Radiolytically-induced novel materials and their application to waste processing

In the present NEER project we investigated two different types of gel materials with respect to potential applications in environmental remediation, including mixed waste generated from the nuclear fuel cycles. The materials under study were: (1) silica-polymer based aerogel composites into which specific metallic cations diffuse into and remain, and (2) polymer gels made of thermo-sensitive polymer networks, whose functional groups can be ''tailored'' to have a preferred affinity for specific cations, again diffusing into and remaining in the network under a volumetrically, contractive phase-transition. The molecular, diffusion of specific cations, including those of concern in low-level waste streams, into the gel materials studied here indicates that a scaled, engineered system can be designed so that it is passive; that is, minimal (human) intervention and risk would be involved in encapsulating LLW species. In addition, the gel materials hold potential significance in environmental remediation of and recovery of metallic cations identified in respective domains and physico-chemical processes. In brief, silica gels start as aqueous/liquid solutions of base catalyzed silica hydrogels and metal ions (targeted species), such as silver. The metal ions are reduced radiolytically and migrate through the solution to form clusters. Upon post-irradiation processing, aerogel monoliths, extremely lightweight but mechanically strong, that encapsulate the metals are produced. Interestingly the radiolytic or photonic source can be gamma-rays and/or other rays from ''artificial sources'', such as reactors, or ''inherent sources'' like those characterizing mixed waste. Polymer gels, in contrast exhibit thermally-induced volumetric contraction at 20-50 C by expelling water from the gels physical state. Further, some functional groups that capture di- or tri-valent cations from aqueous solutions can be incorporated into the polymer networks on synthesis, including by radiolytic means. These polymer gels retain cations after volumetric contraction and have the ability to trap solid particulates in liquid waste streams. With both silica and polymer gels, functional design of a prototypic ''recovery'' systems, such as by natural convection in a rectangular cell, appears possible. Additional and specific details are provided in the rest of this Final Report

Proton Spin-Lattice Relaxation of Water Molecules in Ferrous-Ferric/Agarose Gel System

Proton spin-lattice relaxation time (T1) of water in aqueous solutions of ferrous and ferric ions and in the corresponding agarose gel systems have been studied in the light of NMR relaxation theory. The theoretical analysis of 1/T1\u27s has revealed that, at the microscopic level, changes in the solvation states of paramagnetic ions in aqueous or gel environment are greater than difference in the paramagnetism between ferric and ferrous ions. The former change is the primary factor for the exhibition of radiation effect. At the phenomenological level, we have confirmed and demonstrated that: (1) Radiation effect is almost exclusively exhibited through changes in 1/T1 caused by the interactions between water proton and ferrous or ferric ions; and (2) fraction of conversion of ferrous to ferric ions induced by radiation is the “true” representation of the spatial distribution of radiation dose

Temperature Dependence of Density of Polymer Gels: Effects of Ionizable Groups in Copoly(N-isopropylacrylamide/acrylic Acid Or Sodium Acrylate)-water Systems

Effects of ionizable groups in hydrogels of copolymer networks on the volumetric contraction-expansion process were investigated. Polymer networks used were: copoly[N-isopropylacrylamide (NIPA)(1 − x)/acrylic acid (HAc) or sodium acrylate (NaAc)(x)] with mole fraction of minor component (x) assuming 0.0114 and 0.0457. From the temperature (T) dependence of total volume of gels, densities of the polymer and solvent (water) components, and stoichiometry, we evaluated (1) the volume of gels occupied by a single mean polymeric residue and associated water molecules (expressed in units of nm3), mean vsp(gel), and (2) number of water molecules per single mean polymeric residue, mean Ns(gel), from near 273 K to 323 K. These quantities (1) and (2) listed above showed how acid and salt forms affect differently on volumetric changes of gels over 50 K. We developed an approach to evaluate volumetric changes of gels solely caused by a single polymeric residue of a minor component (x \u3c 0.05) plus associated water by applying thermodynamic first-order perturbation theory. They are specific vsp(gel)(T) for a single HAc or NaAc polymeric residue plus associated water and the corresponding specific Ns(gel)(T). Specific vsp(gel)(HAc or NaAc)(T) and the corresponding specific Ns(gel(T)) revealed specific characteristics in thermal behavior near their respective transition temperatures from the swollen to shrunken states. We found these thermal changes shown at the nano-scale match very well with specific changes in the molality(T) of both ionizable groups. In fact, these are directly triggered by varying contents of water in gels. Based on the understanding of dissociative equilibrium attained by ionizable groups, we successfully replaced Na+ in hydrogels of copoly[NIPA(1 − x)/NaAc(x)] (x = 0.0457) by hydrogen ions. Absence of Na+ in treated hydrogels was experimentally verified by 23Na NMR and Na atomic absorption flame photometry. Discontinuity in the volumetric contraction-expansion process from the swollen to shrunken states and vice versa was not observed in contradiction to the previous reports [Hirotsu S, Hirokawa Y, Tanaka T. J Chem Phys 1987;87:1392-5. Matsuo SE, Tanaka T. J Chem Phys 1988;89:1695-703.] obtained by the conventional swelling experiments

Nuclear Quadrupole Relaxation of Spin- 3/2

Nonexponentiality of the nuclear quadrupole relaxation of spin- 3 2 was carefully examined for the nonextreme narrowing case. Two decay constants for 7Li longitudinal relaxation in 11 M aqueous solution (D2O) of LiCI were determined. The ratio of two decay constants is interpreted on the basis of anisotropic reorientational motions of a hydration complex of lithium cation. © 1988

Effect of Intermolecular Interactions on the Anisotropic Rotational Motions of Molecules

2H and 14N spin-lattice relaxation times for the CD3CN and CDCl3 molecules in the CD3CN-CDCl3 liquid system have been determined at temperatures between 250 and 315 K. Analyses of these data led to the determination of rotational diffusion coefficients about the C3 symmetry axis (D∥) and around the axes perpendicular to the symmetry axis (D⊥). Anisotropy of the rotational motions (D∥/D⊥) of CD3CN increases upon addition of CDCl3 to CD3CN liquids and reaches maxima at the mole fraction of CDCl3[χ(CDCl3)] = 0.8. Slowing down of the rotational motions of CDCl3 is also observed, and reaches minima at χ(CDCl3) = 0.6-0.7

1. Temperature Dependence of Density of Polymer Gels: 2. Poly[N-(1,3-dioxolan-2-ylmethyl)-N-methyl-acrylamide] Networks -Water or -Alcohol System

Densities of the polymer and solvent components in gels made of poly[N-(1,3-dioxolan-2-ylmethyl)-N-methyl-acrylamide (DIOMMA)] networks and water, methanol or ethanol were determined from 5 °C to near bp of the respective solvents. From the densities, we have evaluated the following quantities at various temperatures (T): (1) the volume of gels [νsp(gel)] occupied by one single polymeric residue and its associated solvent molecules; (2) mass of solvent in gels per one polymeric residue; (3) the ratio of mass of polymer or solvent vs mass of gels; and (4) the number of solvent molecules per one polymeric residue (Nsp). The results in νsp(gel)(T) revealed the following: (A) νsp(gel) in the hydrogel decreased with increasing it up to 55 °C. This is essentially caused by a loss of water from the gel system. The increase in νsp(gel) beyond 55 °C is brought about by conformational changes in the polymer together with a further inclusion of solvents into gels. (B) Alcohol environments gave the thermally reversed trend in νsp(gel)(T) against the hydrogel. (C) Several changes in the gradient of the plot of νsp(gel) vs T for the gel made of ethanol indicated some conformational changes in the polymer at specific temperatures. These temperatures exactly matched with changes in spin-lattice relaxation times for the OH proton of ethanol that is present in gels. Altogether, the above differences in their thermal behaviors of various gels were elucidated in terms of strengths and modes of the intermolecular polymer-polymer, polymer-solvent, and solvent-solvent interactions that are modulated by thermal motions of molecules

Temperature Dependence of Density of Polymer Gels: 1. A Pycnometry Method Applied to Poly(N-isopropylacrylamide)-Water System

Polymer gels that are in equilibrium with excess solvent(s) are three-component systems consisting of cross-linked polymer networks, solvent(s) in gels, and solvent(s). We have developed a method for the determination of densities of the polymer and solvent components in gels by using a specifically designed pycnometer. The method was applied to the cross-linked poly(N-isopropylacrylamide) and water system from 3.0 to 50.0°C. From the densities of the polymer and solvent components, we have evaluated the total volume of gel per unit mass of the cross-linked polymer (solid) [v(gel)/mp], the ratio of mass of polymer (or solvent) versus mass of gel [mp/m(gel) or ms/m(gel)], and the number of solvent molecules per polymeric residue at various temperatures. The determination revealed how contraction of the total volume of gels is related to temperature dependences of these quantities as follows: (1) The total volume at 3.0°C [v(gel)/mp = 32.61 cm3/(1.0 g of mp)] continuously decreased to a value 10.59 cm3 at 33.5°C. This decrease is essentially brought about by a loss in the mass of water from the gel system to liquid water; (2) The above change corresponds to the changes in mp/m(gel) and ms/m(gel) from their original values 3.055% and 96.94% at 3.0°C to 9.417% and 90.58% at 33.5°C, respectively; and (3) The ratio of mp/m(gel) vs ms/m(gel) asymptotically approached 4.5 vs 5.5 above 34.0°C. The changes in both quantities caused a further shrinkage in total volume but held to less than several percent of the original value (2.017 cm3 at 50°C). The number of water molecules per unit polymeric residue changed from 199 (3°C) to 60.4 (33.5°C) and then to 7.28 (50°C)