Self-Aggregation of Alkyl (C₁₀-, C₁₂-, C₁₄-, and C₁₆-) Triphenyl Phosphonium Bromides and Their 1:1 Molar Mixtures in Aqueous Medium:  A Thermodynamic Study

Abstract

The self-aggregation of alkyl (C10-, C12-, C14-, and C16-) triphenyl phosphonium bromide surfactants (ATPBs) and their equimolar binary mixtures in aqueous medium was studied microcalorimetrically and conductometrically at different temperatures. The thermograms of C10- and C12TPB have shown differences in behavior from those of C14- and C16TPB. Their binary (1:1 mol/mol) mixtures with C10- or C12TPB as one of the components have also evidenced differences in behavior. Individually as well as in mixed conditions, the ATPBs have indicated formation of two states of aggregation corroborated by both calorimetric and conductometric measurements. On the basis of the results, the thermodynamic parameters, free energy (ΔG m°), enthalpy (ΔH m°), entropy (ΔS m°), and specific heat (ΔCpm°), of micellization have been evaluated. The specific heat has been found to vary linearly with the carbon number in the ATPB chain. The ΔH m° and ΔS m° values for the micellization of the pure ATPBs have nicely compensated each other. The free energy of transfer of a mole of CH2 from an aqueous environment to a micelle was found to be −2.0 kJ mol-1.

Thermodynamics, size, and dynamics of zwitterionic dodecylphosphocholine and anionic sodium dodecyl sulfate mixed micelles

“…At higher temperatures, micellization takes place as a singlestep exothermic process with only one cmc ( Table 1). The similar tendency was previously observed for alkyl triphenylphosphonium bromides [29]. The mixed micelles exhibit two inflection points in ITC curves up to a temperature of ca.…”

“…This reveals the formation of only one kind of the micelle at a higher temperature. Existence of two structures is usually attributed to either changes in the composition in the mixed micelles or transition of the shape with the increase in a total surfactant concentration [20,28,29]. As the size of the pure DPC and the DPC/SDS mixed micelles is comparable, as determined by diffusion measurements, we suppose that both kinds of the mixed micelles found at lower temperatures by ITC differ from each other in the content of individual surfactants.…”

“…The presence of two cmcs indicates a two-step aggregation mechanism. Surfactants with at least two cmcs are known as ''multiple-cmc systems'' [26] and have previously been reported elsewhere [20,25,[27][28][29]. Both steps of the micellization processes in the DPC/SDS mixed micelles are endothermic (DH mic = -DH demic ) at low temperatures, and due to proximity of both cmc values, the separation of two reaction enthalpies is difficult (Fig.…”

Comparative study of nucleophilic efficacy of pralidoxime towards phosphorus, sulfur and thiophosphorus based esters

“…It has been already proved that cationic surfactants accelerate the reaction. According to Buncel et al [26], the electrostatic attraction of the cationic head groups of the surfactants at the micelle surface to the nucleophilic anion counterions leads to augmentation of the local concentration of the nucleophile, whereas incorporation of the substrate in the micelle leads to a higher local concentration of There is little information about the effect of the variation of head groups on the micellar structure [27][28][29].…”

Micellization of Cetyl Triphenyl Phosphonium Bromide Surfactant in Binary Aqueous Solvents

“…Palepu et al [13][14][15] studied the surface properties of simple and binary combinations of alkyl triphenyl phosphonium bromides. Recently Palepu et al [16] also investigated the micellar and associative thermodynamic properties of binary mixtures of alkyl triphenyl phosphonium bromides in ethylene glycol and water mixtures.…”