The self‐assembly behaviors of mixtures of sodium bis(2‐ethylhexyl) sulfosuccinate (AOT) and didodecyl dimethylammonium bromide (DDAB) in polyethylene glycol 200 (PEG 200) and in water were investigated by surface tension, conductivity, steady‐state fluorescence and dynamic light scattering (DLS) methods. The results show that the oppositely charged binary surfactant system can form micelles in PEG 200; the critical micellization concentration (CMC) decreases for the binary system versus those of either surfactant alone. Although there is no charge screening in the PEG 200 system, the CMC values significantly increase and the system does not precipitate or show turbidity at any proportion of AOT to DDAB, while a multiphase composition gap exists in water due to the strong electrostatic attraction. It is speculated that the weak polarity of PEG 200, the decreased solvophobic interaction between the alkyl chain and PEG 200, and the loose structure of the resulting micelles might explain the experimental phenomena. Observed from the values of the interaction parameter, it is found that there are a strong attractive interaction and a synergistic effect between AOT and DDAB in aqueous solution, in comparison, the synergy between them in PEG 200 is very weak.
The self‐assembly behaviors of mixtures of sodium bis(2‐ethylhexyl) sulfosuccinate (AOT) and didodecyl dimethylammonium bromide (DDAB) in polyethylene glycol 200 (PEG 200) and in water were investigated by surface tension, conductivity, steady‐state fluorescence and dynamic light scattering (DLS) methods. The results show that the oppositely charged binary surfactant system can form micelles in PEG 200; the critical micellization concentration (CMC) decreases for the binary system versus those of either surfactant alone. Although there is no charge screening in the PEG 200 system, the CMC values significantly increase and the system does not precipitate or show turbidity at any proportion of AOT to DDAB, while a multiphase composition gap exists in water due to the strong electrostatic attraction. It is speculated that the weak polarity of PEG 200, the decreased solvophobic interaction between the alkyl chain and PEG 200, and the loose structure of the resulting micelles might explain the experimental phenomena. Observed from the values of the interaction parameter, it is found that there are a strong attractive interaction and a synergistic effect between AOT and DDAB in aqueous solution, in comparison, the synergy between them in PEG 200 is very weak.
The micellization of dodecyltrimethyl/ethyl/propyl/butylammonium bromide (C 12 NM, C 12 NE, C 12 NP, and C 12 NB) was investigated by electrical conductivity measurements at different temperatures T. In the investigated temperature range, (15 to 45) °C, both the critical micelle concentration (cmc) and the degree of counterion association (β) decreased with the increase of headgroup size. The cmc as a function of T showed a typical U-shaped relationship. The temperature of the minimum of U-shaped curve (T min ) increased with the incremental chain length in the headgroups, which was the reverse to the previous results for quaternary ammonium surfactants that T min decreased with the increment in the hydrophobic tails. The β approximately exhibited a linear decrease with raising T. Nonlinearity was observed both in ln(cmc) versus N c and in Δ mic G°versus T, where N c was the carbon number in the headgroups and Δ mic G°was the standard Gibbs energy of micellization. C 12 NM and C 12 NE resembled each other in the thermodynamics of micellization, but they behaved considerably differently from either C 12 NP or C 12 NB in the dependence of ln(cmc) on N c , in the decreasing rate of Δ mic G°versus T, and in the variation of thermodynamic properties with T. All of the surfactants exhibited the enthalpy-entropy compensation phenomenon. The large value of standard entropy of micellization (Δ mic S°) of C 12 NB compared with the others could be attributed to the strong hydrophobicity of the tributyl headgroup.
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