ABSTRACT
Micellization behavior of oppositely charged gemini surfactants (anionic surfactant; phosphoric acid, P,P'-1,4-butanedieyl, P,P'-didodecylester, disodium salt (12-4-12A), and cationic surfactant; butanediyl-1,4, bis (N,N-hexadecyl ammonium) dibromide (16-4-16) or (D-isosorbate-1,4-diyl bis(N,N-dimethyl-N-hexadecylammonium acetoxy) dichloride (16-Isb-16)) has been studied (individually or of a gemini mixture) by conductivity and surface tension measurements. Critical micelle concentration (CMC) data show both synergistic (for 12-4-12A + 16-Isb-16) and antagonistic (for 12-4-12A + 16-4-16) interactions between the two components. Small angle neutron scattering (SANS) measurement shows formation of various aggregates, spherical (or ellipsoidal), rod-shaped, and vesicular, by changing the mole fraction (at fixed total surfactant concentration, 10 mM). Viscosity, zeta (ζ)-potential, and transmission electron microscopy (TEM) data are found in conformity of SANS results. Surprisingly, two morphologies (vesicles and rod-shaped micelles) show stability in a wide temperature range (303-343 K). The behavior has been explained on the basis of temperature induced dehydration and depletion of micellar charge. Aqueous gemini mixtures, of different morphologies, have been used for the determination of solubilization efficacy (using UV-visible spectrophotometer) toward polycyclic aromatic hydrocarbons (PAHs: anthracene; pyrene or fluorene). Molar solubilization ratio (MSR) data suggest that vesicles enhance the solubilization efficacy. SANS analysis shows that vesicle bilayer thickness increases upon PAH solubilization. The order of bilayer thickness increase is found to be anthracene > pyrene > fluorene, which is in the same order as the aqueous solubility of PAHs. This is the first report which correlates morphology to the solubilization efficacy.
ABSTRACT
Clouding phenomenon in ionic surfactant solution is fairly a new addition to the conventional phenomenon observed with nonionic counterpart. Various scattering and spectroscopic techniques, dynamic light scattering (DLS), small angle neutron scattering (SANS), and nuclear magnetic resonance (NMR), have been used to draw information regarding the aggregate morphologies (formed by an ionic surfactant, tetra-n-butylammonium dodecylsulphate, TBADS) when the surfactant solution passes through the cloud point (CP). DLS measurements have shown that two morphologies are present when the system approaches the CP. The data revealed that individual micelles (~5 nm) convert to giant aggregates (~500 nm) over the range of temperature including the CP. SANS experiments have been performed to draw the information regarding individual micellar fraction below and above the CP. NMR spectra at different temperatures have been collected for TBADS solution. The broadening and the downfield shift of -N-CH(2) and -O-CH(2) proton peaks support the micellar growth as the sample was heated. The above peaks show splitting (into two each) confirming the presence of two morphologies around the CP. It is noted that conversion of only a small fraction of individual micelles is responsible for the clouding.
ABSTRACT
Silver nanoparticles were prepared by a simple hydrothermal route and chemical reduction using carbohydrates (sucrose, soluble and waxy corn starch) as reducing as well as stabilizing agents. The crystallite size of these nanoparticles was evaluated from X-ray diffraction (XRD) and transmission electron microscopy (TEM) and was found to be 25nm. The effect of carbohydrates on the morphology of the silver nanocomposites was studied using scanning EM (SEM). The nanocomposites exhibited interesting inhibitory as well as bactericidal activity against both Gram positive and Gram negative bacteria. Incorporation of silver also increased the thermal stability of the carbohydrates.
