Stimuli-responsive polymer ultrathin films with a binary architecture: combined layer-by-layer polyelectrolyte and surface-initiated polymerization approach

The fabrication of a multicomponent responsive polymer ultrathin film through the combined use of the layer-by-layer (LbL) and surface-initiated polymerization (SIP) techniques is described. Through the use of the weak polyelectrolytes poly(allylamine hydrochloride) (PAH) and poly(acrylic acid) (PAA), and two alternately charged atom transfer radical polymerization (ATRP) macroinitiators, a pH-controlled membrane was prepared capable of SIP. Polymerization of n-isopropylacrylamide to form PNIPAM brushes on top of this membrane surface created a thermally responsive layer. The combination of these two systems created a dual control mechanism for permeability through the membrane where pH control can be utilized on the polyelectrolyte LbL layers and thermal control on the polymer brushes. A series of experiments including electrochemistry, contact angle, and in-situ ellipsometry were used to demonstrate these effects. It is possible that other stimuli-responsive systems can be designed using the two independent macromolecular assembly and synthesis protocols.