A Vibrational and Structural Study of the Solid-Solid Phase Transitions in C10H21NH3Cl

Article abstract of DOI:10.1021/j100350a009

The joint vibrational and structural study of n-decylammonium chloride results in a fair description of the solid phases and their interconversions during the thermotropic phase transitions.Phase i (stable below 312 K) crystallizes as a well-ordered, interdigitated layer structure, whereas phases α (stable above 318 K), β (stable between 318 and 316 K), δ (stable between 316 and 302 K), and ε (metastable below 302 K) represent intermediate states between a very disordered smectic B and a quite densely packed smectic H.The i -> δ transition consists in a reconstructive separation of the n-decylammonium chains, whereas the other transitions entail a successive disordering of the organic layers and the polar lattice.Disorder in the aliphatic chains takes the form of chain defects (G forms, GTG sequences, and kinks).Disorder in the polar lattice consists of jumps of the ammonium groups between several equivalent potential wells inside an appropriately distorted tetragonal chlorine pyramid.Only short-range order exists in phase α, whereas there are some intralayer correlations in phases β, δ, and ε (phase ε reaches an almost completely ordered state at about 80 K).Comparable populations of G forms, GTG sequences and kinks are observed in phases δ, β, and α; different chain tiltings and packings are realized, however.This difference is also reflected in different molecular motions in phases δ, β, and α.