The molecular dynamics in the glass transition of the “quasi”–van der Waals glass salol confined to nanopores (2.5, 5.0, and 7.5 nm) with lubricated inner surfaces is found to be faster (by up to 2 orders of magnitude) than in the bulk liquid. This effect of confinement is more pronounced for smaller pores. It reflects the cooperativity of molecular motions in the glass transition and enables its length scale to be determined quantitatively.

Broadband dielectric spectroscopy (${10}^{\mathrm{-}2}$ Hz–${10}^9$ Hz) is employed to study the dynamic glass transition of low-molecular-weight glass-forming liquids being confined to nanoporous sol-gel glasses with pore sizes of 2.5, 5.0, and 7.5 nm. As glass-forming liquids, salol (one hydroxy group), pentylene glycol (two hydroxy groups), and glycerol (three hydroxy groups) were chosen. We interpret the dielectric spectra in terms of a two-state model with dynamic exchange between a bulklike phase in the pore volume and an interfacial phase close to the pore wall. This enables one to analyze in detail the interplay between the molecular dynamics in the two subsystems (bulklike and interfacial), its dynamic exchange, and hence their growth and decline in dependence on temperature and strength of the molecular interactions. For glycerol it is shown that a bulklike dynamic glass transition takes place in subvolumes as small as about 1 nm. © 1996 The American Physical Society.

Granular physics has made considerable progress during the past decades in the understanding of static and dynamic properties of large ensembles of interacting macroscopic particles, including the modeling of phenomena like jamming, segregation and pattern formation, the development of related industrial applications or traffic flow control. The specific properties of systems composed of shape-anisotropic (elongated or flattened) particles have attracted increasing interest in recent years. Orientational order and self-organization are among the characteristic phenomena that add to the special features of granular matter of spherical or irregularly shaped particles. An overview of this research field is given.

Shear induced alignment of elongated particles is studied experimentally and numerically. We show that shear alignment of ensembles of macroscopic particles is comparable even on a quantitative level to simple molecular systems, despite the completely different types of particle interactions. We demonstrate that for dry elongated grains the preferred orientation forms a small angle with the streamlines, independent of shear rate across three decades. For a given particle shape, this angle decreases with increasing aspect ratio of the particles. The shear-induced alignment results in a considerable reduction of the effective friction of the granular material.

Orientational order in the isotropic phase of liquid crystals confined to 0.2-μm-diam cylindrical channels of Anopore membranes is measured by deuterium nuclear magnetic resonance. At temperatures deep in the isotropic phase, the measurements reveal the order of the first molecular layer at the cavity wall, while at temperatures near the isotropic-nematic transition the measurements are primarily sensitive to order penetrating into the cavity in a manner described by the Landau–de Gennes theory. The degree of order ${\mathit{S}}_0$ at the cavity wall is measured and the surface coupling constant determined for various treatments of the cavity wall. Wide variations of ${\mathit{S}}_0$ are found for different surface treatments. Treatments that yield both perpendicular and parallel molecular anchoring are explored. The angular dependence of the surface-induced nematic order is investigated following the ${\mathit{P}}_2$(cosθ) expression independent of molecular anchoring at the surface.

Broadband dielectric spectra are usually fitted to a superposition of contributions from one or several parametrized processes (Debye, Havriliak-Negami, etc.). This work proposes instead to extract continuous distributions of relaxation times from complex dielectric spectra by solving a Fredholm integral equation using the Tikhonov regularization technique with a self-consistent choice of the regularization parameter. This method is stable with respect to the noise and resolves multiple dynamical processes. An experimental example of salol adsorbed on microporous glass is analyzed.