Investigation on the Interaction between Sodium Dodecyl Sulfate and Polyethylene Glycol by Electron Spin Resonance, Ultraviolet Spectrum, and Viscosity

Abstract

The hydrophobically modified nitroxide radical molecule 2,4-dinitrophenylhydrazone of 2,2,6,6-tetramethyl-4-piperidind-1-oxyl (DNPHTEMPO) was synthesized and used as electron spin resonance (ESR) and a UV probe to investigate the interaction between sodium dodecyl sulfate (SDS) and poly(ethylene glycol) (PEG). The ESR results showed that the headgroups of SDS adsorbed on PEG were more tightly packed than those of the unperturbed micelles and a more compact structure was formed at the binding site of the polymer−micelle aggregate due to a strong decrease of the viscosity at the micelle−polymer interface. The nitroxide group of DNPHTEMPO consisted of ∼55 % water and ∼45 % hydrocarbon. The two breakpoints of the SDS + PEG system critical aggregation concentration (cac) and polymer saturation point (PSP) were obtained from the maximum absorption bands λmax at room temperature and the viscosity measurement at different temperatures. The average location of 2,4-dinitrophenylhydrazone in the micelle consisted of an environment containing approximately 90 % water and 10 % hydrocarbon. The η/Cp (viscosity/PEG concentration) decreased with the increase of PEG concentration and temperature and exhibited a polyelectrolyte character. The electroviscosity effect increased with increasing SDS concentration. The PEG concentration had little effect on the cac of the SDS + PEG system.