Physical Chemistry and Acid-Base Properties of Surfaces

Jean-Charles Joud, Marie-Geneviève Barthés-Labrousse

• Publisher: Wiley-ISTE
• Year: 2015
• Print ISBN:
  9781848218437
• eBook ISBN:
  9781119145417
• Edition: 1
• Topic: Technologie et ingénierie
• Subtopic: Science des matériaux

The first part of this book looks at the consequence of chemical and topological defects existing on real surfaces, which explain the wettability of super hydrophilc and super hydrophobic surfaces. There follows an in-depth analysis of the acido-basicity of surfaces with, as an illustration, different wettability experiments on real materials.  The next chapter deals with various techniques enabling the measurement of acido basicity of the surfaces including IR and XPS technics.

The last part of the book presents an electrochemical point of view which explains the surface charges of the oxide at contact with water or other electrolyte solutions in the frame of Bronsted acido-basicity concept.  Various consequences are deduced from such analyses illustrated by original measurement of the point of zero charge or by understanding the basic principles of the electrowetting experiments.

1
Wettability of an Ideal Surface: Overview

1.1. Wetting angle

Young’s relationship and definition of the work of adhesion.

Figure 1.1. Equilibrium of a liquid droplet on an ideal solid substrate

When a liquid droplet is placed in a solid, it takes on a given configuration according to the interactions which take place between the solid and the liquid.

The system evolves toward a configuration of minimum free energy characterized by an angle of equilibrium θ_E.

If there is no chemical reaction at the solid–liquid interface, the geometry is simple, as shown in Figure 1.1.

Young’s relationship [YOU 05] provides the equilibrium of forces at the triple line. Interfacial tensions are described as forces per unit of triple line length [DEF 66, DE 03]

[1.1]

where θ _E is the wetting angle and γ is the interfacial tension of solid–vapor, liquid–vapor and solid–liquid, respectively.

COMMENT 1.1.– γ_SV is the interfacial tension of the solid in equilibrium with the vapor phase. This value is generally different from the surface tension of the solid in equilibrium with vacuum or a neutral gas, denoted as γ_S. This difference is known as spreading pressure: π_e

[1.2]

Young’s equation can therefore be written as follows:

[1.3]

The same result as Young’s equation can be deduced from a virtual thermodynamic cycle (there are a number of different variations of this demonstration):

Figure 1.2. Virtual thermodynamic cycle for the equilibrium of a liquid droplet

Using a droplet with the interfacial area Ώ placed on the solid, it can be assumed first that the droplet can be separated from the substrate without changing its shape.

Subsequently, the raised droplet undergoes a variation in contact area dΩ corresponding to the equilibrium situation. As a result, there is a variation in the area of the droplet cap: dΩ cosθ (Figure 1.3).

Figure 1.3. Area variation of the liquid droplet when it reaches the state of equilibrium

Hence:

In the third stage, the droplet is placed back onto the solid:

The overall outcome is: ΔG = ΔG₁+ΔG₂+ΔG₃.

Hence:

At equilibrium, this gives: dΔG /dΩ = O.

Hence:

This does indeed bring us back to Young’s equation.

1.2. Adhesion effect

Dupré definition, spreading coefficient.

The work of adhesion W_SL is the variation of free energy per unit area involved in the following transformation sh...

Table of contents

• Cover
• Table of Contents
• Title
• Copyright
• Introduction
• Chapter 1: Wettability of an Ideal Surface: Overview
• Chapter 2: Real Surfaces
• Chapter 3: Components of the Surface Energy
• Chapter 4: The Acid-Base Component in the Work of Adhesion
• Chapter 5: Experimental Determination through Wettability Measurements
• Chapter 6: Acid-Base Properties of Surfaces: Experimental Approaches
• Chapter 7: Oxide-Solution Interfaces: Surface Charges
• Chapter 8: Electrocapillarity Applications
• Conclusion
• Bibliography
• Index
• End User License Agreement