Concentration-Dependent Dual Behavior of Hydrophilic Ionic Liquid in Changing Properties of Aqueous Sodium Dodecyl Sulfate

Abstract

Modifying physicochemical properties of aqueous surfactant solutions in favorable fashion by addition of environmentally benign room-temperature ionic liquids (ILs) has enormous future potential. Due to its unusual properties, an IL may demonstrate a unique role in altering the properties of aqueous surfactant solutions. Changes in the properties of aqueous sodium dodecyl sulfate (SDS), an anionic surfactant, upon addition of a common and popular "hydrophilic" ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate [bmim][BF4] are presented. Addition of low concentrations of [bmim][BF4] (i.e., <or=2 wt %) to aqueous SDS results in a decrease in critical micelle concentration (cmc) as well as an increase in aggregation number (N(agg)) and average micellar size. An increase in dipolarity and a decrease in microfluidity of the micellar phase is reported by solvatochromic fluorescence probes pyrene and 1,3-bis-(1-pyrenyl)propane as up to 2 wt % [bmim][BF4] is added to aqueous SDS. The IL is observed to behave similarly to common electrolytes in the concentration range 0 < [bmim][BF4] <or= 2 wt %. A further increase in [bmim][BF4] concentration to 30 wt % results in an increase in cmc which is accompanied by a decrease in N(agg) and average micellar size. Change in the microfluidity of the micellar phase is observed to become insignificant in this concentration range. Evidence of the presence of micellar aggregates at such high concentration of [bmim][BF4] is furnished by dynamic light scattering. The role of an IL in altering the properties of aqueous SDS in the range 2 wt % < [bmim][BF4] <or=30 wt % is similar to those of polar cosolvents. The concentration-dependent dual role of the IL [bmim][BF4] in altering physicochemical properties of aqueous SDS is demonstrated.

Effect of [C n mim][Br] Based Ionic Liquids on the Aggregation Behavior of Tetradecyltrimethylammonium Bromide in Aqueous Medium

“…of the ILs in solution. Trends in conductance of aqueous cationic TTAB in the presence of ILs are similar to those observed by Zhang et al [48] for the aqueous Triton X-100 surfactant system in the presence of [C 12 mim][BF 4 ]; these trends are different from those observed for aqueous cationic, anionic, nonionic and aqueous zwitterionic surfactants upon addition of IL [21][22][23][24][25][26][27][28][29][36][37][38][39][40]. For a fixed concentration of TTAB, as the concentration of the ILs was increased from 0.2 to 1.0 wt%, the specific conductance increased by a reasonable amount.…”

“…The effect of the hydrophobicity of the alkyl groups of the ILs and surfactant anions on the CMCs, size distributions and thermodynamics of micellization has also been investigated [27,34,35]. Physicochemical properties of aqueous cationic, anionic, non-ionic and zwitterionic surfactants such as the CMC, size of the aggregates, aggregation number, dipolarity and microfluidity have been systematically modified by adding ILs [21][22][23][24][25][26] 4 ] on the physicochemical properties of aqueous anionic and cationic surfactants [28,29,[36][37][38][39][40]. ILs composed of different cations and anions have been extensively studied by various research groups in the field of colloid and interface science and some extensive reviews are available [41][42][43][44][45][46][47][48].…”

“…At lower concentrations, ILs behave as electrolytes and decreases the CMC values of aqueous surfactants, whereas at higher concentrations the CMC of the aqueous surfactant increases, which may be due to cosolvent-type behavior of the ILs [22,24,43]. The cations and anions of the ILs have a profound impact on the physicochemical properties of aqueous surfactant solutions [20][21][22][23][24][25][26][27]47]. Looking at such wider roles for ILs, scientist are encouraged to conduct further research on the unexplored features of the systems for better applications in industry.…”

Catanionic surfactant formation from the interaction of the cationic surfactant hexadecyltrimethylammonium bromide (CTAB) and the ionic liquid 1-butyl-3-methylimidazolium octyl sulfate (bmim-octyl SO4) in aqueous solution

“…In some cases the IL acts as an aqueous cosolvent and modifying some surfactant properties such as the critical micelle concentration (cmc) with respect to the value in neat water because of the weaker solvophobic interaction between the alkyl chain of the surfactant and the IL aqueous solution [1][2][3][4][5][6][7]. The effect of the ionic liquid on the surfactant properties depends on the IL structure and concentration.…”

“…The effect of the ionic liquid on the surfactant properties depends on the IL structure and concentration. Behera and Pandey [1,4,8] reported that at low concentration some ILs act similarly to an electrolyte decreasing the surfactant cmc whereas at high concentration they behave as a cosolvent increasing this parameter. In the case of the cationic surfactant hexadecyltrimethylammonium bromide (CTAB) the effect of ILs on the surfactant cmc confirms the trend above described [8][9][10][11][12][13].…”