Solvent-Imprinted Mesogen Packing for Rate-Dependent Dissipation in Polydomain Liquid Crystal Elastomers

Processing solvents are usually regarded as transient auxiliaries that leave no trace once removed. Here, we show that the synthesis solvent leaves a persistent structural imprint that controls mesogen packing and mechanical dissipation in main-chain liquid crystal elastomers (LCEs) long after its removal. Polydomain LCEs with identical monomer stoichiometry, cross-linker content, and solvent loading were synthesized in six aprotic solvents spanning a broad range of polar Hansen solubility parameters. Comparable gel fractions (approximately 90%) and swelling ratios (approximately 1.4) confirmed equivalent network formation, yet higher-polarity solvents lowered the glass-transition and nematic–isotropic transition temperatures (Tg and TNI) and accelerated both initial and late-time creep, indicating reduced kinetic resistance to director-network reorganization. In cyclic loading at Tg + 10 °C, the energy dissipated per cycle decreased by more than 17% from the toluene- to the propylene-carbonate-derived LCE at 0.002 s–1, whereas the normalized dissipation coefficient increased from 89.0% to 93.4% at 40% strain because the loading work decreased more strongly than the hysteresis-loop area. The solvent-dependent differences in energy dissipation remained after extraction of soluble species and were also reflected in the impact-force response. Polarized optical microscopy and wide-angle X-ray scattering revealed similar overall polydomain orientation across all samples, indicating that the mechanical differences did not arise from global mesogen alignment. Instead, the dried networks exhibited distinct mesogen spacings and cross-link heterogeneity induced by the processing solvent. These results suggest that the solvent imprints persistent local packing structures and network heterogeneity during network formation, and that these features govern rate-dependent dissipation even after the solvent is removed.