Stretchable composites with high oxide loading

Oxide/elastomer composites combine the functional attributes of metal oxides with the mechanical deformability of elastomers, but face the challenge of balancing oxide loading and stretchability as ceramic fillers decrease the entropic elasticity of polymer networks. Here, we report an interfacial composite design that enables high oxide fraction and large stretchability by minimizing the contact area yet maximizing the binding strength between the oxide and elastomer. The elongation at break for an interfacial composite with 80 vol% of oxides reaches 500%, whereas that of a regular bulk composite with the same oxide fraction is 20%. These composites are synthesized based on a Marangoni co-assembly process with tuned interfacial tension and reaction at the water-oil interface. The assembly chemistry is nearly independent of oxides' sizes, compositions, geometries, and functions, making this interfacial structure broadly applicable to optical, electric, magnetic, and thermal-conducting oxides. Compared to bulk composites, the interfacial composites deliver larger magnetic actuation, lower thermal resistance, and higher conformability with nonplanar surfaces, providing rich implications for designing intelligent and electronic systems.