CONTROL OF COLLOIDAL STABILITY THROUGH ZETA POTENTIAL
(With a closing chapter on its relationship to cardiovascular disease)
Thomas M. Riddick
Consulting Engineer and Chemist (and Technical Director)
Thomas M. Riddick and Associates
New York, New York
Copyright © 1968 by Thomas M. Riddick
Library of Congress Catalogue Number 67–18001
All rights reserved.
A Word from the Author
In 1948, an outstanding authority on Zeta Potential stated:
"What is most needed in the present state of the theory are better experimental data to compare
with the theory."
I hope that the concepts and working curves presented herein may be of value to practical
workers, as well as scientists concerned principally with the theoretical aspects of Zeta Potential.
There are fundamental reasons for the existence of Zeta Potential, and they become more
apparent when one approaches them from a teleological viewpoint. As one alternates between
simple manmade inorganic systems and sophisticated organic natural systems, one finds that
the same basic principles apply to both. Prior to Mendelyeev, much of chemistry was a jumble of
"factors." His placing the then known elements in proper rows and columns brought a high
degree of order out of chaos. Similarly, an orderly and proper view of Zeta Potential brings order
to the vast present knowledge of practical and theoretical colloid stability.
Above all, it stresses the real importance of di, tri, and polyvalent ions and their overwhelming
control of coagulation when associated with the cation; or their control of dispersion when
associated with the anion. These concepts are not new, having been stressed eighty–five years
ago by Schulze and Hardy. They well understood these forces, but lacked the tools to
adequately measure them. And, at this same time, Helmholtz was developing basic concepts of
Zeta Potential — which later rationalized the experimental evidence of Schulze and Hardy.
Development of the theory of Zeta Potential and its use as a working tool has been considerably
retarded by improper, inadequate techniques. At the risk of appearing dogmatic, I have
consciously laid great stress upon detail procedures — particularly sample preparation. And
these aspects are equally vital to the theorist and to the laboratory worker. For example, it has
been confirmed that simple dilution of dispersed slurries to reduce opacity for cell
electrophoresis can produce nothing but grossly erroneous data and conclusions. Therefore I
feel obligated to make a detailed explanation of the techniques employed to reach the
conclusions set forth herein.
Basic facets have been presented in a gradually evolving sequence — starting with dispersion
of simple inorganics such as clays, and ending with complex organics such as blood. The intent
is to simplify and unify the overall concept of Zeta Potential and colloid stability. It seemed
expedient to omit from the main text several germane though diverting aspects in order to avoid
undue interruption of sequence and thought. These are therefore presented individually in the
Appendix.
It was decided to postpone discussion of basic concepts of Zeta Potential — and in particular
the double layer. — until the major aspects of practical colloid behavior had, from many
divergent angles, been well established. I hope the reader will find these sequences an aid to
easy comprehension and ready reference.
The curves presented herein are arranged in logical sequence to develop, step by step, the role
Zeta Potential plays in the control of colloid stability. Text has been held to a minimum, the
graphs telling the story. Included are many types of curves: adsorption; desorption; anionic
dispersion; bulk–stress — indicating; particle–charge distribution; PH–ZP; CMC; reagent
concentration — Specific Conductance; bulk– stress — forcing; and coagulation.
Appropriate employment of both dilute and concentrated suspensions is sufficiently detailed to
enable direct application to both research and practical problems encountered in industrial
colloid systems. Also discussed are nonionic systems where stability is attained through steric
hindrance.
It has long been known that colloidal stability is due to adsorption. But it has not been properly
recognized that Zeta Potential can accurately measure adsorption in liquid–solids systems of
both low and high solids concentration.
Admitting the existence of "too many chemical terms in the literature," the term "bulk–stress"
has been coined to categorize the several forces inherent in the liquid phase of colloid systems.
If one is to properly appraise the action of an applied surfactant, these forces must be taken into
full account. In reality, the action is about the same as if one added to a dialyzed colloid system a
surfactant of known characteristics and amount, and then superimposed a number of
extraneous, unknown and often unwanted electrolytes. Appropriate Zeta Potential curves can
elucidate the nature of "bulk–stress."
The curves represent my investigation of many industrial colloid systems, and no attempt has
been made to establish absolute values. However, to demonstrate basic principles, I have
employed a "test colloid" ( Minusil ) in many prepared systems. Surfactants are plainly identified
but, with few exceptions, industrial colloids are not. For ready comprehension, curves and their
pertinent text have been grouped, wherever possible, on the same or opposite pages — despite
some "imbalance" of text.
Since highly valuable information can be gained by viewing the colloid, this subject, as well as
photomicrography, is treated in some detail before discussing the means of controlling colloid
stability.
Certain concepts, as well as technical procedures, have intentionally been repeated for
emphasis. Upon occasion it has been necessary to make abrupt changes in subject matter to
demonstrate that Zeta Potential is a basic law of Nature, which functionally controls the stability
of its aqueous systems. The most vital are blood and urine, which are too complex for direct
analytical approach. Before application to complex systems, the basic principles of Zeta
Potential must be progressively developed by graduated, detailed procedures with systems of
increasing complexity starting with silica, clay, carbon, latex, milk, albumin and then blood.
This book deals principally with the stability of industrial colloid systems, but there emerge many
appropriate leads into such physiological systems as blood. As a result of the very nature of my
continued work with colloids and suspensoids in liquid systems, gradually there developed a
number of sophisticated and completely related aspects concerning blood, body fluids, etc.,
which I feel should be mentioned and, upon occasion, stressed.
But I must emphasize that all opinions expressed or implied concerning blood or other body
fluids, are based entirely upon concepts of physical chemistry and Zeta Potential, and not upon
physiology or other disciplines conventionally related to and under the professional purview of
medical practice.
Significantly, I have found that the professional physical chemist possesses a far greater
comprehension of my work than most members of the medical profession. I can understand this.
There are exceptions, however. I have come in contact with a few medical doctors whose
discipline enabled their ready comprehension of my findings — although some had no previous
knowledge of Zeta Potential. I have derived much benefit from an interchange of ideas, and they
seem to feel that the concepts we developed deserve a vital place in basic physiology.