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

Ultrathin polymer capsules prepared by stepwise deposition of oppositely ch arged polyelectrolytes onto melamine formaldehyde latex particles and biolo gical cells with subsequent dissolution of the core have been examined by s canning force microscopy (SFM) in the dried state. Folds generated during t he drying induced collapse of the shells are observed. The thickness of a s ingle polyelectrolyte layer in the dried state was determined as 1.3 +/- 0. 3 nm. Imaging at high resolution revealed the existence of domains and inva ginations. 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 t o the core decomposition, a surface separation into defined domains is not observed. The nature and size of the domains are discussed in relation to t he drying and the molecular parameters of the layer constituents.