Dielectric approach to polystyrene microcapsule analysis and the application to the capsule permeability to potassium chloride

Dielectric Analysis of Microcapsule-Immobilized Composite Capsules Suspension: Substances Release

Dielectric spectroscopy has unique advantages in monitoring drug release. In this work, a dielectric measurement was carried out on the release of the substances of microcapsule-immobilized composite capsules, which were fabricated by encapsulating the Perinereis aibuhitensis extract-loaded gum Arabic/gelatin microcapsules (PaE: GA/GE-MCs) in calcium alginate hydrogel (PaE: CA/GA/GE-CCs). We established the dielectric model of PaE: CA/GA/GE-CCs and got in-depth information on the systems. There are two relaxations in the dielectric spectroscopy, both of which are caused by interfacial polarization. The relaxation mechanisms correspond to the interfacial polarization of the PaE-loading core/calcium alginate shell interface and the calcium alginate shell/solution interface, respectively. Besides, the swelling of composite capsules and substance migration in the composite capsules were observed by analyzing phase parameters. Finally, the characteristic release of calcium alginate composite capsules was confirmed, and the substance release mechanism of composite capsules, namely, the swelling-diffusion mechanism, was obtained.

Nontronite and intercalated nontronite as effective and cheap absorbers of electromagnetic radiation

The paper presents the thermal, structural and dielectric properties of natural nontronite and nontronite intercalated with DMSO, ethylene glycol and formamide. These materials were tested for the electromagnetic wave absorption ability. It was shown that nontronite and its intercalates were better absorbers than the materials previously obtained from kaolinite and halloysite.

Accurate determination of the dielectric parameters of spherical shells in suspension

A novel, self-consistent, algebraic method is developed within the framework of Maxwell-Wagner theory (i.e., 'mixture formula' and single shell model) for obtaining the dielectric parameters, such as epsilon(s), kappa(s) and f(Q) of spherical shells. The efficacy of the procedure that-in contrast to previous ones-is void of any approximations, was successfully tested by reanalyzing existing data on polystyrene microcapsules.

Dielectric analysis of a nanoscale particle in an aqueous solution of low electrolyte concentration

The dielectric spectra of aqueous suspensions of nanoscale silica particles (8 and 24 nm) with low electrolyte concentrations were investigated as a function of the particle concentration. Obvious dispersions observed in the frequency range of 10-10(5) kHz are explained by the multiple effects of the interfacial polarization and the polarization of counterions by using a two-step model and the corresponding dielectric analytical method arising from the combination of Hanai's method and O'Konski's theory. The phase parameters, which reflect the inner properties of constituent phases of the system, are calculated and discussed in detail. The validity of the two-step model was tested in terms of the standard electrokinetic model deduced from pure theories.

Dielectric relaxation spectroscopy and some applications in the pharmaceutical sciences

With a few exceptions, dielectric relaxation spectroscopy (DRS) has been largely neglected by pharmaceutical scientists, despite the potential for this technique as a noninvasive and rapid method for the structural characterization and quality control of pharmaceutical materials. DRS determines both the magnitude and time dependency of electrical polarization (i.e. the separation of localized charge distributions) by either measuring the ability of the material to pass alternating current (frequency domain DRS) or by investigating the current that flows on application of a step voltage (time domain DRS). DRS is thus (i) sensitive to molecular mobility and structure, (ii) non-invasive, and (iii) employs only mild stresses (a weak electromagnetic field) in order to measure the sample properties. The technique covers a broad-band frequency window (from 10(-5) to 10(11) Hz) and therefore enables the investigation of a diverse range of processes, from slow and hindered macromolecular vibrations and restricted charge transfer processes (such as proton conductivity in nearly dry systems) to the relatively fast reorientations of small molecules or side chain groups. The dielectric response provides information on (i) structural characteristics of polymers, gels, proteins, and emulsions, (ii) the interfacial properties of molecular films, (iii) membrane properties, (iv) water content and states of water (and the effects of water as a plasticizer), and (v) lyophilization of biomolecules. This review article details the basis of dielectric theory and the principles of measuring dielectric properties (including a comprehensive account of measurement artifacts), and gives some applications of DRS to the pharmaceutical sciences.