Thickness-Dependent Macroscopic Properties of Highly Filled Composite Elastomers: Role of Hierarchical Filler Network...

Highly filled thin composite elastomers are crucial for thermomechanical applications in electronics packaging and engineered interfaces. However, most current research focuses on bulk-like materials and performance optimization. This work is the first to investigate the thickness-dependent macroscopic properties of such composites, establishing a distinction between film-like and bulk-like behaviors based on specific properties. Using polydimethylsiloxane-based composite elastomers containing 90 wt % aluminum as a model, we identify two critical thicknesses (200 and 800 μm). Above 800 μm, the material exhibits bulk-like behavior, with mechanical and viscoelastic properties becoming thickness-independent. Below 800 μm, these properties show a pronounced thickness dependence. In contrast, the out-of-plane thermal conductivity exhibits enhancement only below 200 μm, which can be attributed to the anisotropic characteristics of the polymer-mediated hierarchical filler networks. This regime exhibits film-like characteristics, with thermomechanical properties diverging from bulk-like behavior. These findings bridge the gap between basic research and practical applications in thickness-constrained packaging applications.