Mesogen–Mesogen Registry Tunes Thermomechanical Actuation in Surface-Aligned Liquid Crystalline Elastomers

Liquid crystalline elastomers (LCEs) couple liquid-crystalline order with elastomeric deformability. Their self-assembly reflects a balance between cohesive interactions among aromatic mesogenic cores and the fluidity imparted by aliphatic chains. Here, we examine the contribution of mesogen-mesogen packing to thermomechanical response by comparing LCEs prepared from nearly identical mesogens while holding spacer length, network chemistry, and stoichiometry constant. Relative to its unmethylated analogue C6Sym, the canonical methylated mesogen C6M forms a nematic LCE characterized by reduced packing coherence and a broader, lower-temperature actuation response. The correlation between mesogen-mesogen registry and actuation is further evident in LCEs prepared from isomeric smectogens C6Sym and C6Asym. Although both neat monomers form smectic phases, intermediate blends exhibit expanded mesogen spacing and reduced longitudinal coherence, losing smectic character. As with C6M, expanded lateral mesogen spacing in these blends accompanies weaker strain-temperature coupling and lower-temperature actuation. At 50% C6Sym, the temperature of maximum strain-temperature coupling is approximately 70–84 °C below those of the neat endpoints. Across both comparisons, disrupted packing and altered mesogen spacing correlate with weaker strain-temperature coupling and broader, lower-temperature actuation.