Anisotropic wetting and de-wetting of drops on substrates patterned with polygonal posts
Soft Matter 9:3 (2013) 674-683
Abstract:
We present results showing how water drops, produced by ink-jet printing, spread on surfaces patterned with lattices of diamond or triangular posts. Considering post widths typically ∼7 μm and lattice spacings between 15 and 40 μm, we observe drop shapes with 3, 4 and 6-fold symmetry, depending on both the symmetry of the lattice and the shape of the posts. This is a result of the different mechanisms of interface pinning and depinning which depend on the direction of the contact line motion with respect to the post shape. Lattice Boltzmann simulations are used to describe these mechanisms in detail for triangular posts. We also follow the motion of the contact line as the drops evaporate showing that they tend to return to their original shape. To explain this we show that the easy direction for movement is the same for spreading and drying drops. We compare the behaviour of small drops with that of larger drops created by jetting several drops at the same position. We find that the contact line motion is unexpectedly insensitive to drop volume, even when a spherical cap of fluid forms above the posts. The findings are relevant to micro-fluidic applications and to the control of drop shapes in ink-jet printing. © 2013 The Royal Society of Chemistry.Time evolution of local observables after quenching to an integrable model
(2013)
Confined active nematic flow in cylindrical capillaries
Physical Review Letters 110:2 (2013)
Abstract:
We use numerical modeling to study the flow patterns of an active nematic confined in a cylindrical capillary, considering both planar and homeotropic boundary conditions. We find that active flow emerges not only along the capillary axis but also within the plane of the capillary, where radial vortices are formed. If topological defects are imposed by the boundary conditions, they act as local pumps driving the flow. At higher activity, we demonstrate escape of the active defects and flow into the third dimension, indicating the importance of dimensionality in active materials. We argue that measuring the magnitude of the active flow as a function of the capillary radius allows determination of a value for the activity coefficient. © 2013 American Physical Society.Reply to Comment on 'Length Scale Dependence of DNA Mechanical Properties'
ArXiv 1301.1541 (2013)