Controlled synthesis of core-shell iron-silica nanoparticles and their magneto-dielectric properties in polymer composites.

Low loss core-shell iron-silica nanocomposites with improved magneto-dielectric properties at radio frequencies (1 MHz-1 GHz) were successfully fabricated. A new simple method was developed to synthesize metallic iron (Fe) nanoparticles with uniform size distribution in an aqueous environment at room temperature. Citric acid and oleic acid served as surface-capping agents to control the particle size of the synthesized Fe nanoparticles. Smaller Fe nanoparticles with narrower particle size distribution were obtained as the concentration ratio of iron ions to carboxylic acid groups decreased. The Fe nanoparticles were subsequently coated with silica (SiO(2)) layers to prevent the iron cores oxidizing. Polymer composites were prepared by incorporating Fe@SiO(2) nanoparticles with polydimethylsiloxane (PDMS) elastomers. Experimental results showed that the dielectric permittivity (ε) and magnetic permeability (µ) of the polymer composite increased with increasing amount of Fe@SiO(2) nanoparticle doping. The dielectric loss (tanδ) was near 0.020 at a frequency of 1 GHz.

Molecularly imprinted polymer hydrogels displaying isomerically resolved glucose binding.

Non-covalent molecular imprinting of poly(allylamine hydrochloride) (PAA HCl) with glucose phosphate mono-sodium salt produced molecularly imprinted polymer (MIP) hydrogels capable of quantitative, isomerically specific binding of glucose. By ionic association of a template molecule, glucose phosphate mono-sodium salt, to the polymer prior to covalent crosslinking, MIP hydrogels were created with an affinity for binding glucose. In this study we have synthesized MIPs using epichlorohydrin, ethylene glucol diglycidyl ether, and glycerol diglycidyl ether as crosslinkers in order to evaluate their effectiveness with respect to molecular imprinting for glucose. MIP hydrogels were also synthesized with the different crosslinkers and varying amounts of the template molecule in an attempt to elucidate the impact of imprint quantities on the effectiveness of the imprinting technique. Batch equilibration studies, using each of the MIPs and similar non-molecularly imprinted polymers were performed to determine their binding capacities with respect to glucose and fructose. The binding capacity data are discussed and employed in the evaluation of the specificity imparted by the imprinting procedure. MIP hydrogels with binding capacities in excess of 0.5 g of glucose per gram of dried gel were synthesized. Isomeric specificity in hydrogels imprinted for glucose was demonstrated by higher binding capacities of glucose than those of fructose in the same polymers.

Development of methods for quantitative characterization of network morphology in pharmaceutical hydrogels.

We have employed a variety of methods which satisfactorily characterize the structure of polymeric hydrogels beyond the level of information provided by a single swelling test. We applied these techniques to gels which have potential for use as pharmaceuticals for the control of elevated phosphorous levels in patients suffering from chronic kidney failure. These 'fingerprinting' techniques help us understand the effects of various processing parameters on the gel morphology. Wide-angle X-ray diffraction experiments verified the structure and reproducibility across synthesized hydrogel batches. Measurements of the temperature- and frequency-dependent dielectric relaxation provided information on the network topology. Real-time diffusion experiments were performed using inductively coupled plasma atomic emission spectroscopy. Spherical gel particles (510 microns diameter) were used to measure equilibrium phosphate loadings of 4.5 mmoles g-1 from direct measurement of the decrease in phosphate ion concentration in aqueous solutions.

Hydrogels prepared by electron irradiation of poly(ethylene oxide) in water solution: unexpected dependence of cross-link density and protein diffusion coefficients on initial PEO molecular weight.

Under ionizing radiation aqueous solutions of water-soluble polymers become cross-linked and form hydrogels, primarily by radiolysis of water-generating hydroxyl radicals which attack the polymer chains. The chain radicals thus formed create cross-links by coupling. In particular, hydrogels formed from poly(ethylene oxide) are of interest for biomedical applications, including those in which it is necessary to transport large molecules such as growth factors, in addition to nutrients, to cells attached to the surface. We sought a rapid and simple method for estimating diffusion coefficients by observing the diffusion of two red-coloured proteins: cytochrome C and hemoglobin of respective molecular weights 12,000 and 67,000. In the course of this we discovered a previously unreported effect of the primary molecular weight of the polymer, before cross-linking, on the cross-link density finally achieved and on the diffusion coefficient of the proteins.