807 research outputs found
Polymer Shape Anisotropy and the Depletion Interaction
We calculate the second and third virial coefficients of the effective
sphere-sphere interaction due to polymer depletion. By utilizing the anisotropy
of a typical polymer conformation, we can consider polymers that are roughly
the same size as the spherical inclusions. We argue that recent experiments can
confirm this anisotropy.Comment: 4 pages, 4 eps figures, RevTe
Forced motion of a probe particle near the colloidal glass transition
We use confocal microscopy to study the motion of a magnetic bead in a dense
colloidal suspension, near the colloidal glass transition volume fraction
. For dense liquid-like samples near , below a threshold force
the magnetic bead exhibits only localized caged motion. Above this force, the
bead is pulled with a fluctuating velocity. The relationship between force and
velocity becomes increasingly nonlinear as is approached. The
threshold force and nonlinear drag force vary strongly with the volume
fraction, while the velocity fluctuations do not change near the transition.Comment: 7 pages, 4 figures revised version, accepted for publication in
Europhysics Letter
Properties of cage rearrangements observed near the colloidal glass transition
We use confocal microscopy to study the motions of particles in concentrated
colloidal systems. Near the glass transition, diffusive motion is inhibited, as
particles spend time trapped in transient ``cages'' formed by neighboring
particles. We measure the cage sizes and lifetimes, which respectively shrink
and grow as the glass transition approaches. Cage rearrangements are more
prevalent in regions with lower local concentrations and higher disorder.
Neighboring rearranging particles typically move in parallel directions,
although a nontrivial fraction move in anti-parallel directions, usually from
pairs of particles with initial separations corresponding to the local maxima
and minima of the pair correlation function , respectively.Comment: 5 pages, 4 figures; text & figures revised in v
Depletion forces near curved surfaces
Based on density functional theory the influence of curvature on the
depletion potential of a single big hard sphere immersed in a fluid of small
hard spheres with packing fraction \eta_s either inside or outside of a hard
spherical cavity of radius R_c is calculated. The relevant features of this
potential are analyzed as function of \eta_s and R_c. There is a very slow
convergence towards the flat wall limit R_c \to \infty. Our results allow us to
discuss the strength of depletion forces acting near membranes both in normal
and lateral directions and to make contact with recent experimental results
Hard Spheres in Vesicles: Curvature-Induced Forces and Particle-Induced Curvature
We explore the interplay of membrane curvature and nonspecific binding due to
excluded-volume effects among colloidal particles inside lipid bilayer
vesicles. We trapped submicron spheres of two different sizes inside a
pear-shaped, multilamellar vesicle and found the larger spheres to be pinned to
the vesicle's surface and pushed in the direction of increasing curvature. A
simple model predicts that hard spheres can induce shape changes in flexible
vesicles. The results demonstrate an important relationship between the shape
of a vesicle or pore and the arrangement of particles within it.Comment: LaTeX with epsfig; ps available at
http://dept.physics.upenn.edu/~nelson/index.shtml Phys Rev Lett in press
(1997
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