Title Page
Abstract
Contents
Chapter 1. Introduction 19
1.1. Wettability 20
1.2. Laser-based fabrication process for extreme wettability surface 22
1.3. Research goals and objectives 25
1.4. Thesis organization 26
Chapter 2. Fabrication of nanosecond-pulse laser-textured stainless steel for robust superhydrophobic surface 28
2.1. Overview 29
2.2. Experiment 30
2.2.1. Fabrication process 30
2.2.2. Effect of laser process parameters 32
2.2.3. Effect of silicone oil and heat in surface modification 34
2.2.4. Effect of heat treatment time 36
2.2.5. Robustness of superhydrophobic surface 36
2.3. Discussion 38
2.4. Summary 42
Chapter 3. Fabrication process for robust, repairable superhydrophobic metallic surface with tunable water adhesion 43
3.1. Overview 44
3.2. Experiment setup 47
3.2.1. Materials and pretreatment 47
3.2.2. Fabrication process 47
3.2.3. Repair process 49
3.3. Results and discussion 49
3.3.1. Effect of laser parameter on water adhesion 49
3.3.2. Mechanical durability and repairability 54
3.3.3. Chemical stability and repairability 57
3.3.4. Mechanisms of change in the wetting property 59
3.3.5. Performance stability, durability, and repairability of superhydrophobic surfaces on other metals 64
3.4. Summary 64
Chapter 4. Superhydrophobic aluminum surface with enhanced corrosion resistance characteristics through nano-micro heterostructure formation 66
4.1. Overview 67
4.2. Experiment 69
4.2.1. Material 69
4.2.2. Laser system and fabrication parameters 69
4.2.3. Surface modification processing 71
4.2.4. Surface characterization 72
4.2.5. Corrosion resistance tests 73
4.3. Results & discussion 73
4.3.1. Wetting properties 73
4.3.2. Effect of the surface modification procedure 75
4.3.3. Effect of laser processing parameters 87
4.4. Summary 90
Chapter 5. Green manufacturing of extreme wettability contrast surfaces with superhydrophilic and superhydrophobic patterns on aluminum 92
5.1. Overview 93
5.2. Experiment 96
5.2.1. Fabrication process 96
5.2.2. Stability in the air and under the water 99
5.2.3. Thermal stability 100
5.2.4. Mechanical durability 101
5.3. Discussion 102
5.3.1. Effect of micro-/nano-structure on the durability of superhydrophobic aluminum surface in boiling water 102
5.3.2. Mechanism 104
5.3.3. Patterning of superhydrophilic regions on superhydrophobic surface for potential applications 109
5.4. Summary 111
Chapter 6. Conclusions 113
Bibliography 117
Appendix: Credits & Copyright Permissions 140
Table 2.1. Fabrication parameter of laser texturing 32
Table 2.2. Results of contact angle and sliding angle on laser textured surface with different step size, laser speed after post process and fabricating time on... 33
Table 2.3. Results of contact angle and sliding angle on laser textured surface after post process with different silicone oil concentration 34
Table 2.4. Chemical composition on the flat area between fabricated paths and on the burrs of laser textured surface before and after post process 41
Table 3.1. Results of CAs and SAs with Average Values and Standard Deviations from Four Samples, Laser Texturing Time t(s) for a 1 × 1 mm² Area, and Laser Areal Fluence FA (J/mm²) with Different Step Sizes △ₓ (μm), Laser Scanning Speeds vₛ... 51
Table 3.2. Chemical composition of the burrs on the Ti surface after laser-texturing, after silicone oil heat treatment, after 300-cm abrasion length, and after repairing... 63
Table 4.1. Laser parameters including laser speed v, step size △x, laser process time t(s) for a 20x20 mm² area, and laser power of 10 W with laser areal fluence... 71
Table 4.2. Chemical composition of Al surface after different surface modification procedures 79
Table 4.3. Impedance analysis of Al surface at different processing conditions 85
Table 4.4. Corrosion test analysis parameters deduced from Tafel analysis and the Stern Geary equation 90
Table 5.1. Stability of the superhydrophilic/superhydrophobic pattern after 90 days of exposure to ambient air and after 7 days of immersion in water. 99
Table 5.2. Chemical composition on the burrs of the surface after laser texturing, after 1st boiling water treatment, after silicone oil heat treatment, and after 2nd... 107
Figure 1.1. Schematic of water droplet's CAs with different surface wettability 20
Figure 1.2. Effects of surface morphology and surface energy on wettability 21
Figure 1.3. Image of the whole laser system 24
Figure 2.1. Laser surface texturing system and beam path design 31
Figure 2.2. Procedure of laser texturing and surface modification 32
Figure 2.3. Effects of laser texturing, heat treatment, and silicone oil: CAs on (a) bare flat surface, (b) laser-textured surface, (c) laser-textured surface with IPA... 35
Figure 2.4. Effect of heat treatment time 36
Figure 2.5. Stability of the laser-textured samples at 10 mm/s laser scan speed after heat treatment with IPA and silicone oil: (a) contact angles, and (b) sliding... 37
Figure 2.6. Tape test results of (a) the samples prepared only with heat treatment for 12 hours, and (b) the samples with heat treatment using silicone oil for 10 minutes. 38
Figure 2.7. FE-SEM images on the flat area between fabricated paths and on the burrs of laser textured surface 39
Figure 2.8. (a) XRD and (b) FT-IR result of laser-textured surfaces before and after surface modification 40
Figure 2.9. Patterned superhydrophobic surface, (b) bouncing of a 10 μL water droplet on the superhydrophobic surface, and (c) self-cleaning 42
Figure 3.1. Schematic of the laser processing system and beam path design. 48
Figure 3.2. Schematic of wetting scenarios and the effect of laser areal fluence on water adhesion behavior 52
Figure 3.3. Time-lapse photos with increasing tilt angle (SAs) showing a surface that has integrated different water adhesion behavior. 53
Figure 3.4. Laser scanning time and post-treatment time in this work as compared with other existing superhydrophobic Ti fabrication methods 54
Figure 3.5. Illustration of the sandpaper abrasion test of the prepared superhydrophobic Ti surface, and the plot of the changes in wettability after 300... 56
Figure 3.6. (a) Sparse and (b) intensive crosshatches were scratched into the prepared superhydrophobic Ti surfaces, and (c) the intensively crosshatched... 57
Figure 3.7. (a) Chemical durability test results of the superhydrophobic Ti surfaces after immersion in solutions of pH=2, 7, and 13 for 12 hours, and after... 59
Figure 3.8. Schematic diagram of superhydrophobic surface fabrication, damage by abrasion, and the repair process with the surface chemistry, surface... 60
Figure 3.9. SEM images and 3D profiles of a Ti surface (a) after laser texturing, (b) after silicone oil heat treatment, (c) after 300 cm of abrasion length under... 61
Figure 3.10. (a) XRD and (b) FTIR results of a Ti surface after laser texturing, after silicone oil heat treatment, after the scratching test, and after repairing the... 62
Figure 3.11. Shapes of liquid droplets of water, coffee, milk, pH=2 solution, and pH=13 solution on different superhydrophobic metal surfaces: stainless steel,... 65
Figure 4.1. Schematic of laser surface texturing system and the laser beam tracks 70
Figure 4.2. Procedure of surface modification steps for the analyzed samples. 72
Figure 4.3. (a) Water contact angle and (b) water sliding angle of flat and laser-textured Al surface after each modification step 74
Figure 4.4. FE-SEM images of (a) flat Al, (b) laser-treated, (c) laser & silicone oil heat treated, (d) flat Al surface & boiling water treated, (e) laser & boiling... 76
Figure 4.5. Comparison between XRD results of Al surfaces after different surface modification procedures. 77
Figure 4.6. Fourier transform infrared spectroscopy (FT-IR) spectra of Al surfaces for different surface modification procedures. 79
Figure 4.7. Raman spectra of Al after different surface modification procedures. 80
Figure 4.8. (a) Potentiodynamic plot of treated Al surface at different conditions in the form of a Nyquist plot, and (b-d) the corresponding Bode plots of Al... 83
Figure 4.9. The wettability of Al samples before the corrosion test and the visual inspection of (a) the flat Al surface, (b) laser-treated, (c) laser & silicone oil heat... 84
Figure 4.10. Schematic diagram for the surface modification procedure, corresponding wetting behavior, and electrochemical equivalent circuit for EIS. 87
Figure 4.11. Potentiodynamic plots of superhydrophobic Al surface at laser powers of (a) 5 W and (b) 10 W. (c) The variation of corrosion potential (Vcorr)...[이미지참조] 88
Figure 5.1. Laser surface texturing system and beam path design 96
Figure 5.2. Procedure of surface modification of superhydrophilic/superhydrophobic patterns 97
Figure 5.3. Stability of the superhydrophilic/superhydrophobic patterns in high temperature (200℃) and low temperature (-10℃) 100
Figure 5.4. Tape test results of the superhydrophilic/superhydrophobic patterns 102
Figure 5.5. Effect of the 1st boiling water treatment time on the durability of superhydrophobic aluminum surface after 10 minutes in the 2nd boiling water treatment 104
Figure 5.6. Schematic diagram for the surface modification procedure with the surface morphology, surface chemistry, and associated wetting behavior 105
Figure 5.7. FE-SEM images of pure Al surfaces after 1st laser texturing (a-c), after 1st boiling water treatment (d-f), and after silicone oil heat treatment (g-i). 106
Figure 5.8. (a) XRD and (b) FTIR results of the surface after laser texturing, after 1st boiling water treatment, after silicone oil heat treatment, and after 2nd boiling water treatment. 108
Figure 5.9. Superhydrophilic circular, triangular, square, and hexagon patterns for water droplet arrays on superhydrophobic pure aluminum surface. 109
Figure 5.10. Images of complex freeform superhydrophilic patterns of different geometries and sizes filled with DI water on the superhydrophobic aluminum... 110
Figure 5.11. Time-lapsed photos showing (a) the DI water-spreading through superhydrophilic channel on superhydrophobic aluminum alloy surface and (b)... 111