2,970 research outputs found
The encapsulation of hydrophobic drugs in Pluronic F127 micelles: the effects of drug hydrophobicity, solution temperature and pH
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.Comment: 23 pages, includes 8 figure
Formation and Rupture of Ca Induced Pectin Biopolymer Gels
When calcium salts are added to an aqueous solution of polysaccharide pectin,
ionic cross-links form between pectin chains, giving rise to a gel network in
dilute solution. In this work, dynamic light scattering (DLS) is employed to
study the microscopic dynamics of the fractal aggregates (flocs) that
constitute the gels, while rheological measurements are performed to study the
process of gel rupture. As calcium salt concentration is increased, DLS
experiments reveal that the polydispersities of the flocs increase
simultaneously with the characteristic relaxation times of the gel network.
Above a critical salt concentration, the flocs become interlinked to form a
reaction-limited fractal gel network. Rheological studies demonstrate that the
limits of the linear rheological response and the critical stresses required to
rupture these networks both decrease with increase in salt concentration. These
features indicate that the ion-mediated pectin gels studied here lie in a
`strong link' regime that is characterised by inter-floc links that are
stronger than intra-floc links. A scaling analysis of the experimental data
presented here demonstrates that the elasticities of the individual fractal
flocs exhibit power-law dependences on the added salt concentration. We
conclude that when pectin and salt concentrations are both increased, the
number of fractal flocs of pectin increases simultaneously with the density of
crosslinks, giving rise to very large values of the bulk elastic modulus.Comment: 21 pages, 8 figure
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