ABSTRACT
I. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 497
II. Measurement of the z Potential of Bubbles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 498 A. Methods Dependent on Gravity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 499
1. Method Using the Deviation by a Horizontal Electric Field . . . . . . . . . . . 499
2. Method Adding or Subtracting an Electric Force . . . . . . . . . . . . . . . . . . . 499
3. Method Minimizing the Gravity Effect . . . . . . . . . . . . . . . . . . . . . . . . . . 499
B. Methods Independent of Gravity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 500
1. Method Using Weightless Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . 500
2. Method of the Spinning Bubble . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 500
C. Indispensable Precautions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 501
1. Purification of the Immersing Liquid . . . . . . . . . . . . . . . . . . . . . . . . . . . . 501
2. Control of Electro-osmosis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 501
III. Experimental Results and Prospects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 502
A. Main Trends . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 502
B. New Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 503
C. New Prospects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 504
IV. On the Origin of the z Potential of Bubbles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 505 V. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 506
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 507
The study of electrokinetic phenomena has evolved considerably, since the first studies were carried
out by Quincke, Helmholtz, and Lipman in the nineteenth century. In the last 30 years, at least five
books have been devoted to the subject [1-5]. Among the parameters which can be deduced from
electrokinetic measurements, z potential is profoundly related to colloid science because the “stability” of dispersions, emulsions, and foams depends on its value.
