Research ArticleMATERIALS SCIENCE

The cold Leidenfrost regime

See allHide authors and affiliations

Science Advances  28 Jun 2019:
Vol. 5, no. 6, eaaw0304
DOI: 10.1126/sciadv.aaw0304
  • Fig. 1 Water drops on hot hydrophilic and superhydrophobic materials.

    (A) Water drops (Ω = 4 μl) on a hydrophilic silicon wafer (blue frame) or on a superhydrophobic Glaco-treated wafer (red frame) brought to temperature T. Scale bar, 1 mm. While boiling occurs above 100°C in the hydrophilic case, neither boiling nor apparent change in shape is observed on the repellent solid. Both drops only become similar above 210°C, in a common Leidenfrost state. (B) Lifetime τ of water drops (Ω = 20 μl) as a function of the substrate temperature T on bare aluminum (blue data) and Glaco-treated aluminum (red data). Each point is an average over at least five measurements, and error bars represent standard deviations. The Leidenfrost transition is observed at TL ≈ 210°C on the hydrophilic substrate, whereas τ(T) monotonically decreases in the repellent situation. Beyond TL, both curves superimpose.

  • Fig. 2 Adhesion of water on hot repellent materials.

    (A) Sketch of the experiment: A water drop with volume Ω and contact radius r is placed on a substrate brought to a temperature T and tilted until the drop departs. At departure (tilting angle α), contact angles at the drop edges are the receding and advancing angles θr and θa, respectively. (B) Roll-off angle α as a function of temperature T for Ω = 3.9 μl (blue data), Ω = 5.4 μl (red data), and Ω = 9.2 μl (green data). Error bars show the standard deviation for a minimum of five measurements. (C) Contact angle hysteresis Δcosθ = cosθr – cosθa deduced from Furmidge’s equation: Water adhesion is nonmonotonic as a function of T, and it becomes nonmeasurable above ~130°C.

  • Fig. 3 Adhesion of water on two kinds of hot hydrophobic nanotexture.

    (A) SEM (scanning electron microscopy) image of a Glaco-coated brass substrate. Hydrophobic nanobeads deposited on the substrate provide a submicrometric roughness. Scale bar, 500 nm. (B) SEM picture of a dense array of nanocones (height, 115 nm; spacing, 52 nm) textured in silicon and coated by fluorosilanes. Scale bar, 200 nm. The picture is adapted from the work of Checco et al. (25). (C) Contact angle hysteresis Δcosθ of a water drop (Ω = 3.9 μl) on Glaco coating (a, blue data) and on nanocones (b, red data) as a function of the substrate temperature T.

  • Fig. 4 Focus on the base of water drops placed on hot repellent substrates.

    (A) Setup: A drop is deposited on a Glaco-treated sapphire brought to a temperature T. The contact zone is observed from below with an inverted microscope. (B) Visualization of the contact area whose radius r is 0.4 mm for a drop with radius R = 1.0 mm at T = 51°C (left), T = 75°C (center), and T = 150°C (right). Vapor patches appear around 70°C, and we highlight their contour in red. (C) Close-up on the fringes seen in the central region of the vapor patches seen in (B) at T = 75°C. (D) Fraction ϕv occupied by the vapor patches as a function of temperature T and measured 0 to 10 s after drop deposition. Each data point is an average over at least three drops, and error bars represent standard deviations. The bars are large in the critical regime of vapor formation and get smaller at larger T where they even become negligible when reaching the vapor patch stationary state at large time t.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/5/6/eaaw0304/DC1

    Fig. S1. Contact radius r of a water drop placed on a hot superhydrophobic solid, as defined in Fig. 2A.

    Fig. S2. Contact angle hysteresis Δcosθ on Glaco-coated substrates as a function of T for drops having initially either a temperature Td = 20°C (blue data) or the same temperature as the substrate (Td = T, red data).

    Fig. S3. Water adhesion on heated brass coated by a commercial colloidal repellent material (Ultra-Ever Dry, UltraTech International).

    Fig. S4. Water adhesion on heated micrometric posts.

    Fig. S5. Morphology of a vapor patch.

    Fig. S6. Internal flow in water drops (R ≈ 1.5 mm) placed on a hot superhydrophobic solid (Glaco-coated wafer).

  • Supplementary Materials

    This PDF file includes:

    • Fig. S1. Contact radius r of a water drop placed on a hot superhydrophobic solid, as defined in Fig. 2A.
    • Fig. S2. Contact angle hysteresis Δcosθ on Glaco-coated substrates as a function of T for drops having initially either a temperature Td = 20°C (blue data) or the same temperature as the substrate (Td = T, red data).
    • Fig. S3. Water adhesion on heated brass coated by a commercial colloidal repellent material (Ultra-Ever Dry, UltraTech International).
    • Fig. S4. Water adhesion on heated micrometric posts.
    • Fig. S5. Morphology of a vapor patch.
    • Fig. S6. Internal flow in water drops (R ≈ 1.5 mm) placed on a hot superhydrophobic solid (Glaco-coated wafer).

    Download PDF

    Files in this Data Supplement:

Navigate This Article