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Abstract

The freezing and melting behavior of water in poly hydroxy ethyl methacrylate (pHEMA) hydrogels of different cross-linker and water contents was investigated in relation to the glass transition temperature (Tg) of the gels. After prolonged cooling at -15 degrees C a constant amount of 1.7 mol water per monomeric unit did not freeze, regardless of both the cross-linker and the water content of the gels. At this water content and temperature, pHEMA gels were below their Tg, and the water molecules were prevented from diffusing to the ice crystals formed in the gel. Therefore, the inability of part of the water in pHEMA gels to freeze is not a thermodynamic phenomenon but is caused by kinetic factors.

Thermal analysis of polymer–water interactions and their relation to gas hydrate inhibition

“…This type of water is referred to as NFBW to distinguish it from the water that crystallizes on cooling (FBW) 3–13. NFBW has been determined in the literature through an analysis of the crystallization and melting of bulk water for a large number of polymers, such as PVP,3, 5 PVCap,3 poly( N ‐vinyl‐ N ‐methylformamide),3 poly(ethylene oxide),5 poly(methacrylic acid),5 poly(hydroxyethyl methacrylate),6–8 and polyzwitterions 8. Some of these polymers, for example, PVCap and PVP, that bind a large amount of water have shown good performance as hydrate inhibitors, whereas others that bind poorly to water have low amounts of bound water [ca.…”

“…Thermal analysis [differential scanning calorimetry (DSC)] is used to quantify polymer–water interactions and provide insights into the mechanism of gas hydrate inhibition. The literature contains many reports on the use of DSC to study water–polymer interactions3–17 and indicates that these interactions are strongly dependent on the chemical structure of the polymer. There are several systems where interactions can be quite strong so that water can fail to crystallize on cooling and, shows only a glass transition 13.…”

Hydrogen-bonds structure in poly(2-hydroxyethyl methacrylate) studied by temperature-dependent infrared spectroscopy

“…Only glass transition temperature for PMMA is higher than that for PHEMA because of non-bulky side chain, which enhances the main chain interaction. Glass transition temperature for PHEMA hydrogels is reduced by increasing a content of water in the matrix (Roorda et al, 1988). These also support the conclusion that the mobility of the PHEMA main chain is induced by the dissociation of the OH…OH type of hydrogen-bonds among the side chains, since water molecules also hydrated to both OH and C=O groups in the PHEMA side chain via the OH…OH and C=O…HO types of hydrogen-bonds (Tsuruta, 2010).…”

“…A dry PHEMA solid is brittle, since its glass transition temperature is higher than ambient temperature. On the other hand, a PHEMA hydrogel, i.e., a water sorbed PHEMA, becomes soft material, because its glass transition temperature is reduced to be lower than ambient temperature (Roorda et al, 1988). These imply macromolecular properties in PHEMA are characterized by non-covalent interactions of hydrogen-bonds among the polymer chains as well as the hydrated water molecules.…”

LF-NMR water self-diffusion and relaxation time measurements of hydrogel contact lenses interacting with artificial tears

“…The negatively charged hyaluronic acid, permeating the gel, changes both the water structure and the possibility of solubility of the salts contained by the arti cial tears [18]. At the origin of these phenomena there are the interactions of the macromolecules with the matrix; the negatively charged ionic lens prevents these kinds of interactions because of electrostatic repulsions.…”