Molecular structure and vibrational spectra at water/poly(2-methoxyethylacrylate) and water/poly(methyl methacrylate) interfaces: A molecular dynamics simulation study

Classical molecular dynamics simulations at the interfaces of two (meth)acrylate polymers, poly(2-methoxyethylacrylate) (PMEA) and poly(methyl methacrylate) (PMMA), upon contact with water are performed to elucidate interfacial molecular structures from the interface-specific nonlinear spectroscopic point of view. PMEA has methoxy oxygen in the side chain, while PMMA does not have it, and its impacts on the interfacial structure are particularly focused on. The force fields of PMEA and PMMA used in the classical simulation are modeled so as to reproduce the radial distribution functions and the vibrational density of states calculated by ab initio molecular dynamics simulations, where a stronger hydrogen-bonding interaction between water and methoxy oxygen of PMEA than the conventional molecular modeling predicts is found. The imaginary part of the second order nonlinear susceptibility is theoretically calculated for these two interfaces, showing a definite difference between them. The origin of the spectral difference is discussed on the basis of the decomposition analysis of the spectra and the interfacial molecular structures.