On the characterization of amine molecules behaviors in the nanochannels forming in calcium silicate hydrate gel

Abstract

Determining the amine molecules behaviors in the nanochannels enables the interpretation of the microstructure and macroscopic properties of amines modified cement based materials. In this study, quantitative analysis were performed on the behaviors of amine molecules (TEPAs, PAMs and TEAs) by molecular dynamics (MD) simulation in the nanochannels of C–S–H gel. According to the interaction of amine molecules with C–S–H gel substrates or water molecules, research works revealed that amine molecules with special spatial structures illustrate different aggregation behaviors. TEPAs with linear structures tend to aggregate in a regular sequence at the center of the C–S–H gel nanochannels. Instead, PAMs and TEAs with branched structures prefer dispersing in the aqueous solution in the C–S–H gel nanochannels. Such different aggregation behaviors allow amine molecules to have various penetration depth and residence time in the interfacial regions. It was found that oxygen atoms and active hydrogen atoms in PAMs and TEAs can form stable interaction with calcium ions and oxygen atoms of C–S–H gel substrates, respectively. The oxygen involved bonds are stronger than nitrogen involved ones for all the molecules due to great electronegativity. There is no formation of hydrogen bonds in TEPAs, but polar atoms in PAMs and TEAs can interact through hydrogen bonding. Moreover, TEPAs cannot form strong hydrogen bonding with water molecules due to their aggregation behavior, whereas PAMs and TEAs formed strong hydrogen bonding with surrounding water molecules. In addition, formation of more hydrogen bonding with amine molecules leads to a lower diffusion coefficient of water molecules. Breakage of hydrogen bonds of water molecules causes the final failure of C–S–H/amine molecules nanocomposites subjected to tensile loads.