Kamalakanta Behera

Ionic Liquid Induced Changes in the Properties of Aqueous Zwitterionic Surfactant Solution

Modifying properties of aqueous surfactant solutions by addition of external additives is an important area of research. Unusual properties of ionic liquids (ILs) make them ideal candidates for this purpose. Changes in important physicochemical properties of aqueous zwitterionic N-dodecyl- N, N-dimethyl-3-ammonio-1-propanesulfonate (SB-12) surfactant solution upon addition of hydrophilic IL 1-butyl-3-methylimidazolium tetrafluoroborate, [bmim][BF 4], are reported. Dynamic light scattering results indicate a dramatic reduction in the average micellar size in the presence of [bmim][BF 4]; micellar (or micelle-like) aggregation in the presence of as high as 30 wt % [bmim][BF 4] is confirmed. Responses from fluorescence probes are used to obtain critical micelle concentration (cmc), aggregation number ( N agg), and dipolarity and microfluidity of the micellar pseudophase of aqueous SB-12 in the presence of [bmim][BF 4]. In general, increasing the amount of [bmim][BF 4] to 30 wt % results in decrease in N agg and increase in cmc. Increase in the dipolarity and the microfluidity of the probe cybotactic region within the micellar pseudophase is observed on increasing [bmim][BF 4] concentration in the solution. It is attributed to increased water penetration into the micellar pseudophase as [bmim][BF 4] is added to aqueous SB-12. It is proposed that IL [bmim][BF 4] behaves similar to an electrolyte and/or a cosurfactant when present at low concentrations and as a polar cosolvent when present at high concentrations. Electrostatic attraction between cation of IL and anion of zwitterion, and anion of IL and cation of zwitterion at low concentrations of [bmim][BF 4] is evoked to explain the observed changes. Presence of IL as cosolvent appears to reduce the efficiency of micellization process by reducing the hydrophobic effect.

Modifying Properties of Aqueous Cetyltrimethylammonium Bromide with External Additives: Ionic Liquid 1-Hexyl-3-methylimidazolium Bromide versus Cosurfactant n-Hexyltrimethylammonium Bromide

Understanding the effect of external additives on the properties of aqueous surfactant solutions is of utmost importance due to widespread applications of surfactant-based systems. Role of ionic liquids (ILs) in this regard may turn out to be crucial as these substances are known to possess unusual properties. To unambiguously understand and establish the role of ILs in modifying properties of aqueous surfactant systems, changes in the physicochemical properties of aqueous cetyltrimethylammonium bromide (CTAB) upon addition of an IL 1-hexyl-3-methylimidazolium bromide ([hmim][Br]) are compared with those when a cosurfactant n-hexyltrimethylammonium bromide (HeTAB) is added to aqueous CTAB. Important physicochemical properties, such as critical micelle concentration (cmc), aggregation number (N(agg)), solution conductance and microfluidity, and average aggregate size and polydispersity, are observed to change as either [hmim][Br] or HeTAB is added to aqueous CTAB; the experimental outcomes clearly imply the changes in most of the physicochemical properties to be significantly more dramatic in case of IL [hmim][Br] addition. The fact that, between the two, only IL [hmim][Br] may show cosolvent-type behavior at high concentrations is evoked to explain the differences in the behavior of the two additives. It is demonstrated that both [hmim][Br] and HeTAB show electrolytic as well as cosurfactant-type behavior within aqueous CTAB when present at low concentrations, with the changes in physicochemical properties being very similar. At high concentrations, although HeTAB still acts as a cosurfactant forming mixed micelles with CTAB, IL [hmim][Br] behaves partly as a cosolvent toward altering the physicochemical properties of aqueous CTAB. The unique role of IL in changing properties of aqueous surfactant systems is demonstrated.

Ionic Liquid-Induced Unprecedented Size Enhancement of Aggregates within Aqueous Sodium Dodecylbenzene Sulfonate

Physicochemical properties of aqueous micellar solutions may change in the presence of ionic liquids (ILs). Micelles help to increase the aqueous solubility of ILs. The average size of the micellar aggregates within aqueous sodium dodecylbenzene sulfonate (SDBS) is observed by dynamic light scattering (DLS) and transmission electron microscopy (TEM) to increase in a sudden and drastic fashion as the IL 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF(6)]) is added. Similar addition of [bmim][PF(6)] to aqueous sodium dodecyl sulfate (SDS) results in only a slow gradual increase in average aggregate size. While addition of the IL [bmim][BF(4)] also gives rise to sudden aggregate size enhancement within aqueous SDBS, the IL 1-ethyl-3-methylimidazolium tetrafluoroborate ([emim][BF(4)]), and inorganic salts NaPF(6) and NaBF(4), only gradually increase the assembly size upon their addition. Bulk dynamic viscosity, microviscosity, dipolarity (indicated by the fluorescent reporter pyrene), zeta potential, and electrical conductance measurements were taken to gain insight into this unusual size enhancement. It is proposed that bmim(+) cations of the IL undergo Coulombic attractive interactions with anionic headgroups at the micellar surface at all [bmim][PF(6)] concentrations in aqueous SDS; in aqueous SDBS, beyond a critical IL concentration, bmim(+) becomes involved in cation-π interaction with the phenyl moiety of SDBS within micellar aggregates with the butyl group aligned along the alkyl chain of the surfactant. This relocation of bmim(+) results in an unprecedented size increase in micellar aggregates. Aromaticity of the IL cation alongside the presence of sufficiently aliphatic (butyl or longer) alkyl chains on the IL appear to be essential for this dramatic critical expansion in self-assembly dimensions within aqueous SDBS.

Interaction between ionic liquid and zwitterionic surfactant: A comparative study of two ionic liquids with different anions

Room temperature ionic liquids (ILs) may have enormous potential as far as modifying the properties of aqueous surfactant solutions is concerned. A comparative study on the changes in the physicochemical properties of aqueous solution of a commonly used zwitterionic surfactant N-dodecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate (SB-12) in the presence of up to 2 wt% of two ILs with same cation but different anions is undertaken using conductance, fluorescence spectroscopy, and dynamic light scattering. The two ILs used are 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF(4)]) and 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF(6)]). It is demonstrated that the addition of IL alters the important properties of aqueous SB-12. Critical micelle concentration, aggregation number, micellar size, and microfluidity of micellar pseudo-phase change when the IL is added to aqueous SB-12. The extent to which these properties are altered is observed to be significantly more for [bmim][PF(6)] as compared to that for [bmim][BF(4)]. The results demonstrate the presence of electrostatic attractive interactions between the ions of ILs and the zwitterion of SB-12 to be the major reason for these observations. While the interaction between the IL cation and the anionic sulfonate termini of SB-12 is same for the two ILs, that between IL anion and cationic quaternary ammonium of SB-12 is proposed to be more efficient for [bmim][PF(6)] due to the bigger size of PF(6)(-). Important role of IL anion in modifying properties of aqueous SB-12 is demonstrated. It is noted that the changes in the properties of aqueous surfactant systems upon IL addition depend strongly on the nature of the surfactant head group.

Temperature-dependent solvatochromic probe behavior within ionic liquids and (ionic liquid + water) mixtures.

Spectroscopic responses of absorbance probes, betaine dye 33, N,N-diethyl-4-nitroaniline, and 4-nitroaniline, and fluorescence dipolarity probes, pyrene (Py) and pyrene-1-carboxaldehyde (PyCHO) within ionic liquids (ILs) 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF6]) and 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF4]), and aqueous mixtures of [bmim][BF4] are used to assess the changes in important physicochemical properties with temperature in the range 10-90 degrees C. ETN obtained from betaine dye 33, indicating dipolarity/polarizability and/or hydrogen bond donating (HBD) acidity, decreases linearly with increasing temperature within the two ILs. Changes in Kamlet-Taft parameters dipolarity/polarizability (pi*), HBD acidity (alpha), and HB accepting (HBA) basicity (beta) with temperature show interesting trends. While pi* and alpha decrease linearly with increasing temperature within the two ILs, beta appears to be independent of the temperature. Similar to ETNand pi*, the first-to-third band intensity ratio of probe Py also decreases linearly with increasing temperature within the ILs. The lowest energy fluorescence maxima of PyCHO, though it decreases significantly within water as the temperature is increased from 10 to 90 degrees C, it does not change within the two ILs investigated. The temperature dependence of the dipolarity/polarizability as manifested via betaine dye 33 behavior is found to be more within the aqueous mixtures of [bmim][BF4] as compared to that within neat [bmim][BF4] or neat water. The sensitivity of pi* toward temperature increases as IL is added to water and that of alpha decreases. The temperature dependent Py behavior shows no clear-cut trend within aqueous mixtures of [bmim][BF4]; insensitivity of the PyCHO response toward temperature change is reasserted within aqueous IL mixtures. All-in-all, the temperature-dependent behavior of solvatochromic probes within [bmim][PF6], [bmim][BF4], and aqueous mixtures of [bmim][BF4] is found to depend on the identity of the probe.

Visual Evidence for Formation of Water-in-Ionic Liquid Microemulsions

The hygroscopic nature of ILs (even those considered “hydrophobic”), however, renders the characterization of such w/IL microemulsions difficult due to the uncertainties regarding the state of the dispersed water within bulk ILs. [5] Thus, whether the amount of water above the aqueous solubility limit of the hydrophobic IL is simply dispersed within the solution assisted by the surfactant or is helping to form water pools of the w/IL microemulsions is rather difficult to assess. The low but appreciable solubility of water in most hydrophobic ILs further complicates the characterization of w/IL microemulsions. Out of very few investigations relating to the formation of w/IL microemulsions, [4j–m] a surfactant that commonly forms water/oil (w/o) microemulsions, aerosol OT (or AOT), is proposed to form w/IL microemulsions with the IL [C8mim][Tf2N] only in the presence of a cosurfactant 1-hexanol. [4j] Though the formation of w/IL microemulsions using the nonionic surfactants Tween 20 [4k] and Triton X-100 [4l,m] with the hydrophobic IL [bmim][PF6] is reported, the characterization of the proposed microemulsions is either performed using cumbersome techniques with largely inconclusive evidence or is mostly ambiguous and unsatisfactory. The lack of a method that can characterize w/IL microemulsions in a direct, simple, and accurate fashion with concrete evidence is clearly evident. For example, the ternary phase diagrams of such IL/surfactant/ water systems are fairly complicated and ambiguous in nature (usually based on visual inspection), making it difficult to predict whether w/IL microemulsions exist at a given composition. [4k,m] Herein, we present a simple and accurate method that provides clear evidence for the formation of w/IL microemulsions. Our system is composed of the hydrophobic IL 1-butyl-3-methylimidazolium hexafluorophosphate, [bmim][PF6], as the bulk oil phase with triton X-100 (TX-100), which is nonionic, as the surfactant. The presence of w/IL microemulsions is observed visually from the color change associated with Co II in the solution.

Ionic Liquid-Based Optical and Electrochemical Carbon Dioxide Sensors.

Due to their unusual physicochemical properties (e.g., high thermal stability, low volatility, high intrinsic conductivity, wide electrochemical windows and good solvating ability), ionic liquids have shown immense application potential in many research areas. Applications of ionic liquid in developing various sensors, especially for the sensing of biomolecules, such as nucleic acids, proteins and enzymes, gas sensing and sensing of various important ions, among other chemosensing platforms, are currently being explored by researchers worldwide. The use of ionic liquids for the detection of carbon dioxide (CO2) gas is currently a major topic of research due to the associated importance of this gas with daily human life. This review focuses on the application of ionic liquids in optical and electrochemical CO2 sensors. The design, mechanism, sensitivity and detection limit of each type of sensor are highlighted in this review.

Hybrid green nonaqueous media: tetraethylene glycol modifies the properties of a (choline chloride + urea) deep eutectic solvent

Deep eutectic solvents (DESs) have emerged as easy-to-prepare inexpensive environmentally benign media with the potential for applications in various areas of chemistry. A judiciously selected cosolvent can modify the properties of a DES in a favorable manner. Tetraethylene glycol (TEG)-modified DES composed of choline chloride and urea in a 1:2 molar ratio, named Reline, is investigated over the complete composition regime within 298–358 K for its properties. The empirical solvent polarity parameter, ENT, obtained using the solvatochromic absorbance probe response of a betaine dye, along with Kamlet–Taft parameters, dipolarity/polarizability (π*), H-bond donating acidity (α), and H-bond accepting basicity (β) suggest the presence of interactions, mainly H-bonded, between TEG and the components of Reline. The H-bond accepting basicity (β) of TEG-modified Reline is found to be unusually high. Responses from dipolarity as well as intramolecular charge-transfer fluorescence probes further support these outcomes, suggesting that a small amount of TEG can effectively alter the properties of Reline. Negative molar excess volumes and positive excess logarithmic viscosities estimated from density and dynamic viscosity measurements, respectively, at all compositions and temperatures for (Reline + TEG) mixtures indicate the presence of stronger inter-species H-bonding interactions between Reline–TEG as compared to the intra-species H-bonding interactions between Reline–Reline and between TEG–TEG. FTIR absorbance and Raman spectral measurements indicate unusually high H-bond accepting basicity (β) of the (Reline + TEG) mixture to be due to the decreased involvement of urea functionalities in H-bonding with choline chloride, with possible increase in H-bonding between the adequate functionalities of TEG with those of choline chloride.

Self‐Probing of Micellization within Phenyl‐Containing Surfactant Solutions

The propensity of amphiphilic molecules to accumulate at the interface between the solution and adjacent gaseous, liquid, or solid phases is responsible for many remarkable physicochemical properties of aqueous surfactant systems such as wetting, foaming, emulsification, dispersion, adsorption, micellization, detergency, synergistic interactions with other surfactants, solubility, and solubilization, among others.

Self-aggregation of bio-surfactants within ionic liquid 1-ethyl-3-methylimidazolium bromide: A comparative study and potential application in antidepressants drug aggregation

Aggregation behavior of bio-surfactants (BS) sodium cholate (NaC) and sodium deoxycholate (NaDC) within aqueous solution of ionic liquid (IL) 1-ethyl-3-methylimidazolium bromide [Emim][Br] has been investigated using surface tension, conductivity, steady state fluorescence, FT-IR and dynamic light scattering (DLS) techniques. Various interfacial and thermodynamic parameters are determined in the presence of different wt% of IL [Emim][Br]. Information regarding the local microenvironment and size of the aggregates is obtained from fluorescence and DLS, respectively. FT-IR spectral response is used to reveal the interactions taking place within aqueous NaC/NaDC micellar solutions. It is noteworthy to mention that increasing wt% of [Emim][Br] results in an increase in the spontaneity of micelle formation and the hydrophilic IL shows more affinity for NaC as compared to NaDC. Further, the micellar solutions of BS-[Emim][Br] are utilized for studying the aggregation of antidepressants drug promazine hydrochloride (pH). UV-vis spectroscopic investigation reveals interesting outcomes and the results show changes in spectral absorbance of PH drug on the addition of micellar solution (BS-[Emim][Br]). Highest binding affinity and most promising activity are shown for NaC as compared to NaDC.