DIFFUSION BEHAVIOR OF LIPID VESICLES IN ENTANGLED POLYMER-SOLUTIONS

Dynamic light scattering was used to follow the tracer diffusion of ph ospholipid/cholesterol vesicles in aqueous polyacrylamide solutions an d compared with the diffusive behavior of polystyrene (PS) latex spher es of comparable diameters. Over the range of the matrix concentration examined (C-p = 0.1-10 mg/ml), the diffusivities of the PS spheres an d the large multilamellar vesicles exhibited the Stokes-Einstein (SE) relation, while the diffusivity of the unilamellar vesicles did not fo llow the increase of the solution's viscosity caused by the presence o f the matrix molecules. The difference between the diffusion behaviors of unilamellar vesicles and hard PS spheres of similar size is possib ly due to the flexibility of the lipid bilayer of the vesicles. The un ilamellar vesicles are capable of changing their shape to move through the entangled polymer solution so that the hindrance to their diffusi on due to the presence of the polymer chains is reduced, while the rig id PS spheres have little flexibility and they encounter greater resis tance. The multilamellar vesicles are less flexible, thus their diffus ion is similar to the hard PS spheres of similar diameter.