Chemical reactivity of plasma polymerized allylamine (PPAA) thin films on Au and Si: Study of the thickness influence and aging of the films

In this work, we investigate the surface reactivity of substrates coated with thin layers (estimated thickness <= 30 nm) of plasma polymerized allylamine films (PPM), an amine-functionalized polymer deposited by plasma-enhanced chemical vapor deposition (PECVD) with radiofrequency (RF) discharges. Our results show that very thin layers, or islands, can retain on their surface molecules that are able to react through their NH(2) functions. We have tested and assessed by X-Ray Electron Spectroscopy (XPS) and Quartz Crystal Microbalance (QCM) the surface density of chemical functions vs. layer thicknesses by using chemical derivatization with two types of agents: imine formation by a reaction of primary amine from the coating with aldehyde (Pentafluorobenzaldehyde, PFBA) and amide-bond formation by reaction with an activated carboxylic group (Succinimidyl Succinate Terminated Polyethylene glycol, EGSS). Results show that the PPAA coatings-even for very thin layers of a few nanometers-promote the chemisorption of the tagging molecules. The aging under air and evolution of reactive amine surface concentration with time under air are also presented. (C) 2011 Elsevier B.V. All rights reserved.