Effect of polyoxybutylene chain length on the properties of alkyl sodium sulfates in aqueous solution

Abstract

The micelle formation and adsorption phenomena at the airwater interface of polyoxybutyl-enenated higher alcohol sodium sulfates (RO[CH₂CH (C₂H₅)O]_m SO₃Na where R = C₈H₁₇, C₁₀H₂₁, C₁₂H₂₅, C₁₄H₂₉ and m = 1, 2, 3, and 4) were investigated in aqueous solution by surface tension measurements over a concentration range 10⁻⁵-10⁻² mol/dm³ at 20 °C. These were synthesized from C₈-Cl4 alcohols and α-butylene oxide and subsequently sulfated with CISO₃H. The critical micelle concentration (CMC) and Gibbs free-energy change of micellization, ΔG ^°_mic , were determined from the surface tension data of the solutions. It was found that the CMC values of the compounds studied decrease with the increasing chain length of polyoxybutylene and the increasing number of carbon atoms in the alkyl group. The change in cohesion energy, W _bo = 1.85 kT, for polyoxybutylene chains was determined (0.60 per oxybutylene unit). This is comparable with the van der Waals energy of interaction per CH₂ group, W _{ch 2}, in adjacent hydrocarbon chains due to micelle formation.