(159h) Surface Modification of Kaolinite for Tunable Surface Characteristics and High Sustainability: Multi-Scale Modeling Approach

Kaolinite (Si2Al2O5(OH)4) is a 1:1 dioctahedral phyllosilicate and the main constituent of kaolin which has been widely and massively used in the paper industry as pigment for filler and coating. In this study, we focused on the modified kaolinite-polymer interaction to investigate the adsorption energy and the conformational statistics of polymers on the modified kaolinite (001) surface at atomistic/molecular level, which will provide fundamental information on understanding the interaction of Kaolinite with polymer. First, we investigated the characteristics of the kaolinite (001) surface and its interaction with â-D-glucose and cellobiose using quantum mechanical (QM) density functional theory (DFT) calculations. We found that the adsorption energy of the monomer on kaolinite depends on the surface of kaolinite, the hydroxylated (001) surface or the siloxane (001) surface, and a molecular orientation of the monomer on the surface. The adsorption energy of the monomer on the hydroxylated (001) surface is significantly stronger than that on the siloxane (001) surface. By analyzing a hydrogen bonding between the monomer and kaolinite, it is confirmed that the hydrogen bonding takes an important role to describe the interaction between a proton donor/acceptor group of the hydroxylated (001) surface and the monomer. Second, after calculating rigorous monomer adsorption energy on kaolinite (001) surface, we prepared the potential energy functions for non-bonded interaction between kaolinite and cellulose to run larger scale MD simulations. We carried out the full-atomistic molecular dynamics (MD) simulations in order to investigate the effect of surface modification of kaolinite on the cellulose-kaolinite interaction: we grafted polyethylene glycol (PEG) branches onto the kaolinite (001) surface, which may enhance the molecular interaction between kaolinite and cellulose. Indeed, the adsorption energy of the PEG-grafted kaolinite is larger (~ 2 times) than that of bare kaolinite. We also applied the mechanical force to the cellulose on normal and shear direction of the kaolinite (001) surface. The mechanical force causing the cellulose displacement is larger on the PEG-grafted kaolinite surface than on the bare kaolinite surface.