Modeling water states in polyvinyl alcohol-fumed silica nano-composites

We proposed a mathematical model to account for water contents in different states as a function of filler concentration in polymer–filler composites. The water states were characterized in polyvinyl alcohol (PVA) and PVA–fumed silica (FS) composites using low temperature differential scanning calorimetry. This model takes into consideration the inert filler dilution effect, the equilibrium of bound water to free and freezable water states associated with FS nano-particles, and the suppressed hydrogen-bonding ability of hydroxyl groups in polymer chains caused by FS shielding. Predicted results were in excellent agreement with experimental data. This model can yield a great understanding of the distribution of water states into bound and free (and freezable) water states for homogeneous, heterogeneous or micro-phase separated polymers, and especially perfluorosulfonic acid membranes and water-retaining hydrogels.