Local Viscosity of Interfacial Layers in Polymer Nanocomposites Measured by Magnetic Heating

The strength of interfacial attractions between polymer chains and nanoparticles is known to control the mobility of chains and viscoelastic properties in polymer nanocomposites. We chose the interfacial layers around magnetic nanoparticles to consist of two different miscible polymers and measured the energy absorption rates as particles dissipate energy while they rotate under a high-frequency alternating magnetic field. Local viscosities were calculated from the measured rotational relaxation times using the classical absorption model. The changes in local viscosities were attributed to the rigidity of adsorbed polymers and chemical heterogeneities of their interfacial layers. The highest viscosity was measured with the flexible, shorter adsorbed poly(methyl methacrylate) chains. The weak interphases between poly(methyl acrylate) and highly rigid polymers such as poly(2-vinyl pyridine), and poly(bisphenol A carbonate) allowed particles to rotate easily in a diffusive mode, yielding the lowest viscosity that matched to the viscosity prediction of an unentangled matrix polymer. Chemical and dynamic heterogeneity of interfacial layers around nanoparticles highly depend on the rigidity of chains. Measuring the local viscosity of interfacial polymer layers is essential for interfacial layer-controlled mechanisms of stress transfer, reinforcement, and thermal conductivity in polymer nanocomposites.