Aggregation properties and thermodynamics of micellization of gemini surfactants with diethyl ether spacer in water and water–organic solvent mixed media

Abstract

The aggregation properties and thermodynamics of micellization of three cationic gemini surfactants (n–EO1–n) containing diethyl ether spacer group with varying carbon number (n=12, 14 and 16) in the hydrophobic tails have been studied in water and water–organic solvents mixed media over the range of temperature (298.15 to 328.15)K using the conductometric method. Ethylene glycol (EG) and 1,4-dioxane (DO) were used as organic co-solvents with three different volume percentages due to their unique nature than other solvents. With increasing tail length, the critical micellar concentration (cmc) of gemini surfactants decreased. The effect of the diethyl ether spacer group on aggregation behaviour has been compared with other reported spacer groups. The micellization process is delayed in the presence of organic co-solvents as compared to pure water giving a positive value for the Gibbs energy of transfer (ΔGtranso). The degree of counter ion dissociation (α) increases with increasing tail length of gemini surfactants. It also increases with increase in the percentage of organic co-solvents and it is more prominent in DO–WR than EG–WR mixed media. The standard Gibbs energy of micellization (ΔGmo) is found to increase with increasing volume percentage of an organic co-solvent and also with decrease in the chain length of gemini surfactants. The ΔGmo has been correlated with Gordon parameter. The ΔGmo increases with increasing temperature which is more prominent in the presence of high percentage of an organic co-solvent and also in the presence of an organic co-solvent with less polarity. The enthalpies of micellization in all cases are exothermic in nature. The compensation between the enthalpy and entropy for the formation of micellar aggregates has been observed.