The importance of polyacrylamide hydrogels as sieving matrix materials for electrophoresis DNA, proteins, and other charged biomolecules is well known. More recently, the ability to photopolymerize these hydrogels by exposure to UV light has become a vital tool in the design of microfluidic bio-analysis systems because this process allows gels to be precisely positioned within a microchannel network. Despite increasing interest in these materials, however, less work has been done to study the influence of polymerization conditions on the mechanical properties and pore structure of the resulting gel network. Furthermore, the studies that do exist have been performed only under chemically initiated polymerization conditions.

In this paper, we present the results of a series of in-situ dynamic small-amplitude oscillatory shear measurements during photopolymerization of crosslinked polyacrylamide electrophoresis gels. These data are then used to investigate the relationship between rheology and parameters associated with the gelation process including UV intensity, monomer and crosslinker composition, and reaction temperature. We also describe a simple model based on classical rubber elasticity theory that yields estimates of average gel pore size in agreement with corresponding data obtained from analysis of DNA electrophoretic mobility in gels polymerized under the same conditions.