Table of Contents
Preface to the second edition vii
Preface to the first edition ix
Symbol Index xi
1 What is surface tension? 1
1.1 Surface tension and its definition 1
1.2 Physical origin of the surface tension of liquids 2
1.3 Temperature dependence of the surface tension 5
1.4 Surfactants 5
1.5 The Laplace pressure 6
1.6 Surface tension of solids 8
1.7 Values of surface tensions of solids 8
Additional Reading 9
Appendix 1A The short-range nature of intermolecular forces 9
Appendix 1B The Laplace pressure from simple reasoning 10
Bullets 11
References 11
2 Wetting of ideal surfaces 13
2.1 What is wetting? The spreading parameter 13
2.2 The Young equation 14
2.3 Wetting of flat, homogeneous, curved surfaces 17
2.4 Line tension 19
2.5 Disjoining pressure 20
2.6 Wetting of an ideal surface: influence of absorbed liquid layers and the liquid vapor 22
2.7 Gravity and wetting of ideal surfaces: a droplet shape and liquid puddles 24
2.8 The shape of the droplet and the disjoining pressure 26
2.9 Distortion of droplets by an electric field 27
2.10 Capillary rise 29
2.11 The shape of a droplet wetting a fiber 31
2.12 Wetting and adhesion: the Young-Dupré equation 33
2.13 Wetting transitions on ideal surfaces 33
2.14 How is the surface tension measured? 35
2.14.1 The Du Noüy ring and the Wilhelmy plate methods 35
2.14.2 The pendant drop method 36
2.14.3 Maximum bubble pressure method 37
2.14.4 Dynamic methods of the measurement of surface tension 38
2.15 Measurement of the surface tension of solids 40
Additional Reading 41
Appendix 2A Transversality conditions 41
Appendix 2B Zisman plot 42
Appendix 2C Antonoff's rule 43
Bullets 43
References 44
Additional Reading 46
3 Contact angle hysteresis 47
3.1 Contact angle hysteresis: its sources and manifestations 47
3.2 Contact angle hysteresis on smooth homogeneous substrates 49
3.3 Strongly and weakly pinning surfaces 50
3.4 Qualitative characterization of the pinning of the triple line 53
3.5 The zero eventual contact angle of evaporated droplets and its explanation 55
3.6 Contact angle hysteresis and line tension 55
3.7 More physical reasons for contact angle hysteresis on smooth ideal surfaces 56
3.8 Contact angle hysteresis on chemically heterogeneous smooth surfaces: the phenomenological approach. Acquaintance with the apparent contact angle 57
3.9 The phenomenological approach to the hysteresis of the contact angle developed by Vedantam and Panchagnula 59
3.10 The macroscopic approach to contact angle hysteresis, the model of Joanny and de Gennes 60
3.10.1 Elasticity of the triple line 60
3.10.2 Contact angle hysteresis in the case of a dilute system of defects 61
3.10.3 Surfaces with dense defects and the fine structure of the triple line 62
3.11 Deformation of the substrate as an additional source of contact angle hysteresis 63
3.12 How contact angle hysteresis can be measured 65
3.13 Roughness of the substrate and contact angle hysteresis 66
3.14 Use of macroscopic contact angles for characterization of solid surfaces 67
Additional Reading 68
Appendix 3A A droplet on an inclined plane 68
Bullets 70
References 71
Additional Reading 73
4 Dynamics of wetting 75
4.1 The dynamic contact angle 75
4.2 The dynamics of wetting: the approach of Voinov 75
4.3 The dynamic contact angle in a situation of complete wetting 77
4.4 Dissipation of energy in the vicinity of the triple line 78
4.5 Dissipation of energy and the microscopic contact angle 79
4.6 A microscopic approach to the displacement of the triple line 80
4.7 Spreading of droplets: Tanner's law 81
4.8 Superspreading 81
4.9 Dynamics of the filling of capillary tubes 82
4.10 The drag-out problem 83
4.11 Dynamic wetting of heterogeneous surfaces 85
Additional Reading 86
Bullets 86
References 86
Additional Reading 87
5 Wetting of rough and chemically heterogeneous surfaces: the Wenzel and Cassie Models 89
5.1 General remarks 89
5.2 The Wenzel model 89
5.3 Wenzel wetting of chemically homogeneous curved rough surfaces 91
5.4 The Cassie-Baxter wetting model 93
5.5 The Israelachvili and Gee criticism of the Cassie-Baxter model 94
5.6 Cassie-Baxter wetting in a situation where a droplet partially sits on air 95
5.7 The Cassie-Baxter wetting of curved surfaces 97
5.8 Cassie-Baxter impregnating wetting 98
5.9 The importance of the area adjacent to the triple line in the wetting of rough and chemically heterogeneous surfaces 99
5.10 Wetting of gradient surfaces 103
5.11 The mixed wetting state 104
5.12 Considering the line tension 105
Appendix 5A Alternative derivation of the Young, Cassie, and Wenzel equations 107
Bullets 109
References 110
Additional Reading 111
6 Superhydrophobicity, superhydrophilicity, and the rose petal effect 113
6.1 Superhydrophobicity 113
6.2 Superhydrophobicity and the Cassie-Baxter wetting regime 114
6.3 Wetting of hierarchical reliefs: approach of Herminghaus 115
6.4 Wetting of hierarchical structures: a simple example 116
6.5 Superoleophobicity 118
6.6 The rose petal effect 119
6.7 Superhydrophilicity 121
Additional Reading 122
Bullets 122
References 122
Additional Reading 124
7 Wetting transitions on rough surfaces 125
7.1 General remarks 125
7.2 Wetting transitions on rough surfaces: experimental data 126
7.3 Time-scaling of wetting transitions 127
7.4 Origin of the barrier separating the Cassie and Wenzel wetting states: the case of hydrophobic surfaces 128
7.4.1 The composite wetting state 128
7.4.2 Energy barriers and Cassie, Wenzel, and Young contact angles 130
7.5 Critical pressure necessary for wetting transition 132
7.6 Wetting transitions and de-pinning of the triple line; the dimension of a wetting transition 133
7.7 The experimental evidence for the 10 scenario of wetting transitions 136
7.8 Wetting transitions on hydrophilic surfaces 137
7.8.1 Cassie wetting of inherently hydrophilic surfaces: criteria for gas entrapping 137
7.8.2 Origin of the energetic barrier separating Cassie and Wenzel wetting regimes on hydrophilic surfaces 138
7.8.3 Surfaces built of ensembles of balls 140
7.9 Mechanisms of wetting transitions: the dynamics 142
Additional Reading 143
Bullets 143
References 144
Additional Reading 146
8 Electrowetting and wetting in the presence of external fields 147
8.1 General remarks 147
8.2 Electrowetting 147
8.3 Wetting in the presence of external fields: a general case 148
Additional Reading 150
Bullets 150
References 150
Additional Reading 151
9 Nonstick droplets 153
9.1 General remarks 153
9.2 Leidenfrost droplets 153
9.3 Liquid marbles 155
9.3.1 What are liquid marbles? 155
9.3.2 Liquid marble-support interface 157
9.3.3 Liquid marble-vapor interface 157
9.3.4 Effective surface tension of liquid marbles 158
9.3.5 Scaling laws governing the shape of liquid marbles 159
9.3.6 Properties of liquid marbles: the dynamics 160
9.3.7 Actuation of liquid marbles with electric and magnetic fields 161
9.3.8 Applications of liquid marbles 162
9.4 Nonstick drops bouncing in a fluid bath 162
Additional Reading 163
Bullets 163
References 164
Additional Reading 165
10 Wetting of Lubricated surfaces 167
10.1 General remarks 167
10.2 Capillarity-inspired effects on wet (lubricated), flat, solid surfaces 167
10.2.1 The effect of wettability on the tribology of ideal lubricated surfaces 167
10.2.2 Impact of droplets: collision with wet, flat substrates 167
10.3 Wetting of impregnated (infused), solid, rough substrates 168
10.4 Impact of water droplets on oil-infused surfaces 170
10.5 Electrowetting of lubricated surfaces 170
Bullets 171
References 171
11 Reactive wetting 173
11.1 General remarks 173
11.2 Kinetics of reactive wetting 173
Bullets 175
References 175
Index 177
