INTERACTION OF HYDROPHOBICALLY MODIFIED (HYDROXYETHYL)CELLULOSE WITH VARIOUS ADDED SURFACTANTS

The effects of the addition of various anionic and nonionic surfactants on the rheological properties of aqueous solutions of hydrophobically modified (hydroxyethyl)cellulose (HMHEC) have been investigated using oscillatory measurements. Significant polymer/surfactant interaction was observed in the vast majority of systems at surfactant concentrations considerably lower than the critical micelle concentration of the free surfactant in water. For any individual surfactant, the observed rheological effects were found to be strongly dependent upon the level of surfactant addition, with at first an increase and then a decrease in the storage and loss moduli of the HMHEC/surfactant system occurring with increasing surfactant concentrations due to the enhancement and then subsequent breakdown of the network structure. At high surfactant concentrations, complete disruption of the polymer network was evident, with the HMHEC/surfactant systems exhibiting rheological characteristics typical of a dilute polysaccharide solution. The magnitude of the observed rheological effects was also found to be dependent upon both the alkyl chain length and the nature of the hydrophilic head group of the added surfactant. The interaction of HMHEC with the anionic surfactant sodium dodecyl sulfate (SDS) has been studied in greater detail using rheological and electrochemical techniques. From this, and previously reported spectroscopic data, a mechanism for the HMHEC/SDS interaction at various levels of surfactant addition is proposed.