Chapter Twelve - Influence of the pH and the Ionic Strength of Water on Contact Angles Measured with Drops of Aqueous Solutions on Electrically Charged, Amphoteric and Uncharged Surfaces

Abstract

Publisher Summary This chapter discusses the influence of the pH and the ionic strength of water on contact angles measured with drops of aqueous solutions on electrically charged, amphoteric and uncharged surfaces. It is only completely uncharged materials whose surface properties are not influenced by either changes in pH or by the admixture of salts. The lack of influence of pH on electrically uncharged surfaces includes hydrophilic as well as hydrophobic surfaces, although entities with hydrophobic surfaces cannot be insolubilized in aqueous systems, because they already are insoluble. Also, aqueous solutions with low salt concentrations, of 0.2 M or less, does not influence the surface properties of, for example, living mammalian cells. On the other hand, measurements of contact angles with water of different pH values and/or with water containing lots of salt, significantly influence the surface properties of all regularly electrically charged as well as of amphoteric surfaces and should under virtually all circumstances be avoided. The same holds true for the use of water containing low concentrations of plurivalent counterions vis-a-vis electrically charged or amphoteric entities. It is emphasized in the chapter that pH changes of water are especially hazardous to the integrity of the original surface properties of amphoteric materials.