A variety of simple bent-core molecules exhibit smectic liquid crystal phases of planar fluid layers that are spontaneously both polar and chiral in the absence of crystalline order. We found that because of intralayer structural mismatch, such layers are also only marginally stable against spontaneous saddle splay deformation, which is incompatible with long-range order. This results in macroscopically isotropic fluids that possess only short-range orientational and positional order, in which the only macroscopically broken symmetry is chirality--even though the phases are formed from achiral molecules. Their conglomerate domains exhibit optical rotatory powers comparable to the highest ever found for isotropic fluids of chiral molecules.

The diffusive dynamics of 100 nm to 400 nm diameter polystyrene nanoparticles dispersed in water were studied using brightfield and fluorescence based differential dynamic microscopy (DDM) and compared to those obtained from dynamic light scattering. The relaxation times measured with brightfield and fluorescence DDM over a broad range of concentration of nanoparticles (10 À6 # 4 # 10 À3) and scattering vectors (0.5 mm À1 < q < 10 mm À1) are in excellent agreement with each other and extrapolate quantitatively to those obtained from DLS measurements. The diffusion coefficients extracted from the q-dependent relaxation times using all three methods are independent of the nanoparticle concentration.

Using a model colloid-polymer suspension, we show that confinement induces solidification in attractive colloidal suspensions via a fundamentally different route from that active in hard sphere colloidal suspensions. For a range of polymer concentrations, the suspensions undergo a phase transition from a colloidal fluid of clusters to a colloidal gel as confinement increases while polymer and particle concentration are held constant. In both fluid- and solidlike attractive suspensions, effects of confinement on the structure and dynamics appear at much larger thicknesses than for hard-sphere suspensions. The solidification does not originate from structuring of the colloids by the walls. Instead, by analyzing cluster size distributions in the fluid phase and particle dynamics in the gel phase as a function of confinement, we find that the strength of the effective interparticle attraction increases as the samples are confined. We show that the increase in the effective attraction can be understood as a consequence of the increasing importance of excluded volume due to the walls to the free energy of the polymer as confinement is increased.

The diffusive motion of colloidal particles dispersed in a premelting solid is analyzed within the framework of irreversible thermodynamics. We determine the mass diffusion coefficient, thermal diffusion coefficient and Soret coefficient of the particles in the dilute limit, and find good agreement with experimental data. In contrast to liquid suspensions, the unique nature of premelting solids allows us to derive an expression for the Dufour coefficient and independently verify the Onsager reciprocal relation coupling diffusion to the flow of heat.The melting of any material is normally initiated at one of its free surfaces at temperatures below the bulk melting temperature, T m , by the formation of a thin liquid -interfacially premelted -film. This surface phase transition has been observed at the interfaces of solid rare gases, quantum solids, metals, semiconductors and molecular solids including ice, allowing the liquid phase to persist in the solid region of the bulk phase diagram [1]. When T ≈ T m the premelted film is thicker than the correlation lengths of the solid-liquid interfaces and hence the total free energy of the (planar-planar) system is represented as a linear combination of bulk and interfacial terms (this latter contains both the interfacial energy and the long ranged volume-volume interactions which are also forces/area in such a system). The total free energy of a curved interfacially melted system includes in addition the Gibbs-Thomson effect, which, while contributing to the premelted film thickness d, one can prove produces no net thermodynamic force over a closed surface [2]. Nonetheless, when a premelted film forms around a foreign particle within a subfreezing solid, the particle can migrate under the influence of a temperature gradient, which produces a thermomolecular pressure gradient, a phenomenon referred to as regelation or thermodynamic buoyancy [2,3]. Here we analyze this and related phenomena within the framework of irreversible thermodynamics and demonstrate that in addition to motion under the influence of a temperature gradient, the particle can undergo constrained Brownian motion owing to thermal fluctuations in the premelted film. We determine the diffusivity in the dilute limit and relate it to the Stokes-Einstein diffusivity of particles in the bulk melt. Furthermore, the motion of a particle is shown to induce a reciprocal effect -a heat flux due to the release and absorption of latent heat on opposite sides of the particle. We show that this effect is described by the Onsager relation coupling mass diffusion to heat flux.We consider a suspension of spherical particles of radius R randomly distributed in a bulk solid. For temperatures T near but less than T m , each particle is surrounded by a premelted film of thickness d that facilitates both the particles' constrained Brownian diffusion and their directed motion parallel to temperature gradients (figure FIG. 1: Schematic diagram of a premelting solid containing colloidal inclusions at local volume fraction φ. 1). ...