Phase diagram of sodium hexametaphosphate and poly(allylamine hydrochloride) mixtures and in situ monitoring of step-by-step deposition in this polyelectrolyte system

Abstract

The step-by-step deposition of poly(allylamine hydrochloride) (PAH) and sodium hexametaphosphate (PSP) leads to coatings displaying interesting intumescent properties and is a fascinating model system to understand the fundamental mechanism behind such a deposition process. In this investigation, the deposition kinetics of (PAH-PSP)n is followed in situ by means of a quartz crystal microbalance with dissipation monitoring, as a function of NaCl concentration. The evolution of the film deposition is analyzed in detail and the data are compared with previous data obtained by ellipsometry on dried films. These results are also compared with the expectations from the PAH/PSP phase diagram. The (PAH-PSP)n films are also able to incorporate hexacyanoferrate anions with an amount of an incorporated redox probe reflecting the film thickness as obtained in the presence of eletrolyte solutions of increasing ionic strength. The in situ measurements and the electrochemical probe experiments reveal details of the film deposition mechanism that are not accessible by dry-state characterization methods.