Water in hydrogels. 2. A study of water in poly(hydroxyethyl methacrylate)

Abstract

Collated brcad-line NMR and DSC measurements sensitively probe the behavior of water in hydrated poly(hydroxyethy1 methacrylate) (PHEMA). NMR reveals that bound water becomes mobile at -180 K in keeping with observations in many other hydrated polymers; DSC is insensitive to events at these temperatures. In samples with a high water content, a fraction of this mobile water subsequently freezes between 230 and 260 K. The amount of freezable and nonfreezable water in hydrated PHEMA is determined quantitatively. Preliminary cross-relaxation experiments at 253 and 293 K indicate that NMR spin-lattice relaxation rates for water will be overestimated if the effects of cross-relaxation between the polymer and water proton spin systems are neglected. Although PHEMA is less hydrophilic than poly(N-vinyl-2pyrrolidone/methyl methacrylate), studied in part 1, the relative fraction of bound water is significantly higher. Hysteresis effects in hydrated PHEMA are investigated in some detail.

Hydration of Hydroxypropylmethyl Cellulose: Effects of pH and Molecular Mass

“…Therefore, the T 2 measurements of acidic solvent protons presented in Fig. 3 have been interpreted, like in other polysaccharides gels [21][22][23][24][25], in terms of a fast exchange which takes place between the free and bound state of water. However, in order to explain the reduction in the relaxation time observed for neutral and especially for acidic solvents, we have to assume that in addition to the fast exchange of water molecules, other mechanisms of the relaxation take place.…”

Preparation and properties of a slow release NP compound fertilizer with superabsorbent and moisture preservation

“…The SRFSMP would be swollen by water when it was added into solutions; urea and (NH 4 ) 2 HPO 4 were then dissolved in this part of water. At first, the water in solution constantly came into the network and did not come out before the emergence of the free water in the swollen network, 19,20 which could exchange with the water in solutions through the mesh of the swollen network and formed a dynamic equilibrium. The urea and (NH 4 ) 2 HPO 4 dissolved in the network would slowly diffuse into the solutions through the dynamic exchange.…”

“…Before the emergence of the free water in the swollen network, 19,20 the fertilizer solution in the network could not release out, and so do the fertilizers. But there existed a dynamic exchange between the free water in the hydrogel and the water in soil solution, the fertilizer would slowly release into the soil through the griddings of the swollen network with this kind of dynamic exchange.…”

Water transport in 2-hydroxyethyl methacrylate copolymer irradiated by ? rays in air and related phenomena

“…The content of freezing water is affected by the chain mobility or crosslink density of the polymer. 13,14 Thus, the determination of two types of water in the hydrogel is helpful to understand the crosslink and scission effect or the destruction of the hydrophilic group induced by ␥ rays. During the heating process of the DSC analysis, an endothermic melting peak appeared in the freezing water at 0°C, but not in the nonfreezing water.…”

“…Thus, both types of water in the hydrogel can be determined by the DSC analysis. [12][13][14]49 The endothermic melting peaks of freezing water at 0°C for the saturated hydrogel are shown in Figure 6. The peak area covered for the melting of freezing water is calculated (⌬H freezing water ), then the content of freezing water (S f ) can be obtained by the following equation 49 :…”