Molecularly Dissipative Liquid Crystal Elastomer Foams for Impact and Vibration Attenuation

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, PDMS, TPU, and commercial 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.