Depletion Interactions among Hard Spheres inside Vesicles
Abstract
We demonstrate that hard spheres diffusing inside a rigid vesicle of complex shape are pushed by <A HREF=http://www.lrsm.upenn.edu/ dinsmore/vesdiff.html>entropic excluded-volume interactions</A> to the surface of the vesicle and pushed along the vesicle's surface in the direction of increasing curvature(A.D. Dinsmore, A.G. Yodh and D.J. Pine, Nature 383), 239 (1996).. Rigid, multilamellar SOPC vesicles (3 μm in diameter) contained water, polystyrene spheres and enough salt to screen out long-range electrostatic interactions. A lone 0.47-μm diameter sphere diffused freely inside the vesicle. When smaller spheres (0.08 μm, volume fraction = 0.3) were present, the free energy of the mixture decreased by ≈ kT as the larger sphere moved from bulk to flat surface, and further decreased by kT as it moved from a flat surface to a curved region of the surface. The force will be explained within the depletion-force model by considering the volume accessible to the small spheres as a function of large-sphere position and surface shape. The possibility of membrane curvature induced by the particles will be discussed. Supported by NSF Grant No. DMR93-06814 and Materials Research Grant No. DMR91-20668. AGY also supported in part by the NSF PYI program and by the Alfred P. Sloan Foundation.
- Publication:
-
APS March Meeting Abstracts
- Pub Date:
- March 1997
- Bibcode:
- 1997APS..MAR.A1609D