Effect of side group modification on the glass transition and adhesion properties of polysiloxane at the atomic scale

Polysiloxane is a typical biomimetic dry adhesive, and polysiloxane-silica interface is a typical interface widely existing in test systems and wall-climbing robots. Studying the glass transition temperature (Tg) of polysiloxane and its adhesion properties on silica surfaces has important theoretical guiding significance and practical value for developing and applying a new generation of dry adhesion functional surfaces and devices. However, the effect of the type and content of side groups on the Tg and adhesion properties of polysiloxane is still unclear. Therefore, three side group combinations are included in the established modified polysiloxane models, with each type corresponding to five different side group contents. Molecular dynamics (MD) is used to investigate the effect of side group modification on the Tg of polysiloxane and the adhesion properties on the silica surface. The results show that, compared with polydimethylsiloxane (PDMS), introducing phenylmethyl or diphenyl into the polysiloxane increases the Tg in the studied range of side group contents. The introduction of diethyl decreases the Tg. The corresponding interfacial interactions are enhanced when the diethyl content is 2%, 4% and 10%, the phenylmethyl content is 4%-10% and the diphenyl content is 2%-10%. The interfacial interactions are weakened at the unmentioned side group content. The ratio of van der Waals energy to the interfacial interaction energy is above 94.5% in all interfaces, which means that van der Waals interaction dominates the interaction between polysiloxane and silica surface. The present model provides a deeper insight into polysiloxane, which may contribute to designing future bioinspired dry adhesives.