Self-organisation through size-exclusion in soft materials

Abstract

A number of materials derived from 4-undecyloxy-4′-cyanobiphenyl but with varying terminal groups were prepared in order to better understand how such a group influences the type, and local structure of mesophases formed. Whereas electron poor terminal groups (fluoroaromatics and halogen atoms) were found to destabilise the smectic A phase through unfavourable electrostatic interactions, bulky silane, siloxane and hydrocarbon groups can be incorporated into the structure of the phase with only minor reductions in clearing point. An increase in the layer spacing of the smectic A_d phase in materials with bulky groups suggests that microphase segregation is not the driving force, but rather exists as a consequence of steric crowding at the smectic layer interface. Electrooptic studies reveal that ‘carbosilane’ end groups, such as tetramethyldisilapropane, are significantly more electrochemical stable than their siloxane counterparts whilst retaining their desirable thermal properties.