Degrafting polyelectrolyte brushes by elastic force

Polymer brushes grafted on a surface at high densities have been of great interest in the past two decades due to their high stability at the interface. Previous reports have revealed that covalent bonds between the polymer brush and the surface can break in buffer solutions, leading to degrafting of polymer chains from the surface. We report a systematic study of degrafting covalently attached polyelectrolyte brushes. Poly(2-dimethylaminoethyl methacrylate) (PDMAEMA) brushes were grown on silicon substrates by surface-initiated atom transfer radical polymerization (SI-ATRP) and incubated in aqueous solutions at varying pH with constant ionic strength. Increasing the degree of quaternization increases the swelling ratio and the elastic force. By degrafting at different pH, with constant elastic force, the main mechanism of degrafting is shown to be base-catalyzed hydrolysis at the Si-O groups and/or the ester group of the SI-ATRP initiator. Stronger elastic force on the initiator induces more degrafting. Brush degrafting increases slightly with increasing the molecular weight of the brush.