Crosslinking inert liquidlike polydimethylsiloxane brushes using bis-diazirine chemical insertion for enhanced mechanical durability

Abstract

Inert polymer brushes offer excellent omniphobic and antifouling properties but enhancing their durability remains a challenge, since their chemical inertness also means they lack the functionality necessary for traditional crosslinking reactions. We report the crosslinking of nanoscale polydimethylsiloxane (PDMS) brushes on surfaces through a chemically non-destructive C–H insertion. bis-Diazirine crosslinkers are employed to covalently link methyl groups (i.e., insertion into Si–C–H bonds) along neighboring PDMS chains upon thermal activation. The successful crosslinking of PDMS brushes is evidenced directly by X-ray photoelectron spectroscopy analysis and indirectly through mechanical durability characterization using Martindale abrasion. The apparent contact angles and low contact angle hysteresis of crosslinked PDMS brushes are well-maintained post abrasion, indicating enhanced mechanical durability as compared to uncrosslinked brushes. The longevity of the liquidlike character of crosslinked PDMS brushes is also improved following mechanical wear, with a shear ice adhesion strength half that of uncrosslinked brush surfaces. The crosslinked surfaces are also resistant to acid corrosion, heating, sonication, and tape peeling, indicating that the physicochemical stability of PDMS brushes is not degraded upon crosslinking. Finally, crosslinked brushes are additionally deposited on polycarbonate substrates, and the optical transparency, enhanced durability, and droplet shedding capability of the coated substrates are demonstrated. Overall, this study provides a new pathway for the design of durable inert nanoscale coatings that maintain their attractive surface properties after mechanical wear.