CiteULike: di dchen Bibette

Measuring the Kinetics of Biomolecular Recognition with Magnetic Colloids

Cohen Tannoudji — 2008-05-07T23:01:32-00:00

Physical Review Letters, Vol. 100, No. 10. (2008)

We introduce a general methodology based on magnetic colloids to study the recognition kinetics of tethered biomolecules. Access to the full kinetics of the reaction is provided by an explicit measure of the time evolution of the reactant densities. Binding between a single ligand and its complementary receptor is here limited by the colloidal rotational diffusion. It occurs within a binding distance that can be extracted by a reaction-diffusion theory that properly accounts for the rotational Brownian dynamics. Our reaction geometry allows us to probe a large diversity of bioadhesive molecules and tethers, thus providing a quantitative guidance for designing more efficient reactive biomimetic surfaces, as required for diagnostic, therapeutic, and tissue engineering techniques.

Stability criteria for emulsions

J Bibette — 2008-04-28T16:23:12-00:00

Physical Review Letters, Vol. 69, No. 16. (19 October 1992), 2439.

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.

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.

Elasticity of Compressed Emulsions

TG Mason — 2008-04-26T23:57:13-00:00

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

Irreversible Shear-Activated Aggregation in Non-Brownian Suspensions

J Guery — 2008-04-23T18:01:46-00:00

Physical Review Letters, Vol. 96, No. 19. (2006)

We have studied the effect of shear on the stability of suspensions made of non-Brownian solid particles. We demonstrate the existence of an irreversible transition where the solid particles aggregate at remarkably low volume fractions (0.1). This shear-induced aggregation is dramatic and exhibits a very sudden change in the viscosity, which increases sharply after a shear-dependent induction time. We show that this induction time is related exponentially to the shear rate, reflecting the importance of the hydrodynamic forces in reducing the repulsive energy barrier that prevents the particles from aggregating.