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Enthalpy vs. friction: heat flow modelling of unexpected temperature profiles in mechanochemistry of metal-organic frameworks.

ABSTRACT: Mechanochemical reactions by ball milling are becoming increasingly popular across a wide range of chemical sciences, but understanding and evaluation of temperature during such processes remains a persistent challenge, especially for organic and metal-organic materials. Here, we describe the first methodology for precise real-time measurement of sample temperature during mechanochemical transformations. Using this technique coupled with real-time in situ reaction monitoring by synchrotron X-ray diffraction and numerical simulations of heat flow, we have shown that the temperature profiles of mechanochemical reactions are dominantly determined by the energy dissipated through friction between the sample and the moving milling assembly, while the reaction enthalpy will usually be comparatively insignificant. With the changes in composition during mechanochemical reactions, frictional properties of the milled material change, leading to either better or worse energy absorption upon collisions in the process of milling. This approach explains unexpected and rapid temperature drops during exothermic transformations of ZIF-8 polymorphs. Since reaction kinetics are highly sensitive to changes in temperature, precise temperature profiles provided here will be mandatory to understand kinetics and its changes during milling, and will aid in developing the comprehensive model of mechanochemical reactivity.

SUBMITTER: Uzarevic K

PROVIDER: S-EPMC5911823 | biostudies-other | 2018 Mar

REPOSITORIES: biostudies-other

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Enthalpy <i>vs.</i> friction: heat flow modelling of unexpected temperature profiles in mechanochemistry of metal-organic frameworks.

Užarević Krunoslav K Ferdelji Nenad N Mrla Tomislav T Julien Patrick A PA Halasz Boris B Friščić Tomislav T Halasz Ivan I

Chemical science 20180123 9

Mechanochemical reactions by ball milling are becoming increasingly popular across a wide range of chemical sciences, but understanding and evaluation of temperature during such processes remains a persistent challenge, especially for organic and metal-organic materials. Here, we describe the first methodology for precise real-time measurement of sample temperature during mechanochemical transformations. Using this technique coupled with real-time <i>in situ</i> reaction monitoring by synchrotro ...[more]

PMID: 29732130

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Project description:The chemical composition of small organic molecules is often very similar to amino acid side chains or the bases in nucleic acids, and hence there is no a priori reason why a molecular mechanics force field could not describe both organic liquids and biomolecules with a single parameter set. Here, we devise a benchmark for force fields in order to test the ability of existing force fields to reproduce some key properties of organic liquids, namely, the density, enthalpy of vaporization, the surface tension, the heat capacity at constant volume and pressure, the isothermal compressibility, the volumetric expansion coefficient, and the static dielectric constant. Well over 1200 experimental measurements were used for comparison to the simulations of 146 organic liquids. Novel polynomial interpolations of the dielectric constant (32 molecules), heat capacity at constant pressure (three molecules), and the isothermal compressibility (53 molecules) as a function of the temperature have been made, based on experimental data, in order to be able to compare simulation results to them. To compute the heat capacities, we applied the two phase thermodynamics method (Lin et al. J. Chem. Phys.2003, 119, 11792), which allows one to compute thermodynamic properties on the basis of the density of states as derived from the velocity autocorrelation function. The method is implemented in a new utility within the GROMACS molecular simulation package, named g_dos, and a detailed exposé of the underlying equations is presented. The purpose of this work is to establish the state of the art of two popular force fields, OPLS/AA (all-atom optimized potential for liquid simulation) and GAFF (generalized Amber force field), to find common bottlenecks, i.e., particularly difficult molecules, and to serve as a reference point for future force field development. To make for a fair playing field, all molecules were evaluated with the same parameter settings, such as thermostats and barostats, treatment of electrostatic interactions, and system size (1000 molecules). The densities and enthalpy of vaporization from an independent data set based on simulations using the CHARMM General Force Field (CGenFF) presented by Vanommeslaeghe et al. (J. Comput. Chem.2010, 31, 671) are included for comparison. We find that, overall, the OPLS/AA force field performs somewhat better than GAFF, but there are significant issues with reproduction of the surface tension and dielectric constants for both force fields.

Dataset Information

Enthalpy vs. friction: heat flow modelling of unexpected temperature profiles in mechanochemistry of metal-organic frameworks.

Publications

Enthalpy <i>vs.</i> friction: heat flow modelling of unexpected temperature profiles in mechanochemistry of metal-organic frameworks.

Similar Datasets

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