Hydrogen-bond structure at the interfaces between water/poly(methyl methacrylate), water/poly(methacrylic acid), and water/poly(2-aminoethylmethacrylamide).

The molecular dynamics approach was employed to study the structural characteristics at the interface of water/poly(methyl methacrylate) (PMMA), water/poly(methacrylic acid) (PMAA), and poly(2-aminoethylmethacrylamide) (PAEMA). It is found that the water on the PMAA surface shows a significant increase in the density at the interface, with a greater number of water molecules permeating into the bulk of the substrate region. The structure of hydrogen bonds of water and the radial distribution function for given polar atoms in the polymer substrate are calculated. We found that a network structure of hydrogen bonding between water and the polar atom of the polymer forms at the interface. PMAA exhibits a more hydrophilic property than PMMA and PAEMA because it generates a shell-like structure of water molecules around its functional group. Finally, the hydrogen bond numbers of PMMA, PMAA, and PAEMA are also analyzed. The results detail the hydrogen bond structure of each specific atom and find that, in all three cases, the carboxyl oxygen attracts the greatest number of water molecules compared with other atoms.