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The effect of addition of 3-methyl-1-pentylimidazolium tetrafluoroborate ([C5mim][BF4]) on the micellization of a nonionic surfactant, Triton X-100 (TX-100), has been investigated. The techniques employed to study the aggregation behavior are fluoremetry, dynamic light scattering (DLS), and transmission electron microscopy (TEM) and the concentration range covered is 0–2 wt% [C5mim][BF4]. The probes, viz. pyrene and pyrene-1-carboxaldehyde (PyCHO), have been used for fluorescence analysis. According to the findings, the addition of pentyl-chained ionic liquid (IL) to aqueous TX-100 results in a dramatic increase in critical micelle concentration (cmc) decrease in micellar size, and aggregation number pointing toward an overall “unfavorable” aggregation process.

The micellization behavior of the cationic surfactant, tetradecyltrimethylammonium bromide (TTAB) with the ionic liquid (IL) 3-methyl-1-pentylimidazolium hexafluorophosphate [C 5 mim][PF 6 ] has been investigated using conductometric and spectroscopic techniques. Addition of different wt.% of [C 5 mim][PF 6 ] to aqueous TTAB solution results in an increase in cmc as well as a decrease in aggregation number ( N agg ). The cmc and degree of counterion dissociation ( α ) of the aqueous solution of TTAB containing different amounts of [C 5 mim][PF 6 ] have been determined at various temperatures by means of electrical conductivity. The two popular solvatochromic fluorescence probes pyrene and pyrene-1-carboxaldehyde have been used in order to confirm cmc and to calculate N agg . The preferential site of localization of IL molecules in TTAB micelles was assessed using 1 H NMR spectroscopy. In general, [C 5 mim][PF 6 ] shows an inhibitory effect on the formation of micelles of TTAB and leads to an increase in cmc . The results obtained through conductance measurements are well supported by spectral studies, viz. fluorescence and NMR.

The micellar behavior of a nonionic surfactant, polyoxyethylene (20) sorbitan monolaurate (Tween-20) in different wt% of a hydrophilic ionic liquid, 3-methyl-1-pentylimidazolium tetrafluoroborate ([C5mim][BF4]) was investigated using techniques like fluoremetry and dynamic light scattering. Two fluorescence probes viz. pyrene and pyrene-1-carboxaldehyde were utilized. The critical micelle concentration (cmc) of Tween-20 was found to increase with increasing amount of [C5mim][BF4]. The significant increase in cmc and decrease in aggregation number (Nagg) indicates an “unfavorable” micellization within aqueous Tween-20 solution when [C5mim][BF4] is present. The increase in dipolarity upon [C5mim][BF4] addition suggests increased water penetration due to the presence of [C5mim][BF4] in the micellar pseudophase. Dynamic light scattering studies provide the evidence of micelle-like aggregates even in the presence of 2 wt% [C5mim][BF4].

The effects of ionic liquids (ILs) 3-methyl-1-pentylimidazolium bromide, [C5mim][Br] and 1-heptyl-3-methylimidazolium bromide, [C7mim][Br] on the physicochemical properties of aqueous sodium dodecylsulfate (SDS) solutions were studied. Various micellar parameters such as critical micelle concentration (cmc), degree of counter ion dissociation (α), aggregation number (Nagg) as well as some thermodynamic parameters such as standard free energy of micellization ( Δ G m 0 ), standard enthalpy of micellization ( Δ H m 0 ) and standard entropy of micellization ( Δ S m 0 ) have been evaluated. Significant increase in cmc and decrease in counter ion binding along with decrease in Nagg was observed. 1H NMR technique was applied to reveal the solubilization site of ILs in the SDS micellar solutions.

This paper outlines the effect on micellar behavior of aqueous solutions of cationic surfactants viz. cetyltrimethylammonium bromide (CTAB) and cetyltrimethylammonium chloride (CTAC) upon addition of ionic liquid 3-methyl-1-pentylimidazolium hexafluorophosphate [C 5 mim][PF 6 ]. Important physicochemical properties such as conductance, critical micelle concentration (cmc) and aggregation number ( N agg ) are observed to change as [C 5 mim][PF 6 ] is added to aqueous CTAB/CTAC. The conductivity/concentration data of aqueous solutions of CTAB/CTAC with [C 5 mim][PF 6 ] were determined in the temperature range 298.15, 308.15, 318.15 K. These data were used to determine cmc as a function of temperature and concentration and to evaluate degree of ionization. Using temperature dependence of cmc, various thermodynamic parameters have been evaluated. Behavior of fluorescence probe, pyrene, confirms the interaction between [C 5 mim][PF 6 ] and cationic micellar surface. Further, 1 H NMR studies in micelle solutions containing [C 5 mim][PF 6 ] have also been carried out in order to interpret the preferential solubilization site of [C 5 mim][PF 6 ] on the studied micellar systems.

Conductivities, densities and speeds of sound of 1-butyl-2,3-dimethylimidazolium chloride in aqueous solutions were measured at 15, 25, and 35 °C. These data have been used to characterize the aggregation process of imidazolium based ionic liquid in the aqueous solution. The critical aggregation concentration (cac) and the degree of ionization, α, were determined by conductivity measurements. Both quantities were used to calculate the standard free energy change of aggregation, Δ G a 0 . It shows decrease in α and Δ G a 0 upon growth of temperature. From density data for the ionic liquid, the apparent molar volume, Vϕ, was calculated. The adiabatic compressibility, βs, changes in adiabatic compressibility upon aggregation, Δ β s , agg , and apparent adiabatic compressibilities, βϕ,s, were calculated from measurements of density and ultrasound velocity. Good agreement has been found when comparing with the aggregation properties of 1-butyl-2,3-dimethylimidazolium chloride both from conductivity and molar volume approach.

Changes in the micellization behavior of an anionic surfactant sodium dodecylsulfate (SDS) in aqueous solutions have been investigated at varying concentration of hydrophobic ionic liquid 3-methy-1-pentylimidazolium hexafluorophosphate [C 5 mim][PF 6 ] using techniques like conductometry, densiometry and speed of sound at a temperature range of 298.15–318.15 K. Critical micelle concentration ( cmc ) of SDS increases upon addition of [C 5 mim][PF 6 ], which is also evidenced from fluorescence spectra of pyrene probe. Presence of solvophobic interactions is proposed to be the reason for these observations.

This paper delineates the change in aggregation behavior of aqueous sodium dodecylsulfate (SDS), an anionic surfactant upon addition of “hydrophilic” ionic liquid (IL) 3-methy-1-pentylimidazolium tetrafluoroborate in an increase in critical micelle concentration (cmc). The results demonstrate the presence of electrostatic and hydrophobic interactions between the ions of IL and the head group of the surfactant. From the cmc values and their temperature dependence, the thermodynamic parameters, viz. free energy of micellization ( Δ G m 0 ) and entropy of micellization ( Δ S m 0 ) were evaluated to permit speculation of the interactions existing in the studied aqueous surfactant-IL systems. Further, 1H NMR chemical shift measurements in micelle solutions containing IL have also been carried out. The results obtained are compared with the conclusions drawn from the conductance and fluorescence measurements.