Research ArticleAPPLIED PHYSICS

Mitigating cavitation erosion using biomimetic gas-entrapping microtextured surfaces (GEMS)

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Science Advances  27 Mar 2020:
Vol. 6, no. 13, eaax6192
DOI: 10.1126/sciadv.aax6192
  • Fig. 1 Representative scanning electron micrographs of cuticles and fine hairs on the mesothorax of springtails (Collembola) and sea skaters (H. germanus), respectively.

    (A and B) Springtails have primary granules (triangular) connected by ridges forming honeycomb patterns that prevent the intrusion of liquids on submersion. (C) Long needle-shaped hairs and tiny mushroom-shaped hairs on dorsal and ventral mesothorax of sea skaters provide robust repellency against seawater. (D) Magnified micrograph of mushroom-shaped hairs. Photo credit: Sankara Arunachalam, KAUST.

  • Fig. 2 Illustration summarizing how GEMS prevent damage from cavitation jets.

    (A) Liquid jet from a bubble collapsing close to a solid boundary affecting the substrate and causing erosion. The time scale corresponds to a cavitation bubble of Rmax ≈ 570 μm. (B) The gas entrapped inside the GEMS protrudes near the cavitation bubble and behaves as a free boundary. As a result, the liquid jet from the collapsing bubble is directed away from the substrate. The time scale shown is that of a cavitation bubble of Rmax ≈ 520 μm. The time in μs and maximum bubble radius depicted in (A) and (B) are typical values observed in the experiments. (C) The gas entrapped inside the GEMS expands because of the pressure field generated by the nearby cavitation bubble. Notice that the gas contained in the GEMS bulges outward and reaches an almost hemispherical shape during the expansion of the cavitation bubble as mentioned in the text. Image credit: Xavier Pita, Scientific Illustrator, KAUST.

  • Fig. 3 Scanning electron micrographs of silica-GEMS.

    (A) Tilted cross-sectional view (35°) of the silica-GEMS. (B) Top view of the silica-GEMS comprising circular cavities in a hexagonal distribution. (C) Cross-sectional view of the single cavity shown in (A). (D) Detailed cross-sectional view of the mushroom-shaped edge. This sharp edge stabilizes the intruding liquid meniscus and facilitates the entrapment of air inside the cavity. Photo credit: Sankara Arunachalam, KAUST.

  • Fig. 4 Comparison of wetting behaviors of smooth silica and silica-GEMS with water.

    (A) Smooth silica surfaces are water-wet, characterized by intrinsic contact angles, θo < 90°. (B) Silica-GEMS robustly entrap air underwater and show apparent contact angles, θr > 90°. (C and D) Three-dimensional reconstructions of the air-water interface at the inlets of silica-GEMS underwater realized using confocal laser scanning microscopy. The cross-sectional view in (D) is along the dotted red line in (C). Scale bars are the same in (A) and (B), and the diameter of the cavities in (C) and (D) is D = 200 μm. Photo credit: Sankara Arunachalam, KAUST.

  • Fig. 5 Cavitation bubble dynamics at high standoff parameters.

    (A) Side view of the bubble near a smooth silica surface, γ = 4.8 and Rmax = 630 μm. The bottom black line indicates the location of the surface. (B) Side view for the silica-GEMS, γ = 5.1 and Rmax = 610 μm. The arrow indicates the location of the microcavities. (C) Top view of the microcavities portrayed in (B). Scale bar, 500 μm. The numbers on all the panels refer to time in microseconds after cavitation generation. The dotted lines in (A) and (B) serve to guide the eye for the direction of the jet after the bubbles collapse. These figures are derived from movies S1 to S3. Photo credit: Silvestre Roberto Gonzalez-Avila, OVGU.

  • Fig. 6 Cavitation bubble dynamics on silica-GEMS at low standoff parameters.

    (A) Bubble dynamics for γ = 1.8 and Rmax = 530 μm. (B) Bubble dynamics for γ = 0.7 and Rmax = 430 μm. Scale bars, 500 μm. The numbers on all the panels refer to time in microseconds after the generation of the cavitation bubble. These figures are derived from movies S4 to S5. Bubble dynamics on perfluorinated silica-GEMS for similar γ values can be seen in fig. S8 and movies S7 and S9. Photo credit: Silvestre Roberto Gonzalez-Avila, OVGU.

  • Fig. 7 Comparison between the experimental and simulated results.

    (A) Selected frames of the bubble dynamics. The left half of each frame depicts a simulated result, and the right half is the experimental result from the high-speed images captured. Scale bar, 500 μm. The inset numbers on all the panels refer to time in microseconds after the generation of the cavitation bubble. (B and C) Time series results derived from the numerical simulation and experimental results as shown in Fig. 5. Panel (B) shows the bubble collapsing near a microcavity substrate. The scatter blue data points represent experimental results, and the continuous blue line denotes simulated values. Error bars are equal for each point, and only the error bars of the last data points are shown for better visualization. The scatter black data points represent the position of the bubble’s centroid, while the continuous black line portrays the position of the simulated bubble’s centroid. Panel (C) shows results of a bubble collapsing near a smooth surface. The blue and black lines are the bubble’s radius and the location of the bubble’s centroid, respectively. (D) Simulated radial dynamics of a bubble collapsing near a solid surface. (E) Resulting pressure field on the surface p(x,t). Photo credit: Silvestre Roberto Gonzalez-Avila, OVGU.

  • Fig. 8 Parametric plot built from the numerical results of the model showing the region where coalescence of the entrapped gas in adjacent microcavities is expected to take place.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/6/13/eaax6192/DC1

    Section S1. Microfabrication process of silica-GEMS

    Section S2. MVD of FDTS on silica surfaces

    Section S3. The Cassie-Baxter model

    Section S4. Experimental setup

    Section S5. Bubble dynamics close to GEMS coated with FDTS

    Section S6. Details on the numerical simulation

    Section S7. Movies

    Fig. S1. Schematic of the microfabrication process of silica-GEMS.

    Fig. S2. Schematic of the FDTS deposited onto silica-GEMS.

    Fig. S3. Schematic representation of silica-GEMS with mushroom-shaped cavities.

    Fig. S4. Schematic representation of meniscus displacement if an external pressure is applied onto the liquid or if the trapped air is lost by dissolution in water.

    Fig. S5. Schematic illustration of the laser confocal microscope experiment.

    Fig. S6. Schematic diagram of the bubble cavitation test section.

    Fig. S7. Bubble dynamics of a cavitation bubble next to FDTS-coated silica-GEMS.

    Fig. S8. FDTS-coated silica-GEMS.

    Fig. S9. Selected frames of a cavitation bubble created near partially filled microcavities.

    Fig. S10. Selected frames of microcavity deactivation for different γ values.

    Fig. S11. Schematic representation of the geometry of the numerical simulation.

    Table S1. Table listing the major design parameters for the cavities depicted in fig. S3.

    Table S2. A summary of contact angle with all samples presented in this work: (θo) intrinsic contact angles, (θr) apparent contact angles, (θA) advancing contact angles, (θR) receding contact angles, and (θPr) predicted contact angles, for water droplets.

    Movie S1. Bubble dynamics near a glass substrate, γ = 4.8, Rmax = 630 μm.

    Movie S2. Side view of bubble dynamics beside an uncoated GEMS, γ = 5.1, Rmax = 610 μm.

    Movie S3. Front view of bubble dynamics on uncoated GEMS, γ = 5.1, Rmax = 610 μm.

    Movie S4. Side view of bubble dynamics on coated GEMS, γ = 4.7, Rmax = 600 μm.

    Movie S5. Front view of bubble dynamics on coated GEMS, γ = 4.7, Rmax = 600 μm.

    Movie S6. Bubble dynamics on uncoated GEMS, γ = 1.8, Rmax = 530 μm.

    Movie S7. Bubble dynamics on coated GEMS, γ = 1.7, Rmax = 520 μm.

    Movie S8. Bubble dynamics on uncoated GEMS, γ = 0.7, Rmax = 430 μm.

    Movie S9. Bubble dynamics on coated GEMS, γ = 0.7, Rmax = 470 μm.

    Movie S10. Bubble dynamics on a noncoated GEMS with filled and partially filled microcavities, γ = 2.1, Rmax = 430 μm.

  • Supplementary Materials

    The PDF file includes:

    • Section S1. Microfabrication process of silica-GEMS
    • Section S2. MVD of FDTS on silica surfaces
    • Section S3. The Cassie-Baxter model
    • Section S4. Experimental setup
    • Section S5. Bubble dynamics close to GEMS coated with FDTS
    • Section S6. Details on the numerical simulation
    • Section S7. Movies
    • Fig. S1. Schematic of the microfabrication process of silica-GEMS.
    • Fig. S2. Schematic of the FDTS deposited onto silica-GEMS.
    • Fig. S3. Schematic representation of silica-GEMS with mushroom-shaped cavities.
    • Fig. S4. Schematic representation of meniscus displacement if an external pressure is applied onto the liquid or if the trapped air is lost by dissolution in water.
    • Fig. S5. Schematic illustration of the laser confocal microscope experiment.
    • Fig. S6. Schematic diagram of the bubble cavitation test section.
    • Fig. S7. Bubble dynamics of a cavitation bubble next to FDTS-coated silica-GEMS.
    • Fig. S8. FDTS-coated silica-GEMS.
    • Fig. S9. Selected frames of a cavitation bubble created near partially filled microcavities.
    • Fig. S10. Selected frames of microcavity deactivation for different γ values.
    • Fig. S11. Schematic representation of the geometry of the numerical simulation.
    • Table S1. Table listing the major design parameters for the cavities depicted in fig. S3.
    • Table S2. A summary of contact angle with all samples presented in this work: (θo) intrinsic contact angles, (θr) apparent contact angles, (θA) advancing contact angles, (θR) receding contact angles, and (θPr) predicted contact angles, for water droplets.
    • Legends for movies S1 to S10

    Download PDF

    Other Supplementary Material for this manuscript includes the following:

    • Movie S1 (.avi format). Bubble dynamics near a glass substrate, γ = 4.8, Rmax = 630 μm.
    • Movie S2 (.avi format). Side view of bubble dynamics beside an uncoated GEMS, γ = 5.1, Rmax = 610 μm.
    • Movie S3 (.avi format). Front view of bubble dynamics on uncoated GEMS, γ = 5.1, Rmax = 610 μm.
    • Movie S4 (.avi format). Side view of bubble dynamics on coated GEMS, γ = 4.7, Rmax = 600 μm.
    • Movie S5 (.avi format). Front view of bubble dynamics on coated GEMS, γ = 4.7, Rmax = 600 μm.
    • Movie S6 (.avi format). Bubble dynamics on uncoated GEMS, γ = 1.8, Rmax = 530 μm.
    • Movie S7 (.avi format). Bubble dynamics on coated GEMS, γ = 1.7, Rmax = 520 μm.
    • Movie S8 (.avi format). Bubble dynamics on uncoated GEMS, γ = 0.7, Rmax = 430 μm.
    • Movie S9 (.avi format). Bubble dynamics on coated GEMS, γ = 0.7, Rmax = 470 μm.
    • Movie S10 (.avi format). Bubble dynamics on a noncoated GEMS with filled and partially filled microcavities, γ = 2.1, Rmax = 430 μm.

    Files in this Data Supplement:

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