Preparation, characterization and investigation of ferroelectric properties of sulfonic acid and cholesterol-based liquid crystal ionomers

A series of liquid crystal (LC) ionomers were synthesised using polystyrene sulphonic acid as the matrix, incorporating polyetheramines (D230 and D400) with varying molecular weights and sulphonic acid-functionalised LC monomers. The resulting materials were comprehensively characterised by use of complementary analytical techniques to elucidate their chemical structure, thermodynamic properties, LC phase behaviour and ferroelectric properties. All the ionomers exhibited a smectic C* (SmC*) mesophase. The LC phase behaviour of the ionomers was systematically modulated by ionic crosslinking density, polar interactions and LC ordering. All the ionomers demonstrated ferroelectric behaviour, with maximum saturation polarisation (Ps) and remanent polarisation (Pr) values of 160.36 nC/cm2 and 56.44 nC/cm2, respectively. The D400-based ionomers exhibit a more relaxed ionic network constraint relative to those D230–based systems, facilitating the formation of an ordered SmC* layered structure, improving the orientational order of effective dipoles and consequently enhancing both Ps and Pr. Dielectric analysis revealed that the dielectric constant and dielectric loss of the ionomers decreased gradually with increasing frequency. For all the ionomers, the D400–based series demonstrated superior polarisation response characteristics due to its balanced cross-linked network, which enhanced chain segment mobility and optimised the distribution of polar groups.