CiteULike: dchen's Mason

Slippery diffusion-limited aggregation

Clair Seager — 2008-06-27T08:16:01-00:00

Colloidal particles that interact through strong, short-range, secondary attractions in liquids form irreversible “slippery” bonds that are not shear-rigid. Through event-driven simulations of slippery attractive spheres, we show that space-filling fractal clusters still emerge from the process of “slippery” diffusion-limited aggregation (DLA). Although slippery and classic DLA clusters have the same fractal dimension, df=2.5, their average coordination numbers are quite different: zS=6 whereas zC=2. Local tetrahedral attractive jamming of the particles leads to a structure factor, S(q), that exhibits dense cluster peaks at higher wave numbers, q, and a fractal power-law rise toward lower q.

Structure and rheology of organoclay suspensions

Jr — 2008-06-11T21:58:58-00:00

Physical Review E (Statistical, Nonlinear, and Soft Matter Physics), Vol. 75, No. 2. (2007)

We have characterized a montmorillonite-based organoclay dispersed in three different nonaqueous solvents using a combination of x-ray scattering, small-angle neutron scattering (SANS), and ultrasmall angle neutron scattering (USANS), together with rheological measurements. Consistent with these measurements, we present a structural model for the incompletely dispersed clay as consisting of randomly oriented tactoids made of partially overlapping clay sheets, with transverse dimensions of several microns. Intersheet correlation peaks are visible in x-ray scattering, and quantitatively fit by our model structure factor. SANS and USANS together show a power law of about −3 over a wide range of wave numbers below the intersheet correlation peak. Our model relates this power law to a power law distribution of the number of locally overlapping layers in a tactoid. The rheology data show that both storage and loss moduli, as well as yield stress, scale with a power law in volume fraction of about three. Equating the gel onset composition with the overlap of randomly oriented tactoids and taking into account the large transverse dimensions of the tactoids, we predict the gel point to be at or below 0.006 volume fraction organoclay. This is consistent with the rheology data.

Slippery diffusion-limited aggregation

Clair Seager — 2008-06-11T21:34:00-00:00

Physical Review E (Statistical, Nonlinear, and Soft Matter Physics), Vol. 75, No. 1. (2007)

Colloidal particles that interact through strong, short-range, secondary attractions in liquids form irreversible “slippery” bonds that are not shear-rigid. Through event-driven simulations of slippery attractive spheres, we show that space-filling fractal clusters still emerge from the process of “slippery” diffusion-limited aggregation (DLA). Although slippery and classic DLA clusters have the same fractal dimension, df=2.5, their average coordination numbers are quite different: zS=6 whereas zC=2. Local tetrahedral attractive jamming of the particles leads to a structure factor, S(q), that exhibits dense cluster peaks at higher wave numbers, q, and a fractal power-law rise toward lower q.

The microrheology of colloidal dispersions

TGM van de Ven — 2008-04-29T20:01:00-00:00

Colloid & Polymer Science, Vol. 255, No. 8. (1977), pp. 794-804.

Summary A theory of doublet formation, the first step in coagulation of dilute monodisperse spherical sols subjected to shearing motion, in which Brownian motion dominates the effects of shear is presented. Contrary to Smoluchowski's predictions, it is found that the increase in the rate of coagulation due to shear is not proportional to the shear rateG, but toG1/2 with the proportionality constant depending on the perikinetic capture efficiency, the translational diffusion constant and sphere radius. With non-spherical particles the increase rate due to shear also varies with G1/2 and depends, in addition, on particle size and shape.

Nanoemulsions: formation, structure, and physical properties

Mason — 2006-10-08T01:37:08-00:00

Journal of Physics: Condensed Matter, Vol. 18, No. 41. (18 October 2006), pp. R635-R666.

Particle Tracking Microrheology of Complex Fluids

TG Mason — 2006-08-30T16:25:45-00:00

Physical Review Letters, Vol. 79, No. 17. (27 October 1997), 3282.

We present a new method for measuring the linear viscoelastic shear moduli of complex fluids. Using photodiode detection of laser light scattered from a thermally excited colloidal probe sphere; we track its trajectory and extract the moduli using a frequency-dependent Stokes-Einstein equation. Spectra obtained for polyethylene oxide in water are in excellent agreement with those found mechanically and using diffusing wave spectroscopy. Since only minute sample volumes are required; this method is well suited for biomaterials of high purity; as we demonstrate with a concentrated DNA solution.

Yielding and Flow of Monodisperse Emulsions

TG Mason — 2008-04-28T16:14:56-00:00

Journal of Colloid and Interface Science, Vol. 179, No. 2. (10 May 1996), pp. 439-448.

We have measured the yield transition of monodisperse emulsions as the volume fraction, [phi], and droplet radius,a, are varied. We study the crossover from the perturbative shear regime, which reflects the linear viscoelastic properties, to the steady shear regime, which reflects nonlinear, plastic flow. For small oscillatory strains of peak amplitude [gamma], the peak stress, [tau], is linearly proportional to [gamma]. As the strain is increased, the stress becomes nonlinear in [gamma] at the yield strain, [gamma]y. The [phi] dependence of [gamma]yis independent ofaand exhibits a minimum near the critical volume fraction, [phi]c[approximate] 0.635, associated with the random close packing of monodisperse spheres. We show that the yield stress, [tau]y, increases dramatically as the volume fraction increases above [phi]c; [tau]yalso scales with the Laplace pressure, [sigma]/a, where [sigma] is the interfacial tension. For comparison, we also determine the steady shear stress over a wide range of strain rates, [gamma]. Below [phi] [approximate] 0.70, the flow is homogeneous throughout the sample, while for higher [phi], the emulsion fractures resulting in highly inhomogeneous flow along the fracture plane. Above [phi] [approximate] 0.58, the steady shear stress exhibits a low strain rate plateau which corresponds with the yield stress measured with the oscillatory technique. Moreover, [tau]yexhibits a robust power law dependence on [gamma] with exponents decreasing with [phi], varying from to . Below [phi] [approximate] 0.58, associated with the colloidal glass transition, the plateau stress disappears entirely, suggesting that the equilibrium glassy dynamics are important in identifying the onset of the yield behavior.

Suspended Particles in Fluid Flow Through Tubes

RG Cox — 2008-04-27T00:22:57-00:00

Annual Review of Fluid Mechanics, Vol. 3 (1971), pp. 291-316.

Not Available

Shear Rupturing of Droplets in Complex Fluids

TG Mason — 2008-04-27T00:19:24-00:00

Langmuir, Vol. 13, No. 17. (20 August 1997), pp. 4600-4613.

Abstract: We have experimentally studied the shear-induced rupturing of viscous droplets in viscoelastic complex fluids. Remarkably, a premixed emulsion of large, polydisperse droplets can be ruptured into monodisperse emulsions of uniform colloidal droplets. The monodispersity becomes most pronounced when the premixed emulsion is viscoelastic and has a shear-thinning viscosity. Since viscoelastic materials may fracture, we reduce the gap of our shear cell to ensure a spatially uniform strain rate for rupturing. We observe monodispersity whether the viscoelasticity arises from the suspending fluid (e.g., concentrated surfactant solution) or droplet deformation as in compressed emulsions. Our observations suggest that the monodispersity results from droplet rupturing alone and that the capillary instability is inhibited by the partial elasticity of the complex fluid. We use the monodispersity to study how the droplet size depends upon the shear rate and composition.

Model for the Elasticity of Compressed Emulsions

Martin-D Lacasse — 2008-04-27T00:13:18-00:00

Physical Review Letters, Vol. 76, No. 18. (29 April 1996), 3448.

Elasticity of Compressed Emulsions

TG Mason — 2008-04-26T23:57:13-00:00

Physical Review Letters, Vol. 75, No. 10. (1995), 2051.

Radial Distribution of the Random Close Packing of Equal Spheres

JD Bernal — 2008-04-24T18:19:16-00:00

Nature, Vol. 194, No. 4832. (June 1962), pp. 957-958.

Shear-Induced Configurations of Confined Colloidal Suspensions

Itai Cohen — 2008-04-24T16:40:15-00:00

Physical Review Letters, Vol. 93, No. 4. (23 July 2004), 046001.

Linear Viscoelasticity of Colloidal Hard Sphere Suspensions near the Glass Transition

TG Mason — 2007-11-26T18:16:34-00:00

Physical Review Letters, Vol. 75, No. 14. (2 October 1995), 2770.

The frequency-dependent viscoelastic shear modulus of concentrated suspensions of colloidal hard spheres is shown to be strongly modified as the volume fraction approaches the glass transition. The elastic or storage component; G ′ ; becomes larger than the viscous or loss component; G ′′ . The frequency dependence of G ′ develops a plateau while that of G ′′ develops a minimum. We propose a physical model to account for these data; using a description of the glasslike behavior based on mode-coupling theory; and a description of the high-frequency behavior based on hydrodynamic flow calculations.

Directing Colloidal Self-Assembly through Roughness-Controlled Depletion Attractions

Kun Zhao — 2008-03-18T01:40:16-00:00

Physical Review Letters, Vol. 99, No. 26. (2007)

The surfaces of colloidal particles resulting from many new fabrication methods are not molecularly smooth, so understanding how surface roughness can affect the depletion attraction between the particles and their assembly is very important. We show that the depletion attraction between custom-shaped microscale platelets can be suppressed when the nanoscale surface asperity heights become larger than the depletion agent. In the opposite limit, the attraction reappears and columnar stacks of platelets are formed. Exploiting this, we selectively increase the site-specific roughness on only one side of the platelets to direct the mass production of a single desired assembly: a pure dimer phase.