Responsive polymer gels based on hydrophobically modified cellulose ethers and their interactions with ionic surfactants

Responsive gels made by chemically cross-linking two modified cellulose ethers, separately and in mixtures, have been investigated with respect to their swelling in aqueous solutions containing anionic or cationic surfactants and/or added salt. One of the polymers (catHM-HEC) is a salt-sensitive and strongly hydrophobically associating (hydroxyethyl)cellulose modified with cationic hydrophobic side chains. The other polymer, ethyl(hydroxyethyl)cellulose (EHEC), is a temperature-sensitive, weakly self-associating polymer. Both polymers bind ionic surfactants, and it was found that the response of the cross-linked gels to the content of surfactant or salt in the swelling medium reflected the expected surfactant binding isotherms. A maximum in swelling was generally observed when the surfactant concentration in the swelling medium was close to the critical micelle concentration(cmc). The collapse/swelling behavior of pure catHM-HEC gels on addition of cationic and anionic surfactants showed a close correspondence to the previously studied phase behavior of non-cross-linked catHM-HEC in mixtures with the same surfactants. Mixed gels of EHEC and catHM-HEC in different proportions showed a behavior intermediate between those of the pure polymer gels. It was thus possible to customize gels with respect to their responses to different influences.