Swelling Porosity Research Articles

Bile salts adsorption on dextran-based hydrogels

Dextran-based gels bearing two types of pendant N, N-dimethyl-N-alkyl-N-(2-hydroxypropyl) ammonium chloride groups with different alkyl chain length substituents (C2 and C12/C16, respectively) at the quaternary nitrogen were synthesized and structural characteristics of the compounds were studied by elemental analysis, potentiometric titration, FTIR and NMR spectroscopy. The morphology and size of polymeric microspheres were examined by SEM and their swelling behavior in water was also investigated. The hydrogels were evaluated as sorbents for sodium cholate (NaCA) and sodium deoxycholate (NaDCA) in water and 10 mM NaCl solutions. Different isotherm models (nearest-neighbor-interaction, Langmuir, Freundlich, Dubinin-Raduskevich, Sips and Hill) were used to elucidate the adsorption mechanism and established the characteristics of the most efficient polymeric sorbent. The maximum adsorption capacity of the gels was highly controlled by gel hydrophobicity which enhanced gel-bile salt affinity but decreased binding cooperativity. Swelling porosity, ionic strength and ligand lipophilicity were other factors that also affected the adsorption process. The hydrogel having 25 mol% pendant dodecyl groups retained the maximum amount of bile salts (1051 mg NaCA/g and 1138 mg NaDCA/g). All hydrophobically modified hydrogels revealed a better affinity and strength of binding compared to commercial Cholestyramine®.

Porosity evolution study in irradiated UO2 fuel based on fuel matrix swelling

Abstract The volume porosity of irradiated UO2 fuel in the form of a correlation is developed which includes two individual parts as the pore and swelling porosity in terms of the local density and fractional matrix swelling. Based on a low temperature swelling model for UO2 fuel, the matrix swelling terms are calculated and the evolution of porosity up to burn-up levels of 120 MWd/KgU is presented. It is seen that for high burn-up PWR fuel pellet rim, the dominant contribution to total porosity comes from pores generated due to Xe depletion in the ceramic matrix while the nearly constant swelling porosity makes a small contribution to the total porosity. The porosity evolution is also validated by comparing against experimental data and a fairly good agreement was found.

Towards understanding the microstructural and structural changes in natural hierarchical materials for energy recovery: In-operando multi-scale X-ray scattering characterization of Na- and Ca-montmorillonite on heating to 1150 °C

Understanding the changes in the microstructures and structures of clays with varying intercalated metal ions at elevated temperatures is of importance for many applications ranging from the recovery of shale gas from unconventional formations to developing effective nuclear waste containment technologies, and engineering materials such as ceramics for fuel cell applications. In this study, synchrotron-based in-operando multi-scale X-ray scattering analyses are used to determine dynamic microstructural and crystal structural changes in Na- and Ca-montmorillonite on heating from 30°C to 1150°C. Larger cations such as Ca2+ confer more defined morphological regimes compared to Na+ ions in compacted clays, as evident from the ultra-small-angle X-ray scattering results. The hierarchical morphology of clays is characterized to distinguish between nano-scale interlayer swelling porosity, meso-scale porosity, and intergranular pore spaces between powdered clay grains. On heating from ambient temperature to 200°C, the removal of interlayer water reduced the basal distances to 9.6Å. On further heating to 800°C, gradual dehydroxylation of the clay sheets is evident from the structural changes. The effects of sintering at temperatures greater than 800°C are evident from significant reductions in the intrinsic porosities of the clay sheets, and the formation of newer phases such as mullite. By connecting the in-operando microstructural and structural changes across spatial scales ranging from micrometers to Angstroms, the possibility of engineering high temperature processes for achieving morphologies and chemical compositions of interest is presented.

Aminated polysaccharides as bile acid sorbents: in vitro study

Dextran, pullulan, and microcrystalline cellulose were cross-linked with 1-chloro-2,3-epoxypropane and reacted with N-(1-chloroethyl)-N,N-diethylamine or N-glycidyl-N,N,N-trialkylammonium chloride in order to obtain sorbents containing tertiary amino and/or quaternary ammonium groups. In vitro equilibrium sorption of cholic acid on these sorbents was studied in comparison with Cholestyramine®, and in vitro dissociation of ionic complexes of cholic acid-sorbents was determined under dynamic conditions. The sorption capacity and the affinity of these sorbents for cholic acid were investigated in relation to the nature of the polymeric support, the swelling porosity of sorbent, the basicity of amino groups, and the nature of the substituents at the nitrogen atom. The maximum sorption capacity increases with the increase in amino group content, their basicity, and the length of alkyl substituents at the nitrogen atom. The affinity for cholic acid of all polysaccharide-based sorbents is higher than that of Cholestyramine®. Dextran-based sorbents display the highest sorption affinity. It was found that there exists an optimum swelling porosity for the polysaccharide sorbents to attain the highest affinity for cholic acid. The dissociation rate of ionic complexes depends also on the nature of the polysaccharide and the swelling porosity and its lower for sorbents with higher sorption affinity.

Porosity swelling and transmutation contributions to conductivity changes in some neutron-irradiated copper alloys

Fast-neutron irradiation of alloys for fusion-reactor applications produces bulk changes in the density and composition via porosity swelling and transmutation which affect the do volume electrical and thermal conductivities ( σ = 1/ ϱ e and K ). For the Cu materials of our study, neutron fluences of 2 × 10 26 n/m 2 ( E > 0.1 MeV) produced increases in Ni and Zn concentrations of about 0.05 and 0.09 wt%, respectively, and porosity swelling of 0–7%; ϱ e accordingly increased as much as 18%. We also determined the individual ϱ e changes due to both swelling and transmutation via use of an appropriate mixing rule and of Matthiessen's law to unmask any residual effects present, e.g., phase or microstructural changes. For four materials — two pure copper and two alumina-dispersion-strengthened (ADS) alloys — subtraction of these δϱ e 's from the irradiated values yielded or nearly yielded the respective control values. In contrast, the two precipitation-strengthened (PS) alloys studied, MZC and AMZIRC, had relatively large negative residues, apparently indicating effective radiation-induced conductivities.