This is a collaborative work with Prof. D.A. Beysens at PMMH, ESPCI‑ParisTech, Paris (France). The experiments have been performed at our laboratory. Dew formation may occur when humid air is in contact with a surface at a temperature, for which the humid air would be supersaturated of water vapor. At those conditions, dew appears depending on the contact angle, on the surface formation energy, and on the presence of impurities or defects ([D. Beysens, C. R. Phys. 7 (2006) 1082, and references therein]). If the system has a humidity sink (e.g. a highly hygroscopic localized region), the atmosphere humidity close to the sink diminishes and might not be able to produce drop-wise condensation (in nature, dew), or Breath Figures. Consequently, in the surroundings of the humidity sink there is a Region of Inhibited Condensation (RIC) [R. Williams et al., J. Chem. Phys. 74 (1981) 4675][ C. Schäfle et al., Europhys. Lett. 63 (2003) 394 ][R.N. Leach et al., Langmuir 22 (2006) 8864]. Here, we focus on the Breath Figures dynamics, by using a NaCl crystal or a NaCl saturated water droplet as sinks.

Our main contribution was in the experimental part (J. Guadarrama-Cetina and R. Narhe), modelling (W. González-Viñas), and analysis of the data (W. González-Viñas, R. Narhe and J. Guadarrama-Cetina).

The main findings were that a) once the salt crystal absorbs enough water to be completely dissolved the system is equivalent to the one with a saturated salty drop, b) the salty drop, as it adsorbs water vapor, becomes more diluted and its sink effect reduces; while in the case of a salt crystal the sink capacity remains constant until it is dissolved, c) the salty drop growth rate follows an isolated drop growth model [M. Sokuler et al., Europhys. Lett. 89 (2010) 36004], but taking into account that the initial size of the salty droplet is finite and that the hygroscopicity decreases as the droplet grows, d) the RIC size changes in time accordingly, e) outside the RIC, (pure) water droplets growth locally follows the expected 1/3 power law for a drops carpet [M. Sokuler et al., Europhys. Lett. 89 (2010) 36004], and f) the water vapor concentration profile can be determined from the spatial water droplet size distribution obtained in the experiment. Finally, it is worth noting that our results shed light onto the minimum distance between nucleation sites and onto the last stage of Breath Figures dynamics, when new nucleation exists in the empty spaces between large droplets.

• • J. Guadarrama-Cetina et al. Phys. Rev. E 89 (2014), 012402

  • J. Guadarrama-Cetina, Ph.D. thesis. Universidad de Navarra (2013).

We gratefully acknowledge the comments of A. Yethiraj and V. Nikolayev, after a critical reading of the manuscript, and Erik Norvelle for carefully reading the manuscript. We thank the anonymous reviewers for their useful comments. This work was partly supported by the Spanish MEC (Grant No. FIS2011-24642) and by Departamento de Educación (Gobierno de Navarra). R.D.N. acknowledges the support of a Marie Curie International Incoming Fellowship (MCIIF) within the 7th European Community Framework Program, and J.G.C. acknowledges financial support from the “Asociación de Amigos de la Universidad de Navarra.”

Snapshot of a BF which has appeared in the surrounding of a salty droplet. It can be seen the RIC and the distance to the salty drop dependence of size of (pure) water droplets:

Movie of the Breath Figure dynamics with a salty drop (HFOV 3mm, and the movie is accelerated 1800 times):

Time evolution of size of salty drop R (solid line is a fit to the model) and of the RIC size δ (adapted from fig 2 of [J. Guadarrama-Cetina et al. Phys. Rev. E 89 (2014), 012402]):

Size of (pure) water droplets (BF) re-scaled by the onset of nucleation time:

Humidity profile in arbitrary units as a function of the dimensionless distance to the sink. Type I and II relate to the cases where the sink at the beginning is a salty drop or a crystal salt.