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Polyelectrolyte multilayers were deposited onto polystyrene and melamine formaldehyde latex particles by means of consecutive adsorption. Two different methods of multilayer growth were employed. First, adsorption of polyelectrolytes at a concentration exceeding saturation amounts was combined with the removal of the nonbound polyelectrolyte by means of centrifugation. Second, adsorption of polyelectrolyte was performed at a concentration just sufficient for saturation coverage. Both methods yielded continuous layer growth. The process of film formation was followed by electrophoresis, dynamic light scattering, single particle light scattering and fluorescence intensity measurements. Layer deposition onto partially crosslinked melamine resin latex particles, which were soluble at pH values of less than 1.6, resulted in the production of three‐dimensional thin polyelectrolyte shells upon dissolving the core. The ultrathin shells were observed by means of scanning and transmission electron microscopy. © 1998 John Wiley & Sons, Ltd.

The electrostatic binding of two anionic probe molecules, pyrenetetrasulfonic acid (4-PSA) and 6-carboxyfluorescein (6-CF), to poly(allylamine hydrochloride) (PAH)/poly(sodium 4-styrenesulfonate) (PSS) and poly(diallyldimethylammonium chloride) (PDADMAC)/PSS ultrathin multilayer films assembled onto polystyrene (PS) latex particles has been examined using fluorescence spectroscopy. At the probe concentrations studied, binding was observed only when the outermost layer was oppositely (positively) charged to the probe. The amount of probe bound was found to increase linearly with polyelectrolyte layer number up to about 11 layers (15 nm in thickness for the PAH/PSS films), with saturation binding occurring beyond 11 layers. The binding data reveal that a minimum of about 10−30% of the cationic charges of the polycations in the upper region of the multilayer films (where the probe binds) are not directly electrostatically utilized in the multilayer assembly process through ion-pair binding to oppositely charged sites on the polyanions. The removal of probe bound to multilayers of different thicknesses upon subsequent exposure to PSS has also been examined. Evidence that polyelectrolyte multilayer films are long-range electrostatically coupled systems is presented. The results obtained provide some insight into the role and extent of electrostatic interactions in polyelectrolyte multilayers.

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Osmotically induced deformations (invaginations) of polyelectrolyte capsules were observed in poly(styrene sulfonate, sodium salt) (PSS) solution since PSS of Mw 70 000 is excluded from the capsule interior. It was found that there is a critical osmotic pressure difference at which the initial spherical capsule shape becomes unstable and invaginations are formed. This critical osmotic pressure was obtained as a function of the wall thickness and the capsule size. A theoretical model is provided which describes the relationship between the critical osmotic pressure, the elasticity modulus, the capsule wall thickness, and the capsule radius. The model was verified by measuring the invagination onset as a function of particle radius and wall thickness. The elasticity modulus of the PSS/PAH (polyallylamine hydrochloride) polyelectrolyte multilayer was measured as a function of wall thickness and capsule diameter. The modulus ranges between 500 and 750 MPa, which indicates a relatively strongly interconnected polyelectrolyte multilayer structure. With higher molecular weight PAH the elasticity modulus of the PSS/PAH multilayer was slightly enhanced.PACS. 46.32.+x Static buckling and instability -68.60.Bs Mechanical and acoustical properties

Layer-by-layer (LbL) assembly of oppositely charged polyelectrolytes was used to coat fluorescein particles. These particles, with a size of 4−9 μm, were prepared by precipitation of fluorescein at pH 2. Polystyrensulfonate (PSS) and polyallylamine (PAH) were used to form a polyelectrolyte shell on the fluorescein core. The permeation of fluorescein molecules through the polyelectrolyte shell during core dissolution was monitored at pH 8 by the increasing fluorescence intensity as a result of dequenching. The number of polyelectrolyte layers sufficient to sustain fluorescein release was found to be 8−10. Increasing the number of layers prolonged the core dissolution time for minutes. The permeability of polyelectrolyte multilayers of the thickness of 20 nm for fluorescein is about 10-9 m/s. The features of the release profile and possible applications of the LbL method for shell formation in order to control release properties for entrapped materials are outlined.

Exact control of the film thickness of polyelectrolyte shells (a transmission electron microscopy image is shown) is achieved by colloid-templated consecutive adsorption of polyanions and polycations followed by decomposition of the templating core. Possible areas of application for these shells range from the pharmaceutical, food, cosmetic, and paint industries to catalysis and microcrystallization.