Polyelectrolyte Multilayer Microcapsules Research Articles

Effect of pH and Salt on the Stiffness of Polyelectrolyte Multilayer Microcapsules

By using a combination of atomic force and confocal microscopy, we explore the effect of pH and salt on the stiffness of polyelectrolyte microcapsules with shells composed of strong polyanions and weak polycations. The stiffness of the capsules was found to be largest in water. It decreases slightly with added salt and gets much smaller both in acidic and in alkaline solutions. The moderate softening of the capsules in electrolyte solutions indicates that even high salt concentration does not significantly dissociate polyelectrolytes in the multilayer. The dramatic softening of the capsules at high pH probably reflects a decrease in the charge density of a polycation, which leads to a reduction in the number of ionic cross-links. In contrast, low stiffness of the capsules in acidic solutions seems to be connected mostly with the enhanced permeability of the multilayer shell.

Elasticity of polyelectrolyte multilayer microcapsules.

We present a novel approach to probe elastic properties of polyelectrolyte multilayer microcapsules. The method is based on measurements of the capsule load-deformation curves with the atomic force microscope. The experiment suggests that at low applied load deformations of the capsule shell are elastic. Using elastic theory of membranes we relate force, deformation, elastic moduli, and characteristic sizes of the capsule. Fitting to the prediction of the model yields the lower limit for Young's modulus of the polyelectrolyte multilayers of the order of 1-100 MPa, depending on the template and solvent used for its dissolution. These values correspond to Young's modulus of an elastomer.

Young's Modulus of Polyelectrolyte Multilayers from Microcapsule Swelling

We measure Young's modulus of a free polyelectrolyte multilayer film by studying osmotically induced swelling of polyelectrolyte multilayer microcapsules filled with the polyelectrolyte solution. Different filling techniques and core templates were used for the capsule preparation. Varying the concentration of the polyelectrolyte inside the capsule, its radius and the shell thickness yielded an estimate of Young's modulus of the order of 100 MPa. This corresponds to an elastomer and reflects strong interactions between polyanions and polycations in the multilayer.

Spontaneous deposition of horseradish peroxidase into polyelectrolyte multilayer capsules to improve its activity and stability.

Horseradish peroxidase (HRP) was encapsulated in preformed polyelectrolyte multilayer (PEM) microcapsules by spontaneous deposition with remarkably improved stability and catalytic activity.