This book brings a unique approach to understand, calculate and predict the behaviour of droplets and interfaces in modern microsystems.
Table of ContentsPreface. Introduction
1 Fundamentals of Capillarity 1.1 Abstract
1.2 Interfaces and Surface Tension
1.2.1 The Notion of Interface
1.2.2 The Effect of Temperature on Surface Tension
1.2.3 The Effect of Surfactants
1.2.4 Surface Tension of a Fluid Containing Particles
1.3 Laplace ¯¿½s Law and Applications
1.3.1 Curvature and Radius of Curvature
1.3.2 Derivation of Laplace ¯¿½s Law
1.3.3 Examples of Application of Laplace ¯¿½s Law
1.3.4 Wetting - Partial or Total Wetting
1.3.5 Contact Angle - Young ¯¿½s Law
1.3.6 Work of Adhesion, Work of Cohesion and the Young-Dupr ¯¿½ Equation
1.3.7 Capillary Force, Force on a Triple Line
1.4 Measuring the Surface Tension of Liquids
1.4.1 Using Pressure (Bubble Pressure Method)
1.4.2 Using Gravity: the Pendant Drop Method
1.4.3 Surface Free Energy
1.5 Minimization of the Surface Energy and Minimal Surfaces
1.5.1 Minimization of the Surface Energy
1.5.2 Conclusion
1.6 References
2 Minimal Energy and Stability Rubrics 2.1 Abstract
2.2 Spherical Shapes as Energy Minimizers
2.3 Symmetrization and the Rouloids
2.3.1 Steiner Symmetrization
2.3.2 Rouloids
2.3.3 Rouloid Summary
2.4 Increasing Pressure and Stability
2.4.1 Wedge
2.4.2 In a Square
2.4.3 Round Well
2.4.4 Square Well
2.5 The Double-Bubble Instability
2.5.1 Conditions for the Double-bubble Instability
2.5.2 Plateau-Rayleigh Instability
2.5.3 Plateau-Rayleigh Instability in Corners and Grooves
2.5.4 Instability of a Cylinder on a Hydrophilic Strip
2.5.5 Double-bubble Instability in Bulging Liquid Bridge
2.5.6 Lower-pressure Comparison Theorem
2.6 Conclusion
2.7 References
3 Droplets: Shape, Surface and Volume 3.1 Abstract
3.2 The Shape of Micro-drops
3.2.1 Sessile Droplets ¯¿½ the Bond Number
3.3 Electric Bond Number
3.4 Shape, Surface Area and Volume of Sessile Droplets
3.4.1 Height of a ¯¿½Large ¯¿½ Droplet
3.4.2 Microscopic Drops
3.4.3 Droplets Between Two Parallel Plates
3.4.4 Shape of a Droplet Flattened Between Two Horizontal Planes
3.4.5 Curvature Radius of the Free Interface
3.4.6 Convex Droplet Shape
3.4.7 Volume of a Droplet Flattened by Two Horizontal Planes with Different Contact Angles with the Two Planes (Convex Case)
3.4.8 Surface Area (Convex Case)
3.4.9 Concave Droplet Shape
3.5 Conclusion
3.6 References
4 Sessile Droplets 4.1 Abstract
4.2 Droplet Self-motion Under the Effect of a Contrast or Gradient of Wettability
4.2.1 Drop Moving Over a Sharp Transition of Wettability
4.2.2 Drop Moving Uphill
4.2.3 Dynamic and Quasi-static Approach
4.2.4 Drop Moving Up a Step
4.2.5 Drop Moving Over a Gradient of Surface Concentration of Surfactant
4.2.6 Conclusion
4.3 Contact Angle Hysteresis
4.4 Pinning and Canthotaxis
4.4.1 Droplet Pinning on a Surface Defect
4.4.2 Droplet Pinning on an Edge ¯¿½ Canthotaxis
4.4.3 Droplet Pinning at a Wettability Separation Line
4.4.4 Pinning of an Interface by Pillars
4.5 Sessile Droplet on a Non-ideally Planar Surface
4.6 Droplet on Textured or Patterned Substrates
4.6.1 Wenzel ¯¿½s Law
4.6.2 Cassie-Baxter Law
4.6.3 Contact on Microfabricated Surfaces: the Transition Between the Wen-zel and Cassie Laws
4.7 References
5 Droplets Between Two Non-parallel Planes: From Tapered Planes to Wedges 5.1 Abstract
5.2 Droplet Self-motion Between Two Non-parallel Planes
5.2.1 Identical Young Contact Angle with Both Plates
5.2.2 Different Young Contact Angles
5.2.3 Numerical Simulation ¯¿½ 2D and 3D Cases
5.2.4 A Reciprocal to the Hauksbee Problem
5.2.5 Example of Tapered System for Passive Pumping in Fuel Cells
5.2.6 Discussion
5.3 Droplet in a Corner
5.3.1 Dimensions of the Droplet and Effect of Gravity
5.3.2 Concus-Finn Relations
5.3.3 Numerical Approach
5.3.4 Example of a Liquid in a Micro-beaker
5.3.5 Extended Concus-Finn Relation
5.3.6 Droplet in a Wetting/Non-wetting Corner
5.3.7 Discussion
5.4 Conclusion
5.5 References
6 Microdrops in Microchannels and Microchambers 6.1 Abstract
6.2 Droplets in Micro-wells
6.2.1 Shape of the Liquid Surface in a Micro-well
6.2.2 Evaporation of Liquid in a Micro-well
6.2.3 Filling a Micro-well
6.3 Droplets in Microchannels
6.3.1 Capillary, Weber and Bond Numbers
6.3.2 Non-wetting Droplets and Plugs
6.3.3 Wetting Droplets and Plugs
6.3.4 Trains of Droplets ¯¿½ Compound Droplets
6.4 Conclusion
6.5 References
7 Capillary Effects: Capillary Rise, Capillary Pumping, and Capillary Valve 7.1 Abstract
7.2 Capillary Rise
7.2.1 Cylindrical Tubes: Jurin ¯¿½s Law
7.2.2 Capillary Rise in Square Tubes
7.2.3 Capillary Rise on a Vertical Plate ¯¿½ Surface Tension Measurement by the Wilhelmy Method
7.2.4 Capillary Rise Between Two Parallel Vertical Plates
7.2.5 Capillary Rise in a Dihedral
7.2.6 Capillary Rise in an Array of Four Vertical Square Pillars
7.2.7 Comparison of Capillary Rise Between Wilhelmy Plate and Pillars
7.2.8 Oblique Tubes ¯¿½ Capillary Rise in a Pipette
7.3 Capillary Pumping
7.3.1 Principles of Capillary Pumping
7.3.2 Capillary Pumping and Channel Dimensions
7.3.3 The Dynamics of capillary Pumping: Horizontal Microchannel
7.3.4 The Dynamics of Capillary Pumping: General
7.3.5 Examples of Capillary Pumping
7.4 Capillary Valves
7.4.1 Principles of Capillary Valves
7.4.2 Valving Efficiency and Shape of the Orifice
7.4.3 Examples of Capillary Valves in Microsystems
7.4.3.1 Stop Valve
7.4.4 Delay Valves5
7.5 Conclusions
7.6 References
8 Open Microfluidics 8.1 Abstract
8.2 Droplet Pierced by a Wire
8.2.1 Suspended Droplet
8.2.2 Small Droplet
8.2.3 Effect of Gravity on Small Droplets
8.2.4 Large Droplet
8.2.5 Sessile Droplet Pierced by a Wire
8.3 Liquid Spreading Between Solid Structures ¯¿½ Spontaneous Capillary Flow
8.3.1 Parallel Rails
8.3.2 Spontaneous Capillary Flow Between Parallel Rails
8.3.3 Spontaneous Capillary Flow in U-grooves
8.3.4 Spontaneous Capillary Flow in Asymmetric U-grooves ¯¿½ Spreading of Liquid Glue During Microfabrication
8.3.5 Spontaneous Capillary Flow in a Trapezoidal Channel
8.3.6 Spontaneous Capillary Flow in a Half-pipe
8.3.7 A Universal Law for Capillary Pumping
8.3.8 Spontaneous Capillary Flows in Cracks
8.3.9 Spontaneous Capillary Flow Triggered by a V-groove
8.3.10 Anisotropic Superhydrophilicity
8.3.11 Spontaneous Capillary Flow in Diverging U-grooves
8.3.12 Spontaneous Capillary Flow in Diverging-converging U-grooves
8.3.13 Capillary Flow Over a Hole
8.3.14 Suspended Microfluidics
8.3.15 Application to Droplet Dispensing in EWOD/LDEP Systems
8.3.16 Restriction of the Theory in the Case of Rounded Corners
8.4 Liquid Wetting Fibers
8.4.1 Droplet Between Parallel Fibers 0
8.4.2 Intersecting Fibers
8.4.3 Wicking in a Bundle of Fibers
8.4.4 Total Impregnation ¯¿½ Imbibition
8.4.5 Washburn ¯¿½s Law
8.4.6 Fully Wetted Flow ¯¿½ Darcy ¯¿½s Law
8.4.7 Paper-based Microfluidics
8.4.8 Thread-based Microfluidics
8.5 Conclusions
8.6 References
8.7 Appendix: Calculation of the Laplace Pressure for a Droplet on a Horizontal Cylindrical Wire
9 Droplets, Particles and Interfaces 9.1 Abstract
9.2 Neumann ¯¿½s Construction for Liquid Droplets
9.3 The Difference Between Liquid Droplets and Rigid Spheres at an Interface
9.4 Liquid Droplet Deposited at a Liquid Surface
9.4.1 Introduction
9.4.2 Liquid Droplet Crossing an Interface
9.5 Immiscible Droplets in Contact and Engulfment
9.5.1 Introduction
9.5.2 Physical Analysis
9.5.3 Numerical Approach
9.5.4 Total Engulfment
9.6 Non-deformable (Rigid) Sphere at an Interface
9.6.1 Introduction
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