Molecularly Dissipative Liquid Crystal Elastomer Foams for Impact and Vibration Attenuation

ABSTRACT Polymeric foams dissipate mechanical energy primarily through cellular deformation and pore collapse, while the cell‐wall material usually provides only conventional polymer viscoelasticity. Here, we introduce liquid crystal elastomer (LCE) foams as molecularly dissipative porous materials in which foam‐scale compression is coupled to stress‐driven mesogen reorientation. Open‐cell LCE foams are prepared by infiltrating a thiol–acrylate LCE precursor into humidity‐fused NaCl templates, followed by crosslinking and salt leaching to produce an interconnected porous architecture. Dynamic mechanical analysis confirms that the foam retains the broad viscoelastic signature of the liquid‐crystalline network. Under rate‐dependent compression, the LCE foam exhibits substantially larger and more rate‐amplified hysteresis than non‐liquid‐crystalline BADA, polydimethylsiloxane (PDMS), thermoplastic polyurethane (TPU), and commercial polyurethane (PU) foams, consistent with delayed mesogen reorientation superimposed on progressive pore collapse. This is supported by temperature‐dependent measurements, where hysteresis decreases markedly above the liquid crystal–isotropic transition. In drop‐impact tests, the LCE foam reduces the peak transmitted force to approximately 1 kN, markedly below the reference foams, and broadband vibration measurements show a broad, strongly damped response with a lower effective quality factor. These results establish a design principle for lightweight protective materials in which cellular architecture provides large deformation while liquid‐crystalline cell walls provide an additional molecular dissipation pathway.