X-ray diffraction studies on homologous thallium soaps below the temperature range of the neat phase 1. Calculation and comparison of the structure parameters of unit cells

Abstract

The results of X-ray diffraction patterns of homologous thallium soaps TlC _n (n-8, 9, 10, 11, 12, 14, 15, 16, 17, 18, 20 and 22) in dependence on the temperature showed that the structures of the phases below the temperature range of the liquid-crystalline neat phase (so called phase C₁, phase C₂, phase I, phase II) are crystalline-like, not liquid-crystalline.

As function of the chain length of the fatty acid group, we found the following phase sequences to be a function of temperature: TlC₈: phase I↔neat phase: TlC₉−Tl₁₄: phase C₂↔phase II↔phase I↔neat phase; TlC₁₅, TlC₁₆: phase C₁↔phase II↔phase I↔neat phase; TlC₁₇−TlC₂₂: phase C₁↔phase II↔neat phase.

From the X-ray patterns of the thallium soaps were calculated the lattice parameters and the unit cells of these homologues at various temperatures. The comparison between the lattice parameters of the homologues showed, surprisingly, that these parameters were independent of chain length and temperature. This X-ray data are the basis for the following development of structure models of the phase C₁, phase C₂, phase I, and phase II, including the neat phase (see Part 2).