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The Thermo-Mechanical Mechanisms of Reducing Ice Adhesion on Superhydrophobic Surfaces Niv Cohen, Ana Dotan, Hanna Dodiuk, and Samuel Kenig Langmuir, Just Accepted Manuscript • DOI: 10.1021/acs.langmuir.6b02495 • Publication Date (Web): 31 Aug 2016 Downloaded from http://pubs.acs.org on September 1, 2016
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The Thermo-Mechanical Mechanisms of Reducing Ice Adhesion on Superhydrophobic Surfaces N. Cohen1*, A. Dotan1, H. Dodiuk1, S. Kenig1 1
Department of Polymers and Plastics Engineering, the Pernick Faculty of Engineering, Shenkar College 12 Anna Frank Street, Ramat Gan 52526, Israel.
Corresponding author to N. Cohen: E-mail:
[email protected] ABSTRACT Superhydrophobic (SH) coatings have shown to reduce freezing and ice nucleation rates, by means of low surface energy chemistry tailored with nano/micro roughness. Durability enhancement of SH surfaces is a crucial issue. Consequently the present research on reducing ice adhesion is based on radiation induced radical reaction for covalently bonding SiO2 nanoparticles to polymer coatings to obtain durable roughness. Results indicated that the proposed approach resulted in SH surfaces having high contact angles (>155°) and low sliding angles (150º and SA 155o and low SA 10°).
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FIGURE 3: Shear strength apparatus in the freezing chamber at -20°C: a) Hollow cylindrical silicone columns with (inside) frozen water on SH coated PC substrate, attached to embracing holders, b) SH coated PMMA at same conditions, c) Force-Gauge connected to the arm of the embracing holder measuring the force (accuracy of 0.01 N).
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FIGURE 4: Outdoor durability (in hours of exposure to QUV) for SH treated PC samples via dip coating compared to spray coating. The average CA and SA values following exposure are marked.
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FIGURE 5: a) Haze and LT values for SH treated PC compared to a neat PC, b) Visual comparison between the neat and coated PC to illustrate a high LT for the SH treated PC.
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FIGURE 6: HRSEM topography of SH treated glass surfaces at four magnifications (40, 20, 5 and 1 kX), Comparison between: a) Untested samples, b) After samples peeling (11 cycles).
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FIGURE 7: Roughness comparison between SH treated glass: untested and following 11 cycles of Peeling, and a neat glass slide, using profilometery.
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FIGURE 8: AFM of treated PC surfaces: a) 2D topography (10 µm), b) 3D illustration of the coating's roughness, c) 2D phase image (10 µm), d) Peak depth distribution of AFM histogram.
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FIGURE 9: The SH treated samples (carbon/epoxy composite coated with polyurethane paint) following icing in wind tunnel. Despite ice accretion, the frost layer detached from the substrate easily due to the SH coating, corresponding to a low ice adhesion strength: a) Treated plate after 4 min of icing wind simulation, b) Treated profile at the same conditions.
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FIGURE 10: SH treated PC and neat PC samples in static environmental chamber. Supercooled water droplets impact: a) Neat sample at -10°C, b) SH treated sample at -10°C, c) SH treated sample at -20°C, d) SH treated sample at -30°C, e) SH treated sample at -40°C.
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FIGURE 11: The influence of substrates TC on ice adhesion: a) SH treated PC sample b) SH treated Copper sample. Test conducted by a freezing chamber at -20°C (samples setting angle was fixed at 45°). Red circles mark the location of the frozen drops.
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FIGURE 12: SH treated Copper at the static environmental chamber: temperatures vary between -30 to -40°C, super-cooled water droplets impact: a) A sample at -30°C, b) A sample at -40°C.
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FIGURE 13: The effect of substrate on ice shear strength: a) Average shear strength of ice adhesion of four (coated vs. neat) substrates, b) Calculated interfacial TM effect of the four substrates and frozen ice. A positive value signifies an expansion, while the negative signifies a shrinkage.
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FIGURE 14: The effect of TM on ice shear adhesion.
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FIGURE 15: Roughness of the four SH coated substrates, before (orange profile) and after (blue profile) the shear failure of ice adhesion (a purple profile of neat substrate included for visual comparison): a) SH treated Al, b) SH treated Copper, c) SH treated PC, d) SH treated PMMA, e) Rq values of the roughness profiles, before (untested) and after shearing the ice (tested).
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TABLE 1: Thermal and mechanical properties of substrates [31,49], adhesion reduction factor and wettability of the SH coated substrates followed adhesion test. The standard deviation is based on five measurements.
Substrate Thermal type conductivity [W/m·°K]
Linear TEC [10-6/ °C]
Young's modulus [GPa]
Adhesion reduction factor
Wettability results of coated substrates followed adhesion test CA (0) SA (0)
PC
0.2
75
2.3
8
155±0.5
2±0.1
Al
121
23
70
2
156±0.5
1±0.5
Copper
400
17
117
3
157±0.1
1±0.1
PMMA
0.2
75
3.2
8
157±0.2
1±0.2
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FIGURE 1: Proposed mechanism for free radical reactions using DMPA (UV radiation curing) or BPO (thermal curing). Termination by a hydrogen abstraction mechanism. Figure 1 17x10mm (600 x 600 DPI)
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FIGURE 2: Wettability of the SH coatings on glass substrates expressed by a CA and SA: a) 5 µL water droplets rolled off the SH surface, b) Measurement of CA of 157°, c) Measurement of 30 µL SA (>10°). Figure 2 61x47mm (300 x 300 DPI)
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FIGURE 3: Shear strength apparatus in the freezing chamber at -20°C: a) Hollow cylindrical silicone columns with (inside) frozen water on SH coated PC substrate, attached to embracing holders, b) SH coated PMMA at same conditions, c) Force-Gauge connected to the arm of the embracing holder measuring the force (accuracy of 0.01 N). Figure 3 73x28mm (300 x 300 DPI)
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FIGURE 4: Outdoor durability (in hours of exposure to QUV) for SH treated PC samples via dip coating compared to spray coating. The average CA and SA values following exposure are marked. Figure 4 20x12mm (600 x 600 DPI)
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FIGURE 5: a) Haze and LT values for SH treated PC compared to a neat PC, b) Visual comparison between the neat and coated PC to illustrate a high LT for the SH treated PC. Figure 5 14x7mm (600 x 600 DPI)
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FIGURE 6: HRSEM topography of SH treated glass surfaces at four magnifications (40, 20, 5 and 1 kX), Comparison between: a) Untested samples, b) After samples peeling (11 cycles). Figure 6 60x87mm (300 x 300 DPI)
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FIGURE 7: Roughness comparison between SH treated glass: untested and following 11 cycles of Peeling, and a neat glass slide, using profilometery. Figure 7 17x10mm (600 x 600 DPI)
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FIGURE 8: AFM of treated PC surfaces: a) 2D topography (10 µm), b) 3D illustration of the coating's roughness, c) 2D phase image (10 µm), d) Peak depth distribution of AFM histogram. Figure 8 55x47mm (300 x 300 DPI)
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FIGURE 9: The SH treated samples (carbon/epoxy composite coated with polyurethane paint) following icing in wind tunnel. Despite ice accretion, the frost layer detached from the substrate easily due to the SH coating, corresponding to a low ice adhesion strength: a) Treated plate after 4 min of icing wind simulation, b) Treated profile at the same conditions. Figure 9 73x38mm (300 x 300 DPI)
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FIGURE 10: SH treated PC and neat PC samples in static environmental chamber. Super-cooled water droplets impact: a) Neat sample at -10°C, b) SH treated sample at -10°C, c) SH treated sample at -20°C, d) SH treated sample at -30°C, e) SH treated sample at -40°C. Figure 10 20x20mm (600 x 600 DPI)
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FIGURE 11: The influence of substrates TC on ice adhesion: a) SH treated PC sample b) SH treated Copper sample. Test conducted by a freezing chamber at -20°C (samples setting angle was fixed at 45°). Red circles mark the location of the frozen drops. Figure 11 93x46mm (300 x 300 DPI)
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FIGURE 12: SH treated Copper at the static environmental chamber: temperatures vary between -30 to 40°C, super-cooled water droplets impact: a) A sample at -30°C, b) A sample at -40°C. Figure 12 48x57mm (300 x 300 DPI)
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FIGURE 13: The effect of substrate on ice shear strength: a) Average shear strength of ice adhesion of four (coated vs. neat) substrates, b) Calculated interfacial TM effect of the four substrates and frozen ice. A positive value signifies an expansion, while the negative signifies a shrinkage. Figure 13 27x33mm (600 x 600 DPI)
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FIGURE 14: The effect of TM on ice shear adhesion. Figure 14 17x10mm (600 x 600 DPI)
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FIGURE 15: Roughness of the four SH coated substrates, before (orange profile) and after (blue profile) the shear failure of ice adhesion (a purple profile of neat substrate included for visual comparison): a) SH treated Al, b) SH treated Copper, c) SH treated PC, d) SH treated PMMA, e) Rq values of the roughness profiles, before (untested) and after shearing the ice (tested). Figure 15 20x19mm (600 x 600 DPI)
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