Counterions between charged polymers exhibit liquid-like organization and dynamics.

Proc Natl Acad Sci U S A 103:21 (2006) 7962-7967

Authors:

Thomas E Angelini, Ramin Golestanian, Robert H Coridan, John C Butler, Alexandre Beraud, Michael Krisch, Harald Sinn, Kenneth S Schweizer, Gerard CL Wong

Abstract:

Current understanding of electrostatics in water is based on mean-field theories like the Poisson-Boltzmann formalism and its approximations, which are routinely used in colloid science and computational biology. This approach, however, breaks down for highly charged systems, which exhibit counterintuitive phenomena such as overcharging and like-charge attraction. Models of counterion correlations have been proposed as possible explanations, but no experimental comparisons are available. Here, collective dynamics of counterions that mediate like-charge attraction between F-actin filaments have been directly observed in aqueous solution using high-resolution inelastic x-ray scattering down to molecular length-scales. We find a previously undescribed acoustic-like phonon mode associated with correlated counterions. The excitation spectra at high wave-vector Q reveal unexpected dynamics due to ions interacting with their "cages" of nearest neighbors. We examine this behavior in the context of intrinsic charge density variations on F-actin. The measured speed of sound and collective relaxation rates in this liquid agree surprisingly well with simple model calculations.

Rheology of cholesteric blue phases

(2006)

Authors:

A Dupuis, D Marenduzzo, E Orlandini, JM Yeomans

Dynamics of sliding drops on superhydrophobic surfaces

(2006)

Authors:

A Dupuis, JM Yeomans

Polymer Packaging and Ejection in Viral Capsids: Shape Matters

Physical Review Letters 96 (2006) 208102 4pp

Authors:

JM Yeomans, I Ali, D Marenduzzo

Electric-field-induced disclination migration in a Grandjean-Cano wedge

Journal of Applied Physics 99:6 (2006)

Authors:

JF Strömer, D Marenduzzo, CV Brown, JM Yeomans, EP Raynes

Abstract:

The behavior of a disclination line in a Grandjean-Cano wedge is investigated under an electric field applied normal to the cell substrates. The focus of attention is the first disclination, separating the untwisted and the π -twisted area. This disclination line shows a field dependent migration process that was observed in the cholesteric mixture ZLI-1132/S811. The dynamics of this migration process is studied experimentally and is compared with two theoretical models. One model utilizes a two-dimensional lattice Boltzmann approach to predict the initial migration movement, whereas a one-dimensional continuum model allows a full analysis of the experimental results. © 2006 American Institute of Physics.