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Langmuir 2001, 17, 1314-1314
Comments Comments on “Electroacoustic Phenomena in Concentrated Dispersions: New Theory and CVI Experiment” by A. S. Dukhin et Al.
In the above paper,1 Dukhin and coauthors attribute some flawed theoretical results to me and then proceed to criticize these results as the “O’Brien-Levine theory” and “O’Brien’s hybrid theory”. They demonstrate what awful theories these areshow they fail to satisfy a theoretical test and fail to agree with their experiments. In this way, the authors cast doubt on my work in the area of electroacoustics. The purpose of this comment is to remove that doubt by making it clear to readers that my name should not be linked to either of the above theories. I do not dispute the fact that the theories are very poor pieces of work, but they are not my work, and I do not want my name associated with them in any way. First, some background: Dukhin and his colleagues have written several papers over the years on the calculation of electroacoustic effects in concentrated colloids. In the course of this work, they have used a number of “cell model” theories to model the effect of particle interactions on the flow and electric field distributions in the colloid. Simply speaking, the effect of the surrounding particles is represented in these cell models as an outer spherical surface. Thus, to calculate the flow field and the electric field one simply solves the governing equations for these quantities for a spherical particle sitting at the center of the spherical shell. The gap between the sphere and the outer boundary is filled with solvent. The thing that distinguishes one cell model from another is the type of boundary conditions that are applied on the outer surface. Two types of cell models are referred to in this Dukhin paper: the “Levine” model and the “ShilovZharkikh model”. In the introduction to this paper, Dukhin et al. claim that I “applied the Levine cell model trying to expand the dynamic electrophoretic theory to concentrated suspensions” and they point to my patent2 as the reference. They (1) Dukhin, A. S.; Shilov, V. N.; Ohshima, H.; Goetz, P. J. Electroacoustic Phenomena in Concentrated Dispersions: New Theory and CVI Experiment. Langmuir 1999, 15 (20), 6692-6706.
call the formula that they derived, using the Levine model, the “O’Brien-Levine” theory. Now, the point is that I have never written a paper where I have used the Levine cell model. On page 8 of the patent, I suggested that such a model could be used to try to account for particle interactions, but I did not attempt to do so. The reason that I never went to press with this formula is that I wanted to test it experimentally first. We carried out those tests at Sydney University some years ago and found that the Levine model significantly underestimated the particle interactions at high frequencies. For this reason, I never published the formula. Now, I find that not only is it attributed to me but another formula that I had nothing whatsoever to do with is also attributed to me, under the title “hybrid O’Brien theory”. This one uses the second cell model referred to above. You would think that because Dukhin and co-workers actually derived both these formulas they should be honored in their naming, but they chose not to do so, not for reasons of modesty but because they found that the formulas were wrong. In fact, these “O’Brien theories” are bad news, and the authors seem to delight in pointing out their shortcomings at numerous places in the abstract and text of this paper. Readers who are new to the field of electroacoustics or who are not theoreticians (and that is likely to be the majority) would probably accept these criticisms at face value, because Langmuir is, after all, a prestigious journal. I would not blame them for concluding that my work had passed its use-by date. I hope that by writing this note I will have removed this misapprehension. Richard O’Brien
Colloidal Dynamics Pty Ltd, The Australian Technology Park, Eveleigh, NSW 1430, Australia Received March 31, 2000 In Final Form: September 12, 2000 LA000492T (2) O’Brien, R. W. Determination of Particle Size and Charge. U.S. Patent 5,059,909, Oct 22, 1991.
10.1021/la000492t CCC: $20.00 © 2001 American Chemical Society Published on Web 01/20/2001
