Surface “Priming” for Layer-by-Layer Deposition:  Polyelectrolyte Multilayer Formation on Allylamine Plasma-Modified Poly(tetrafluoroethylene)

Abstract

Allylamine plasma polymerization is reported as a method to surface-modify PTFE and to prepare substrates that promote layer-by-layer assembly of polyelectrolytes. Two conditions for the plasma polymerization that differ in radiofrequency power were studied. Both conditions (10 and 50 W) produce substrates that support layer-by-layer assembly, and well-defined multilayer structures are apparent in samples with greater than ∼10 layers. The substrates prepared at lower power yield more reproducible initial layer data; infrared spectra indicate a higher surface density of amine groups in the samples prepared at 10 W that likely leads to a higher surface charge density upon exposure to acidic aqueous solution. Poly(allylamine hydrochloride) and poly(sodium styrenesulfonate) were used to construct multilayer assemblies. XPS and contact angle data indicate stratified layers. XPS analysis also indicates that the stoichiometry of the assembly process is two ammonium ions per sulfonate group and that the average individual layer thickness is ∼6.1 Å.