CiteULike: Tag dinsmore

Flow and Fracture in Drying Nanoparticle Suspensions

ER Dufresne — 2008-04-24T18:38:32-00:00

Physical Review Letters, Vol. 91, No. 22. (24 November 2003), 224501.

Microscopic Structure and Elasticity of Weakly Aggregated Colloidal Gels

AD Dinsmore — 2007-09-19T16:41:52-00:00

Physical Review Letters, Vol. 96, No. 18. (2006)

We directly probe the microscopic structure, connectivity, and elasticity of colloidal gels using confocal microscopy. We show that the gel is a random network of one-dimensional chains of particles. By measuring thermal fluctuations, we determine the effective spring constant between pairs of particles as a function of separation; this is in agreement with the theory for fractal chains. Long-range attractions between particles lead to freely rotating bonds, and the gel is stabilized by multiple connections among the chains. By contrast, short-range attractions lead to bonds that resist bending, with dramatically suppressed formation of loops of particles.

Direct imaging of three-dimensional structure and topology of colloidal gels

AD Dinsmore — 2008-04-29T22:57:53-00:00

Journal of Physics: Condensed Matter, Vol. 14, No. 33. (2002), pp. 7581-7597.

We present novel measurements of the structure of colloidal gels. Using confocal microscopy, we obtain the precise three-dimensional positions of a large number of particles. We develop quantitative descriptions of the topology of the gel, including the number of bonds per particle, the chemical or bond fractal dimension, the number of flexible pivot points and other topological parameters that describe the chainlike structure. We investigate the dependence of these parameters on the particle volume fraction and the strength of the attraction that holds the particles together. While all samples have approximately the same fractal and chemical dimensions, we find that gels formed with stronger attraction or larger volume fraction have fewer bonds per particle, more filamentous chains and a greater number of flexible pivot points. Finally, we discuss the topological results in the context of the gel's elasticity. Measurements of the elastic constants of individual chainlike segments are explained with a simple model. The distribution of elastic constants, however, has a general form that is not understood.

Nanoparticle Assembly at Fluid Interfaces: Structure and Dynamics

Y Lin — 2008-04-29T22:19:44-00:00

Langmuir, Vol. 21, No. 1. (4 January 2005), pp. 191-194.

Abstract: The self-assembly of nanoparticles at fluid interfaces, driven by the reduction in interfacial energy, was investigated. With spherical, tri-n-octyl-phosphine-oxide covered cadium selenide (CdSe) nanoparticles (1-8 nm), thermal fluctuations compete with the interfacial segregation giving rise to a size-dependent self-assembly of the particles. The structure of the nanoparticle assembly was studied using electron microscopy, atomic force microscopy, and X-ray scattering in situ, which indicate that the particles form a densely packed monolayer. The energetics of the adsorption of nanoparticles onto the interface was revealed by time-dependent fluorescence studies on a mixture of two different sized nanoparticles at the interface. The dynamics of the nanoparticles at the fluid interface, probed using fluorescence photobleaching methods, suggests a liquid-like behavior. The results have implications in the design of hierarchical self-assemblies of nanoparticles for the one-step fabrication of devices on multiple length scales.

Colloidosomes: Selectively Permeable Capsules Composed of Colloidal Particles

AD Dinsmore — 2007-04-05T12:51:02-00:00

Science, Vol. 298, No. 5595. (1 November 2002), pp. 1006-1009.

10.1126/science.1074868

Measurement of Forces Inside a Three-Dimensional Pile of Frictionless Droplets

J Zhou — 2008-01-01T22:04:40-00:00

Science, Vol. 312, No. 5780. (16 June 2006), pp. 1631-1633.

We present systematic and detailed measurements of interparticle contact forces inside three-dimensional piles of frictionless liquid droplets. We measured long-range chainlike correlations of the directions and magnitudes of large forces, thereby establishing the presence of force chains in three dimensions. Our correlation definition provides a chain persistence length of 10 mean droplet diameters, decreasing as load is applied to the pile. We also measured the angles between contacts and showed that the chainlike arrangement arises from the balance of forces. Moreover, we found that piles whose height was comparable to the chain persistence length exhibited substantially greater strain hardening than did tall piles, which we attributed to the force chains. Together, the results establish a connection between the microscopic force network and the elastic response of meso- or macroscopic granular piles. The conclusions drawn here should be relevant in jammed systems generally, including concentrated emulsions and piles of sand or other heavy particles. 10.1126/science.1125151

Self-assembled Shells Composed of Colloidal Particles: Fabrication and Characterization

MF Hsu — 2008-04-23T21:31:14-00:00

Langmuir, Vol. 21, No. 7. (29 March 2005), pp. 2963-2970.

Abstract: We construct shells with tunable morphology and mechanical response with colloidal particles that self-assemble at the interface of emulsion droplets. Particles self-assemble to minimize the total interfacial energy, spontaneously forming a particle layer that encapsulates the droplets. We stabilize these layers to form solid shells at the droplet interface by aggregating the particles, connecting the particles with adsorbed polymer, or fusing the particles. These techniques reproducibly yield shells with controllable properties such as elastic moduli and breaking forces. To enable diffusive exchange through the particle shells, we transfer them into solvents that are miscible with the encapsulant. We characterize the mechanical properties of the shells by measuring the response to deformation by calibrated microcantilevers.