Journal of Physical Chemistry, Vol.99, No.11, 3823-3831, 1995
Phase-Diagrams of Mixtures of a Nonionic Polymer, Hexanol, and Water - An Experimental and Theoretical-Study of the Effect of Hydrophobic Modification
The phase behavior of two ethyl hydroxyethyl celluloses, one regular (EHEC) and one hydrophobically modified (HM-EHEC), in aqueous solutions has been investigated. Phase diagrams have been obtained in the two- and three-component mixtures, with hexanol as the third component. On hydrophobically modifying the polymer, a lowering of the cloud point in the binary system, water/polymer, was recorded. A more unexpected change of the cloud point was seen in the ternary systems. In an aqueous solution of a fixed EHEC concentration, the addition of hexanol at first only gives rise to a minor cloud-point depression but when a certain hexanol concentration is reached, there is a rapid drop. With HM-EHEC the cloud point displays a smooth decrease over the whole hexanol concentration regime investigated. The observed differences in the behavior of the two polymers were analyzed and could be understood when the partial three-component phase triangles were established. The difference is explained in terms of a transfer from one two-phase region to another on increasing the hexanol concentration in the aqueous solutions of EHEC, while in the case of HM-EHEC the same two-phase region is reached on increasing the temperature independently of the hexanol concentration. The main features of the experimentally observed phase diagrams of the two polymers, and notably the differences mentioned, could be reproduced semiquantitatively using a modified Flory-Huggins theory.
Keywords:PYRENE-LABELED (HYDROXYPROPYL)CELLULOSE;POLY(ETHYLENE OXIDE);ASSOCIATIVE THICKENERS;FLUORESCENCE;SURFACTANT;BEHAVIOR;SYSTEMS;MODEL