Sokol has recently begun studies of the collective excitations of liquid 4He confined in porous glasses. The effects of geometrical confinement on the macroscopic properties has been well studied. The confinement of the super fluid in porous glasses can profoundly affect its behavior, even to the extent of changing the critical exponents. However, until recently, there were no microscopic studies exploring how the dynamics of the liquid were changed by confinement. Sokol's recent work has shown that the energy of the collective excitations is shifted by confinement and that these shifts can be related to the observed changes in the macroscopic super fluid fraction. The origin of these changes in the microscopic excitation spectrum are not understood at present. Future work will concentrate on the effects of pore size and morphology, the behavior of excitations close to the super fluid transition, and the effects of 3He.

Sokol has also applied high-energy inelastic neutron scattering is also being employed to obtain microscopic information on the local environment of light atoms and molecules in a variety of environments. Hydrogen atoms and molecules in environments, such as physisorbed or chemisorbed on surfaces or in intercalation compounds, which are of technological importance in a variety of applications, such as fuel storage.

Another area of interest is the effect of restricted geometries on the structure, dynamics, and phase transitions of liquids and solids. The properties of liquids and solids confined in very small pores is interesting from both fundamental and practical standpoints. At the fundamental level, the interactions with surfaces and the effects of finite size and geometrical interconnection can be explored in these systems. At the practical level, these systems are of great importance in areas such as interfacial adhesion, lubrication, theology, tribology, and material engineering. A number of interesting effects, such as super cooling and hysteresis of liquid-solid and solid-solid phase transitions, have been observed for various substances in the pores.

Despite the importance of these materials, there has been little direct information on the microscopic structure and dynamics of the liquid or solid in the pores. Structural information, obtained via elastic neutron and X-ray scattering, provides the most fundamental characterization of the condensed phases. Studies are under way for a broad range of materials, including quantum liquids, such as helium and hydrogen, classical liquids, such as neon and krypton, molecular liquids, such as oxygen and nitrogen, polar liquid, such as water, and liquid crystals. Diffraction studies of the condensed phases of these systems in porous materials have provided evidence for new and interesting behavior for these systems. Upon solidification, crystalline phases can be formed in pores with diameters on the order of 50 Å. Surprisingly, the size of the crystallites in the pore can be several hundred angstroms, indicating that the interconnected geometry of the porous material is quite important. These studies have also indicated that, depending on the material and the pore size, a variety of crystal structures are possible. Thus, the material in the pore can crystallize in the bulk-structure, a new structure, or no long-range structure at all (i.e., a glass).