Pramila K. Misra

Micellization of ionic surfactants in tetrahydrofuran-water and acetonitrile-water mixed-solvent systems

Abstract The effect of the dipolar aprotic solvents, tetrahydrofuran (THF) and acetonitrile, on the micellization of ionic surfactants, cetyltrimethylammonium bromide (CTAB) and sodium lauryl sulphate (NaLS) was studied by (i) a spectral method at 25°C and (ii) a conductance method at different temperatures. It was observed that the critical micellar concentration (c.m.c.) is temperature dependent. The c.m.c. is found to increase with increase in mole fraction of acetonitrile and THF in aqueous solution. The increase in c.m.c. is more marked with CTAB than with NaLS in the same solvent and the c.m.c. change is greater in THF than in acetonitrile. The increase in the c.m.c. is discussed on the basis of water structure and hydrophobic interaction. The thermodynamics of micellization are also discussed.

Organization of amphiphiles. Part XI: Physico-chemical aspects of mixed micellization involving normal conventional surfactant and a non-ionic gemini surfactant

A systematic study on the behaviour of mixtures of p-phenylenediamine-tertiarybutyloxy-carbonyl-bis-glycamide (BAM) with ionic hexadecyl-trimethyl-ammonium bromide (CTAB), and sodium salt of dodecyl sulphate (SDS), and non-ionic surfactant (TritonX-100) in solution has been investigated through different physico-chemical measurements. The mixtures of BAM (0.0194 mM) with various amount of CTAB/SDS/TritonX-100 have been analyzed through absorbance, conductivity, surface tension and zeta potential measurements. The mixed system is found to be more surface active than the individual surfactants, the synergistic interaction being more prominent in system involving ionic surfactants compared to that of non-ionic surfactant. The mixed micellization behaviour is evidenced from the appearance/disappearance of the excimer of the fluorescent probe, maximum adsorption density at the interface, aggregation numbers of the surfactant mixtures and the surface charge of the conventional surfactants. A suitable interaction model, elucidating the organizational hierarchy of gemini-conventional surfactant at the micelle-water and air-water interface has been proposed.

Organization of amphiphiles: V. In situ fluorescence probing of the adsorbed layers of polyoxyethylated alkyl phenols at silica–water interfaces

The sensitivity of the pyrene monomer emission spectrum to the polarity of a medium has been exploited to probe the adsorbed layer of a series of polyoxyethylated alkyl phenols on silica surface. Both the hydrophobicity and hydrophilicity of the surfactants are found to control the adsorption of the surfactants at the silica-water interface. In a series of surfactants having the same hydrophobic chain length but with different hydrophilic chain lengths, the presence of a smaller number of hydrophilic oxyethylene units leads to a conspicuous increase in adsorption density in the premicellar region compared to surfactants having a larger number of oxyethylene units. This has been attributed to the formation of small aggregates (hemimicelles) on the silica surface in the former. The formation of the aggregates gets support from the emission characteristics of pyrene. The number of surfactants constituting different aggregates has been determined.

Organization of amphiphiles: XII. Evidence in favor of formation of hydrophobic complexes in aqueous solution

The effects of nonionic surfactants OP-10 and OP-30 (polyoxyethylated octyl phenols with 10 and 30 oxyethylene groups, respectively) in surfactant mixtures with ionic surfactants hexadecyltrimethylammonium bromide (CTAB) and sodium dodecyl sulphate (SDS) have been investigated by a conductometric method in conjunction with fluorescence, surface tension, zeta potential, and DLS measurements. The interactions are found to be antagonistic in nature for each of the systems; i.e., micellization of CTAB as well as SDS is hindered on addition of the nonionic surfactants. The antagonism is found to be more prominent in the presence of OP-10 compared to that of OP-30. Two types of mechanistic paths, path A operating below the critical micellar concentration and path B operating beyond the critical micellar concentration of nonionic surfactants, have been suggested. In path A, the retardation in micellization has been attributed to a decrease in monomeric concentration of the ionic surfactants from solution as a result of the formation of a hydrophobic complex between nonionic and ionic surfactants. In path B, the decrease in monomer concentration is due to the solubilization of the ionic surfactant in micelles of the nonionic surfactants in a 1:1 stoichiometric ratio. A theoretical treatment to the interaction in each ionic-nonionic pair yields a positive value of the interaction parameter supporting the concept of antagonism. The formation of the hydrophobic complex is supported by fluorescence and surface tension measurements. A schematic representation of the stabilization of these hydrophobic complexes has been suggested. The association of ionic surfactants by nonionic micelles is suggested by zeta potential and DLS studies.

Organization of amphiphiles Part X: Studies on the interaction between polyoxyethylated (30) octylphenol and cetyltrimethylammonium bromide in aqueous solution.

The solution behavior of the mixture of cetyltrimethylammonium bromide (CTAB) and polyoxyethylene (30) octylphenol (OP-30) has been investigated by measuring the conductance, fluorescence intensity, surface tension and absorbance of the surfactant mixtures. A strong interaction between the two surfactants is indicated from each of the measurements. The critical micelle concentration of CTAB is found to increase with increase in the amount of OP-30 in the mixture. This delaying in micellization of CTAB has been attributed to the diminution of its effective hydrophobicity due to interaction with monomers or micelles of OP-30. Below CMC of OP-30, the monomeric concentration of CTAB decreases due to the formation of a hydrophobic complex between OP-30 and CTAB. Above CMC of OP-30, CTAB monomers get solubilized into micellar core of OP-30 in 1:1 stoichiometric ratio. Micropolarity and the aggregation numbers of the mixed systems have been determined from fluorescence studies. The thermodynamics of micelle formation of CTAB coupled with fluorescence studies of the mixtures indicates that the complex grows in size with increase of OP-30 concentration till the micelle of latter is formed at higher concentrations. The treatment of theoretical model to the interaction of OP-30 and CTAB yields a positive interaction parameter showing antagonism behavior. A schematic model of interaction of OP-30 with CTAB below and above its CMC has been suggested.

Fluorescence Probing of the Surfactant Assemblies in Solutions and at Solid-Liquid Interfaces

Surfactant assemblies such as micelles, reverse micelles and solloids or hemimicelles, are fluctuatingand disordered assemblages of surfactants. These assemblies are formed when the concentration ofthe surfactants, in polar or nonpolar solvents exceeds a threshold value. Because of their vastapplications in both industrial and house-hold affairs, there has been considerable research on theformation and properties of surfactant assemblies in solution and at solid–liquid interfaces.Despite many studies of these organized assemblies using X-ray, NMR, light scattering, conductivityand calorimetry, information on their nanostructures, particularly at solid–liquid interfacesis still very limited. In this article, we review the application of fluorescence techniques to investigateaggregate characteristics such as size, micropolarity, nanoviscosity and aggregation number.

Preparation of Biodiesel Using Ultrasonication Energy and its Performance in CI Engine

Fatty acid methyl ester (FAME), a renewable liquid biofuel popularly known as biodiesel, is emerging as a suitable replacement to common diesel fuel (CDF) in unmodified Compression Ignition (CI) engine. Present article reports the development of a process to reduce the operating cost during the conversion of vegetable oil to biodiesel through the application of ultrasound energy. Around 98% yield of FAME could be achieved with low reaction parameters such as methanol-oil molar ratio, catalyst concentration, reaction time, and temperature. The optimum condition for the maximum 98% yield was 1.0 wt% of NaOH catalyst, 5:1 methanol: oil molar ratio and temperature 55°C under a sonication frequency of 20 kHz. With these reaction parameters the conversion occurred in just 5 minutes. The FAME obtained was purified in an effective way by water washing followed by passing over a bed of silica gel. The purified FAME was subjected to the evaluation of its fuel characteristics in a four-stroke, single-cylinder CI engine, which could operate with variable compression ratio. The engine performance study revealed that lower blends of biodiesel up to B20 could be an efficient fuel for an unmodified CI engine.

Organization of Amphiphiles, Part VII: Effect of Variation of Composition and Salt on the Phase Behavior of Some Ethoxylated Surfactants

The effect of variation in composition of the emulsifier and presence of salt on the phase and clouding behavior of a pseudo‐ternary system of the type H2O‐oil‐emulsifier has been investigated at 300±1 K. The emulsifier constitutes polyoxyethylated alkyl phenol/polyoxyethylated alkyl ethers and isobutanol in different mole ratios. Large numbers of domains are observed when composition of surfactant and cosurfactant in emulsifier is varied. Appearance of these domains in the phase diagram has been attributed to the formation of different type of organized assemblies. The electrical conductivity of BL‐9‐isobutanol(1∶1)‐hexane‐2% brine versus various compositions of the emulsifier is found to increase slowly with the addition of water, followed by rapid increase to a plateau leading to a sigmoidal plot. This significant change in electrical conductivity for small change in weight fraction of water is attributed to the percolation transition. The three arms of the electrical conductivity plot are suggested due to W/O to O/W microemulsion transition through bicontinuous structure, and the bicontinuous phase area is delineated. The ordering of water molecule around surfactant molecules has been arrived at through electrical conductivity and cloud point measurements.

Comprehensive Understanding of the Kinetics and Mechanism of Fluoride Removal over a Potent Nanocrystalline Hydroxyapatite Surface

Hydroxyapatite (HAp) was successfully synthesized from egg shells, a low cost and easily available biodegradable waste, by the precipitation method and characterized by X-ray diffraction (XRD), scanning electron microscopy, Fourier transform infrared, and Brunauer–Emmett–Teller (BET) surface area analysis. The surface area of HAp was found to be 144 m2/g with a crystalline size of 9–99 nm from the BET and XRD data. The maximum fluoride removal efficiency within 1 h using 0.3 g of the synthesized adsorbent at pH 6 was 95%. The adsorption of fluoride followed second-order kinetics, indicating that chemisorptions are the rate-limiting step. The experimental data were well fitted with Langmuir and Freundlich isotherms, validating both monolayer and multilayer sorption during the fluoride adsorption onto the porous HAp. The positive adsorption of F– ions at the HAp interface can be attributed to ion exchange/ion pairing and H-bonding below the pHpzc of HAp (pHpzc = 8), and the negative adsorption can be attributed to the electrostatic repulsion between O– and F– ions at alkaline pH. Both physical and chemical adsorption phenomena were also evidenced from the molecular parking area data. The results of a batch experiment show that the HAp synthesized from egg shells can be used as an effective, low-cost adsorbent for fluoride removal from a contaminated aqueous solution as well as groundwater compared to other adsorbents.

Studies on Extraction of Potassium from Feldspar by Roast-leach Method Using Phosphogypsum and Sodium Chloride

ABSTRACT The extractions of potassium value from feldspar via roasting and leaching route was studied with a focus on the effects of the roasting time, temperature, additives, and particle size. Sodium chloride and phosphogypsum (PG) were used as a source of chloride and calcium, respectively, and played the important role during the roasting of feldspar. When the feldspar sample was roasted at 900°C with sodium chloride alone, the extraction of potassium was limited to 61%. The extraction could go up to 92.5% by the addition of phosphogypsum along with sodium chloride. The optimum conditions of potassium extraction were found to be, particle size 100 µm, roasting temperature 900°C and roasting time of one hour. The X-ray diffraction study indicated the formation of sylvite (KCl) in the roasted product and its disappearance in roast-leach residue due to its high water solubility. The morphological changes during the roasting process were clearly observed by field emission scanning electron microscope (FESEM) images. The extraction of potassium from feldspar was best fitted by the Ginstling and Brounshtein kinetic model. The activation energy of 238.6 KJ/mole and 28.73 KJ/mole for low and high-temperature regions indicated that the overall extraction process follows two-steps reaction path.