Journal of Colloid And Interface Science, 01 April 2012, Vol.371(1), pp.73-81
► The headgroup alkyl chain affects the thermodynamic properties of gemini surfactants. ► The temperature of the minimum of cmc ( ) increases with increasing the headgroup alkyl chain length. ► Log (cmc) does not vary linearly with carbon number of the headgroup alkyl chain. ► The enthalpy–entropy compensation plots exhibit excellent linearity. A series of cationic gemini surfactants butanediyl-1,4-bis(dodecyldialkylammonium bromide), C H N (C H ) C H N (C H ) C H ·2Br , where = 1, 2, 3, 4, referred to as C C C (Me), C C C (Et), C C C (Pr), and C C C (Bu), respectively, were synthesized, and their thermodynamic properties of micellization were studied by electrical conductivity measurements. There existed a minimum critical micelle concentration (cmc) in the curve of cmc versus temperature, and the temperature of the minimum of cmc ( ) increased with increasing the headgroup alkyl chain length. The values of log (cmc) depended linearly on carbon number of the alkyl chains, but that was not true for the carbon number of the headgroup substituents. The temperature dependence of cmc and degree of counterion association ( ) were used to calculate the Gibbs free energy (Δ °), enthalpies (Δ °) and entropies (Δ °) of micelle formation for these gemini surfactants, and well correlated enthalpy–entropy compensation was observed. The analyses showed C C C (Me) and C C C (Et) behaved similarly in terms of thermodynamics of micellization, but they behaved differently from C C C (Pr) and C C C (Bu), which could be ascribed to the hydrophobicity and the location of the headgroup alkyl chains in the aggregates. These initial results indicate the headgroup alkyl chain plays an important role in influencing the thermodynamic properties of gemini surfactants.
Gemini Surfactants ; Headgroup ; Micellization ; Thermodynamic Properties ; Enthalpy–Entropy Compensation ; Engineering ; Chemistry
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