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Report

Teaser, summary, work performed and final results

Periodic Reporting for period 1 - ENACT (Enhancing sustainable chemical technologies through the synergy of computer simulation and experiment)

Teaser

Summary

More efficient, sustainable, environmentally-friendly technologies are a necessity in a global scale. It is then important to develop strategies to realize the full potential of existing and new technologies, taking into account these factors. It is relatively easy to screen solid-state materials for applications using high-throughput computational methods. In chemical technologies, liquid phases are more desirable than solids because of their amenability to continuous flow processing and the flexibility in tuning their properties. However, they are more difficult to study.

Within ENACT, this goal is achieved by first gaining an understanding of the properties of a variety of systems by computer simulation, which allow us to tune the choice of materials and external conditions. This knowledge is then transferred to the experimental partners who synthesize and characterize the selected systems. Six independent themes are tackled in parallel under a single umbrella, thus enabling the exchange of ideas and methods.

Work performed

Confined Ionic Liquids:

We conducted a combined neutron scattering and computer simulation study of a series of liquids embedded into various solid porous matrices. The liquids studied were the environmentally benign ionic liquids, and benzene and cyclohexane, which are similar but have different shape and aromaticity. For the solids we considered metal-organic frameworks (MOF) and disordered porous silica. IL simulations are inconclusive. In the case of benzene and cyclohexane, an important difference is that the latter appears to form a glassy layer next to the walls, while the former is much more fluid.

Porous Liquids:

We designed, synthesised and characterised a series of liquids composed of hollow cage-like molecules. These are the first synthesized free-flowing liquids with permanent porosity. Experiment showed an 8-fold increase in solubility of methane. A one-step, multi-gram scale-up route for highly soluble â€˜scrambledâ€™ porous cages prepared from a mixture of commercially available reagents was demonstrated. To screen the properties of these PLs we developed a model for binding energy and solubility of guest molecules in the cage as a function of the volume of the molecule.

Dye-sensitized solar cells:

We studied the structural and dynamical properties of a room temperature ionic liquid (IL) solvating a dye molecule adsorbed on titania, a model for dye-sensitized solar cells. We showed that changing the approximation to the electronic structure lead to modifications of the geometry of the IL in the vicinity of the dye. At this interface, these combine in ways that are often subtle, with important electronic and vibrational effects. We also modelled the charge transport process in the crystal phase of an IL, showing that diffusion happens through a combination of I2 transfer and triiodide diffusion. The rate-determining step was an I2 transfer in a twisted geometry.

Heat storage:

We investigated the thermal conductivity (TC) of the graphene-water system to assess the effect of nanoparticle inclusion. Experiments show an enhancement of TC that disappears with the addition of a surfactant. Simulations show a water depletion near graphene that hinders energy transfer between the two components, thus decreasing TC. Continuum simulations of graphene in water and paraffin wax, with and without surfactant, were conducted with COMSOL. These studies showed an average TC enhancement of 25%, which does not explain the experimental 100%. The latter can be achieved by introducing a semi-solid layer of TC larger than water.

Biomimetic membranes:

We studied the opening of transmembrane pores in a variety of biological membranes in the presence of electric fields. We elucidated the origin of the capacitance of a free-standing membrane and proposed a test of accuracy for capacitance-based phenomenological models to predict the energetics of electroporation. We investigated the transport of ionic peptides (CPP) across a membrane, and found that CPP translocation is facilitated by transmembrane potential. We then investigated the mechanism by which CPP-functionalized cargos cross a lipid bilayer.

Mechanochemical reactions:

We studied collisions and indentations between an aspirin and a meloxicam cluster with the aim of understanding the first step in the co-crystallization process via mechanochemical synthesis (pestle and mortar, ball milling, extrusion). This was done with no solvent and with a small amount of chloroform. The simulations showed the mixing of the two nanocrystals in which, after after retraction, part of the meloxicam molecules remain attached to the aspirin nanocrystal and a smaller number vice versa. Nothing different happens in the presence of chloroform. It probably plays a more important role facilitating the re-crystallization process.

Training:

A community of about 25 researchers was assembled. The cohort of ESR was trained in computer modelling and non-technical professional skills.

Final results

1. The most important achievement was the development of the first porous liquids (PL). There is enormous potential for exploitation of PLs, which are able to dissolve gasses in a much higher proportion than regular solvents. This has potential implications in the reduction of environmental impact of chemical processes. This work was published in Nature, and has attracted a lot of attention form the media.

2. We began to understand complex mechanochemical reactions at the atomistic level, in particular the co-crystallization of pharmaceutical drugs. The possibility of producing these via extrusion is of interest to the pharmaceutical industry, and has implication in health care. Moreover, the limited or no use of organic solvents in the synthesis has an important environmental impact.

3. A significant advance has been made in the field of biomimetic membranes. Here, understanding the conditions under which it is possible to create pores and introduce desired molecules into cells has potential in the health care sector (drug delivery).

4. Progress has been made in understanding the effect of nanoparticles in heat storage systems. Nanofluids are hoped to exhibit higher thermal conductivities than regular fluids. Phase transitions (solidification-melting) can be used to store energy in the form of latent heat. There is potential impact in the energy sector.

5. The process of charge transfer and regeneration in dye-sensitised solar cells has been studied in ionic liquid electrolytes. We see potential for improving the efficiency of the charge cycle in these devices, with implications in the energy agenda.

6. Computer simulation-aided neutron scattering experiments were used to determine the structure of complex solid-fluid systems. This unlocks the possibility of studying chemical reactions in real time. Of particular interest are catalytic systems, which contribute to the energy sector.