The effects of reaction conditions on the electrical conductivity of PAAG hydrogels

The effects of reaction conditions: concentration of crosslinker, monomer, initiator and gelatin and neutralization degree (ND) of acrylic acid (AA), of a graft radical crosslinking polymerization of AA and gelatin, on the specific electrical conductivity and the primary structural parameters of synthesized poly(acrylic acid)-g-gelatin (PAAG) hydrogels were investigated. It was established that: (a) electrical conductivity of all of the investigated hydrogels is higher than of distilled water; (b) the increasing concentration of crosslinker, monomer and initiator leads to the two linear distinct increases of electrical conductivity with different slopes (c) the increasing ND of AA leads to linear decrease in electrical conductivity and (d) gelatin concentration does not significantly influence the electrical conductivity of hydrogel. An analyses of the primary structural parameters of synthesized PAAG xerogels reveals that: (a) values of molar mass between crosslinks and distance between polymer chains are power form function on crosslink density (rho(c)); (b) the critical value of rho(c) corresponds to the percolation threshold of H+/K+ ions through the hydrogels network and (c) electrical conductivity of PAAG hydrogels is a power form function on rho(c). Fractal model of conductivity of hydrogel is suggested and explained. (C) 2012 Elsevier Ltd. All rights reserved.