Turbulent drag reduction in a dilute polymer solution has been studied using the technique of photon-correlation homodyne spectroscopy to measure velocity differences in a concentric cylinder cell, in which the inner cylinder rotates. A large anisotropic suppression of turbulent velocity differences is found in the bulk region of the turbulent fluid. The suppression effect occurs at various length scales up to ∼ 1 mm, which is far beyond the Kolmogorov dissipation length ℓd (∼ 0.04 mm). The large-scale velocity fluctuations are suppressed, but their statistical properties remain unchanged. The small-scale fluctuations, on the other hand, are damped out much more strongly, resulting in a different functional form for the velocity density function. The latter observation is consistent with the notion that the polymer-turbulence interaction causes a truncation of the turbulent energy cascade at small scales.

The mode and strength of poly(acrylic acid), PAA, interchain complexation was strongly influenced by the presence of salts and cationic surfactants. Addition of salts to the shearing PAA solution disrupted the complexation, while modification of the PAA with surfactant enhanced the complexation but only below a critical concentration that depended on the surfactant chain length and pH employed. The chain morphology developed by such interchain complexation of PAA is a rigid rod-like chain cluster. The PAA self-complexation in the presence of poly(ethylene oxide), PEO, is strongly affected by pH and PEO molecular weight. With a high molecular weight PEO, the PAA self-complexation is drastically suppressed, whereas the PAA complexation and thus, the chain rigidity is markedly enhanced in the presence of a low molecular weight PEO, probably due to physical crosslinking of the PEO between the elongated PAA molecules.

We describe x-ray scattering studies of the nematic and smectic-A phases of the thermotropic liquid crystal 8CB and the Lα, and L3 (lamellar and sponge) phases of the lyotropic liquid crystal system: SDS, dodecane, pentanol and water. In the thermotropic system a series of orientational states of the nematic director is observed before entering the smectic-A phase where the smectic density wave and nematic director are oriented normal to the shear plane at high shear rates. In the lyotropic system lamellar fluctuations in the sponge phase (L3) become oriented by shear and in the lamellar phase (Lα) at high shear the layers orient preferentially along the velocity-gradient direction, in highly anisotropic cylindrical multilamellar liposome-like structures.

We study linear fluctuations about the steady states of thermotropic liquid crystals under planar sheax flow. Near the non-equilibrium critical point we find a single critical mode whose singular behavior at the critical point may be selectively probed by polarized light scattering. This critical mode is a combination of both amplitude and orientation fluctuations of the order parameter, which distinguishes it from conventional Ising-like critical modes, which are purely amplitude fluctuations. There are at least two distinct signatures of the critical point, depending on whether the critical strain rate is in the (material-dependent) strong or weak shear regimes.

We investigate the effects of shear-flow on the smectic phase of thermotropic and lyotropic liquid crystals. We show that shear-flow transforms a Smectic-A thermotropic into an orthorombic solid by the suppression of undulation fluctuations. In contrast, the lyotropic Lα phase exhibits, in addition, a very striking enhancement of shortwavelength concentration fluctuations - a phenomenon which is closely analogous to a well-known effect in polymer solutions. We demonstrate this result using both hydrodynamic theory as well as a microscopic model based on the Helfrich theory of membranes. The dispersion relation of the concentration fluctuations is in qualitative agreement with recent experiments on the Lα phase in shear flow.

This paper presents a nonlinear numerical analysis of the orientational instabilites, textures, and flow patterns of a characteristic rod-like nematic liquid crystal in steady simple shear flow. The parameter vector V=(λ,E) is given by the reactive parameter (λ) and the Ericksen number (E). There are two stationary solutions: in-plane(IP) and out-of-shear-plane(OP), according to whether the average orientation lies in or out of the plane of shear. For a given λ the in-plane stationary solutions may undergo a continuous transition (second order) to two dissipatively equivalent OP solutions when E=Eo or a discontinuous transition (first order) to a highly distorted IP solution when E=Ei. The continuous transition at E=Eo is a supercritical (pitchfork) bifurcation and the discontinuous transition at E=Ei is a limit point instability. Nonlinear numerical analysis shows that for the studied liquid crystal Eo < Ei. The orientation phase diagram for stable stationary solutions therefore consist of a region of OP solutions separated from a region of IP solutions by the curve Vo = (λ,Eo), describing a set of continuous supercritical bifurcations. These stable OP solutions are characterzied by the absence of sharp splay and bend deformations and by the presence of complex secondary flows arising from the three dimensional orientation. Presented results also include the dependence of the three dimensional texture, primary and secondary velocity fields on E.

Rheo-optical studies on aligned and unaligned melts of a main chain thermotropic polyester with flexible spacers are discussed in terms of the predictions of the Ericksen-Leslie equations. It is shown, using conoscopy, that the director is flowaligning at temperatures close to TNI and nonflow-aligning close to a smectic to nematic (TSN) phase transition. The implications of these results are discussed in terms of the change in sign of one of the Leslie viscosity coefficients and interpreted in the framework of the Ericksen-Leslie Theory.

Rheological measurements have been used to study the kinetics of shear induced association for rod-shape micelles formed by mixtures of ADHAB and salicylic-sodium salt. Pronounced hysteresis and large fluctuations were found in the stress-shear rate diagram. We investigate the association and dissociation mechanism through stress quench experiments where viscosity measurements study the system relaxation. The association process was found to be a single exponential with a relaxation time of about 1 minute, whereas the dissociation process was much slower and was non-exponential. In the semidilute regime, the critical shear rates increase with concentration, contradictory with existing theories.

Phase separation in an off-critical binary mixture is studied under an uniform and steady shear flow. The nucleation and subsequent growth of droplets in aweakly supersaturated mixture (volume fraction of the new phase smaller than 10%) is studied by small angle scattering and turbidity measurements. The completion of the nucleation process is shown to be accelerated by the shear flow. At very low supersaturation, a strong effect of shear is detected which can be related to shear-triggered nucleation. In situ measurements ’of the surface tension between the two phase-separating phases obtained by studying the deformation and tilt of the growing droplets is discussed.

In a strong electric field, the qualitative behavior of electrorheological fluids is dominated by the dipolar interactions between the colloidal particles. When thermal effects can be ignored, the ground state of a system of dipolar particles is an ordered solid. However, long-range ordered structures are rarely seen in experiment. When a high electric field is applied to a fluid, dielectric columns oriented parallel to the field rapidly form. The relaxation of these columns is a much slower process. I calculate the shape of the columns formed and the time scale for the relaxation of the columnar structure. I also discuss how this structure formation is altered in the presence of a shear flow.

The electrorheological (ER) response is characterized by a reversible increase in suspension viscosity on application of large electric fields. Suspensions displaying this behavior are typically composed of a polar solid phase suspended in a low conductivity oil (1-3). In the past five years considerable work investigating the mechanisms controlling the ER response has established that increases in viscosity are associated with the formation of electrode spanning particulate structures which are degraded by shear (4-8). The structures are the result of polarization interactions produced by the dielectric mismatch between the solid and continuous phases. Extensive modelling studies have shown that much of the rheological behavior of ER suspensions can be understood in terms of a balance of viscous and electrical polarization forces as written in terms of the Mason number, Mn = ηc ṙ/(2ε0εc(βE)2) (9). Here ηc, is the continuous phase viscosity, ṙ is the shear rate, and E is the applied field strength. The relative polarizability of the particulate phase is given in terms of β = (εp−εc)/(εp+2εc) where εp is the particle dielectric constant and γc is the continuous phase dielectric constant. The relative viscosity of many suspensions can be reduced to a single universal function of Mason number and often display a yield stress which scales with E2.

Ferrofluids are colloidal suspensions of magnetic particles which we model as a dilute gas of dipolar hard spheres. At low particle density the osmotic pressure and magnetic susceptibility may be expanded in a virial series. We evaluate the second virial coefficients for fluids confined to a line, or to a plane, as well as ordinary three dimensional fluids in ellipsoidal containers. We focus our attention on anisotropy of the magnetic susceptibility and point out the role of particle chaining in determining the magnetic anisotropy of low dimensional ferrofluids.

For the first time, response of magnetic fluid microdrops to time dependent magnetic fields are tested in two different experimental conditions (rotating field, crossed static and alternating fields). In both cases, a new shape instability is observed leading to cog-wheels either rotating either motionless. A simple model account for the stability range of oblate ellipsoidal shapes and for the lateral peak instability leading to the cogs which crown the cog-wheel.

Two magnetic latex preparations have been measured by polarized and depolarized dynamic light scattering. The adherence of the latexes to a simple physical model, that of a bar magnet embedded in a plastic sphere, is judged adequate in one case, but not the other. Preliminary efforts to use the latex spheres as probes of sodium polystyrene sulfonate solutions are described. A few observations are made concerning the dynamic light scattering behavior of the magnetic latex under the influence of an externally applied, oscillating magnetic field.

Colloidal suspensions are remarkable analogues of molecular fluids. In particular, at high volume fraction (Φv) they share two characteristic features with super-cooled molecular liquids: the appearance of two distinct modes of translational motion (fast and slow diffusive modes), and a critical retardation of the latter as Φv approaches random close packing (a colloidal “glass transition”). These phenomena have been studied extensively by photon correlation spectroscopy (PCS) [1-4] and are the subject of many theoretical analyses [5-12]. This paper concerns the use of forced Rayleigh scattering (FRS) to address questions not resolved by existing data or theory. We report: 1) properties of a hydrophobic silica colloid bearing photoactive azo-dye groups suitable for FRS studies, and 2) preliminary results from FRS measurements which reveal some unanticipated features regarding the transition from short-time to long-time self-diffusion at small k.

Polymethylmethacrylate (PMMA) particles are suspended without additional free polymer in benzyl alcohol, where they swell to nearly three times their dry radius. The single particle properties are examined by static and dynamic light scattering measurements, as well as by intrinsic viscosity measurements. A colloidal liquid/crystal phase diagram is determined as a function of effective volume fraction determined from the intrinsic viscosity. The samples are subjected to oscillatory shear flows to determine the influence of flow on the particle microstructure. A nonequilibrium phase diagram is constructed indicating a correlation between spontaneous ordering at equilibrium and shear induced ordering. These results are compared with previous work done for hard PMMA sphere suspensions.

The two-particle correlation function serves as an important connection between suspension microstructure, scattering experiments, and macroscopic properties. Formal relationships between the experimentally accessible structure factor for suspensions undergoing simple shear, bulk stresses, and flow dichroism and birefringence are demonstrated. Measurements of flow dichroism using variable wavelength incident radiation provide a method to map out the nonequilibrium microstructure.

Idealised models of sheared suspensions are studied by computer simulation. In this and the companion paper [1], non-equilibrium phase diagrams are evaluated for two models: one for electrorheology (this paper), the other for aggregation due to depletion (companion paper [1]). Distinct structural phases and their associated rheology are reported.

A Brownian dynamics algorithm described in the companion paper [1] is used to simulate sheared suspensions of particles interacting via a depletion potential. The shear and interaction forces interplay to give a complex non-equilibrium phase diagram: a variety of shear induced agglomerates form at low shear rate, but, for shear rates above a non-equilibrium phase boundary the agglomerates develop interfaces predominantly orientated parallel to the plane of shear gradient and flow.

Shear induced birefringence was measured for dilute and semidilute rigid PTFE rod suspension. Orientational order of the rods is deduced from the birefringence data and compared with theory by Doi and Edwards′. Although the theory was for dilute solution, the renormalized data agree qualitatively with the theory even far into the nonlinear regime. At high shear the order parameter approaches a saturated value, and at low shear it depends on the shear rate square. The major discrepancy between the theory and experiment comes from the expected slowing down of rod reorientation at higher concentrations. At high concentrations, the slowing down is more than what can be accounted for by the macroscopic viscosity along.