Erratum: Droplet pattern and condensation gradient around a humidity sink [Phys. Rev. E 89, 012402 (2014)].

This corrects the article DOI: 10.1103/PhysRevE.89.012402.

Dew condensation on desert beetle skin.

Some tenebrionind beetles inhabiting the Namib desert are known for using their body to collect water droplets from wind-blown fogs. We aim to determine whether dew water collection is also possible for desert insects. For this purpose, we investigated the infra-red emissivity, and the wetting and structural properties, of the surface of the elytra of a preserved specimen of Physasterna cribripes (Tenebrionidæ) beetle, where the macro-structure appears as a series of "bumps", with "valleys" between them. Dew formation experiments were carried out in a condensation chamber. The surface properties (infra-red emissivity, wetting properties) were dominated by the wax at the elytra surface and, to a lower extent, its micro-structure. We performed scanning electron microscope on histological sections and determined the infra-red emissivity using a scanning pyrometer. The emissivity measured (0.95±0.07 between 8-14 µm) was close to the black body value. Dew formation occurred on the insect's elytra, which can be explained by these surface properties. From the surface coverage of the condensed drops it was found that dew forms primarily in the valleys between the bumps. The difference in droplet nucleation rate between bumps and valleys can be attributed to the hexagonal microstructure on the surface of the valleys, whereas the surface of the bumps is smooth. The drops can slide when they reach a critical size, and be collected at the insect's mouth.

Droplet pattern and condensation gradient around a humidity sink.

We describe the evolution of a water drop saturated with NaCl and the growth of pure water droplets in a breath figure pattern (BF) condensing around it. This salty drop acts as a humidity sink, inhibiting the BF inside a ring at a distance r=δ from the sink center and slowing down BF growth outside the ring. The initial salty drop is taken either from a salt-saturated solution (type I experiment) or by placing an NaCl crystal on the substrate (type II experiment). The results are similar, provided that the initial time for type II evolution is taken at the end of the crystal dissolution. The evolution of the salty drop radius R is deduced from the establishment of a three-dimensional hyperbolic concentration profile around the salty drop. This profile scales with r/δ. Accounting for the salt concentration decrease with salty drop growth, R is seen to grow as t5. In the region r>δ, water droplets nucleate and grow. The rate of evolution of the water droplets at constant r/δ can be used to determine the local water pressure. The corresponding data reasonably agree with a hyperbolic water vapor profile around the salty drop. These results can be applied to the growth of BF patterns to determine whether hyperbolic or linear water vapor profiles apply.

The Kibble-Zurek mechanism in a subcritical bifurcation.

We present a study of the freezing dynamics of topological defects in a subcritical system by testing the Kibble-Zurek (KZ) mechanism while crossing a tri-stable region in a one-dimensional quintic complex Ginzburg-Landau equation. The critical exponents of the KZ mechanism and the horizon (KZ-scaling regime) are predicted from the quasistatic study, and are in full accordance with the quenched study. The correlation length, in the KZ freezing regime, is corroborated from the number of topological defects and from the spatial correlation function of the order parameter. Furthermore, we characterize the dynamics to differentiate three out-of-equilibrium regimes: the adiabatic, the impulse and the free relaxation. We show that the impulse regime shares a common temporal domain with a fast exponential increase of the order parameter.

Breath figures of two immiscible substances on a repellent surface.

The understanding of the competition between different substances while condensing on a cold surface is of high interest in situations in which it is desirable to control their condensation rates and the formed morphologies. We do the experiments for mixtures of water and hexamethyldisiloxane vapors at several concentrations. The dropwise condensation of the vapors forms breath figures on a substrate that is repellant to both substances. We report the average radius of the drops for each specie as a function of time. Also, we pay attention to the evolution of the corresponding morphologies and the appearance of hybrid clusters.

One-dimensional cluster array at the three-phase contact line in diluted colloids subjected to ac electric fields.

Colloidal particles provide an efficient means of building multiple scale structured materials from colloidal dispersions. In this Brief Report we account for experimental evidence on the formation of a colloidal cluster array at a three-phase contact line. We study the influence of low frequency external alternating electric fields on a diluted colloidal dispersion opened to the air. We focus on the cluster formation and their evolution in the meniscus by measuring characteristic times and lengths. We observe that the clusters are separated by a well-defined length and that, in our experimental conditions, they survive between 5 and 15 min. These new results could be of technological relevance in building tailored colloidal structures in nonpatterned substrates.

Contact-line speed and morphology in vertical deposition of diluted colloids.

We report experimental results on the speed of a receding contact line, in a vertical deposition configuration, during the deposition of polystyrene colloidal particles. We study the effects of the initial concentration of the suspension and compare the measured speeds with the corresponding dried deposit. It is observed that multilayer structures are associated with high speeds. This result is explained through a region in the bulk of the suspension where the concentration of particles increases until multilayer is formed depending on the porosity of the previously deposited structures.

Testing the Kibble-Zurek mechanism in Rayleigh-Bénard convection.

We report experimental evidence of the fact that, in an emerging Rayleigh-Bénard structure, the density of defects which appear scales as a power law in the rate of change of the control parameter. The scaling exponents agree with those calculated from the Kibble-Zurek mechanism. This is the first evidence to our knowledge that this mechanism works in a hydrodynamical system.

Topological defects after a quench in a Bénard-Marangoni convection system.

We report experimental evidence of the fact that, in a Bénard-Marangoni conduction-convection transition, the density of defects in the emerging structure scales as a power law in the quench time needed for the control parameter to ramp through the threshold. The obtained scaling exponents differ from the ones predicted and observed in the case in which the defects correspond to zeros in the amplitude of the global two-dimensional field.