Cosolvency-Induced Switching of the Adhesion between Poly(methyl methacrylate) Brushes

We present a simple method to reversibly switch the adhesive force between two surfaces that are decorated with poly(methyl methacrylate) (PMMA) graft polymers. By employment of a PMMA/isopropanol/water or a PMMA/ethanol/water cosolvent system, we can tune the swelling of the brushes. In pure isopropanol or ethanol the polymer grafts are collapsed, and the adhesion is high when the contacting brushes are pulled apart. In an 80-20 vol % isopropanol-water or ethanol-water composition, the brushes are swollen. In these systems the adhesion is approximately 5 times smaller compared to the adhesion measured in the pure solvent systems. Moreover, we show that PMMA/isopropanol/water cosolvent systems perform better as switchable adhesives than PMMA/ethanol/water cosolvent systems. In the latter pulling events can arise when the swollen brushes are kept in contact for a longer time, such that the adhesion hysteresis can become large and the surface coating can be damaged due to bond-breaking events.