Rheology and porosity control of poly(2-hydroxyethyl methacrylate) hydrogels

Swelling and dynamic mechanical behavior in a broad frequency range of homogeneous and porous poly(2-hydroxyethyl methacrylate) gels were studied in relation to their matrix structure, gel morphology and nature of the swelling medium. Very lightly cross-linked gels showed up relatively large mechanical losses caused by slow relaxation of hydrophobic physical associates still proceeding at frequency 10(-3) Hz. The macroporous gels of fused-spheres type morphology contained many dangling aggregates not bearing the stress which caused concentration of the stresses in the load bearing paths through the matrix. This is the reason for the sudden drop of storage modulus. In the alpha-relaxation region, the loss factors for homogeneous and porous gels merged into a single master curve. Reswelling of gels in a poor solvent caused a decrease of the swelling degree and shifted their alpha-relaxation to lower frequencies; reswelling in good solvent shifted the maximum of alpha-relaxation to higher frequencies. (C) 2012 Elsevier Ltd. All rights reserved.