (stress vs. shear rate) where we observe a negative slope in shear thickening regime. By combining fast confocal microscopy with rheometer (parallel plate geometry), we investigate the possible mechanism for shear thickening in our suspension and rule out order-disorder transition. This indicates that the shear thickening might be a consequence of formation of hydroclusters which is confirmed by modifying sur-face properties of these colloids where a thermo responsive microgel PNIPAM was used as a shell to the silica core. The advantage of using PNIPAM is that the polymer brush remains fully swollen below the lower critical solution temperature (LCST) and shrinks above the LCST (34 oC) acting as hard particles. Thus by controlling the temperature, the interparticle separation can be tuned. We observe a pure shear thinning and shear thickening behaviour below and above LCST respectively. We show that by changing the interparticle separation we can avoid hydrocluster formation arsing due to the hydrodynamic lubrication forces re-sponsible for the shear thickening. The calculation the order parameter and measurements on core-shell particles illustrate that microscopic origin of shear thickening is the formation of hydroclusters and not order-disorder transition. Chapter 6 deals with the 2D interfacial rheology of antibiotic alamethecin film at air-water interface. Fluorescence microscopy of alamethicin monolayers revealed a coexistence of liquid expanded (LE) and solid phases at the surface concentrations studied. Interfa-cial oscillatory shear measurements on alamethicin monolayers indicate that its viscoelastic properties are determined by the area fraction of the solid domains. The role of zwitterionic phospholipids dioleoylphosphatidyl choline (DOPC) and dioleoylphosphatidyl ethanolamine (DOPE) on the peptide aggregation behaviour was investigated. Fluorescence microscopy of alamethicin/phospholipid monolayers revealed an intermediate phase (I) in addition to the solid and LE phase. In mixed monolayers of phospholipid (L)/alamethicin (P), with increase in L/P, the monolayer transforms from a viscoelastic to a viscous fluid with the increase in area fraction of the intermediate phase. Further, a homogeneous mixing of alamethicin/lipid molecules is observed at L/P>4. Our studies also confirm that the visco-elasticity of alame-thicin/phospholipid monolayers is closely related to the alamethicin/phospholipid interac-tions at the air-water interface.