In this paper evaluation of surface active and application properties in liquid detergent formulations containing binary mixtures of anionic–nonionic, and anionic–cationic surfactants is discussed. Surfactants used include: linear alkylbenzene sulfonate (LAS), alcohol ether sulfate (AES‐2EO), alcohol ethoxylate (AE‐7EO), lauryl dimethyl amine oxide, and alkyl hydroxyethyl dimethyl ammonium chloride (AHDAC). Surface active parameters relating to the effectiveness and efficiency of surface tension reduction were determined from the surface tension data. Non‐ideal solution theory was used to determine the degree of interactions between the two surfactants, and the conditions under which a mixture of two surfactants show synergism in surface active properties. Our data indicated that synergism in mixed surfactants increases with the degree of charge difference between the surfactants. In both mixed micelle and mixed monolayer formation, the degree of interactions between the two surfactants in the mixture increased in the following order: LAS/AE < AES‐2EO/amine oxide < AES‐2EO/AHDAC. This synergistic behavior as presented in this paper leads to unique application properties and improved performance in terms of foam volume, and soil removal which has applications in formulation of dishwashing liquids, and laundry detergents.

SynopsisThe application of low-angle laser light scattering (LALLS) and combined GPC/LALLS for the measurement of absolute molecular weight distribution of a styrene-butylacrylate (30/70) emulsion copolymer is discussed. From the static light scattering measurements in four different solvents, i.e., toluene, tetrahydrofuran (THF), methyl ethyl ketone (MEK), and dimethylformamide (DMF), the true weight average molecular weight (mu) and heterogeneity parameters are determined. The apparent mu obtained from the static measurement in THF was in good agreement with the mu, determined from the multiple solvent analysis, suggesting the validity of using THF as the mobile phase in the combined GPC/LALLS analysis.

Linear alkylbenzene sulfonate (LAS) is the most widely used surfactant in household products. The dominance of LAS is particularly apparent in laundry detergents, dishwashing liquids, household cleaners, and institutional/industrial cleaners, where it accounts for over 3 million tons per year worldwide consumption. However, detergency performance of LAS is decreased in hard water due to lower solubility and surfactant loss in the presence of calcium and magnesium ions. In this study behavior of an aqueous binary surfactant mixture composed LAS and nonionic surfactants was investigated. Ethoxylated alcohols (C12–C14) with 7 EO and 2 EO units were mixed with LAS in laundry detergent formulations, and performance factors including detergency, solubility, and efficiency and effectiveness of surface tension reduction were examined. Analysis of surface tension data indicated strong molecular interaction between LAS and nonionic surfactant. The results indicated that the addition of low amounts of the nonionic surfactant lowers significantly CMC of the mixed surfactant system, and causes the formation of mixed micelles containing predominantly nonionic molecules which provide water hardness protection for LAS. The overall improvement in detergency appears to be due to: lower CMC of the mixed surfactant system which improves soil solubilization, solubilization of Ca(LAS)2, and reduction of free calcium ions which frees up soluble LAS in solution to adsorb at fabric-soil interfaces for enhanced soil removal.

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