Micellization of a Series of Dissymmetric Gemini Surfactants in Aqueous Solution

Abstract

A series of dissymmetric gemini surfactants, [C m H 2m+1 (CH 3 ) 2 N(CH 2 ) 6 N(CH 3 ) 2 C n H 2n+1 ]Br 2 (designated as C m C 6 C n Br 2 , with constant m + n ) 24 and m ) 12, 13, 14, 16, 18), have been investigated by electrical conductivity measurement, steady-state fluorescence measurement, and time-resolved fluorescence quenching. The critical micelle concentration (CMC) and the micelle aggregation number (N) were determined and the micropolarity of micelle was characterized. The micelle ionization degree (R) was obtained using a combination of electrical conductivity data and N. Furthermore, the Gibbs free energy of micellization (∆G mic ) and the entropy of micellization (∆S mic ) were studied. The results have shown that the degree of dissymmetry (m/n) has an important effect on the micellization in aqueous solution. As the m/n ratio increases, the CMC value decreases linearly, the N value at the CMC increases slightly (from 22 to 30), and R decreases slightly down the series. The value of ∆G mic becomes more negative for greater m/n ratios, which supports the belief that the micellization will be more spontaneous and the contribution, per CH 2 unit, to micellization increases as the m/n ratio increases. The calculated thermodynamic parameter |T∆S mic | is much larger than |∆H mic |, which indicates that the micellization of the C m C 6 C n Br 2 series is entropy-driven. However, the micropolarity of the micelle that is sensed by pyrene varies little, irrespective of the m/n ratio.

Sulfonic-Hydroxyl-Type Heterogemini Surfactants Synthesized from Unsaturated Fatty Acids

“…This is not rationalized by the consideration of surfactant geometry on the basis of packing parameter 13 , since rough calculations do not suggest remarkable differences in the overall packing parameter between the two surfactants. We note that Wang and co-workers have reported opposite behaviors 7 . They have studied aqueous solution properties of cationic heterogemini surfactants α-6-β, where α and β represent the hydrocarbon chain lengths under the fixed total carbon number of α β 24 as a function of their dissymmetry i.e., α/β and found the decreased cmc with decreasing symmetry.…”

“…3.3 Effects of molecular symmetry on the physicochemical properties of aqueous SOH-9,9-Am10 and SOH-12,6-Am10 solutions It has been reported that molecular symmetry of heterogemini surfactants plays a signifi cant role in their aqueous solution properties 7 . In our current work, we have studied this effect using two heterogemini surfactants, SOH-9,9-Am10 and SOH-12,6-Am10.…”

“…Wang and co-workers have reported that molecular symmetry signifi cantly impacts the aqueous solution properties of heterogemini surfactants 7 . In our current case, changing the hydrocarbon chain length also results in a change in the molecular symmetry.…”

Solution Properties of Dissymmetric Sulfonate-type Anionic Gemini Surfactants

“…Sikirić et al investigated the effect of spacer length on dissymmetric surfactants 12,13 and found that the Krafft temperature increases linearly with spacer length and that both adsorption at the air/water interface and micellization in aqueous solution are heavily dependent on the spacer length. Yan et al synthesized C m C 6 C n Br 2 with m n 24, where m 12, 13, 14, 16, or 18, and found that, as the m/n ratio was increased, the surface activities improved, the CMC values decreased linearly, and the aggregation numbers at the CMC increased slightly 14,15 . These studies investigating dissymmetric surfactants focused on the choice of whether to fix the total carbon numbers of the hydrocarbon chains and their spacers or not.…”

Dissymmetric Gemini Surfactants Generated by Disulfide Exchange in Mixed Micelles

“…With the increase in the degree of dissymmetry, the critical micelle concentration (cmc) decreases linearly, the micelle aggregation number increases slightly, the micelle ionization degree decreases slightly, and so on. Wang et al suggested that the intermolecular and intramolecular interactions between the hydrophobic alkyl chains exist for the symmetric gemini surfactants, while the intramolecular interaction weakens as the degree of dissymmetr y increases 4 ) . Thus, the hydrophobic interaction of dissymmetric gemini surfactants must be different from that of symmetric ones.…”