EFFECT OF HYDROPHOBIC MODIFICATION OF A NONIONIC CELLULOSE DERIVATIVEON THE INTERACTION WITH SURFACTANTS - RHEOLOGY

The interactions between various surfactants (anionic, cationic, and n onionic) and a nonionic ethyl(hydroxyethyl)cellulose (EHEC) polymer or a hydrophobically modified analogue (HM-EHEC) have been examined. The study has been performed as a comparative investigation between the h ydrophobically modified polymer and the unmodified parent polymer usin g theology. The rheological results have been analyzed with the aid of a simple modified Maxwell model. Information about the low-frequency behavior was extracted from this model, and the rheological features w ere presented in terms of the complex viscosity and a characteristic r elaxation time. In the presence of an ionic surfactant, the rhelogical measurements revealed significant polymer/surfactant interaction for both EHEC and HM-EHEC, but the interaction peak, observed in the diffe rent rheological quantities, was more pronounced and located at a lowe r surfactant concentration for the hydrophobically modified polymer. I n the presence of a nonionic surfactant, the polymer/surfactant intera ction was weaker. By considering the temperature effect, an important difference in the polymer dynamics between the hydrophobically modifie d polymer and the unmodified analogue was established. The hydrophobic ally modified polymer shows a normal temperature dependency, while the motion of the unmodified analogue is slowed down with increasing temp erature. The finding for the unmodified polymer is attributed to incre ased polymer/polymer attractions with an increased temperature. It has also been shown that the hydrophobically modified polymer has feature s regarding the formation and breakdown of the polymer/surfactant comp lex in common with other hydrophobically modified polymers (both nonio nic and ionic). At a certain surfactant concentration the network star ts to lose its connectivity, however, because of an increased surfacta nt aggregation number of the mixed micelles, the breakdown process is postponed when the surfactant chain length is increased.