Probing electric field response of LC thermosets via time-resolved X-ray and dielectric spectroscopy

Curing of LCTs in an AC electric field was studied to understand the interplay between crosslink reaction and formation of a liquid crystalline (LC) phase and its effect on mechanical thermal properties on resulting thermosetting films. We show that dicyanate thermosetting monomers with ester functionality exhibit the ability to realign even after long curing times and allow poling of the LC director in resulting thermosetting films. To probe the details of the underlying process that leads to reorientation of the LC director model compounds were synthesized and their frequency and temperature dependent behavior under electric fields was studied. Curing reactions under electric fields show that the dual-frequency characteristics of the dicyanate mesogens behave very differently than epoxy thermosets. Size exclusion experiments reveal a prolonged gelation point in this system responsible for orientational switching even after long curing times. Finally, the ability to change orientation of the LC director allows tuning of modulus and thermal coefficient of expansion, making these thermoset films potential candidates for underfills, encapsulation materials and protective coatings for LC displays and active matrix substrates which require match in refractive index and mechanical/thermal properties.