Effects of surfactant micelles on viscosity and conductivity of poly(ethylene glycol) solutions.
The neutral polymer-micelle interaction is investigated for various surfactants by viscometry and electrical conductometry. In order to exclude the well-known necklace scenario, we consider aqueous solutions of low molecular weight poly(ethylene glycol) (2-20)x10(3), whose radial size is comparable to or smaller than micelles. The single-tail surfactants consist of anionic, cationic, and nonionic head groups. It is found that the viscosity of the polymer solution may be increased several times by micelles if weak attraction between a polymer segment and a surfactant exists, epsilon<k(B)T. Similarly, ion migration in polymer solutions may be significantly hindered by cooperative interactions between polymers and micelles. Even though epsilon is small, the interaction energy between a macromolecule and a micelle can be a few k(B)T due to many contacts, and thus leads to polymer adsorption on micelles' surfaces. The rapid growth of the viscosity with surfactant concentration is therefore attributed to the considerable cross links among micelles and polymers (transient network). In addition to substantial alteration of the transport properties, this weak interaction also influences the onset point of thermodynamic instability associated with polymer-surfactant solutions. The examples include the decrease of critical aggregation concentration for ionic surfactant and clouding point for nonionic surfactant due to PEG addition.
Wang
Shun-Cheng
SC
Department of Chemical and Materials Engineering, National Central University, Jhongli City, Taiwan 320, Republic of China.
Wei
Tzu-Chien
TC
Chen
Wun-Bin
WB
Tsao
Heng-Kwong
HK