Biopolymer gelation- exponents and critical exponents

The gelation of biopolymer systems has been studied, at least, empirically for many years, but only more recently have the methods of macromolecular science been applied. A number of following studies have tended to concentrate on measuring power law exponents, and have ignored details of the network structure. Biopolymer physical gels are more complicated than “simple” chemically crosslinked systems, which means that approaches designed, for example, for crosslinked melts have to be applied with caution. Consequently, while measuring exponents alone can give some valuable information, and some apparent “universalities” are seen, the details of pre-exponential factors can often prove more significant and useful. In this article we re-examine the mapping of generalised percolation parameters (for example p, pc) unto either a time or a concentration axis. In this we consider the assumptions behind such an approach, and the applicability of critical exponent treatments in a regime that is typically a long way away from critical, at least when judged in terms of absolute (Ginzburg) criteria.