Encapsulation of Hydrophobic Drugs in Pluronic F127 Micelles: 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

Use of Ultrasound Attenuation Spectroscopy to Determine the Size Distribution of Clay Tactoids in Aqueous Suspensions

The dispersion processes of aqueous samples of clay are studied using ultrasound attenuation spectroscopy. The attenuation spectra that are acquired in the frequency range 10–100 MHz are used to determine the particle size distributions (PSDs) for different concentrations and ages of the clay suspensions. Our analysis, using equivalent spherical diameter (ESD) for circular discs under Stokes drag in samples of concentrations greater than 1.5% w/v, shows that a substantial fraction of the aggregates in suspension are actually tactoids that are composed of more than one platelet. This is in contrast to the general belief that clay disperses into individual platelets in the concentration range where their suspensions exhibit glassy behavior. We conclude that the incomplete fragmentation of the clay tactoids arises from the rapid enhancement of the intertactoid Coulombic repulsion

Dynamic Light Scattering Study and DLVO Analysis of Physicochemical Interactions in Colloidal Suspensions of Charged Disks

The interparticle interactions in colloidal suspensions of charged disks of Laponite clay in water were investigated using dynamic light scattering (DLS) and Derjaguin–Landau–Verwey–Overbeek (DLVO) theory. We studied the effects of clay concentration (<i>C</i>_L), the concentration of externally added salt (<i>C</i>_S), and temperature (<i>T</i>) on the microscopic dynamics of the clay suspensions. The fast (τ₁) and mean slow relaxation times (⟨τ_ww⟩) of Laponite suspensions were extracted from intensity autocorrelation functions measured at different waiting times (<i>t</i>_w) after sample preparation. Comprehensive Laponite concentration–salt concentration–temperature–time superpositions of both the microscopic diffusive time scales and the stretching exponent corresponding to the slow relaxation process highlight the self-similar nature of the energy landscapes of the Laponite suspensions. The evolution of the sodium ion concentration in the aging suspension with <i>t</i>_w, measured for several values of <i>C</i>_L, <i>C</i>_S, and <i>T</i>, was used in a DLVO analysis of the free energy of the suspension for two charged disks parallely approaching one another. This analysis confirms that, in addition to repulsive interparticle interactions, attractive interactions also play a pivotal role in the microscopic dynamics of spontaneously evolving Laponite suspensions