Interferometric study of concentration profiles in solutions near membrane surfaces

C. Forgacs; J. Leibovitz; R. N. O'Brien; K. S. Spiegler

doi:10.1016/0013-4686(75)80006-5

Interferometric study of concentration profiles in solutions near membrane surfaces

C. Forgacs, J. Leibovitz, R. N. O'Brien, K. S. Spiegler

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27 Scopus citations

Abstract

A new technique for the observation and interpretation of concentration profiles in diffusion layers at membrane-solution interfaces was developed. The concentration profiles in dilute (0·01N) KCl solutions near an ion-exchange membrane were observed in a modified O'Brien-type wedge laser interferometer while electric current (1·15 and 2·3 mA cm^-2) passed through the solution (25°C). After current reversal, following prepolarization periods of 5-60 s, a concentration minimum develops. The image of this minimum in relation to the membrane surface is not subject to optical deflection and can therefore be accurately determined. From its trajectory, the salt concentration at the membrane surface at the time of current reversal was determined. It was found that as this concentration dropped to the order of 10^-3-10^-4M ("critical concentration") significant deviations occurred between observed trajectories and those computed from a theory based on the Nernst-Planck equations. These deviations are believed to be caused by substantial migration of H⁺ and OH^-. While these measurements indicate the order of magnitude of the critical concentration, additional measurements are necessary for quantitative determination of this concentration under different physicochemical and hydrodynamic conditions.

Original language	English
Pages (from-to)	555-563
Number of pages	9
Journal	Electrochimica Acta
Volume	20
Issue number	8
DOIs	https://doi.org/10.1016/0013-4686(75)80006-5
State	Published - 1 Jan 1975
Externally published	Yes

ASJC Scopus subject areas

General Chemical Engineering
Electrochemistry

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10.1016/0013-4686(75)80006-5

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title = "Interferometric study of concentration profiles in solutions near membrane surfaces",

abstract = "A new technique for the observation and interpretation of concentration profiles in diffusion layers at membrane-solution interfaces was developed. The concentration profiles in dilute (0·01N) KCl solutions near an ion-exchange membrane were observed in a modified O'Brien-type wedge laser interferometer while electric current (1·15 and 2·3 mA cm-2) passed through the solution (25°C). After current reversal, following prepolarization periods of 5-60 s, a concentration minimum develops. The image of this minimum in relation to the membrane surface is not subject to optical deflection and can therefore be accurately determined. From its trajectory, the salt concentration at the membrane surface at the time of current reversal was determined. It was found that as this concentration dropped to the order of 10-3-10-4M ({"}critical concentration{"}) significant deviations occurred between observed trajectories and those computed from a theory based on the Nernst-Planck equations. These deviations are believed to be caused by substantial migration of H+ and OH-. While these measurements indicate the order of magnitude of the critical concentration, additional measurements are necessary for quantitative determination of this concentration under different physicochemical and hydrodynamic conditions.",

author = "C. Forgacs and J. Leibovitz and O'Brien, {R. N.} and Spiegler, {K. S.}",

note = "Funding Information: .4ckilo~~/ecige,nfnts--Thea uthors thank Prof. C. W. -I-ob~as. N. Ihl. Dr. R. Miiller and Dr. K. W. Beach for their advice, and Mr. I{\textquoteright}. G. Young for his invaluable machining skill. Financial support by the Water Resources Ccntcr. Univcrslty of California, and the Ofic~ of Saline Water. U.S. Departmenl of the Interior, is gratefully acknowledged.",

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AU - Forgacs, C.

AU - Leibovitz, J.

AU - O'Brien, R. N.

AU - Spiegler, K. S.

N1 - Funding Information: .4ckilo~~/ecige,nfnts--Thea uthors thank Prof. C. W. -I-ob~as. N. Ihl. Dr. R. Miiller and Dr. K. W. Beach for their advice, and Mr. I’. G. Young for his invaluable machining skill. Financial support by the Water Resources Ccntcr. Univcrslty of California, and the Ofic~ of Saline Water. U.S. Departmenl of the Interior, is gratefully acknowledged.

PY - 1975/1/1

Y1 - 1975/1/1

N2 - A new technique for the observation and interpretation of concentration profiles in diffusion layers at membrane-solution interfaces was developed. The concentration profiles in dilute (0·01N) KCl solutions near an ion-exchange membrane were observed in a modified O'Brien-type wedge laser interferometer while electric current (1·15 and 2·3 mA cm-2) passed through the solution (25°C). After current reversal, following prepolarization periods of 5-60 s, a concentration minimum develops. The image of this minimum in relation to the membrane surface is not subject to optical deflection and can therefore be accurately determined. From its trajectory, the salt concentration at the membrane surface at the time of current reversal was determined. It was found that as this concentration dropped to the order of 10-3-10-4M ("critical concentration") significant deviations occurred between observed trajectories and those computed from a theory based on the Nernst-Planck equations. These deviations are believed to be caused by substantial migration of H+ and OH-. While these measurements indicate the order of magnitude of the critical concentration, additional measurements are necessary for quantitative determination of this concentration under different physicochemical and hydrodynamic conditions.

AB - A new technique for the observation and interpretation of concentration profiles in diffusion layers at membrane-solution interfaces was developed. The concentration profiles in dilute (0·01N) KCl solutions near an ion-exchange membrane were observed in a modified O'Brien-type wedge laser interferometer while electric current (1·15 and 2·3 mA cm-2) passed through the solution (25°C). After current reversal, following prepolarization periods of 5-60 s, a concentration minimum develops. The image of this minimum in relation to the membrane surface is not subject to optical deflection and can therefore be accurately determined. From its trajectory, the salt concentration at the membrane surface at the time of current reversal was determined. It was found that as this concentration dropped to the order of 10-3-10-4M ("critical concentration") significant deviations occurred between observed trajectories and those computed from a theory based on the Nernst-Planck equations. These deviations are believed to be caused by substantial migration of H+ and OH-. While these measurements indicate the order of magnitude of the critical concentration, additional measurements are necessary for quantitative determination of this concentration under different physicochemical and hydrodynamic conditions.

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Interferometric study of concentration profiles in solutions near membrane surfaces

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