Silicone Methacrylate Brushes Prepared by Atom Transfer Radical Polymerization Exhibit Solvent-Regulated Adhesion and Friction

Abstract Despite their widespread application as low-friction surface coatings, existing pathways for the preparation of surface-tethered silicone coatings lack precise control over the nanostructure of the polymer layer and therefore its interfacial properties. To address this limitation, we report the controlled grafting-from synthesis of a silicone methacrylate brush, poly(3-[tris(trimethylsiloxy)silyl]propyl methacrylate) (PSiMA), using surface-initiated atom transfer radical polymerization (SI-ATRP). PSiMA brushes with dry thicknesses ranging from 5 to 75 nm and angstrom-scale surface roughness can be prepared, demonstrating a degree of tunability that is not readily accessible when preparing comparable surface-tethered silicone films. Neutron reflectometry and in situ ellipsometry reveal a pronounced solvent-modulated structure of the PSiMA brushes: the brush is fully desolvated in water and short-chain alcohols, partially collapsed in isopropanol, and adopts a diffuse, swollen structure in chloroform and hydrocarbons. Switching between these solvents drives marked and reversible changes in the adhesive and frictional properties of the brushes as measured by atomic force microscopy, with swollen brush conformations reducing friction by up to a factor of 4 and significantly decreasing adhesion. This reduction is evident even when the brush is partially collapsed in isopropanol, expanding the scope of conditions under which PSiMA brushes display lubricating behavior. These PSiMA brushes enable the design of next-generation silicone surface coatings with switchable friction and adhesion.