Stretchable Water-Free Liquid Crystalline Polyelectrolyte Complexes

Abstract

Polyelectrolyte complexes (PECs), formed by electrostatic association of oppositely charged polyelectrolytes, are promising low-environmental-impact materials. However, their extreme brittleness in the absence of water and a general lack of stimuli-responsive functionality severely limit practical applications. Here, we introduce a strategy to overcome both limitations by designing liquid crystalline polyelectrolyte complexes (LCPECs). Main-chain liquid crystalline (LC) polyanions with systematically varied charge densities and neutral flexible domains are first synthesized via a facile one-pot two-step polymerization combining Michael addition and thiol–ene chemistry. The LC polyanions are then complexed with poly(diallyldimethylammonium chloride) (PDADMAC) to form LCPECs with tunable properties. X-ray scattering reveals a fractal-like network with nanoscale phase separation between electrostatically associated and neutral flexible domains, alongside nematic ordering of the mesogens. Increasing the neutral monomer content lowers the glass transition temperature from 58 °C to −10 °C and transforms the mechanical response from stiff and brittle to soft and highly stretchable, achieving an elongation of 1160%, far exceeding the stretchability of any previously reported water- and salt-free PEC. Rheological analysis shows that higher charge density raises both moduli and delays chain relaxation, confirming that electrostatic interactions function as tunable physical cross-links. Uniaxial stretching induces macroscopic mesogen alignment, enabling reversible thermal actuation with 20% dimensional change upon cycling across the LC–isotropic transition. Furthermore, well-defined mesh structures are successfully prepared by melt electrowriting, demonstrating the processability of these materials through advanced additive manufacturing. This work establishes tuning of ionic cross-link density and backbone flexibility as a general strategy for transforming inherently brittle PECs into mechanically robust, stimuli-responsive, and processable materials.