Characterization of molecular diffusion in liquids with dissolved gases
Third party funded individual grant
Start date : 01.07.2019
End date : 31.03.2022
Extension date: 30.06.2023
Project details
Short description
Scientific Abstract
The proposed research should further promote the fundamental understanding of molecular diffusion in binary mixtures consisting of liquids and dissolved gases. Still ongoing work within the first funding period shows that dynamic light scattering (DLS) experiments and molecular dynamics simulations (MDS) are suitable for the characterization of diffusive mass transport in such systems in macroscopic thermodynamic equilibrium. While DLS analyzes microscopic statistical concentration fluctuations to get access to the Fick diffusivity D11, the latter is obtained from equilibrium-MDS by combining kinetic and structural contributions in form of the Maxwell-Stefan diffusivity and the thermodynamic factor. It has been shown that D11 data obtained from DLS for various binary mixtures with dissolved gases close to infinite dilution agree with the self-diffusivities of the gases calculated by MDS. Newly identified relations between characteristic properties of the gases and the diffusivity data contributed to the development of a simple correlation for the tracer diffusivity of the studied gases dissolved in n-alkanes. For the model system n-hexane/CO2, D11 data determined for the entire concentration range give first indications regarding the influence of the liquid structure on Fickian diffusion. The main aim of the proposed second funding period is the acquisition of comprehensive knowledge on diffusion-related structure-property relationships by a systematic expansion of the studied classes of liquids and gases. While for the selected gases molar mass, size, and polarity vary over broad ranges, the chosen liquids differ not only in alkyl chain length, but also in the degrees of branching and oxygenation for acyclic and of hydrogenation for cyclic compounds having the same number of carbon atoms. For the additional systems, the performance of MDS regarding the prediction of D11 should be tested again by comparison with the experimental results from DLS. Based on all obtained data and further insights into the liquid structure gained from MDS, the fundamental understanding how the different characteristics of liquids and dissolved gases influence Fickian diffusion should be improved. These influences can be analyzed separately for liquids and gases by investigations close to infinite dilution. Concentration-dependent studies shed light on the effects of the liquid structure and kinetic aspects on D11. Information on the liquid structure will be compared with results from Raman spectroscopy. All experimental and calculated results should be used to establish quantitative relations between the different kinds of diffusion coefficients for various ideal and non-ideal binary systems. These findings should contribute to the further development of more comprehensive prediction schemes for the Fick diffusivity for binary systems consisting of liquids with dissolved gases.
Involved:
Andreas Paul Fröba
Project Leader
Michael Rausch
Project Member
Tobias Klein
Project Member
Maximilian Piszko
Project Member
