Reversible gelation in hydrophobic polyelectrolyte/protein mixtures: An example of cross-links between soft and hard colloids

Measurements were conducted on the linear viscoelastic properties of hydrophobically modified poly(sodium acrylate) reversibly cross-linked with proteins to form gels. The native structure of proteins was not markedly affected upon association with the amphiphilic polyelectrolyte. Hydrophobic interaction was shown to overcome Coulombic effects on interpolymer complexation. Because of their relative hydrophobicity, neutral papain and positively charged lysozyme were found to be less efficient cross-linking agents than negatively charged bovine serum albumin: These reversible gels exhibited similarities with chemically cross-linked macromolecules such as a plateau modulus at high frequency and characteristic scaling at the transition point between sol and gel. The sol-gel transition diagrams were determined. A semiquantitative approach, based on scaling laws, was able to capture the essential rheological properties of these mixtures, namely sol-gel transition and variations of storage modulus.