Hollow polyelectrolyte shells: Exclusion of polymers and donnan equilibrium

Hollow polyelectrolyte capsules were fabricated by means of stepwise adsorp tion of polyelectrolytes followed by dissolution of the templating core. Th e capsule wall thickness was approximately 20 nm. The diameter of the capsu les is given by the size of the templates (3.3 mu m). These capsules exclud e poly(styrenesulfunate) (P-SS) from a molecular weight of 4200 upward but are permeable for small ions and 6-carboxyfluorescein (6-CF). By means of a dding PSS in acidic form to the bulk solution, a Donnan equilibrium between the bulk and internal solution encapsulated within the capsules was create d. The pH in the capsule interior is more basic. This difference in pH is l arger than a unit for capsules of 3.3 mu m in diameter. Addition of NaCl de creases 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 togeth er with its interior according to its capacitance, and an osmotic balance o f the system. The developed shell system represents a novel class of stable colloids combining the compartmentalization of an aqueous solution with th e possibility of creating pH differences on the micrometer scale.