Theoretical investigation of protective graphene-coated metakaolin geopolymer interface under moisture and chemical composition effects

Abstract

Improving the durability of metakaolin aluminosilicate materials (named geopolymer) is a key challenge in the building industry. One approach to enhancing these materials resistance to water infiltration and other aggressive agents is to modify their surface properties. This study investigates the atomic-level interfacial interactions between a nanodroplet of water and a graphene-coated geopolymer surface. Using molecular dynamics and density functional theory methods, we computed the surface adsorption and free energies for metakaolin geopolymer surfaces, varying the chemical composition content between Si and Al atoms. Our MD results demonstrate that graphene-coating increases the geopolymer surface's stability, reducing its surface energy from 151 meV/ Å2 to 7.71 meV/ Å2. Moreover, the graphene-coated surface's contact angle with a water nanodroplet increased remarkedly from 31° to 79°, significantly reducing water permeability. We also found that the mobility of water molecules on the coated surface was twenty times lower, with a diffusion coefficient of 0.131 × 10−10 m2.s−1. Importantly, our study revealed the crucial role of interfacial chemical bonding, with the evaluated elastic and indentation moduli increasing 70 and 39 times, respectively, when the interfacial bonding concentration was 14.15%. Our findings provide fundamental insights into the interactions between graphene-coated geopolymer surfaces and water nanodroplets, representing a crucial step towards the development of superhydrophobic geopolymer materials.