Study On Structures And Properties Of Hydrophilic Polymer/Water Mixtures

The thermal behaviors of the poly(acrylic acid)(PAA)/water mixtures with different polymer Mws were different from those of bulk water. It showed that the polymer chains with different lengths can effect geometrically the crystallization of water, besides the interaction between polymers and water molecules through hydrogen bonding. The effect didn't vary with Mw linearly; there existed a critical Mw. Different chemical structures can also influence the amounts of different states of water and the water crystallization. The content of non-crystalline water in the amorphous phase in the mixtures was constant, regardless of the water content. One exception was poly(vinyl methyl ether)(PVME)/water mixtures, due to its special structure. The ions in the PAA/water mixtures could change the melting point of freezable bound water and melting enthalpy. The heat capacity of water in the PAA/water mixtures showed that the mobility of the bound water was higher than that of the glassy water. With increasing water content, the average interaction between polymer and water decreased. PVME formed association with water; however, the association was not stable. The process that PVME and water hydrated during cooling was slow. The different thermal histories could affect the amount of different states of water. The Tm of the freezable bound water didn't vary with the water content evidently, while the ones of free water changed. Time for free water and bound water to interact with PVME is different, due to various interactions. The investigation on the Cp of water in the PVME/water mixtures revealed that the the interaction between PVME and water was small and didn't change with water content. The content of non-freezable water indicated that the non-freezable water is mainly responsible for the phase separation. The permeabilities of different commercial contact lenses showed that the free volume theory provided the best fitting results for the experimental values. NaCl permeability in lenses increased with the content of freezable water and the ratio of freezable water to non-freezable water, showing that the freezable water is mainly responsible for salt diffusion in the polymer hydrogels. The permeability could be increased by increasing the content of freezable water.