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Broadband dielectric spectroscopy (10 Ϫ2 Hz-10 9 Hz͒ 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 group͒, pentylene glycol ͑two hydroxy groups͒, and glycerol ͑three hydroxy groups͒ 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 interfacial͒, 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. ͓S1063-651X͑96͒08711-9͔

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.

The alignment, ordering, and rotation of elongated granular particles was studied in shear flow. The time evolution of the orientation of a large number of particles was monitored in laboratory experiments by particle tracking using optical imaging and x-ray computed tomography. The experiments were complemented by discrete element simulations. The particles develop an orientational order. In the steady state the time- and ensemble-averaged direction of the main axis of the particles encloses a small angle with the streamlines. This shear alignment angle is independent of the applied shear rate, and it decreases with increasing grain aspect ratio. At the grain level the steady state is characterized by a net rotation of the particles, as dictated by the shear flow. The distribution of particle rotational velocities was measured both in the steady state and also during the initial transients. The average rotation speed of particles with their long axis perpendicular to the shear alignment angle is larger, while shear aligned particles rotate slower. The ratio of this fast/slow rotation increases with particle aspect ratio. During the initial transient starting from an unaligned initial condition, particles having an orientation just beyond the shear alignment angle rotate opposite to the direction dictated by the shear flow.

Broad-band dielectric spectroscopy (10 −2 Hz-10 7 Hz) is employed to study the molecular dynamics of three low-molecular-weight glass-forming H-bonded liquids being confined in (dielectrically inactive) porous glasses with pore sizes of 2.5 nm, 5.0 nm and 7.5 nm. From the relaxation time distribution of the dielectric spectra, a three-layer model is deduced, consisting of molecules having solid-like, interfacial and bulk-like dynamics, respectively. The quantitative analysis of the different contributions shows that the bulk-like fraction scales with the pore size, the interfacial and solid-like layers remaining relatively unchanged. Our results restrict the possible existence of cooperatively rearranging clusters in the system below nanometer scale.

Granular gases are convenient model systems to investigate the statistical physics of nonequilibrium systems. In the literature, one finds numerous theoretical predictions, but only few experiments. We study a weakly excited dilute gas of rods, confined in a cuboid container in microgravity during a suborbital rocket flight. With respect to a gas of spherical grains at comparable filling fraction, the mean free path is considerably reduced. This guarantees a dominance of grain-grain collisions over grain-wall collisions. No clustering was observed, unlike in similar experiments with spherical grains. Rod positions and orientations were determined and tracked. Translational and rotational velocity distributions are non-Gaussian. Equipartition of kinetic energy between translations and rotations is violated.

Granulate 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 irregular particles. An overview of this research field is given.Final version published in Soft Matter,

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