Surface Wetting (eBook)

Dr. Kock-Yee Law is a researcher in nanotechnology and surface design with over 120 peer-reviewed publications and 105 granted US patents to date. Dr. Hong Zhao is an Assistant Professor at Virginia Commonwealth University, School of Engineering, Mechanical, and Nuclear Engineering. 

Preface 6
Contents 8
Chapter 1: Background 11
References 15
Chapter 2: Contact Angle Measurements and Surface Characterization Techniques 17
2.1 Introduction 17
2.2 Determination of Static Contact Angle 20
2.2.1 Basic Measurement and Techniques 20
2.2.2 Best Practices and Critical Details 21
2.2.3 Effect of Drop Size 23
2.2.4 Drop Image Capturing and Drop Shape Analysis 26
2.2.5 Captive Bubble Method 31
2.3 Determination of Sliding Angle 31
2.3.1 Measurement Procedures and Details 31
2.3.2 Effect of Drop Size 33
2.4 Determination of Advancing and Receding Contact Angle 35
2.4.1 Needle-embedded Sessile Drop Method 35
2.4.2 Tilting Plate Method 36
2.5 Wilhelmy Plate Technique 38
2.6 Summary 41
References 42
Chapter 3: Wetting on Flat and Smooth Surfaces 45
3.1 The Young’s Equation 46
3.2 Wetting Dynamics on Smooth Surfaces 46
3.3 The Four Measurable Contact Angles 50
3.4 Wetting States on Smooth Surfaces 53
3.5 What Determines Contact Angle? Contact Line or Contact Area 55
3.6 Effects of Solvent and Temperature 59
References 63
Chapter 4: Wetting on Rough Surfaces 65
4.1 The Two Classic Wetting Models 66
4.2 Wetting in the Wenzel State 69
4.2.1 The Metastable and Most Stable Wetting State 69
4.2.2 Unexpected Wettability 71
4.2.3 Roughness Geometry on Wettability and Wetting Dynamics 73
4.2.4 Practical Consequences 81
4.3 Wetting in the Cassie–Baxter State 83
4.3.1 The Lotus Effect 83
4.3.2 Artificial Superhydrophobic Surfaces 86
4.3.3 Cassie–Baxter to Wenzel State Transition 90
4.3.4 Superoleophobicity 91
4.4 Directional Wetting and Spreading 96
4.5 A Word About Technology Implementation 104
References 105
Chapter 5: What Do Contact Angles Measure? 109
5.1 Background 109
5.2 Contact Angles and Liquid–Solid Interactions 111
5.2.1 Contact Angles 111
5.2.2 Wetting and Adhesion Force Measurements 112
5.2.3 Wetting Interaction and Contact Angles 115
5.2.4 Adhesion Interaction and Contact Angles 116
5.3 Sliding Angle 119
5.4 Contact Angle Hysteresis 122
5.4.1 What Does It Measure? 122
5.4.2 Mechanisms for Contact Angle Hysteresis 123
5.5 Surface Characterization Recommendations 125
5.6 Myths in Adhesion and Contact Angle Hysteresis 126
References 129
Chapter 6: Terminologies and Definitions 132
6.1 Background 132
6.2 Common Terminologies and Languages 133
6.2.1 Terminologies 133
6.2.2 Languages and Descriptors 134
6.3 Definitions 137
6.3.1 Hydrophilicity, Hydrophobicity, and Superhydrophobicity 137
6.3.2 Oleophilicity, Oleophobicity, and Superoleophobicity 139
6.4 Summary and Outlook 141
References 141
Chapter 7: Determination of Solid Surface Tension by Contact Angle 143
7.1 Introduction 144
7.2 Approaches to Determine Solid Surface Tension by Contact Angle 145
7.2.1 Zisman Method 145
7.2.2 Surface Tension Component Methods 147
7.2.3 Equation of State 150
7.2.4 Assessment of the Different Methods 151
7.3 Fundamental Issues and Outlook 153
7.3.1 Solid Surface Energy Versus Surface Tension 153
7.3.2 Which Contact Angle One Should Use? 153
7.3.3 Path Forward 154
References 154
Chapter 8: Summary and Final Remarks 157
8.1 Misconceptions in the Young’s Equation 157
8.2 Concepts that Are Turning the Corners 159
8.3 Outlook and Recommendations 160
8.3.1 Surface Characterization 160
8.3.2 Guidelines for Best Practices 161
References 162
Index 164