Polyelectrolyte Multilayer Formation on Neutral Hydrophobic Surfaces

Pyrene-labeled poly(allylamine hydrochloride) (PAH-Py) has been used to trace the conformational and depletion behaviors of polyelectrolyte chains on neutral hydrophobic Teflon-AF, octadecyltrichlorosilane, or poly(dimethylsiloxane) during assembling by the layer-by-layer deposition technique. The results are used to qualitatively describe how the final quality of multilayer thin films relies on salt stabilization. PAH-Py chains adsorb onto the surfaces in a stretched conformation and form a uniform and dense layer, confirming Dobrynin and Rubinstein's theory. Without an added electrolyte in the polyelectrolyte solutions used for building up multilayers, the PAH-Py layer was seriously depleted, and the extended chains on the surface recoiled during the assembly process, forming coagulated structures of polyelectrolyte complex. In comparison, uniform and flat multilayer thin films were achieved on the surfaces with an added electrolyte, presenting a significant role of salt stabilization on the multilayer.