Solvent Optimization Studies for a New EURO-GANEX Process with 2,2’-Oxybis( N,N -di- n -decylpropanamide) (mTDDGA) and Its Radiolysis Products

The diglycolamide 2,2’-oxybis(N,N-di-n-decylpropanamide) (mTDDGA) is being studied as an extractant for actinides and lanthanides in the European Grouped Actinide Extraction (EURO-GANEX) process. The aim is the development of a more simplified process using a single extractant instead of a mixture of extractants used in the current EURO-GANEX process. This work presents solvent optimization studies of mTDDGA, with regards to the extraction characteristics of the different diastereomers of mTDGA and of mixed diastereomer solutions. Also radiolysis behavior has been studied by irradiation of solvent extraction systems in a gamma irradiation facility using $^{60}$Co. The availability of irradiated organic solutions made it possible to gain valuable insights into the plutonium loading capacity after gamma-irradiation of the solvent up to 445 kGy and to quantify degradation compounds. Solvent extraction characteristic of the major degradation compounds themselves were determined. Like other methylated diglycolamides, we found a remarkable difference in extraction of up to two orders of magnitude between the two diastereomers. High plutonium loading (36 g L$^{−1}$) is feasible using this single extractant, even after absorbing a dose of 445 kGy. This remarkable observation is possibly promoted by the presence of the main degradation compound which extracts plutonium verywell

Liquid-crystalline complexes of transition metals and rare earths with substituted 1,10-phenanthroline ligands.

Starting from the facts that 1,10-phenanthroline is a frequently used ligand in coordination chemistry and that it is able to form stable complexes with a wide variety of d-block and f-block metals, we have selected1,10-phenanthroline as a building block for the synthesis of a new class of metal-containing liquid crystals. The aim of this work was to design luminescent liquid crystals and liquid crystals with an unusual geometry. Although different substitution patterns are possible for 1,10-phenanthroline, 3,8-disubstituted 1,10-phenanthrolines were selected as the first target molecules (this work was performed in collaboration with Prof. Duncan W. Bruce, who carried out pioneering research on liquid-crystalline phenanthrolines). This substitution pattern is a logical choice if one wants to obtain compounds with an extended rodlike aromatic core and thus with the necessary anisotropic shape for the formation of mesophases. For the synthesis, 3,8-dibromo-1,10-phenanthroline was used as the starting product, which can be functionalized by Sonogashira coupling reactions. The advantage of this approach is that the aromatic rings, which build up the rigid part of the mesogenic molecule, are linked to one another by an acetylene linking group. It is known from the literature that acetylene linking groups are in general much more stable than for instance ester groups. The dibromation of 1,10-phenanthroline in the 3- and 8-positions turned out to be a difficult task because different brominatedspecies were obtained. The side products include not only the monobrominated 3-bromo-1,10-phenanthroline, but also other isomers of the dibrominated product and polybrominated species. Even small quantities ofimpurities of these side products cause serious problems for the purification of the final product after Sonogashira coupling reactions. Due tothe tedious purification of the mesomorphic 1,10-phenanthroline derivatives, we were able to synthesize only one 1,10-phenanthroline derivative, i.e. a tetracatenar compound with four terminal alkoxy chains. The structure of this ligand was determined by single-crystal X-ray diffractionand examination of the thermal behavior indicated that the ligand exhibits a smectic C phase. Unfortunately, the ligand could not be obtained in sufficient quantities to allow the synthesis of metal complexes. Facing the problems with the 3,8-disubstituted 1,10-phenanthrolines, another type of functionalized 1,10-phenanthrolines was considered, i.e. 1,10-phenanthrolines mono-functionalized in the 5-position or difunctionalized in the 5- and 6-positions. In a search for the most suitable precursor, we first worked with 5-amino-1,10-phenanthroline, but it turned out that the 1,10-phenanthroline-5,6-dione is a more useful starting product. 1,10-Phenanthroline-5,6-dione is easily accessible in high purity byoxidation of 1,10-phenanthroline and the product itself is much more stable than 5-amino-1,10-phenanthroline. By reaction between 1,10-phenanthroline-5,6-dione and a benzaldehyde in the presence of ammonium acetate and acetic acid, a 2-phenyl-imidazo[4,5-f]-1,10-phenanthroline canbe obtained. This is a versatile approach because the imidazo[4,5-f]-1,10-phenanthroline can be modified by replacing the benzaldehyde by a substituted benzaldehyde. Another route to modify the ligand is the alkylation of one of the nitrogen atoms of the imidazole ring.In first instance, we decided to promote mesomorphism in the imidazo-[4,5‑f]-1,10-phenanthrolines by coupling mesogenic 4‑cyanobiphenyl groups via a long, flexible alkyl spacer to a substituted imidazo[4,5-f]-1,10-phenanthroline, which acts as the coordinating group. Three different ligands were designed, bearing one, two, and three mesogenic groups, respectively. Complexes of rhenium(I), yttrium(III), lanthanum(III), neodymium(III), samarium(III), europium(III), erbium(III), and ytterbium(III) were synthesized. In the case of the rare-earth complexes, 2-thenoyltrifluoroacetonate was used as the coligand. The rhenium(I) complexes contain the bromotricarbonylrhenium(I) moiety. All the compounds exhibit enantiotropic mesophases, except the rhenium(I) complex of the ligand bearing only one mesogenic group, which forms only a monotropic mesophase. The ligands and corresponding rhenium(I) complexes show a nematic or a lamello-columnar phase, depending on the number of attached mesogenic groups. All the rare-earth complexes systematically exhibit a nematic mesophase. The luminescence properties of the neodymium(III), samarium(III), europium(III), erbium(III), and ytterbium(III) complexes were examined. The spectroscopic and photophysical properties of these complexes are comparable with those of the [Ln(tta)3(phen)] complexes, where Ln = Nd, Sm, Eu, Er, Yb, tta = 2-thenoyltrifluoroacetonate, and phen= 1,10-phenanthroline. However, an interesting feature of these rare-earth complexes is their good solubility in nematic liquid-crystal solvents, so that by a doping procedure luminescent liquid crystals can be obtained. These could be of interest as active components in emissive liquidcrystal displays. Although a 4-cyanobiphenyl group was chosen as the mesogenic promoter and a 1,10-phenanthroline derivative as the coordinating group, the concept of decoupling of the mesophase-inducing groups and the coordination groups can be extended to other mesogenic groups and ligands. The advantage of this approach is that high coordination number metallomesogens showing a nematic mesophase can be obtained. Traditionally, to obtain high coordination number metallomesogens, a large number oflong alkyl chains are attached to the central metal core, which usuallyleads to (viscous) columnar mesophases. There are however some problemsassociated with this new approach. The most serious problem is that such compounds with complex molecular architectures cannot be easily aligned by external electric or magnetic fields, even not when they exhibit a nematic phase. The linker avoids that phase separation occurs but the mesogenic groups and the coordination group act rather independently. Finally, in the third strategy, 2-aryl-substituted imidazo[4,5-f]-1,10-phenanthrolines were used as building blocks for the synthesis of metal-containing liquid crystals by attaching alkoxy chains in different positions of the phenyl ring. Their molecular shape and space fillingrequirements can be tuned by the choice of an appropriate alkoxy-substituted benzaldehyde for the ligand synthesis. Metal complexes were made with different d-block transition metals, including nickel(II), palladium(II), platinum(II), ruthenium(II), and rhenium(I), as well as with lanthanides and uranyl. The ligands do not form a stable mesophase; they showat best a monotropic mesophase. The most striking feature is the influence of solvent molecules on the thermal behavior of the ligands, as the ethanol adduct of the ligand with hexadecyloxy chains in the 3- and 4-positions shows two mesophases, a transient hexagonal columnar phase and a smectic phase.Mesomorphism can be induced in the ligands by coordination to a metal center. The thermal behavior of the metal complexes depends on the metal-to-ligand ratio, but also on the substitution pattern and on the alkyl chain length. Although the palladium(II) and platinum(II) complexes exhibit enantiotropic (unidentified) mesophases with an extended temperature range, complexes with a metal-to-ligand ratio of 1:1 are in general not liquid-crystalline or they exhibit only a monotropic mesophase. Nickel(II) complexes with a 1:2 metal-to-ligand ratio form enantiotropic mesophases with an extended temperature range for most types of ligands. The uranyl complex, with a 1:3 metal-to-ligand ratio, has a propeller-like shape and exhibits a hexagonal columnar mesophase. The uranyl ion acts as a template to bring the ligands in the correct position so that propeller-shaped units can arrange into columns . It was somewhat disappointing that we were not able to synthesize liquid-crystalline lanthanide complexes of this type of imidazo[4,5-f]-1,10-phenanthrolines. This is due to the small differences in solubility behavior of the ligands and metal complexes. Lanthanide complexes with shorter alkyl chains could be synthesized, but these complexes were not mesomorphic. The photophysical properties of the rhenium(I) complexes and of the (non-mesomorphic) lanthanide complexes are being investigated at the moment (ongoing work by Jan Ramaekers). The attachment of long alkyl chains to the 2-phenyl-imidazo[4,5-f]-1,10-phenanthroline core was a more classic approach. Although stable mesophases were observed forsome complexes (for instance for the uranyl compound), the stability ofthe mesophases did in general not meet the expectations. Relatively fewmetal complexes were mesomorphic and the mesophases were difficult to characterize or were not stable. No new types of mesophases were observed. This PhD work is hopefully the initiation of further research using 1,10-phenanthroline derivatives as building blocks for liquid crystals and especially for metallomesogens. It is possible to highlight some directions for further research concerning these systems. The functionalizationof 1,10-phenanthroline in the 3- and 8-positions deserves a more careful investigation, because our research illustrates that such compounds can indeed exhibit mesomorphic behavior. This further work could include variation of the alkoxy chain length of the tetracatenar compound, in order to examine the polymorphism as a function of the chain length. Although we observed a smectic C phase for the compound we synthesized, analogous series of compounds described in the literature show a gradual change from smectic to columnar mesomorphism. The mesophase behavior can alsobe tuned by choosing other substitution patterns. However, the most interesting study concerns the synthesis of corresponding metal complexes and to examine the influence of metal fragments on the thermal behavior. In order to avoid purification problems, the synthetic methodology should be reconsidered. One approach is to develop a new method for the synthesis of 3,8-dibromo-1,10-phenanthroline in high yield and purity. A second approach is to synthesize the mesomorphic branches in the first stageand to form the 1,10-phenanthroline core in the last step via methods similar to the Skraup synthesis of 1,10-phenanthroline.The idea of linking mesogenic units via a flexible alkyl chain to a coordinating unit can of course be generalized. Variations of the coordinating unit, metal ion, coligand, length of the flexible linker, type and number of mesogenic groups could be made and could result in a large number of different metallomesogens. Such molecules are of interest from a fundamental point of view because these complex molecular architectures can lead to new types of mesophases. The results obtained from a systematic variation of the constituents of these complexes could be useful to make predictions on the mesophase behavior of this type of mesomorphic compounds.The approach of attaching long alkyl chains to the 2-phenyl-imidazo[4,5-f]-1,10-phenanthroline core was not as successful as that of attaching mesogenic groups via a flexible linker, although there are at least two aspects that deserve further investigation. First of all, the thermal behavior of the nickel(II) and uranyl complexes give the impression that the ionic character of these compounds aid to the stabilization of the mesophases. Research in the future can be directed to the design of ionic metallomesogens based on 1,10-phenanthroline. Another aspect for furtherstudy is the influence of H-bonding on the stability of the mesophases of these complexes. Indeed, it was observed that mesomorphism was lost when the proton on the nitrogen atom of the imidazole ring was replaced by an alkyl group, and cocrystallization of the mesogenic compounds with protic solvents has a large influence on the mesophase behavior.Finally, further research will be directed to the functionalization of 1,10-phenanthroline in the 4- and 7-positions in order to design bent-core liquid crystals.status: publishe

Decoupling of coordinating units and mesophase-inducing groups in metallomesogens

poster presented by Thomas Cardinaelsstatus: publishe

Piperidinium, Piperazinium and Morpholinium Ionic Liquid Crystals

Piperidinium, piperazinium and morpholinium cations have been used for the design of ionic liquid crystals. These cations were combined with several types of anions, namely bromide, tetrafluoroborate, hexafluorophosphate, dodecylsulfate, bis(trifluoromethylsulfonyl)imide, dioctylsulfosuccinate, dicyclohexylsulfosuccinate, and dihexylsulfosuccinate. For the bromide salts of piperidinium containing one alkyl chain, the chain length was varied, ranging from 8 to 18 carbon atoms (n = 8, 10, 12, 14, 16, 18). The compounds show a rich mesomorphic behavior High-ordered smectic phases (crystal smectic E and T phases), smectic A phases, and hexagonal columnar phases were observed, depending on the type of cation and anion. The morpholinium compounds with sulfosuccinate anions showed hexagonal columnar phases at room temperature and a Structural model for the self-assembly of these morpholinium compounds into hexagonal columnar phases is proposed.status: publishe

Compatibilization of polymer blends by Janus particles

Due to their strong tendency for demixing, immiscible polymers require compatibilization to ensure that immiscible polymer blends with a fine and stable morphology as well as adequate interfacial adhesion are obtained. Classically, compatibilization is performed with either copolymers or nanoparticles. Janus particles, which are particles having two sides with distinct chemical or physical properties, combine the amphiphilic character of copolymers with the physical characteristics of particles. In the present work, compatibilization by means of Janus particles is reviewed, with a particular emphasis on polymer blends. After providing a short overview of the different Janus particle types and production routes as well as their compatibilization mechanisms, the available literature on polymer blends compatibilized with Janus particles is reviewed. Janus particles are more efficient morphology stabilizers, leading to a larger reduction in domain sizes and more significant slowing down of phase separation kinetics as compared to homogeneous nanoparticles. Hence, the use of Janus particles forms a very promising route to generate nano- or microstructured high-performance materials from polymer blends with a tuneable organization on two levels, namely that of the Janus particles at the interface as well as that of the global blend morphology. In this endeavor, one of the major challenges is the development of large-scale production routes for Janus nanoparticles, which would allow their use on industrial scale

Thorium and thorium-plutonium fuel research in Belgium

status: publishe

Accurate lattice parameter measurements of stoichiometric uranium dioxide

The paper presents and discusses lattice parameter analyses of pure, stoichiometric UO2. Attention was paid to prepare stoichiometric samples and to maintain stoichiometry throughout the analyses. The lattice parameter of UO2.000±0.001 was evaluated as being 547.127 ± 0.008 pm at 20 °C, which is substantially higher than many published values for the UO2 lattice constant and has an improved precision by about one order of magnitude. The higher value of the lattice constant is mainly attributed to the avoidance of hyperstoichiometry in the present study and to a minor extent to the use of the currently accepted Cu Kα1 X-ray wavelength value. Many of the early studies used Cu Kα1 wavelength values that differ from the currently accepted value, which also contributed to an underestimation of the true lattice parameter.status: publishe