The Steric Influence on the Formation of Smectic Layers in Binary Systems

The layer spacings d, measured by an X-ray small angle equipment, have been used to characterize the smectic layers in binary systems. In mixtures consisting of conventional rod-like molecules the d-values show additive behaviour. By systematic modification of the molecular shape it can be evidenced, that in branched compounds the steric interaction causes a cage effect. In consequence of this the layer spacings do not behave longer additively and-under special conditions-induced SA phases (“filled SA phases”) can be generated.