Abstract
Abstract The critical micellar concentration of aqueous solutions of hexadecyltrimethylammonium bromide (HTAB) containing various amounts of N,N-dimethylformamide (DMF) has been determined at 25 and 40 °C by means of surface tensiometric measurements. The standard free energy (ΔGm°), enthalpy (ΔHm°) and entropy (ΔSm°) of micellization were also determined. The experimental results indicate that: (1) micelle formation is somewhat hindered by a raise in temperature, and (2) DMF has an inhibitory effect on the formation of micelles of HTAB. This effect is relatively small at low DMF concentrations, but it increases drastically as the mole fraction of DMF approaches 0.33. The changes in the ΔGm°, ΔHm°, and ΔSm° values indicate that the formation of HTAB micelles in the water-DMF mixtures is an entropy directed process at lower concentrations of DMF and the inhibitory effect of DMF on micelle formation is attributed to an increase in the orderliness of this system with increasing DMF concentration.
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