Scanning force microscopy investigation of polyelectrolyte nano- and microcapsule wall texture

Ultrathin polymer capsules prepared by stepwise deposition of oppositely charged polyelectrolytes onto melamine formaldehyde latex particles and biological cells with subsequent dissolution of the core have been examined by scanning force microscopy (SFM) in the dried state. Folds generated during the drying induced collapse of the shells are observed. The thickness of a single polyelectrolyte layer in the dried state was determined as 1.3 +/- 0.3 nm. Imaging at high resolution revealed the existence of domains and invaginations. This typical lateral pattern has been quantified by means of an autocorrelation analysis of the SFM images. A characteristic domain size of 50-100 nm is found. If the polyelectrolytes have been cross-linked prior to the core decomposition, a surface separation into defined domains is not observed. The nature and size of the domains are discussed in relation to the drying and the molecular parameters of the layer constituents.