Motion of phospholipidic vesicles along an inclined plane: Sliding and rolling

The migration of giant phospholipidic vesicles along an inclined plane in a quiescent fluid was observed as a function of the mass and the radius R of the vesicles, and as a function of the angle of inclination of the plane. Vesicles were swollen, and did not adhere to the substrate surface. It was observed from a side-view chamber that they have quasispherical shapes. The vesicles mainly slide along the plane, but also roll. The ratio $\omega R/v$ of rotational to translational velocities is of the order of 0.15 for vesicles of radius ranging from 10 to $30\hspace{0.5em}\mu \mathrm{m}.$ Values of this ratio, and variations of $v$ versus R, are well described by Goldman et al.’s model developed for the motion of rigid spheres close to a wall [Chem. Eng. Sci. 22, 637 (1967)]. In this framework, the thickness of the fluid film between the vesicle and the substrate derived from fitting experimental data was found to be equal to 48 nm.