Wetting of Real Surfaces (eBook)

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E. Bormashenko, Ariel University Center of Samaria.

Preface 7
Notation 9
1 What is surface tension? 19
1.1 Surface tension and its definition 19
1.2 Physical origin of the surface tension of liquids 20
1.3 Temperature dependence of the surface tension 23
1.4 Surfactants 24
1.5 The Laplace pressure 24
1.6 Surface tension of solids 26
1.7 Values of surface tensions of solids 27
Appendix 1A. The short-range nature of intermolecular forces 28
Appendix 1B. The Laplace pressure from simple reasoning 28
Bullets 29
References 30
2 Wetting of ideal surfaces 31
2.1 What is wetting? The spreading parameter 31
2.2 The Young equation 32
2.3 Wetting of flat homogeneous curved surfaces 35
2.4 Line tension 37
2.5 Disjoining pressure 38
2.6 Wetting of an ideal surface: influence of absorbed liquid layers and the liquid vapor 40
2.7 Gravity and wetting of ideal surfaces: a droplet shape and liquid puddles 42
2.8 The shape of the droplet and the disjoining pressure 45
2.9 Distortion of droplets by an electric field 47
2.10 Capillary rise 48
2.11 The shape of a droplet wetting a fiber 51
2.12 Wetting and adhesion. The Young-Dupre equation 53
2.13 Wetting transitions on ideal surfaces 54
2.14 How the surface tension is measured? 55
2.14.1 The Du Nouy ring and the Wilhelmy plate methods 55
2.14.2 The pendant drop method 56
2.14.3 Maximum bubble pressure method 57
2.14.4 Dynamic methods of measurement of surface tension 58
2.15 Measurement of surface tension of solids 61
Appendix 2A. Transversality conditions 62
Appendix 2B. Zisman plot 63
Bullets 64
References 64
3 Contact angle hysteresis 68
3.1 Contact angle hysteresis: its sources and manifestations 68
3.2 Contact angle hysteresis on smooth homogeneous substrates 70
3.3 Strongly and weakly pinning surfaces 71
3.4 Qualitative characterization of the pinning of the triple line 75
3.5 The zero eventual contact angle of evaporated droplets and its explanation 76
3.6 Contact angle hysteresis and line tension 77
3.7 More physical reasons for the contact angle hysteresis on smooth ideal surfaces 78
3.8 Contact angle hysteresis on chemically heterogeneous smooth surfaces: the phenomenological approach. Acquaintance with the apparent contact angle 79
3.9 The phenomenological approach to the hysteresis of the contact angle developed by Vedantam and Panchagnula 80
3.10 The macroscopic approach to the contact angle hysteresis, the model of Joanny and de Gennes 81
3.10.1 Elasticity of the triple line 81
3.10.2 Contact angle hysteresis in the case of a dilute system of defects 84
3.10.3 Surfaces with dense defects and the fine structure of the triple line 84
3.11 Deformation of the substrate as an additional source of the contact angle hysteresis 86
3.12 How the contact angle hysteresis can be measured 87
3.13 Roughness of the substrate and the contact angle hysteresis 89
3.14 Use of contact angles for characterization of solid surfaces 89
Appendix 3A. A droplet on an inclined plane 91
Bullets 92
References 93
4 Dynamics of wetting 96
4.1 The dynamic contact angle 96
4.2 The dynamics of wetting: the approach of Voinov 96
4.3 The dynamic contact angle in a situation of complete wetting 98
4.4 Dissipation of energy in the vicinity of the triple line 100
4.5 Dissipation of energy and the microscopic contact angle 101
4.6 A microscopic approach to the displacement of the triple line 101
4.7 Spreading of droplets: Tanner’s law 102
4.8 Superspreading 103
4.9 Dynamics of filling of capillary tubes 103
4.10 The drag-out problem 105
4.11 Dynamic wetting of heterogeneous surfaces 106
Bullets 107
References 108
5 Wetting of rough and chemically heterogeneous surfaces: the Wenzel and Cassie models 110
5.1 General remarks 110
5.2 The Wenzel model 110
5.3 Wenzel wetting of chemically homogeneous curved rough surfaces 112
5.4 The Cassie-Baxter wetting model 114
5.5 The Israelachvili and Gee criticism of the Cassie-Baxter model 115
5.6 Cassie-Baxter wetting in a situation where a droplet partially sits on air 116
5.7 The Cassie-Baxter wetting of curved surfaces 119
5.8 Cassie-Baxter impregnating wetting 119
5.9 The importance of the area adjacent to the triple line in the wetting of rough and chemically heterogeneous surfaces 121
5.10 Wetting of gradient surfaces 125
5.11 The mixed wetting state 126
5.12 Considering the line tension 127
Appendix 5A. Alternative derivation of the Young, Cassie, and Wenzel equations 129
Bullets 131
References 132
6 Superhydrophobicity, superhydrophilicity, and the rose petal effect 134
6.1 Superhydrophobicity 134
6.2 Superhydrophobicity and the Cassie-Baxter wetting regime 135
6.3 Wetting of hierarchical reliefs: approach of Herminghaus 137
6.4 Wetting of hierarchical structures: a simple example 138
6.5 Superoleophobicity 140
6.6 The rose petal effect 141
6.7 Superhydrophilicity 143
Bullets 143
References 144
7 Wetting transitions on rough surfaces 147
7.1 General remarks 147
7.2 Wetting transitions on rough surfaces: experimental data 147
7.3 Time-scaling of wetting transitions 149
7.4 Origin of the barrier separating the Cassie and Wenzel wetting states: the case of hydrophobic surfaces 150
7.4.1 The composite wetting state 150
7.4.2 Energy barriers and Cassie, Wenzel, and Young contact angles 152
7.5 Critical pressure necessary for wetting transition 155
7.6 Wetting transitions and de-pinning of the triple line the dimension of a wetting transition
7.7 The experimental evidence for the 1D scenario of wetting transitions 159
7.8 Wetting transitions on hydrophilic surfaces 160
7.8.1 Cassie wetting of inherently hydrophilic surfaces: criteria for gas entrapping 160
7.8.2 Origin of the energetic barrier separating Cassie and Wenzel wetting regimes on hydrophilic surfaces 161
7.8.3 Surfaces built of ensembles of balls 164
7.9 Mechanisms of wetting transitions: the dynamics 165
Bullets 166
References 167
8 Electrowetting and wetting in the presence of external fields 170
8.1 General remarks 170
8.2 Electrowetting 170
8.3 Wetting in the presence of external fields: a general case 171
Bullets 173
References 173
9 Nonstick droplets 174
9.1 General remarks 174
9.2 Leidenfrost droplets 174
9.3 Liquid marbles 176
9.3.1 What are liquid marbles? 176
9.3.2 Liquid marble/support interface 178
9.3.3 Liquid marble/vapor interface 179
9.3.4 Effective surface tension of liquid marbles 179
9.3.5 Scaling laws governing the shape of liquid marbles 180
9.3.6 Properties of liquid marbles: the dynamics 181
9.3.7 Actuation of liquid marbles with electric and magnetic fields 182
9.3.8 Applications of liquid marbles 183
9.4 Nonstick drops bouncing a fluid bath 183
Bullets 184
References 184
Index 187

lt;P>"Although the book is not primarily meant for mathematicians, all mathematicians concerned with modelling some aspects of wetting will benefit from this book that can be used as a guide to understand the physical mechanisms behind wetting." Mathematical Reviews

"[…] it [the book] is an easily accessible text, treating real surfaces as the title promises. It will be very useful for practicing colloid chemists in industrial research and development, in addition to serving as an excellent text for advanced undergraduate and graduate studies. In fact, my spontaneous reaction to the book was: "I wish it had been available 50-60 years ago, when I was a young graduate student." […] I urgently recommend this book to professionals in both academia and industry." Stig E. Friberg, Journal of Dispersion Science and Technology, 2015