Unveiling the Elasticity of Confined Multilayer Hybrid Materials

The superior elasticity and processing easiness of polymers render them promising as an interfacial filler material. With the progress in hybrid materials fabrication and manufacturing precision, the thickness of interfacial polymer layers has gone down to the nanometer range that can feature strong confinement. A critical question of scientific and applied importance is how the confined polymer layers affect the effective mechanical properties of the hybrid material. In this contribution, we utilize Brillouin light scattering experiments and a continuum-mechanics based model to examine the anisotropic elastic properties of confined hybrid materials composed of alternating polyvinylpyrrolidone and hectorite nanolayers. The clear resolution of the direction-dependent quasi-longitudinal, quasi-transverse, and pure-transverse phonon modes from the Brillouin scattering experiments leads to the full elastic properties of these highly anisotropic samples. We find that as the polymer layer thickness increases from about 1 to 3 nm, the material’s Young’s moduli in the directions parallel and perpendicular to the layers drop by nearly 50%, implying the crucial role of polymer confinement on the sample’s mechanical properties.