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The effect of different alkyl chains of anionic surfactants on properties of binary anionic-nonionic mixed surfactant systems was studied. These systems included octyl-, dodecyl-, and cetylsulfoacetates mixed with isooctyl phenol nonyl ethoxylate. The critical micelle concentration of mixed surfactants shifted to lower values compared to those of the single anionic surfactants. Effectiveness values increased with decreases in the mole fraction of anionic surfactants. The negative values of interaction parameter (β) increased with increases in the chain length of anionic surfactants.Paper no. S1210 in JSD 4, 293-296 (July 2001).KEY WORDS: Alkyl-sulfoacetates, binary mixed surfactants, interaction parameters.Most surfactants used in practical applications are mixtures. Hence, understanding both the structure and properties of mixed micelles containing anionic and nonionic surfactants is essential for many industrial uses of surfactants. Mixed surfactant systems are also of great theoretical interest in their own right. In solutions containing mixtures of surfactants, the tendency to form aggregates is substantially different from that in solutions of single surfactants. It has been reported that the effect of a mixed surfactant system on surface activity is superior to that of a single surfactant system (1-3). Various investigations covering different aspects of solution properties relevant to monolayers formed by mixtures of ionic and nonionic surfactants have been published (4-8). A number of solution properties have been measured for mixed anionic-nonionic surfactants systems (9-11).Our approach used Rubingh's method (12) to calculate the mole fraction, interaction parameters, and activity coefficients of binary surfactant mixtures in micelles. EXPERIMENTAL PROCEDURESMaterials. The anionic surfactants octyl-, dodecyl-, and cetylsulfoacetates (A 8 , A 12 and A 16 ) were prepared as reported previously (13). The nonionic surfactant isooctyl phenol nonyl ethoxylate [9 moles ethylene oxide (EO)] used in this study was supplied by the Hüls Company, Germany.Surface tension measurements. Surface tension was measured using a Du Nouy ring tensiometer (type 8451 Krüss; Hamburg, Germany) with platinum ring at fixed temperature (25°C).Preparation of mixed surfactant solutions. Doubly distilled water from all-glass apparatus was used to prepare all solutions. Surface tension of water was 72.8 dyne cm −1 at 25°C. Into several 100-mL beakers, aliquots of a given concentration of anionic surfactants (1 × 10 −2 mol/L) were placed, followed by the addition of a given concentration of isooctyl phenol nonyl ethoxylate (1 × 10 −2 mol/L). The mixtures were diluted stepwise with water. These mixtures were stirred for 30 min under thermostatted conditions at 30°C in order to establish equilibrium. RESULTS AND DICUSSIONChange of critical micelle concentration (CMC) and effectiveness with mole fraction under a constant total concentration. The surface tension of single nonionic nonyl phenol ethoxylate, single anionic surfactants (A 8 , A...

A series of ethoxylated sodium monoalkyl sulfosuccinate (ESMASS) ester surfactants were prepared by reacting polyethylene glycol (molecular weight 600) with sodium monoalkyl sulfosuccinate (SMASS). The esters were prepared by reacting octyl, lauryl, or cetyl alcohol with sodium sulfosucci