Thermodynamics of Micellization of Triton X-100 in Aqueous Glycine: Tensiometric and Ultrasonic Studies

Abstract

Abstract Surface tension and compressibility behavior of p-(1,1,3,3-tetramethylbutyl) phenoxypoly(oxyethylene glycol) (Triton X-100, TX-100) in aqueous mixture of glycine (Gly) have been studied at 298.15, 303.15, 308.15, and 313.15 K below and above the micellar composition range. Critical micelle concentration, cmc, of the surfactant TX-100 was obtained by surface tension, γ, density, ρ, and ultrasonic velocity, u, measurements at different temperatures. From the surface tension data, the surface excess concentration, Γ  max  σ , minimum area per molecule, A  min , Gibbs free energy, ΔG mic 0, enthalpy, ΔH mic 0, and entropy, ΔS mic 0 of micelle formation have been evaluated. Apparent molar adiabatic compressibility, κ ϕ , was calculated from density and ultrasonic velocity data. The values of κ ϕ and apparent molar adiabatic compressibility at infinite dilution, κ ϕ 0, in the pre-micellar region and apparent molar compressibility upon micellization, Δκ ϕ m , were obtained. The observed cmc of TX-100 in aqueous glycine is found to be smaller than its value in pure water. A comparison of Γ  max  σ in aqueous glycine with that in pure water suggests higher adsorption of TX-100 molecules at the air–liquid interface in the former solvent than in the latter one. This was attributed to the highly hydrophilic nature of glycine molecules, causing dehydration of the surfactant molecules, thereby, facilitating the adsorption of TX-100 molecules at the air–liquid interface in the presence of glycine than in its absence. The calculated values of the Gordon parameter, G parameter, suggest that aqueous glycine acts as a good solvent for the micellization of TX-100 amphiphiles. Negative values of ΔG mic 0 and ΔH mic 0 indicate that the process of micellization of the surfactant is spontaneous and exothermic. Moreover, higher values of − TΔS mic 0 than those of ΔH mic 0 truly endorse the view that micellization of TX-100 in aqueous glycine is primarily governed by the entropy gain due to the transfer of hydrophobic groups of the surfactant from the solvent environment to the interior of the micelle. The trends in the behavior of the compressibility parameters also endorse the micellization of TX-100 in aqueous glycine.