Bappaditya Naskar

Solution behavior of normal and reverse triblock copolymers (pluronic L44 and 10R5) individually and in binary mixture.

Solution properties of pluronics L44 or L [(PEO)(10)(PPO)(23)(PEO)(10)] and 10R5 or R [(PPO)(8)(PEO)(22)(PPO)(8)] were studied individually as well in their binary mixtures in aqueous medium. The critical micelle concentration (CMC), critical micelle temperature, and cloud point (CP) were determined. Ideal and nonideal behaviors of their mixtures in the formation of CMC and CP were observed; the energetics of the studied processes were determined. Spectrophotometry, isothermal titration calorimetry and dynamic light scattering (DLS) methods were used for evaluations. Morphologies of the dispersed L, R, and their mixtures along with their polydispersities were determined from DLS measurements. Atomic force microscopy was also employed. The interfacial properties of L and R were investigated forming Langmuir monolayers in a surface balance. The surface pressures (π) generated by the compounds were moderate, the area per molecule was higher for R than L. R has shown antibacterial activity against both gram positive and gram negative bacteria whereas L was inactive in this respect.

Amphiphile behavior in mixed solvent media I: self-aggregation and ion association of sodium dodecylsulfate in 1,4-dioxane-water and methanol-water media.

Mixed aquo-organic solvents are used in chemical, industrial, and pharmaceutical processes along with amphiphilic materials. Their fundamental studies with reference to bulk and interfacial phenomena are thus considered to be important, but such detailed studies are limited. In this work, the interfacial adsorption of sodium dodecylsulfate (SDS, C12H25SO4(-)Na(+)) in dioxane-water (Dn-W) and methanol-water (Ml-W) media in extensive mixing ratios along with its bulk behavior have been investigated. The solvent-composition-dependent properties have been identified, and their quantifications have been attempted. The SDS micellization has been assessed in terms of different solvent parameters, and the possible formation of an ion pair and triple ion of the colloidal electrolyte, C12H25SO4(-)Na(+) in the Dn-W medium has been correlated and quantified. In the Ml-W medium at a high volume percent of Ml, the SDS amphiphile formed special associated species instead of ion association. The formation of self-assembly and the energetics of SDS in the mixed solvent media have been determined and assessed using conductometry, calorimetry, tensiometry, viscometry, NMR, and DLS methods. The detailed study undertaken herein with respect to the behavior of SDS in the mixed aquo-organic solvent media (Dn-W and Ml-W) is a new kind of endeavor.

Amphiphilic behavior of two phosphonium based ionic liquids.

Solution and surface chemical behavior of two phosphonium based ionic liquids triisobutyl (methyl) phosphonium tosylate (IL-1) and trihexyl (tetradecyl) phosphonium bis 2,4,4-(trimethylpentyl)phosphinate (IL-2) have been studied. The polar IL-1 is surface active and water soluble, whereas the weakly polar IL-2 is more surface active with very low aqueous solubility. IL-1 does not form micelles but affects the micellization properties of ionic, nonionic, and zwitterionic surfactants more strongly than conventional electrolytes. IL-2 itself forms micelles and mixed micelles with Triton X-100 (TX-100) in aqueous solution. It also forms Langmuir monolayers of liquid expanded type, at the air/water interface. IL-1 can replace water in forming microemulsions with the oil isopropylmyristate (IPM), stabilized by IL-2 (surfactant)+isopropanol (IP as a co-surfactant) like the IL-1/IPM/(IL-2+IP) system. It produces a large monophasic zone in the pseudoternary phase diagram. The thermodynamics of formation of the microemulsions of IL-1 in oil (IPM) have been examined. The dimensions and the polydispersity of the dispersed nano-droplets in the microemulsions have been determined by DLS. The thermal stability of the microemulsion forming systems has also been studied. ILs studied against Sarcoma-180 cell lines have evidenced proficient anti-cancer activity of IL-1 and moderate activity of IL-2.

Self-aggregation of MEGA-9 (N-nonanoyl-N-methyl-D-glucamine) in aqueous medium: physicochemistry of interfacial and solution behaviors with special reference to formation energetics and micelle microenvironment.

Self-aggregation of MEGA-9 (N-nonanoyl-N-methyl-D-glucamine), a nonionic sugar-based surfactant, was studied with respect to the effect of salt (NaCl) and ionic liquid (1-butyl-3-methylimidazolium tetrafluoroborate) on its critical micelle concentration (cmc), aggregation number, hydrodynamic dimensions, energetics of micellization, and micellar microenvironment. Fluorimetry (both steady state and time resolved) was used to understand the microenvironments under the influence of additives. NaCl was found to decrease cmc, increase aggregation number (N), increase micellar size, and decrease enthalpy of micelle formation; the IL effect on the parameters was mostly opposite. The microscopic properties of micelles were probed using two fluorophores: one nonpolar C-153 (2,3,5,6-1H,4H-tetrahydro-8-trifluormethylquinolizino-(9,9a,1-gh)coumarin) and the other fairly polar ANS (8-anilinonaphthalene-1-sulfonate); they delivered information on the palisade layer and the peripheral region of the micelle interface, respectively. Energy of activation and entropy of activation of the dynamics of the probes were evaluated from their decay time, lifetime, and rotational movements in the regions of residency in the micelles. Density functional theory (DFT) calculations showed that the ternary combination MEGA-9/IL/H2O had the maximum interaction energy compared to any of the binary combinations. Thus, the ionic liquid reduced MEGA-9 self-association to a large extent.

Surfactant-assisted synthesis and characterization of stable silver bromide nanoparticles in aqueous media.

Colloidal dispersions of silver bromide (AgBr) in aqueous surfactant medium have been prepared using a surfactant-assisted synthesis approach with hexadecyltrimethylammonium bromide (CTAB). The surfactant acts both as source of bromide ion as well as the stabilizing agent. Upon progressive addition of silver nitrate to aqueous CTAB solution, stable AgBr dispersions were obtained. Formation of surfactant cation (CTA(+)) stabilized AgBr was confirmed by way of XRD, FTIR and NMR studies. Thermal behavior of the isolated nanoparticles was investigated by differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA), where the occurrence of phase transition in the surfactant-stabilized nanoparticles was observed. Kinetics of the particle growth was investigated by dynamic light scattering measurements, which predicted the formation of surfactant bilayered structures associated with the nanoparticles of AgBr. Band gap of the nanoparticles was determined by suitably analyzing the UV-visible spectral data, which concluded that the particles behaved like insulators. Morphology of the particles, studied by TEM measurements, was found to be spherical. Finally, enthalpy of formation of surfactant-stabilized AgBr, determined calorimetrically, was found to be dependent on the concentration of the precursors.

Behavior of the amphiphile CHAPS alone and in combination with the biopolymer inulin in water and isopropanol-water media.

Self-aggregation of the zwitterionic surfactant 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate (CHAPS) in water and isopropanol-water media, and interaction of the amphiphile with the biopolymer inulin in these media were investigated. The micellar properties of the zwitterionic surfactant and its associated interfacial and bulk properties along with the related energetic, and aggregation number were determined. The different stages of interaction of the CHAPS-inulin combines were identified and assessed. The complexes were formed and aggregated in solution at different stages of their molecular compositions. The aggregated sizes were determined by dynamic light scattering study and the morphology in the solvent removed states were examined using scanning electron microscope and transmission electron microscope techniques. The results witnessed formation of ensembles of varied and striking patterns.

Interaction of normal and reverse pluronics (L44 and 10R5) and their mixtures with anionic surfactant sodium N-dodecanoylsarcosinate

Interaction of monomeric normal L44 [(PEO)10(PPO)23(PEO)10]) and reverse 10R5 [(PPO)8(PEO)22(PPO)8] pluronics designated as L and R, respectively, and their mixtures with the anionic surfactant sodium N-dodecanoylsarcosinate (SDDS) in aqueous medium has been studied by tensiometry, conductometry, calorimetry and dynamic light scattering methods. The critical aggregation concentration (CAC), concentration of maximum binding (CS), and the extended critical micelle concentration (CMCe) of SDDS resulted from the interaction have been presented. L has shown the formation of CAC, CS and CMCe, whereas R has shown the absence of CAC but the presence of both CS and CMCe. Micellization of SDDS is an endothermic process whereas the formation of CAC and CMCe is exothermic events, the formation of CS is endothermic. The hydrodynamic diameter (Dh) and zeta potential of L and R, and their SDDS interacted species have been determined. Dh decreased with increasing SDDS concentration for L whereas it was invariant for R. Mixed L and R in varied proportions have been also examined in the solution state to probe into their mutual interaction, and interaction with SDDS. The formation of CAC of their mixtures was absent; CMCe formation was exothermic while that of CS was endothermic like their individuals.

Organic–inorganic hybrid: a novel template for synthesis of nanostructured Ag

We herein demonstrate that the amino acid arginine (Arg) can interact with phosphotungstate (Keggin) anions generating an excellent template for the synthesis of nanostructured silver wherein the Arg–PTA hybrid host plays the role of a UV-switchable reducing agent. The binding strength of the complex between arginine and phosphotungstate (PW12O40)3− i.e. the Keggin ions in aqueous medium has been assessed by the isothermal titration calorimetric technique. It is shown that the Arg–PTA complex may be used as a new class of organic–inorganic scaffolds in the synthesis of nanostructured silver. The crystalline Arg–PTA host can be photochemically reduced, resulting in electron transfer to the entrapped silver ions to form nanoparticle assemblies on the underlying colloidal template.