Unveiling the essence of fracture energy in composite elastomers with micro-sizes fillers

Abstract

Understanding the mechanisms underlying fracture-energy enhancement in composite elastomers is critical for their practical applications such as stretchable electronics and soft robotics. While nanocomposite elastomers have been extensively studied, the role of micro-sized fillers in reinforcing composite elastomers remains less well defined. In this work, model composite elastomers consisting of polydimethylsiloxane and micro-sized aluminum fillers ranging from 1 μm to 50 μm were systematically investigated. Mechanical testing revealed that decreasing filler size significantly increased fracture energy, with the highest value observed in composites containing 1 μm aluminum. We demonstrate that this enhancement was attributed primarily to interfacial energy between fillers and the polymer matrix, as established through a refined neo-Hookean constitutive model combined with molecular dynamics simulations. Contrary to the bridging mechanisms observed in nanocomposites, analyses of polymer chain gyration radius, inter-filler spacing, and filler absorption layer thickness demonstrated that polymer chain bridging does not contribute to mechanical reinforcement in micro-filled systems. Instead, a coupling effect between absorption layer thickness and inter-filler distance governs modulus variation. A continental shelf-like model is proposed to conceptualize this coupling effect, and atomic force microscopy measurements validated both the interfacial absorption layer thickness. These findings provide new insights into the design principles governing the mechanical performance of elastomer composites reinforced with micro-sized fillers.