Thermodynamic interactions in copolymeric hydrogels

Abstract

Xerogels comprising n-butyl acrylate and jV-vinyl-2-pyrrolidone (30/70 wt/wt) and varying small amounts of a hexafunctional cross-linking agent have been prepared by y-ray-initiated copolymerization to complete conversion and then swollen in water to equilibrium at several different temperatures (T) within the range 284-349 K. Photographic determination of the sample dimensions afforded the volume fractions of polymer ( 2) and water within the resultant hydrogels, and the effective cross-linking densities (i<e) were obtained via stress-strain measurements. Values of 2 increased with increasing T and with increasing ve. The elastic moduli at 294 K lay within the range 0.21-1.07 MN m"2. Although the enthalpic components (xh) were negative, the large entropic components ( $) were positive and dominant in the overall increase with T of the polymer-water interaction parameter ( ). The negative values for the enthalpy and entropy of dilution are compatible with structuring of water via enhanced hydrogen bonding and by hydrophobic interaction.

Understanding the properties of aerobic sludge granules as hydrogels

“…Environmental factors such as pH and temperature determine the state or charge of bridging segments. The strength of cross-linked polymer matrices is the sum of repulsive and attractive forces so it follows that the storage modulus and swelling of the hydrogels are strongly dependent on environmental conditions (BrannonPeppas and Peppas, 1991; Huglin et al, 1986;Velada et al, 1998). The contention of this article is that aerobic sludge granules also display these hydrogel characteristics.…”

Microstructured Polyacrylamide Hydrogels Prepared Via Inverse Microemulsion Polymerization

“…However, for the materials examined here, this ratio is consistently larger than 3. Huglin et al found similar results for copolymeric hydrogels and provided an explanation (27). Since E is given by the slope of the linear region of Eq.…”

Structurally diverse and readily tunable photocrosslinked chondroitin sulfate based copolymers

“…It has been demonstrated that for hydrogels, the E/G ratio under compression at a finite strain should be about 3.2 for an incompressible gel. 32,33 This is true for almost all formulations, with no trend for the few that fall slightly outside this range. Mooney-Rivlin plots of stress-strain data for pure MCS gels did show deviation from the model in eq 3.…”