Topological regulation in polysilsesquioxanes for achieving super-hard and flexible membranes: insights from molecular simulation

Abstract

Cage-like and ladder-like polysilsesquioxane, named EPOSS and ELPSQ, were synthesized and employed as precursors to develop a UV-curable membrane exhibiting remarkable hardness, superior flexibility, exceptional transparency and excellent friction resistance. Nanoindentation analysis demonstrates that the precise control of the Silicane molecular frameworks by adding a small quantity of EPOSS to ELPSQ can significantly enhance the hardness of the membranes. The resulting hardness value reaches a record 1.56 GPa, which is notably higher than all of the reported rigid polymer membranes. Meanwhile, the membrane displays superior flexural properties with a minimum radius of curvature of 0.35 mm, and after 10 000 folds in the cyclic flexure test, only slight creases were observed even under a polarizing microscope. The molecular dynamics simulation reveals how different molecular stereo topologies endow materials with astonishing hardness and excellent flexibility, thereby formulating a novel strategy for material design. ELPSQ's trapezoidal topology exhibits anisotropy, enabling the material to bend while maintaining super hardness. EPOSS's cage topology endows materials with a higher modulus and improved bending performance. Incorporating an appropriate amount of EPOSS into the ELPSQ can inhibit the movement of molecular chains, thereby enhancing the mechanical properties of the resin. This work presents a new strategy for preparing membranes with super-hardness and high flexibility, and investigates how the cage-like topological structure influences the hardness of resin systems.