Search

Discrete water domains in hydrophobic environment find relevance in aerosols, oil refinery, the human body, etc. The interfacial microstructure plays a crucial role in the stability of such water domains. Over the decades, the amphiphile-induced electrostatic interaction is considered to be the major stabilizing factor operating at these interfaces. Here we take the representative water/AOT/oil microemulsion to show that creating a strong H-bonding network through suitable additive, such as protic ionic liquid (IL) at the interface, helps both the growth and stability of water domains in the hydrophobic phase. On the other hand, common electrolytes and aprotic ILs fail to replicate such behavior as seen by Raman, Fourier transform infrared spectroscopy, dynamic light scattering (DLS), and electron microscopy measurements. Experimental results are further supported by the all-atomic molecular dynamics (MD) simulations that showed extended H-bonding mediated by the protic IL cations that were localized at the interface. High temperature DLS and rheology studies have shown greater thermal stability and mechanical strengths of our biocompatible microemulsions, which have potential to become suitable templates for in situ synthesis of nanoparticle and various organic compounds.

Owing to the fascinating applications of ionic liquids (ILs) based non-aqueous microemulsions (MEs) in the field of chemical reactions due to their high thermal stability compared to that of aqueous MEs and requirement of water-free environment, we designed a high-temperature stable cationic IL-in-oil microemulsions using 1-ethyl-3-propylbenzimidazolium bromide ([EPbim][Br]) as a polar phase for the first time. In order to determine the thermodynamic stability of such type of MEs, we measured the distribution of cosurfactant (herein, 1-octanol) between bulk n-decane phase and interface covered by quaternary ammonium head group of cetyltrimethylammonium bromide (CTAB) at elevated temperature. The spontaneous formulation of high-temperature IL-in-oil MEs with organized IL-oil interface was identified by the negative free energy and entropy change at studied temperature range (358–370 K). Interestingly, we observed temperature-independent exothermic behavior at a specific composition, which probably comes from the cation-π interaction between quaternary ammonium head group of CTAB and aromatic moiety of ILs. We performed phase behavior study to demonstrate a wide range of thermally stable of [EPbim][Br]/CTAB/decane MEs. Surprisingly, the droplet size was decreased with progressive addition of IL, which may be due to the difficulty of formation of strong and favourable H-bond between the polar head groups of CTAB and [EPbim][Br] at higher temperature. Furthermore, the aggregation number and molecular interfacial area at higher temperature were calculated, which have direct correlation with the droplet size. Finally, the nitration reaction with three different aromatic compounds was performed in this MEs media at the temperature-independent composition. The reaction was completed with the highest regioselectivity of para isomer product over the ortho one. Moreover, these results clearly highlight an efficient way towards the formulation of high temperature stable MEs with ILs at ambient pressure and open a wide field of potential applications.

Extensive investigation on self-assembly of DDAB in aqueous medium is severely restricted due to its insolubility. However, DDAB is highly soluble in acetonitrile, which allows investigation in a wide range of concentrations. An unusual aggregation phenomenon is exhibited by DDAB in acetonitrile, displaying six breaks in conductivity-concentration profile in a wide concentration regime. This study along with that of steady state fluorescence measurements indicate the presence of six-step self-assembly phenomena to occur in the system. HRTEM experiments show the presence of fascinating morphologies of the aggregates. The experimental observations are analyzed and the driving forces behind the phenomena are discussed.

The nature of transition from ordinary micelles (of nanometer length scale) of surface active ionic liquid 1-Hexadecyl-3- methylimidazolium chloride, to wormlike micelles (WLM) (micrometer length scale), mediated by hydroxy aromatic π-electron systems 1-Naphthol, 2-Naphthol and 2,3-Dihydroxynaphthalene (2,3-DHN) in salt free condition have been studied under Newtonian as well as non-Newtonian flow regimes. Conductance and tensiometry show that the additives lower the CMC of the ionic liquid. The interaction parameter (β) of the systems at different mole fraction evaluated on basis of Rubingh's Regular solution approach were negative at all SAIL/Additive compositions. UV–vis spectroscopy showed that micelle-bound additives formed hydrogen bonds with interfacial water molecules. Increase in steady state fluorescence anisotropic measurements revealed that the additives increasingly partitioned within the micelles. 1 H NMR study confirmed that although the additives reside at the palisade layer, they perturb the micellar core as well. At higher concentration (100 mM, 1:1), systems formed transparent viscoelastic gel. Rheological study of the viscoelastic gels showed that their zero shear viscosity is a function of temperature. 2,3-DHN interacted most strongly with the SAIL micelles, both in Newtonian and non-Newtonian regimes. This was corroborated by DFT study of binding energy. Hydrogen bonding of the hydroxy functionality along with strong cation-π interaction between the aromatic moieties and the imidazolium ring are considered as the main driving forces behind the morphology change. The viscosity of C 16 -3-MeImCl/1-Naphthol increased as function of salt concentration unlike C 16 -3-MeImCl/NaSal system. A possible mechanism is suggested and discussed. The present study sheds light on understanding the molecular interactions behind the structural change from spherical to elongated micelles, in both microscopic and macroscopic scale, triggered by hydroxy naphthalenes under salt-free condition. The metal tolerance of the gels has huge application prospects as fractured fluids in oil-mining industry.

Using the benefits of superior surface activity of surfactant-like ionic liquids (SAILs) and synergistic interaction of oppositely charged surfactants, herein we formulate the oil/water interface composed of equimolar composition of 1-hexadecyl-3-methy-limidazolium chloride (C(16)mimCl) and polyoxyethylene (20) cetyl ether (Brij-58) for the first time. The primary role of cosurfactant to stabilize the interface of water-in-oil droplets was investigated by using isomeric cosurfactant (e.g., 1-pentanol and isoamyl alcohol). The distribution of cosurfactant in interfacial region of nano droplets and bulk oil was evaluated as a function of different hydration level, and temperature. Energetic studies revealed formation of the organized oil/water interface by releasing heat during transfer of cosurfactant from oil to interface. Droplet morphology was examined to visualize the effect of water content, and added Brij-58. Mechanistic information of percolation behaviour was discussed with help of DLS results. Various hydrogen bonding environment of entrapped water along with partitioning behaviour was established from novel fluorescence deconvolution method and correlated with FTIR and time-resolved fluorescence studies. The antimicrobial activity of microemulsions along with individual components was measured against Gram-negative and Gram-positive bacteria. Mixed C(16)mimCl/Brij-58 micro-emulsion confirmed as efficient antimicrobial agent compared to the individual components.

Mixtures of dissimilar surfactants can have superior properties compared to those of the individual surfactant components involved, which provide impetus for research on interactions between surfactants. It was also demonstrated that a change in the composition of external phase promotes remarkable changes in interfacial properties of reverse micelles (RMs), which are crucial to understand the system in order to use them as nanoreactors. Hence, it should be achievable to explore the influence of non-ionic Tween-85 on the properties of anionic AOT based micelle as well as RMs in fatty acid esters [e.g., ethyl myristate (EM), ethyl palmitate (EP) and ethyl oleate (EO)]. A comprehensive micellization behavior is studied at different mixed compositions (XTween-85) by surface tension method. Non-ideal mixing behaviors along with synergistic interaction between the constituent surfactants in the mixed micelles are evidenced. Mixed micelles illustrate favorable micellization behavior in terms of thermodynamic parameters. Further, fatty acid ester medium-based mixed RM shows synergism in water solubilization capacity. Microstructures of these systems are investigated by conductance, DLS, and FTIR studies. The solvation and rotational relaxation dynamics using picosecond time-resolved emission spectroscopy (TRES) is used to investigate the effect of XTween-85 as well as chemical architecture of fatty acid esters for the first time on the excited state dynamics of fluorophore. The solvation dynamics is found to be faster with an increase in XTween-85 and the average solvation time follows the order, EO

Smart wormlike micellar blends can be readily formed from surfactant micelles in presence of counterion, salt or under varying conditions of pH, concentration, salinity driven by cation-π interaction whereas the role of π-π interaction in the same remains less explored. In this investigation the impact of π-π interaction on nanoaggregates of cationic amphiphile viz., cetylpyridinium bromide (CPB) in contrast with the cation-π interaction in cetyltrimethylammonium bromide (CTAB) in the presence of surface-active aromatic π conjugated hydroxy aromatic derivatives of naphthalene viz., 1 Naphthol, 2 Naphthol and 2,3 Dihydroxynaphthalene is reported. The presence of π-π interaction in CPB enables stronger synergism between the hydroxynaphthalenes compared to the non-aromatic analogue CTAB while face-to-face stacking interaction in CPB-hydroxynaphthalene systems lead to formation of worm like micelle (WLM) with relatively short entanglement lengths as compared to that in CTAB. The modification of surface parameters and molecular interactions of the systems are studied via tensiometry, 1H nuclear magnetic resonance (NMR), 2D-Nuclear Overhauser effect spectroscopy (NOESY) and small angle neutron study (SANS). The non-Newtonian behavior of the complex fluids comprising the cationic amphiphiles and hydroxyaromatic derivatives are studied using static and dynamic rheometry.

The intrinsic viscosity [η] of sodium alginate having different molecular weights (high molecular weight (type A), medium molecular weight (type B) and low molecular weight (type C)) is measured at 293–303 K temperature in various mixtures of water (good solvent), acetone (ACE, poor solvent) and water-ethoxy ethanol (EE, poor solvent). The observed result particularly the Huggins constant (K H) values shows a significant variation of cosolvency as a function of solvent composition (ΦACE/ΦEE) and the temperature. Unperturbed dimensions (K θ) under non-theta condition have been calculated using various equations in different water-acetone and water-ethoxy ethanol mixtures. The value of K θ obtained from three different methods of measurements viz., Burchard-Stockmayer and Fixman (BSF), Berry and Inagaki-Suzuki-Kurata (ISK) agree well with each other except in a few compositions of solvents. The molecular extension factor (α n) and actual end-to-end distance (α n K θ) have also been computed herein. Further, the shear thinning nature of the sodium alginate solutions (representative illustration: type A) in water and water-acetone mixed systems has been investigated at increasing strain rate. Results show that the viscous modulus G″ predominates over the elastic modulus G′ and the systems behave as viscoelastic fluids under present conditions. Higher value of G′ in acetone-water mixed solvent system compared to that in pure water undoubtedly indicates enhancement of the elasticity in alginate system in the presence of acetone. Finally, zeta potential measurement demonstrates that the polymeric surface of sodium alginate (representative illustration: type A) is essentially negatively charged and the zeta potential of the polymer is more responsive to the composition of ethoxy ethanol than that of acetone in the aqueous-organic mixed solvents.