Hollow polyelectrolyte capsules were fabricated by means of stepwise adsorption of polyelectrolytes followed by dissolution of the templating core. The capsule wall thickness was approximately 20 nm. The diameter of the capsules is given by the size of the templates (3.3 μm). These capsules exclude poly(styrenesulfonate) (PSS) from a molecular weight of 4200 upward but are permeable for small ions and 6-carboxyfluorescein (6-CF). By means of adding PSS in acidic form to the bulk solution, a Donnan equilibrium between the bulk and internal solution encapsulated within the capsules was created. The pH in the capsule interior is more basic. This difference in pH is larger than a unit for capsules of 3.3 μm in diameter. Addition of NaCl decreases this pH difference. A theoretical model is developed that describes the observed pH difference. The essential assumptions of the model are the selective permeability of the capsule wall, charging of the capsule together with its interior according to its capacitance, and an osmotic balance of the system. The developed shell system represents a novel class of stable colloids combining the compartmentalization of an aqueous solution with the possibility of creating pH differences on the micrometer scale.

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The mechanism of formation of supported lipid layers from phosphatidylcholine and phosphatidylserine vesicles in solution on polyelectrolyte multilayers was studied by a variety of experimental techniques. The interaction of zwitterionic and acidic lipid vesicles, as well as their mixtures, with polyelectrolyte supports was followed in real time by micro-gravimetry. The fabricated lipid-polyelectrolyte composite structures on top of multilayer coated colloidal particles were characterized by flow cytometry and imaging techniques. Lipid diffusion over the macroscopic scale was quantified by fluorescence recovery after photobleaching, and the diffusion was related to layer connectivity. The phospholipid-polyelectrolyte binding mechanism was investigated by infrared spectroscopy. A strong interaction of polyelectrolyte primary amino groups with phosphate and carboxyl groups of the phospholipids, leading to dehydration, was observed. Long-range electrostatic attraction was proven to be essential for vesicle spreading and rupture. Fusion of lipid patches into a homogeneous bilayer required lateral mobility of the lipids on the polyelectrolyte support. The binding of amino groups to the phosphate group of the zwitterionic lipids was too weak to induce vesicle spreading, but sufficient for strong adsorption. Only the mixture of phosphatidylcholine and phosphatidylserine resulted in the spontaneous formation of bilayers on polyelectrolyte multilayers. The adsorption of phospholipids onto multilayers displaying quarternary ammonium polymers produced a novel 3D lipid polyelectrolyte structure on colloidal particles.