The concentration dependence of biopolymer gel modulus

Abstract

Abstract Gel formation from aqueous biopolymer solutions is a common phenomenon and one of practical importance, yet it is much less well understood and characterised than the condensation of synthetic polymer precursors to form networks. There are many reasons for this, including the complexity of the aggregating species, the diversity of crosslinking mechanisms, the physical nature of the attractive forces, and the complexities introduced by having water as a solvent. In the present paper, however, an attempt is made to adapt classical theories of gelation and of rubber elasticity to treat the biopolymer case and to describe the shear modulus‐versus‐concentration behaviour of such non‐ideal materials. Modulus data for cold‐set gels formed from the polysaccharide agar and the protein gelatin are presented and analysed, as are similar data for substantially different gels formed by heating solutions of globular proteins. It is demonstrated how, by assuming a crosslinking equilibrium, such diverse sets of data can be reduced to a dimensionless master curve form, and the limiting concentration dependence of the modulus at high concentration is discussed in the light of the present work and of a recent theoretical description based on the osmotic scaling relationship.