Difference between revisions of "Charged interfaces"

Introduction

"My own understanding of the need for a fundamental approach to modern electrostatics came from two sources. One was the electrostatics lecture-demonstrations of A.D. Moore, which often leaves experts in electromagnetics amazed by seemingly impossible phenomena. The other was my colleagues in industry, especially Henry Till, who routinely showed that complicated solutions of Laplace's equation had little to do with understanding and using electrostatics." J.M Crowley in Fundamentals of electrostatics."

Interesting Tidbits

Non-smoker attracts smoker's smoke?

Non-smokers complain quite often that they seem to attract cigarette smoke. Smokers regard this as a fairy tale, or else a method to make them stop smoking. However, things are slightly more complex. Measurements carried out with an ion counter show that cigarette smoke carries a predominantly positive charge. The negative charges are flowing to ground through the hand or mouth of the smoker.

Let us assume a situation similar to the figure above. The smoker produces a cloud of positive charged particles and, because previous clouds have also charged the smoker’s clothes positively, the particle cloud is repelled. Because the TV screen is also charged positively, it also repels the cloud. On the other hand, the non-smoker is not charged, being more or less neutral. The repelled smoke particles will thus indeed flow in the direction of the non-smoker. When the non-smoker wears clothing containing polyethylene or rayon fibers, then it is likely that he/she is charged negatively according to the triboelectric series. He/she will then attract the smoke particles.

This also explains why a single visit or meet-up with a smoker will leave the house/clothing of a non-smoker smelling bad for a long time. The gravitational settling of smoke particles also mean that children will be affected more by this selective deposition.

Nose will also serve as preferred deposition site. However, in our case, the nose of a non-smoker will be neutrally charged and the smoke will be positively charged.

Source: The forgotten pollution by Rein A Roos

• Derjaguin (1986)
• Chapter 6.1 – 6.2
• Derjaguin (1989)
• Chapter 7. Electrostatic component of disjoining pressure
• Evans
• Chapter 3. Electrostatic interactions in colloidal systems
• Morrison
• Chapter 17. Electrical charges in dispersions
• The "steric" barrier formed by water molecules associated around an ion provides the energy to keep ions dispersed (so long as the thickness of the hydrate shell is such that when the oppositely charged ions approach each other they are attracted with a energy less than kT. Molecules of nonpolar solvents (read: not water) usually do not form tightly absorbed shells around ions, and thus the ions recombine. p 316
• The layer of counterions surrounding a charged particle is called the diffuse double layer, the concentrations of which is a function of the distance from the surface of the particle and is described by the Poisson-Boltzmann equation. p 316
• Surface charges at the solid-liquid interface exist in nearly all systems. The surfaces spontaneously acquire charge by two principle mechanisms: dissociation of ionogenic groups and preferential adsorption of ions from solution. p. 317
• Norde
• Chapter 9. Electrochemistry of interfaces
• "Together with wettabitlity, the presence of electric charge largely determines the stability of a colloidal dispersion and interfacial processes such as adsorption and adhesion." p. 139
• There are mainly two mechanisms by which surfaces in equilibrium with an aqueous solution can acquire charge": dissociation or association of surface groups, and binding of an excess of anions or cations in the crystal lattice of poorly soluble salts. p. 139
• The compromise between the minimum energy situation in which all counterions are as near as possible to the charged surface and the co-ions expelled away, and the maximum entropy situation where all of the ions are homogeneously distributed in solution, results in an ion distribution of minimum Gibbs energy. " p. 140
• Chapter 10. Electrokinetic phenomena