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

Abstract

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 (Delta f) or the dissipation shift (Delta D) 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.

Electrochemically Triggered Assembly of Films: A One‐Pot Morphogen‐Driven Buildup

“…The ratio between the areas of these two peaks is in agreement with an almost complete reaction between the azide and alkyne groups (see detailed discussion in the Supporting Information). In addition, the peaks centered at 401 and 405 eV characteristic of azides12 are absent from the XPS spectrum. These results provide strong evidence of a quasiquantitative reaction between the two functionalized PAA polyanions.…”

Oscillating Reactions Meet Polymers at Interfaces

“…In 2008, Tang et al reported the oscillatory behavior of a pH-responsive LbL assembly, which was studied by means of QCM-D [ 66 ]. The multilayer was assembled by the assembly and “click” reaction of poly(acrylic acid- co -3-azidopropyl acrylate) (poly(AA- co -Az)) and poly(acrylic acid- co -propargyl acrylate) (poly(AA- co -PA)) directly on the QCM crystal resonator, which was previously functionalized with a primer layer of alkyne-modified branched poly(ethyleneimine) ( Figure 3 a).…”

“… ( a – c ) Chemical structure and schematic representation of the pH-oscillating layer-by-layer assembly, crosslinked with a click chemistry approach. ( d ) Corresponding frequency and dissipation shifts monitored by QCM-D. Reproduced with permission from [ 66 ], American Chemical Society, 2008. …”

Strategies for covalently reticulated polymer multilayers

“…The covalent bonds between PAA chains allow a reversible swelling of the film when the pH is changed after buildup. 192 The optimal buildup conditions for this azide-and alkyne-functional PAA-based system were investigated. 193 The obtained films are thicker when the pH of the solution is adjusted to 2.5, the grafting ratio of PAA is 30%, the adsorption time equal to 10 minutes and the ionic strength fixed to 150 mM.…”