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Encapsulation of hydrophobic drugs in Pluronic F127 micelles: effects of drug hydrophobicity, solution temperature, and pH.
No full textRestricted Access.Three drugs, ibuprofen, aspirin, and erythromycin, are encapsulated in spherical Pluronic F127 micelles. The shapes and the size distributions of the micelles in dilute, aqueous solutions, with and without drugs, are ascertained using cryo-scanning electron microscopy and dynamic light scattering (DLS) experiments, respectively. Uptake of drugs above a threshold concentration is seen to reduce the critical micellization temperature of the solution. The mean hydrodynamic radii and polydispersities of the micelles are found to increase with decrease in temperature and in the presence of drug molecules. The hydration of the micellar core at lower temperatures is verified using fluorescence measurements. Increasing solution pH leads to the ionization of the drugs incorporated in the micellar cores. This causes rupture of the micelles and release of the drugs into the solution at the highest solution pH value of 11.36 investigated here and is studied using DLS and fluorescence spectrocopy
Synthesis and characterization of liquid crystalline azobenzene chromophores with fluorobenzene terminal
No full textRestricted Access.Two series of fluorine-substituted benzoate ester type rod-shaped liquid crystals incorporating the azobenzene as side arm linked with terminal double bonds as polymerizable functional groups were synthesized and characterized by polarized-light optical microscopy (POM), differential scanning calorimetry (DSC) and UV–visible spectroscopy investigations. Thus, rod-shaped monomers, namely 4a and 4b having odd and even number of carbon in the terminal group exhibited nematic phase and SmA type phase was found at lower temperature. Compound 5 showed nematic phase whereas compound 6 showed SmA phase. These rod-shaped molecules exhibit strong photoisomerization behaviour in solution. The photoswitching properties of the compounds showed trans to cis isomerization in about 10 s, whereas the reverse process takes place about 120 min in solutions. Proposed materials may have potential to use it in optical storage device
The Murchison widefield array: solar science with the low frequency SKA Precursor
No full textOpen Access. Proceedings of the conference Eclipse on the Coral Sea: Cycle 24 Ascending (GONG 2012, LWS/SDO-5, and SOHO 27)
12–16 November 2012, Palm Cove, Queensland, AustraliaThe Murchison Widefield Array is a low frequency (80 - 300 MHz) SKA Precursor, comprising 128 aperture array elements (known as tiles) distributed over an area of 3 km diameter. The MWA is located at the extraordinarily radio quiet Murchison Radioastronomy Observatory in the mid-west of Western Australia, the selected home for the Phase 1 and Phase 2 SKA low frequency arrays. The MWA science goals include: 1) detection of fluctuations in the brightness temperature of the diffuse redshifted 21 cm line of neutral hydrogen from the epoch of reionisation; 2) studies of Galactic and extragalactic processes based on deep, confusion-limited surveys of the full sky visible to the array; 3) time domain astrophysics through exploration of the variable radio sky; and 4) solar imaging and characterisation of the heliosphere and ionosphere via propagation effects on background radio source emission. This paper concentrates on the capabilities of the MWA for solar science and summarises some of the solar science results to date, in advance of the initial operation of the final instrument in 2013
Non-hydrothermal synthesis and optical limiting properties of one-dimensional Se/C, Te/C and Se–Te/C core–shell nanostructures
No full textRestricted Access.A single step, nontoxic, non-hydrothermal, low temperature and reproducible method for the preparation of carbon-coated selenium and tellurium nanowires (Se/C and Te/C, respectively), and selenium–telluride (Se–Te/C) nanorods, is presented. Sodium dodecyl sulfate is used as the surfactant, and glucose is employed as the reducing and carbonizing agent. Uncoated nanowires of trigonal Se and Te without the carbon shell are obtained as products, at lower glucose concentrations, whereas at higher glucose concentrations carbon-coated nanowires of trigonal Se and Te are formed. Structural, morphological and compositional properties of the prepared products are examined using X-ray diffraction, scanning electron microscopy, high resolution transmission electron microscopy, and energy dispersive X-ray spectroscopy, respectively. The formation of amorphous carbon shell and the model depicting the growth of core–shell nanowires and nanorods are discussed on the basis of the experimental results. Nonlinear optical transmission of the samples is studied at 532 nm using the open-aperture Z-scan technique employing 5 ns laser pulses. Results show that the samples are efficient optical limiters, and that a three-to-four-fold enhancement in the value of the effective two-photon absorption coefficient (β) can be achieved by coating the nanowires and nanorods with carbon
Reversible shear-induced crystallization above equilibrium freezing temperature in a lyotropic surfactant system
No full textOpen AccessWe demonstrate a unique shear-induced crystallization phenomenon above the equilibrium freezing temperature Graphic in weakly swollen isotropic Graphic and lamellar Graphic mesophases with bilayers formed in a cationic-anionic mixed surfactant system. Synchrotron rheological X-ray diffraction study reveals the crystallization transition to be reversible under shear (i.e., on stopping the shear, the nonequilibrium crystalline phase Graphic melts back to the equilibrium mesophase). This is different from the shear-driven crystallization below Graphic, which is irreversible. Rheological optical observations show that the growth of the crystalline phase occurs through a preordering of the Graphic phase to an Graphic phase induced by shear flow, before the nucleation of the Graphic phase. Shear diagram of the Graphic phase constructed in the parameter space of shear rate Graphic vs. temperature exhibits Graphic and Graphic transitions above the equilibrium crystallization temperature Graphic, in addition to the irreversible shear-driven nucleation of Graphic in the Graphic phase below Graphic. In addition to revealing a unique class of nonequilibrium phase transition, the present study urges a unique approach toward understanding shear-induced phenomena in concentrated mesophases of mixed amphiphilic systems
