In the isotropic to lamellar transition, nonlinear fluctuation terms lower the transition temperature τc and drive the transition first order. Here we show that steady shear, by suppressing the fluctuations, raises τc; in a certain temperature range the lamellar phase can be induced by applying shear. A study of the effective potential indicates that the transition remains first order, though becoming very weak at high shear rate. We argue heuristically that the lamellar ordering first occurs with wavevector normal to both the velocity and the velocity gradient. We estimate the characteristic shear rate for two current experimental systems.

We discuss the effect of shear flow on the nematic to smectic A phase transition. The non-Newtonian flow properties (shear thinning and normal stress) ire correlated with the distortions of the structure-factor S(q). As a function of the Deborah number, we find first a deformation of S(q) and, beyond a critical Deborah number, highly distorted, one-dimensional fluctuations. The suppression of fluctuations by shear flow raises the critical temperature.

We report on synchrotron x-ray scattering studies of the microscopic structure of the nematic (N) and the smectic-A (SmA) phases in the liquid crystal 8CB under dynamic “steady state” shear flow conditions carried out in an x-ray Couette cell. These measurements directly probe length scales less than 100 Å and as large as 104 Å in the vicinity of the N-SmA phase transition away from equilibrium. The N-SmA transition corresponds to the onset of a one-dimensional mass density wave. In the nematic phase close to the smectic-A phase, there are very large pretransitional smectic-A fluctuations because the transition is almost second order. Under shear flow, we find that the nematic director undergoes a series of abrupt transitions between different orientational states of the director. We discuss the stability regimes of these orientational states by considering the fluctuation induced renormalization of one of the nematic shear viscosities and the fluctuation induced torque on the nematic director.

We have investigated the self and tracer-diffusion properties of a labeled diblock copolymer in a weakly-ordered lamellar phase. This phase can be a pure copolymer of equal or different molecular weight, or might contain added homopolymer. The spatially-periodic chemical potential field presented by the lamellar phase is capable of strongly influencing the diffusive motion of the tracer. In general, this field serves to slow diffusion, although the manner in which it acts depends on the wavelength of the potential relative to the labeled copolymer radius-of-gyration and on the composition of the copolymer. In the extreme limit of compositional asymmetry of the diblock tracer, we obtain results for the tracer-diffusion coefficient of a homopolymer.

While recent remrmalization group studies predict shear thickening in the limit of large Weissenberg numbers, scaling theories predict shear thinning. The ocntroversy is related to the question whether the Weissenberg number or the shear rate should be kept fixed when taking the limit of infinitely long polymers.

The flow properties of dispersions are a function of both particle number density and interparticle potential. At high number densities suspensions change from fluid-like behaviour to solid-like. The number density where this transition occurs is controlled by the shape of the interparticle potential function. The material state is clearly indicated from the rheological measurements. Wave propagation, stress relaxation and continuous shear viscometry have been used to study a variety of suspensions of monodisperse particles. Hard sphere, weakly attractive and strongly repulsive systems are discussed.

Rheological measurements have been performed on pectin-calcium systems close to the sol-gel transition. Two different experimental setups - steady state and oscillatory shear measurements - show scaling of the viscoelastic properties. The results of both types of measurements are consistent with each other and with scalar percolation theory.

We study the dynamics of concentrated colloidal suspensions by measuring the frequency dependent structure factor, S(q,w), using light scattering techniques. We introduce Diffusing Wave Spectroscopy, which extends dynamic light scattering to the multiple scattering regime, allowing us to study the lower frequency, diffusive modes of S(q,w), which reflect the Brownian motion of the particles. We study the behavior of the higher-frequency, propagating modes of S(q,w), which reflect acoustic waves, using Brillouin scattering. To study S(q,w) at low qa, where q is the scattering vector and a the particle diameter, we use inverted micelles, and find that the interactions between the micelles has a dramatic impact on the speed of sound as the volume fraction of micelles increases. To study S(q,w) at large qa, we use index matched PMMA particles, allowing us to measure the dispersion curve of phonons in a hard sphere colloid system. Together, these results provide a measure of S(q, w) over a wide range of q and of w.

Polydispersity in charge and in size of colloidal particles strongly influences the static light scattering < I(k) >. These effects are calculated by solving the Ornstein-Zernike integral equation together with the thermodynamically consistent Rogers-Young closure for a multicomponent mixture of up to 10 components. The results for < I(k) > for polydisperse systems show significant differences from results obtained by treating the system as an effective monodisperse one. For <I(k) > a large increase is found at small k as well as a shift in the main peak. Finally, using the above results, high-frequency elastic moduli are predicted for a binary mixture.

On a short time scale, Brownian particles undergo a transition from initially ballistic trajectories to diffusive motion. Hydrodynamic interactions with the surrounding fluid lead to a complex time dependence of this transition. We directly probe this transition for colloidal particles by measuring the autocorrelation function of multiply scattered light and observe the effects of the slow power-law decay of the velocity autocorrelation function.

In the present paper we report the growth of monometallic and multimetallic particles from the reduction of metal sols. In particular the Au and Au–Pd alloys are reported on this work. A number of techniques are applied to the characterization of the particles. It is shown that particles from few nanometers to 100 pm can be prepared with a number of shapes and morphologies. Particularly conspicuous are the shapes with a five–fold symmetry axis.

We apply density functional theory to the screened interactions between macroions in solution. The approach incorporates the strong correlations between screening ions at high densities, and reduces to the Poisson-Boltzmann equations at low densities. Local density functional theory results for the interactions between parallel planes are within ˜ 1% of Monte Carlo (MC) and inhomogeneous hypernetted chain (IHNC) values when the plane separation L ≥ 50Å. Non-local effects are important for divalent ions at small separations and high surface charge densities. A simple weighted density approximation qualitatively reproduces MC and IHNC results in this regime, and provides a simple explanation for the onset of attractive interactions between like-charged plates.

Flow can transfer the microphase separated morphology of block copolymers into a state of global order. For tri-block copolymers with cylindrical domains, this has been demonstrated by Folkes et al. (1973) and Hadziioannou et al. (1979). who established the existence of ‘single crystals’ of hexagonally ordered cylinders with uniform director throughout a sheared sample. The director is aligned with the shear direction. In this study, we investigate the flow induced ordering of cylindrical domain structure at increasing levels of shear.

Microemulsions are thermodynamically stable mixtures of two immiscible fluids, such as oil and water, and one or more surfactants or cosurfactants. These systems have a rich micro-structure and phase behavior which can take the form of a variety of multi-phase and single phase oil- or watercontinuous or bicontinuous fluids with unique and useful properties. The thermodynamic stability, ultra-low interfacial tension, clarity, high solubilization capacity and high interfacial area suggest uses “performance fluids.” The relationship between surfactant ussetsru cfotur reth eansde the phase behavior and properties of microemulsions is the key to their design. Through the proper selection of surfactants, microemulsion phase continuity can be tailored for a variety of applications. Two such applications, coal freeze conditioning and oil spill dispersion, are described in this paper.

The polymerization of acrylamide inside watcr-swollen micellas of Aerosol OT dispersed in toluene has been investigated. Incorporation of acrylamide enhances the interparticular attractive forces as shown by the intensity curves in small angle neutron scattering. It also induces sharp rises in conductivity which were attributed to a percolative process. The percolation threshold is lowered upon increasing the monomer content, reflecting the enhancement of the attractive interactions. In percolating systems, the structure affects the formation of polymer particles. Microscopy experiments show that particle nucleation occurs continuously throughout the polymerization.

Gold colloidal suspensions are produced from both inverse micelle solutions and microemulsions through both chemical and photolytic reduction of the appropriate salt. A variety of surfactant/solvent combinations yield varying results with respect to metalloid growth kinetics and stability as revealed through dynamic light scattering, small-angle x-ray and neutron scattering, and transmission electron microscopy.

The condensation polymerization of resorcinol and formaldehyde catalized by sodium carbonate produces a sol that aggregates to form a gel. Using viscometry the effect of temperature and catalyst concentration on the sol-gel transition was investigated. At a solids concentration of 3%, gelation occurred in 1500 minutes. The rate of increase in viscosity was a function of both catalyst concentration and temperature. The structure of the gels was studied by freeze-fracture TEM. In the sol phase the RF solutions contain particles of 5 to 20 nm diameter. After gelation the particles form a crosslinked network with a pore structure of 100 nm.

Colloidal dispersions are encountered during the processing of chemicals and materials in a number of contexts, generally requiring control of macroscopic properties such as the phase behavior and rheology through the manipulation of the chemistry. This paper surveys several applications, including the fabrication of advanced ceramics and the formulation of coatings, and attempts to identify the limiting science in each case.

Fumed silica/oil gels exhibiting rheological properties characterized by a yield stress followed by shear thinning behavior have been studied for application as waterblocking filling compounds for fiber optic cable. It is found that added signal attenuation in optical fibers after processing into a filled fiber optic ribbon cable is a function of the yield stress of the filling gel. We derive experimentally and apply a model of the relationship to formulate an optimum fumed silica/oil filling gel for fiber optic ribbon cables.

A high-resolution differential quasi-adiabatic calorimeter has been developed to investigate the physical properties of freestanding liquid-crystal films. Our recent heat-capacity studies near the smectic-A-hexatic-B transition of both 65OBC and 46OBC freestanding films clearly demonstrate the evolution towards twodimensional limiting behavior in four-layer films. As the film thickness decreases towards four molecular layers, the heatcapacity anomalies first display separate peaks for the surface and interior transitions and then evolve to one dominated by the surface transition.