Metal oxo clusters, from theory to innovation; Synthesis, mechanism & novel application in recyclable polymers

The world is currently facing major challenges such as climate change, which can be tackled by developing new materials that improve on current processes. One area showing great potential is the nanoparticle field which has been developing rapidly over the past 30 years. A nanoparticle can be thought of as a hybrid inorganic-organic object. The inorganic core dictates the physical properties such as e.g. luminescence, while the organic ligand shell provides colloidal stability and solubility. These materials are promising candidates for catalysis due to their high surface to volume ratio. However, size control remains one of the major challenges in this field. In the best case, these nanoparticles have a polydispersity of 5 %, which means that particles with an average size of 5 nm will also have particles with sizes of 4.75 and 5.25 nm. At the same time as the nanoparticle field, also metal oxo clusters were being reported in the literature. These materials are very similar to the previously mentioned nanoparticles, as they are also hybrid objects consisting of a core and a ligand shell. However, they are usually smaller and have the added advantage of being atomically precise. The latter means that their polydispersity is zero, making them excellent building blocks. However, these metal oxo clusters were mainly characterized using single crystal XRD to obtain structural data. This limited the possible synthesis to short and rigid ligands and introduced tedious and long crystallization processes. These limitations are the reason why this field has been dormant for the last 1-2 decades. Due to the clear advantage of having atomically precise building blocks, we sought to revive this field, by developing a new characterization toolbox that eliminates the need for crystallization. We first optimized the synthesis, after which the formation mechanism was studied. Using the knowledge gained from these projects, the clusters have been developed and used as tunable inorganic monomers in both free radical polymerizations and covalent adaptable networks. Firstly, the cluster synthesis was standardized as the reaction conditions in literature were quite divergent. We found that when a metal (Zr or Hf) alkoxide is reacted with 8 equivalents acetic acid, the M12-acetate cluster is consistently formed. After optimizing this for a short carboxylic acid, we performed the same reaction with longer carboxylic acids, similar to the nanoparticle field. After purification, we elucidated their structure via PDF measurements, thus eliminating the need for crystalline material. Fitting the data proved that clusters are formed regardless of the carboxylic acid used during synthesis. The dimerization of the clusters is controlled only by the sterical hindrance on the alpha-position of the carboxylic acid, not by it's length. If there is something different from a -CH2 on this position the monomeric M6 clusters will form, else the dimeric M12 clusters are formed. Through ligand exchange under the appropriate conditions (vacuum at 70 °C) it was possible to convert monomers into dimers and vice versa. The organic ligand shell was further characterized using NMR, FTIR and TGA. We found that, on top of the coordinated ligand shell, which display different binding modes (bridging & chelating), additional H-bonded ligands are present. Applying our toolbox for hafnium clusters we confirmed that the same conclusions are valid. Finally, we tested Zr12-oleate as catalysts for the esterification reaction between oleic acid and ethanol, since they can be seen as the smallest possible nanoparticle. 5 nm ZrO2 nanoparticles have been used successfully as esterification catalysts in the past. Interestingly, our clusters showed a 5-fold increase in reaction conversion due to their increased surface to volume ratio, creating a better, cheaper and more sustainable catalyst. Secondly, the formation mechanism was studied. Using NMR and FTIR we learned that the first 2 equivalents of carboxylic acid exchange with Zr(OPr)4. It appears that this exchange does not go towards completion but is an equilibrium. Only when the third equivalent is added a signal for free acid appears together with an ester signal. In situ EXAFS taught us, despite the large error, that the Zr complex after exchange with 1 equivalent of acid is most likely a dimer, while the 2 equivalent sample seems to fit a trimeric structure. By following the ester formation over time by NMR, while varying multiple reaction conditions, we found that the Zr concentration should be high in order to have sufficient ester formation. Increasing the length of the carboxylic acid and/or alkoxide or adding sterical hindrance has a strong negative effect on the ester formation. The Zr-Zr degeneracy, which is 4 in the final cluster, increases simultaneously with the ester formation. Finally, by combining our data a preliminary reaction mechanism was proposed where the initial ligand exchange is followed by a fast ester formation, after which a slow ester formation occurs and finally the Zr6 cluster is formed. Zr12-oleate and -linoleate clusters were used unsuccessfully as tunable inorganic monomers for radical polymer synthesis. Under our current conditions, reacting the clusters with AIBN, dicumyl peroxide or without initiator, no polymer networks were formed. It is possible that some low molecular weight polymers were formed but since our objective was to create a polymer network this was not investigated further. Instead, we used 10-undecenoic acid as a ligand, which has a terminal alkene. By reacting these clusters with 10 w% dicumyl peroxide solid polymer networks with excellent insoluble fractions were obtained. This result shows us that the alkene functionalities in oleic and linoleic acid are shielded by the remaining ligand tail, inhibiting successful polymerization. We then switched from alkene ligands to (meth-)acrylate ligands which are more reactive towards free radical polymerization. Using our previous knowledge, samples were synthesized with different amounts of reactive ligands on the surface. It was found that samples where the clusters contained 6 reactive ligands or more on the surface resulted in good insoluble fractions, indicative of a polymer network. When fewer reactive ligands were present on the surface, the insoluble fractions were too high. Whether the high insoluble fractions are due to low cluster functionalization or low cluster loading, is still unclear. Remarkably, the Tg did not change significantly despite the large variation in sample composition, not for the alkene-cluster networks nor the (meth-)acrylate-cluster networks. For the (meth-)acrylate capped clusters, polymer samples synthesized from mono-2-(acryloyloxy)ethyl succinate containing clusters show the most promising features. However, further research should be done to mechanically characterize these materials. Finally, the clusters were used as tunable monomers in covalent adaptable networks. The cluster surface was functionalized with different amounts of custom-made epoxy ligands, after which the clusters were reacted into a polymer network. It was found that the Tg ranges from approximately -5 °C to 40 °C and the insoluble fractions were good for almost all samples. The samples were able to relax stress very rapidly, but in a dissociative manner contrary to the intended associative transesterification. We postulate that a ligand exchange on the cluster core is responsible for the fast relaxation of the polymer networks. So far, no clear trend could be observed upon changing the polymer composition by adding co-monomer, different amounts of catalyst or different amount of epoxide ligands. However, DMA measurements showed that the addition of the clusters, even in small amounts, had a positive effect on the mechanical properties. So not only did we switch the reversible chemistry from a transesterification towards a ligand exchange mechanism, but we also improved the mechanical properties of the materials

Understanding the LHC Controls Challenges

The analysis, design and construction of the LHC control system is a complex problem which will challenge CERN's capability to provide a modern controls infrastructure fulfilling the stringent operational requirements of this machine. The first part of this talk will review the present LHC project context in which several controls initiatives have already been taken. The second part will try to highlight the important technical aspects and engineering steps involved in the process of defining a control system architecture. The importance of understanding the major LHC operational challenges will be stressed along with some practical proposals and examples on how to conduct such activity with all stakeholders

XUIMS: the X-Window User Interface Management System at CERN

The CERN X-Window User Interface Management System (XUIMS) is a modular and highly configurable software development environment allowing the interactive design, prototyping, and production of OSF/Motif Human Computer Interfaces (HCI). Fully compliant with the X11R5 and OSF/Motif industry standards, XUIMS covers complex software areas like the development of schematics, the visualization and on-line interactions with 2D and 3D scientific data, the display of relational database data, and the direct access to CERN SPS and LEP accelerators equipment. The guarantee of consistency across the applications and the encapsulation of complex functionality in re-usable and user-friendly components has also been implemented through the development of home made graphical objects (widgets) and templates. The XUIMS environment is built with commercial software products integrated in the CERN SPS and LEP controls infrastructure with a very limited home-made effort. Productivity and quality have been improved through less coding and better HCI prototyping

The CERN accelerators controls convergence project

Summary form only given. The CERN PS and SL Accelerators controls groups have started in March 1998 a convergence effort aimed at building a common controls infrastructure for year 2001. The first activities concentrated on the definition of an object oriented Accelerator Device Model and Application Programming Interface (API) aimed at offering to high level application software developers a narrow and coherent view of the accelerator components. Efforts have also started to build the underlying middleware architecture that will support this model, including services based on the publish- subscribe paradigm. This presentation will highlight some aspects of this Accelerator Device model as seen form the application software level. A logical view of the associated middleware architecture that will transport Accelerator device data will also be discussed

The new generation of PowerPC VMEbus front end computers for the CERN SPS and LEP accelerators control system

The CERN SPS and LEP PowerPC project is aimed at introducing a new generation of PowerPC VMEbus processor modules running the LynxOS real-time operating system. This new generation of front end computers using the state-of-the-art microprocessor technology will first replace the obsolete Xenix PC based systems (about 140 installations) successfully used since 1988 to control the LEP accelerator. The major issues addressed in the scope of this large scale project are the technical specification for the new PowerPC technology, the re-engineering aspects, the interfaces with other CERN wide projects, and the set up of a development environment. This project offers also support for other major SPS and LEP projects interested in the PowerPC microprocessor technology

The landscape of formal CME in palliative care for GPs in Flanders

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Project management as a breakthrough at CERN

Building and maintaining control systems for high energy physics is becoming an increasingly complex and costly activity. The quickly evolving technology and the tight budget conditions require today a better management of our engineering activities. This situation led us to organise these activities as "projects" and to use modern project management practices already widely spread in industry. In this context, many aspects of the re-engineering of the controls infrastructure of the two CERN largest particle accelerators - SPS and LEP - as well as the supervision of the CERN wide technical services are fully conducted as projects with special control over the costs, resources, objectives, activities and maintenance aspects. This paper presents our experience in project-based management with special emphasis on its applicability in a research environment, on the impact on the current working pratices and on the potential benefits for the future. Some key concepts and techniques of project management are introduced and illustrated through pratical examples