Molecular level investigations of (organo)clays
Title: Molecular level investigations of (organo)clays
DNr: SNIC 2017/1-369
Project Type: SNIC Medium Compute
Principal Investigator: Michael Holmboe <michael.holmboe@umu.se>
Affiliation: Umeå universitet
Duration: 2017-10-01 – 2018-10-01
Classification: 10506 10404 10406
Homepage: http://www.chemistry.umu.se/forskning/group-leaders/michael-holmboe/
Keywords:

Abstract

This medium allocation proposal aims at continue our research efforts enabled by allocations SNIC 2016/1-371 and SNIC 2016/1-375, investigating the molecular organization and mobility of small inorganic solutes and organics in smectite interlayers (i.e. in lamellar pores between 1nm thick clay layers) of (organo-)clay nanocomposites. Smectite clays have a layered structure and an extremely high surface area, enabling intercalation of large quantities of molecular substances leading to nanomaterials with novel and/or improved properties compared to a simple isotropic mixtures. Our ultimate goal is to improve our understanding of the main interactions controlling intercalation and surface adsorption of organics to clay mineral surfaces. Using mostly classical molecular dynamics simulations we will study adsorption and interaction behavior of clay minerals with a range of organic molecules, covering a selected range of functional groups (initially alcohols and amines), using methods developed during our previous (and ongoing) work of similarly hydrated systems, such as free energy and umbrella sampling methods, see: Holmboe+Bourg, J. Phys. Chem. C 2014, 118, 1001−1013 doi: dx.doi.org/10.1021/jp408884g Tinnacher+Holmboe et al, 2016 Geo. et Cosm. Acta 177 (2016) 130–149 doi: 10.1016/j.gca.2015.12.010 Tournassat+Holmboe et al, 2016, Clays and Clay Min. 64, 4, 374–388 doi: 10.1346/CCMN.2016.0640403 Hellrup+Holmboe et al, Langmuir 2016, 32, 13214−13225 doi:10.1021/acs.langmuir.6b01967 Holmboe et al., Langmuir 2016, 32, 12732−12740 doi: 10.1021/acs.langmuir.6b03008 Yang+Holmboe, Journal of Chem. Phys. 2017, 147, 084705 doi: 10.1063/1.4992001 In our group at Umeå University, we have currently implemented two clay-specific forcefields, Clayff (Cygan, 2004) and the charmm-like INTERFACE ff (Heinz, 2005, 2013) (currently also evaluating TraPPE) for Gromacs, and have prior experience of OPLS/aa, gaff and charmm’s general ff for organic molecules. As an initial benchmarking study, we will model i) smectite solvation (of clay surfaces + counter-cations) of pure alcohol and mixed water/alcohol mixtures, to find the dependence on clay basal spacings versus loading, to aid interpretation of experimental XRD diffraction data on the corresponding systems (by subsequent calculation of structure factors and 1D XRD modeling). If successful, these simulations will also be performed for other layered materials such as graphene and graphite oxide, for which a vast amount of experimental XRD data already exists. In another project we will address ion-exchange reactions of the natural occurring cations in clays (Na+, Ca2+, K+) with small tertiary amines and lipids like CTAB, since they are known to easily undergo intercalation, replacing the existing cations. The motivation for this subproject is the potential applications of hydrophobic clay interlayers with tunable pore size. Reported batch sorption experiments have however shown that the ability for intercalation varies substantially with charge, head-group ‘bulkiness’ and change characteristics with the clay lattice - parameters that easily can be controlled in molecular dynamics simulations.