CiteULike: dchen's weeks

The Mysterious Glass Transition

James Langer — 2008-05-03T19:19:58-00:00

Physics Today, Vol. 60, No. 2. (2007), pp. 8-9.

Colloidal Glass Transition Observed in Confinement

Carolyn Nugent — 2007-07-13T19:38:05-00:00

Physical Review Letters, Vol. 99, No. 2. (2007)

We study a colloidal suspension confined between two quasiparallel walls as a model system for glass transitions in confined geometries. The suspension is a mixture of two particle sizes to prevent wall-induced crystallization. We use confocal microscopy to directly observe the motion of colloidal particles. This motion is slower in confinement, thus producing glassy behavior in a sample which is a liquid in an unconfined geometry. For higher volume fraction samples (closer to the glass transition), the onset of confinement effects occurs at larger length scales.

Structure of dense colloidal liquids in tight spaces

Eric — 2008-04-29T18:44:50-00:00

We use three-dimensional confocal microscopy to study the structure of a dense colloidal liquid conﬁned between two parallel glass plates. The colloidal sample is at a volume fraction of 50% and is a binary mixture of 2 µm and 3 µm diameter particles to prevent crystallization. The plate separation ranges from 50 small particle diameters to 3 small particle diameters. While particles form layers immediately adjacent to the conﬁning walls, we otherwise see little inﬂuence of the conﬁnement on structure.

Confocal microscopy of colloids

Semwogerere — 2007-07-27T10:53:20-00:00

Journal of Physics: Condensed Matter, Vol. 19, No. 11. (2007)

Colloids have increasingly been used to characterize or mimic many aspects of atomic and molecular systems. With confocal microscopy these colloidal particles can be tracked spatially in three dimensions with great precision over large time scales. This review discusses equilibrium phases such as crystals and liquids, and non-equilibrium phases such as glasses and gels. The phases that form depend strongly on the type of particle interaction that dominates. Hard-sphere-like colloids are the simplest, and interactions such as the attractive depletion force and electrostatic repulsion result in more non-trivial phases which can better model molecular materials. Furthermore, shearing or otherwise externally forcing these colloids while under microscopic observation helps connect the microscopic particle dynamics to the macroscopic flow behaviour. Finally, directions of future research in this field are discussed.

Forced motion of a probe particle near the colloidal glass transition

Habdas — 2008-04-28T19:13:52-00:00

Europhys. Lett., 67 (3), p. 477 (2004)

We use confocal microscopy to study the motion of a magnetic bead in a dense colloidal suspension, near the colloidal glass transition volume fraction $φ_ g$. For dense liquid-like samples near $φ_ g$, 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 $φ_ g$ 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.

Direct visualization of ageing in colloidal glasses

Rachel Courtland — 2008-04-26T00:03:39-00:00

Journal of Physics: Condensed Matter, Vol. 15, No. 1. (2003), pp. S359-S365.

We use confocal microscopy to directly visualize the dynamics of ageing colloidal glasses. We prepare a colloidal suspension at high density, a simple model system that shares many properties with other glasses, and initiate experiments by stirring the sample. We follow the motion of several thousand colloidal particles after the stirring and observe that their motion significantly slows as the sample ages. The ageing is both spatially and temporally heterogeneous. Furthermore, while the characteristic relaxation timescale grows with the age of the sample, nontrivial particle motions continue to occur on all timescales.

Three-Dimensional Direct Imaging of Structural Relaxation Near the Colloidal Glass Transition

Eric Weeks — 2005-06-19T21:01:36-00:00

Science, Vol. 287, No. 5453. (28 January 2000), pp. 627-631.

Experimental studies of the flow of concentrated hard sphere suspensions into a constriction

L Isa — 2006-06-07T11:46:33-00:00

Journal of Physics: Conference Series, Vol. 40, No. 1. (2006), 124.

Short-~and long-range correlated motion observed in colloidal glasses and liquids

John — 2007-08-29T17:41:41-00:00

Journal of Physics: Condensed Matter, Vol. 19, No. 20. (2007)

We use a confocal microscope to examine the motion of individual particles in a dense colloidal suspension. Close to the glass transition, particle motion is strongly spatially correlated. The correlations decay exponentially with particle separation, yielding a dynamic length scale of O(2-3s) (in terms of particle diameter s). This length scale grows modestly as the glass transition is approached. Further, the correlated motion exhibits a strong spatial dependence on the pair correlation function g(r). Motion within glassy samples is weakly correlated, but with a larger spatial scale for this correlation.

Properties of Cage Rearrangements Observed near the Colloidal Glass Transition

Eric Weeks — 2007-04-02T22:33:06-00:00

Physical Review Letters, Vol. 89, No. 9. (2002), 095704.

We use confocal microscopy to study particle motion in colloidal systems. Near the glass transition; 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 concentrations and higher disorder. Neighboring rearranging particles typically move in parallel directions; although a nontrivial fraction moves in antiparallel directions; usually from particle pairs with initial separations corresponding to local maxima and minima of the pair correlation function g ( r ); respectively.