Localized states in a film-dragging experiment

In Situ Real-Time Radiographic Study of Thin Film Formation Inside Rotating Hollow Spheres

Hollow spheres with uniform coatings on the inner surface have applications in optical devices, time- or site-controlled drug release, heat storage devices, and target fabrication for inertial confinement fusion experiments. The fabrication of uniform coatings, which is often critical for the application performance, requires precise understanding and control over the coating process and its parameters. Here, we report on in situ real-time radiography experiments that provide critical spatiotemporal information about the distribution of fluids inside hollow spheres during uniaxial rotation. Image analysis and computer fluid dynamics simulations were used to explore the effect of liquid viscosity and rotational velocity on the film uniformity. The data were then used to demonstrate the fabrication of uniform sol-gel chemistry derived porous polymer films inside 2 mm inner diameter diamond shells.

Rayleigh and depinning instabilities of forced liquid ridges on heterogeneous substrates

Depinning of two-dimensional liquid ridges and three-dimensional drops on an inclined substrate is studied within the lubrication approximation. The structures are pinned to wetting heterogeneities arising from variations of the strength of the short-range contribution to the disjoining pressure. The case of a periodic array of hydrophobic stripes transverse to the slope is studied in detail using a combination of direct numerical simulation and branch-following techniques. Under appropriate conditions the ridges may either depin and slide downslope as the slope is increased, or first break up into drops via a transverse instability, prior to depinning. The different transition scenarios are examined together with the stability properties of the different possible states of the system.

Periodic knolls and valleys: coexistence of solid and liquid states in granular suspensions

We report the spontaneous emergence of a doubly periodic train of sedimented knolls in a dense suspension. These solidified knolls rise out of, and coexist alongside, a sea of freely flowing liquid in a slowly rotating horizontal bottle. We apply a variable viscosity model that permits simultaneous analysis of fluidlike and solidlike behaviors that are ubiquitous in a variety of sedimenting flows. The model generates qualitative agreement with experiments, and produces new insights into mechanisms by which sedimented structures form.