Effect of initial monomer concentration on the equilibrium swelling and elasticity of hydrogels

Abstract

The linear swelling ratio α and the effective network chain length N of a series of poly( N, N-dimethylacrylamide) (PDMAAm) hydrogels were investigated as a function of the gel preparation concentration ν 2 0 . PDMAAm hydrogels were prepared at a fixed cross-linker ratio but at various initial monomer concentrations. It was found that α is not a monotonic function of ν 2 0 . As ν 2 0 is increased, α first decreases up to about ν 2 0 = 0.10 and remains constant in a narrow range of ν 2 0 , but then it increases continuously. The ν 2 0 -dependence of α is due to the variation of the network chain length N depending on the gel preparation concentration. In the range of ν 2 0 below 0.1, N follows the scaling relationship N ≈ ν 2 0 - 2 , while at higher concentrations, N varies only slightly with ν 2 0 . The increase of α with N obeys the relation α ≈ ν 2 0 N 1 / 5 , as predicted by the Flory–Rehner theory.