Tuning Local Modulus at Liquid Metal‐Polymer Interfaces Regulates Electrocaloric Effect in Ferroelectric Nanocomposites

ABSTRACT Polymer nanocomposites are widely explored to enhance the electrocaloric effect (ECE) through various interfacial modulation. While many prior works focused on all‐solid nanocomposites, in which the both matrix and fillers are solid‐state materials, the role of interfacial mechanical modulus in regulating local dipolar responses and macroscopic entropy changes remains unexplored. Here, we develop ferroelectric polymer nanocomposites incorporating liquid metals as modulus‐tunable fillers to elucidate how the interfacial mechanical properties regulate EC behavior. Mechanically soft and rigid interfaces are constructed by embedding eutectic gallium–indium (EGaIn) alloy and gallium (Ga) nanoparticles, respectively, into a P(VDF‐TrFE‐CFE) matrix. Despite similar surface oxidation and functionalization, structural characterizations reveal that relatively soft interfaces have a stronger effect on the dipolar responses under the external electric field than that of the rigid interfaces. Phase‐field simulations reveal that mechanically compliant interfaces promote enhanced local dielectric permittivity and polarization over an extended interfacial region, whereas mechanically rigid interfaces, although still beneficial relative to the neat matrix, generate a relatively restricted dipolar reorientation. Consistently, the EGaIn‐based nanocomposite exhibits facilitated polarization switching and an enhanced EC response, achieving entropy changes up to 50 J kg −1 K −1 . This work establishes interfacial mechanical modulus as a critical parameter for high‐performance EC polymer nanocomposites.