Chemical Oscillation Induced Periodic Swelling and Shrinking of a Polymeric Multilayer Investigated with a Quartz Crystal Microbalance

Poly(acrylic acid-co-3-azidopropyl acrylate) and poly(acrylic acid-co-propargyl acrylate) have been alternately fabricated into a multilayer via the click reaction. The layer-by-layer deposition was monitored with a quartz crystal microbalance with dissipation (QCM-D) in real time. The response of the multilayer under continuous flow of a bromate−sulfite−ferrocyanide solution with pH oscillation has also been investigated by use of QCM-D. As the pH oscillates between 3.1 and 6.6, either the frequency shift (Δf) or the dissipation shift (ΔD) periodically varies with a constant amplitude, clearly indicating that the multilayer swells and shrinks oscillatedly. The changes of thickness, shear viscosity, and elastic shear modulus further indicate the oscillation.