Morphology of multilayers assembled by electrostatic attraction of oppositely charged model polyelectrolytes

Alternating multilayers assembled stepwise with two prototype polyelectrolytes, i.e. poly(allylamine) hydrochloride (PAA) and poly(vinyl sulfate) potassium salt (PVS), have been examined by means of reflection-absorption infrared (RAIR) spectroscopy and atomic force microscopy (AFM). The growth step revealed by the RAIR spectroscopy was in good agreement with the ellipsometric data. The RAIR spectral data revealed that both macromolecules were randomly oriented in the (PVS/PAA) composite system without any preferential alignment. The atomic force microscopy measurements showed that the morphology of the (PVS/PAA) multilayers prepared in the absence of NaCl were quite homogeneous in agreement with a recent report. However, the morphology of the multilayers prepared in the presence of NaCl was observed to be significantly heterogeneous; the morphology was gradually roughened upon an increase in the number of bilayers. The highly coiled, compact macromolecules present in a NaCl solution seemed preferentially to anchor on the oppositely charged, aggregated surface sites without spreading over the interfacial region. Nonetheless, the morphology of the surface of the (PVS/PAA) system was hardly subjected to change once a stable firm had been assembled, regardless of the presence of NaCl. (C) 1999 Elsevier Science S.A. All rights reserved.