Dielectric relaxation in polyethylene glycol 400: A scale effect

This work reports the dielectric properties of the porous matrix – inclusions system. The porous matrices used were silica gels with different pore sizes. The pores were filled with PEG-400. The synergy of gravimetric method, structural analysis, and the dielectric spectroscopy reveal how the size of the matrix pores affects the parameters of the low-temperature dielectric relaxation of PEG-400. We demonstrate that as the pore size decreases, the influence of the silica gel pore walls on the structure and thermal mobility of PEG 400 inclusions increases. This interaction causes a shift in the dielectric relaxation peak towards higher temperatures for smaller nano-inclusions, along with changes in dielectric relaxation parameters. Notably, the difference in energies between the equilibrium states of the relaxator increases with decreasing pore sizes. This observation can be explained by the fact that one of the relaxator's equilibrium positions is modified by interaction with the pore wall, which behaves differently from typical intermolecular interactions. Moreover, the interaction with the wall reduces the number of relaxators that can be simultaneously activated in a smaller pore, since the energy required for a relaxator to transition to the excited state increases. These characteristics could be beneficial for developing materials with programmable dielectric properties and for designing nanostructured composites with specific temperature- and frequency-dependent dielectric responses.