In situ surface structure study of polyelectrolyte multilayers by liquid-cell AFM

Liquid cell Atomic Force Microscopy (AFM) is used to image in situ self-assembly polyelectrolyte films (SAPFs). We show that the technique is appropriate to study surface structure of these systems. In this work, we report images of layer-by-layer deposition for negative poly(sodium 4-styrenesulfonate) (PSS) and positive poly(allylamine hydrochloride) (PAH), when an initial layer of positive poly(ethylenimine) (PEI) starts the multilayer polymer film on a glass surface. This work is addressed to study first layers of SAPFs. Height AFM images are obtained using contact mode at different pH buffer where polyelectrolytes are initially dissolved. The pH values were: 3.5, 6.8 and 10.5. In all the cases, the polyelectrolyte film surfaces are not flat, they show rough surfaces with average grain domains ranging from 50 to 90 nm in diameter. The roughness and grain domains slightly grow as a function of deposited layer. In order to understand the origin of grain structure observed by AFM, size of positive–negative polyelectrolyte complex was determined by Dynamic Light Scattering. The results suggest that grains of granulate surface are formed by polyelectrolyte complexes. In the present work, we also discuss effects of kinetics and preparation on the surface structure.