Heat Capacity Measurement on Lyotropic Liquid Crystal: Octaoxyethylene-n-hexadecyl ether / Water Binary System

Heat capacity measurement on the lyotropic liquid crystal formed in the binary system, non-ionic surfactant octaoxyethylene-n-hexadecyl ether (C16E8) / water, as started with an adiabatic calorimeter between 290 and 370 K. Samples were prepared in different concentrations of the C16E8 surfactant in water. In the liquid crystal region, the hexagonal (H1) – cubic (V1) and cubic (V1) – lamellar (Lα) phase transitions were observed, and the phase transition temperatures depended on the concentration. The hexagonal – cubic and cubic – lamellar phase transitions are of first-order, as shown by the existence of biphasic regions. Entropy and enthalpy changes at each phase transition and excess heat capacity of each phase are compared with those of the hexaoxyethylene-n-dodecyl ether (C12E6) system. The concentration dependence of enthalpy change is weak at hexagonal – cubuc and cubic – lamellar phase transitions in the C16E8 / water as in the C12E6 / water system.

(by N. Kitamura & K. Saito)

Phase Behavior of the Two-Dimensional Solid of Decane Formed at Solid-Liquid and Gas-Solid Interfaces

Heat capacity measurements have been made to investigate the formation of two solid monolayers of n-decane adsorbed on graphite, the one formed at gas-solid interface and the other at solid-liquid interface. The monolayer at gas-solid interface is found to melt at 199 K, well below the bulk melting point (243.53 K). The monolayer at solid-liquid interface melted at 267 K and showed another transition at 263 K. Some preliminary results obtained for a mixture of n-decane and n-nonane are also presented.

(by T. Kita & A. Inaba)

Vibrational States of
the Monolayers of Some Planer Molecules
Adsorbed on Graphite

An MD simulation study has been performed for the monolayers of benzene and its homologous molecules adsorbed on the surface of graphite, with special attention focused on the vibrations perpendicular to the surface. It is found that the adsorbed monolayer has a mode at 5 meV which is exactly the same as that of the graphite underneath. The results are compared with those obtained from neutron scattering and calorimetry.

(by H. Takei & A. Inaba)

Investigation of Adsorbed Multilayers
by Molecular Dynamics Simulation

An MD simulation study is presented for the multilayer of tetramethylsilane adsorbed on the surface of graphite. A bilayer is found to be formed, where the second layer forms a two-dimensional solid as the first layer does. The X-ray diffraction patterns calculated for each layer demonstrate that the structure is similar between the two layers but is different from that of either the high-temperature phase of the submonolayer or the low-temperature phase.

(by N. Sakisato & A. Inaba)