Impact of Confinement on the Dynamics and H‑Bonding Pattern in Low-Molecular Weight Poly(propylene glycols)

Herein, we explored thermal properties, dynamics, wettability, and H-bonding pattern in various poly­(propylene glycols) (PPG) of M_n = 400 g/mol confined into two types of nanoporous templates: silica (d = 4 nm) and alumina (d = 18 nm). Unexpectedly, it was found that the mobility of the interfacial layer and the depression of the glass transition temperature weakly depend on the pore size, surface functionalization, and wettability. However, interestingly, we have reported strengthening of the hydrogen bonds in samples confined in silica pores. Further, the unique annealing experiments on PPG-OH with the use of Fourier transform infrared spectroscopy revealed the reorganization of oligomers close to the interface and the formation of three distinct fractions, interfacial, intermediate, and bulk-like, in the infiltrated samples. These experiments might shed new light on the variation of the segmental/structural relaxation times due to annealing of materials of different molecular weights infiltrated into pores or deposited in the form of a thin layer.