6533b829fe1ef96bd128a205

RESEARCH PRODUCT

Standard partial molar volumes of alcohols in aqueous dodecyltrimethylammonium bromide solutions

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Density measurements of water-dodecyltrimethylammonium bromide (DTAB)-alcohol ternary systems as a function of alcohol and surfactant concentrations were carried out at 25°C. The alcohols were propanol (PrOH), 2-propanol (2-PrOH) and hexanol (HexOH). The apparent molar volume Vϕ,R of alcohols have been calculated and the standard (infinite dilution) partial molar volumes of alcohols V R at each surfactant concentration were obtained by means of a least squares fit of Vϕ,R vs. the alcohol concentration. The V R vs. surfactant concentration curves have been rationalized in terms of the partial molar volume of alcohol in the aqueous V f and the micellar V b phases and the distribution constant of alcohol between the aqueous and the micellar phases K. The V b values for PrOH and HexOH together with those of butanol and pentanol previously reported satisfy the additivity rule giving a methylene group contribution of 16.7 cm3-mol−1 which is identical to that reported in the literature from the study of pure liquid alcohols. No difference between V b for PrOH and 2-PrOH has been found. From density data of water-alcohol and water-surfactant binary systems and of water-surfactant-alcohol ternary system, the apparent molar volume of the surfactant in the water-alcohol mixed solvent Vϕ,S have been calculated as a function of the surfactant concentration and of the mixed solvent composition. The effect of the alkyl chain length of the alcohols and the effect of isomerization of the alcohols on the Vϕ,S vs. surfactant concentration trends have been analyzed.