X-ray Investigation of Smectic Layers in Homologous Series of Chiral Three Ring Esters

Abstract

Three ring chiral esters, substituted laterally or not with a fluorine atom, having chiral terminal chain of the structure –COOC*H(CH3)C6H13, and achiral terminal chain alkylated CnH2n+1COO(CH2)mO– or partially fluorinated CnF2n+1COO(CH2)mO– (n = 1–7, m = 3–6) were measured by small angle X-ray scattering technique. Most of the fluorinated homologues have high tilted an orthoconic antiferroelectric phase (angle in neighbouring layers is around 90°), which is followed by a SmA phase of like de Vries type. The following parameters are compared: temperature function of d, dA, d/l, dA/l, (d-layer thickness, dA-layer thickness of SmA phase, l-molecular length) upon temperature and relation with the structure is discussed. The preferred structure for formation of the orthoconic antiferroelectric structure is partially fluorinated terminal alkyl chain and biphenylyl benzoate rigid core. The strongest de Vriesation of SmA phase is observed for longer fluorinated terminal alkyl chain (n > 4, m = 6) and phenyl biphenylate rigid core substituted by a fluorine atom in the 2 position of the phenyl ring.