Electroviscous dissipation in aqueous electrolyte films with overlapping electric double layers

F. Liu, A. Klaassen, C. Zhao, F. Mugele, D. van den Ende (Corresponding Author)

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Abstract

We use dynamic atomic force microscopy (AFM) to investigate the forces involved in squeezing out thin films of aqueous electrolyte between an AFM tip and silica substrates at variable pH and salt concentration. From amplitude and phase of the AFM signal we determine both conservative and dissipative components of the tip sample interaction forces. The measured dissipation is enhanced by up to a factor of 5 at tip-sample separations of ≈ one Debye length compared to the expectations based on classical hydrodynamic Reynolds damping with bulk viscosity. Calculating the surface charge density from the conservative forces using Derjaguin-Landau-Verwey-Overbeek (DLVO) theory in combination with a charge regulation boundary condition we find that the viscosity enhancement correlates with increasing surface charge density. We compare the observed viscosity enhancement with two competing continuum theory models: (i) electroviscous dissipation due to the electrophoretic flow driven by the streaming current that is generated upon squeezing out the counterions in the diffuse part of the electric double layer, and (ii) visco-electric enhancement of the local water viscosity caused by the strong electric fields within the electric double layer. While the visco-electric model correctly captures the qualitative trends observed in the experiments, a quantitative description of the data presumably requires more sophisticated simulations that include microscopic aspects of the distribution and mobility of ions in the Stern layer.
Original languageEnglish
Pages (from-to)933-946
Number of pages14
JournalJournal of physical chemistry B
Volume122
Issue number2
Early online date18 Oct 2017
DOIs
Publication statusPublished - 18 Jan 2018

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Electrolytes
dissipation
electrolytes
Viscosity
viscosity
Atomic force microscopy
atomic force microscopy
Surface charge
Charge density
compressing
augmentation
Debye length
Silicon Dioxide
Hydrodynamics
Salts
Damping
damping
hydrodynamics
Silica
Electric fields

Keywords

  • UT-Hybrid-D

Cite this

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abstract = "We use dynamic atomic force microscopy (AFM) to investigate the forces involved in squeezing out thin films of aqueous electrolyte between an AFM tip and silica substrates at variable pH and salt concentration. From amplitude and phase of the AFM signal we determine both conservative and dissipative components of the tip sample interaction forces. The measured dissipation is enhanced by up to a factor of 5 at tip-sample separations of ≈ one Debye length compared to the expectations based on classical hydrodynamic Reynolds damping with bulk viscosity. Calculating the surface charge density from the conservative forces using Derjaguin-Landau-Verwey-Overbeek (DLVO) theory in combination with a charge regulation boundary condition we find that the viscosity enhancement correlates with increasing surface charge density. We compare the observed viscosity enhancement with two competing continuum theory models: (i) electroviscous dissipation due to the electrophoretic flow driven by the streaming current that is generated upon squeezing out the counterions in the diffuse part of the electric double layer, and (ii) visco-electric enhancement of the local water viscosity caused by the strong electric fields within the electric double layer. While the visco-electric model correctly captures the qualitative trends observed in the experiments, a quantitative description of the data presumably requires more sophisticated simulations that include microscopic aspects of the distribution and mobility of ions in the Stern layer.",
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Electroviscous dissipation in aqueous electrolyte films with overlapping electric double layers. / Liu, F.; Klaassen, A.; Zhao, C.; Mugele, F.; van den Ende, D. (Corresponding Author).

In: Journal of physical chemistry B, Vol. 122, No. 2, 18.01.2018, p. 933-946.

Research output: Contribution to journalArticleAcademicpeer-review

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