Composite of Long Polymer Chains and Structured Silica Particles Achieves High Modulus and Low Hysteresis

Many applications require rubber-like materials to fulfill two important requirements: high modulus to resist excessive deformation and low hysteresis to reduce energy loss. High modulus is commonly realized by mixing rubber with inorganic fillers, but the fillers also increase the hysteresis. This conflict between the modulus and hysteresis presents a challenge in material development. Here, we show that a high modulus and low hysteresis are achieved simultaneously in a composite of long rubber chains and structured fillers. We prepare a model system using natural rubber latex with long polymer chains and structured fillers in which primary silica particles fuse into aggregates. Each aggregate has an open structure that occludes the rubber. The composite forms two networks: a network of cross-linked natural rubber chains and a network of percolated silica aggregates. The two networks intertwine with each other and interlink through covalent bonds. We measure the modulus and hysteresis of the composites prepared with various volume fractions of aggregates and molar fractions of the initiator. We discuss the mechanisms by which long rubber chains and structured silica aggregates lower hysteresis while maintaining a high modulus. This work provides insights into the development of rubber products for energy efficiency.