Synergistic interactions involving amphiphilic polymers in solution

Abstract: The properties of hydrophobically modified cellulose derivatives in aqueous mixtures with various other molecules have been investigated. Mixtures of a hydrophobically modified polymer and alkali-sensitive, degradable surfactants gave rise to time-dependent viscosities. With time, the viscosity decreased continuously or went through a maximum, depending on the initial surfactant concentration. The rate of change could be controlled by pH. The alcohol formed by degradation acted as a cosurfactant, and varying the hydrophobic chain length gave rise to different viscosity profiles. Phase separation temperatures and viscosities of aqueous mixtures of the hydrophobically modified cellulose derivatives and block copolymers have been investigated. The block copolymers were hydrophobically modified at one or both ends. The results were consistent with hydrophobic association between the cellulose derivatives and the block copolymers. Moderate viscosity enhancements were found on addition of the block copolymers to the cellulose derivatives and the effects were larger with the block copolymer that was modified at both ends. Amylose can cross-link hydrophobically modified polymers by inclusion complexation, whereby strong, thixotropic, thermoreversible, cold-setting, gels are formed. The gel strength as a function of the architecture of the polymer hydrophobes has been investigated. The hydrophobes were based on linear alkyl chains and longer alkyl chains gave stronger gels. For similar alkyl chain lengths, stronger gels were obtained when a spacer consisting of ethylene oxide units was inserted between the alkyl chain and the polymer backbone. The competition between amylose and cyclodextrin for the formation of inclusion complexes with hydrophobically modified polymers has also been studied. The cyclodextrin molecules competed efficiently with the amylose molecules as seen by rheology, self-diffusion and NMR intensities of the polymer hydrophobes. A detailed study of the hydrophobically modified polymers and cyclodextrin has been performed where it was seen that 2:1 (cyclodextrin:polymer hydrophobe) complexes were formed. Stability, droplet diameter and viscosity of o/w macroemulsions stabilized with lecithin and different types of polymers have been examined. Emulsions without polymers showed essentially no stability against creaming. Unmodified polymers provided limited stability, while hydrophobically modified polymers improved the stability dramatically. The viscosity of emulsions stabilized by hydrophobically modified polymers was significantly increased compared with aqueous solutions of the polymers alone, suggesting network formation including both polymers and emulsion droplets.