Thermal diffusivity of side-chain-polymer smectic liquid crystals

Abstract

The thermal diffusivity in the smectic liquid crystals (LCs) of side-chain PmBEn polymers was measured using the temperature wave method. PmBEn polymers form two types of smectic LCs that differ in their degree of side-chain overlap, which affects the thermal diffusivity. Smectic A1 (SmA1) LCs with fully interdigitated side chains have 20% greater thermal diffusivity than smectic Ad LCs with side chains overlapping at the alkyl tail. The results for magnetically oriented SmA1 LCs show that the thermal diffusivity component along the LC director direction (α//) is larger than that perpendicular to the director direction (α⊥). Upon increasing the number m of methylene units in the spacer from 5 to 12, α// increases from 2.50 × 10−7 to 3.11 × 10−7 m2 s−1 and is larger for odd-m homologues, although α⊥ is almost constant around 1.25 × 10−7 m2 s−1. These variations in thermal diffusivity in PmBEn polymers are correlated with the smectic LC structures characteristic of side-chain LC polymers.