Micro-scale effects of nano-SiO modification with silane coupling agents on the cellulose/nano-SiO interface.

In this study, molecular dynamics simulations were used to investigate the micro-scale effects of modification of nano-SiO with commonly used silane coupling agents (KH550, KH560, KH570, and KH792) on the cellulose/nano-SiO interface. The relative optimum silane coupling agent and grafting density for nano-SiO modification to improve the cellulose/nano-SiO interface were determined. The results showed that at the same grafting density, modification of nano-SiO with KH792 yielded the highest interfacial binding energy and binding energy density, the largest number of hydrogen bonds at the cellulose/nano-SiO interface, the strongest binding to the cellulose chains, and the largest overlapping area at the cellulose/nano-SiO interface. We found that the non-bonding interaction energy played a decisive role in the energy of the model system and the interfacial interaction force mainly consisted of van der Waals forces and the hydrogen-bonding energy. When silane coupling agents with amino groups (KH550 and KH792) were used to modify nano-SiO, the number of hydrogen bonds at the cellulose/nano-SiO interface was larger than that for unmodified nano-SiO. When silane coupling agents without amino groups (KH560 and KH570) were used to modify nano-SiO, the number of hydrogen bonds at the cellulose/nano-SiO interface was lower than the case for unmodified nano-SiO. Nano-SiO modification with various amounts of KH792 was investigated. The results showed that the interfacial bonding energy increased with grafting density. When the grafting density was 1.57 nm, the interfacial bonding energy and number of hydrogen bonds formed at the cellulose/nano-SiO interface was relatively stable, which indicates that the interface had reached a relatively stable state. Modification of nano-SiO with KH792 achieved the greatest improvement of the cellulose/nano-SiO interface; this interface reached a relatively stable state when the grafting density of KH792 was 1.57 nm.