Mechanical property of lipid-coated polyelectrolyte microcapsules

The deformations of lipid coated polyelectrolyte capsules induced by osmotic pressure were determined in poly(styrene sulfonate, sodium salt) (PSS) solution by making use of the fact that PSS molecules with a molecular weight 70000 will not penetrate into the capsules. At a critical osmotic pressure the initial spherical capsules changed their shape and became an invagination. The measurements of single particle light scattering provided the wall thickness of the lipid-coated capsules with 25.6 nm while the thickness for pure polyelectrolyte capsules in solution is about 21.6 nm, indicating that the coating lipid layer has about 4 nm thickness. It demonstrates that DMPA forms a bilayer on the surface of polyelectrolyte capsules. With these data, that the elasticity coefficient of the lipid-coated capsules is about 426 Mpa can be obtained.