Water in an electric field does not dance alone: The relation between equilibrium structure, time dependent viscosity and molecular motions

Baer, Andreas; Miličević, Zoran; Smith, David M.; Smith, Ana‐Sunčana

doi:10.1016/j.molliq.2019.02.055

Cited by 21 publications

(19 citation statements)

References 94 publications

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“… 7 and 8 , were comparable to our measured one). Molecular dynamics simulation results suggest lower f values at fields much higher than in our study ( 4 , 5 , 40 ) and also that the relation of Eq. 1 may not apply at such fields, while our results ( Fig.…”

Section: Discussionsupporting

confidence: 53%

Direct measurement of the viscoelectric effect in water

Jin

Hwang

Chai

et al. 2021

Proc. Natl. Acad. Sci. U.S.A.

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The viscoelectric effect concerns the increase in viscosity of a polar liquid in an electric field due to its interaction with the dipolar molecules and was first determined for polar organic liquids more than 80 y ago. For the case of water, however, the most common polar liquid, direct measurement of the viscoelectric effect is challenging and has not to date been carried out, despite its importance in a wide range of electrokinetic and flow effects. In consequence, estimates of its magnitude for water vary by more than three orders of magnitude. Here, we measure the viscoelectric effect in water directly using a surface force balance by measuring the dynamic approach of two molecularly smooth surfaces with a controlled, uniform electric field between them across highly purified water. As the water is squeezed out of the gap between the approaching surfaces, viscous damping dominates the approach dynamics; this is modulated by the viscoelectric effect under the uniform transverse electric field across the water, enabling its magnitude to be directly determined as a function of the field. We measured a value for this magnitude, which differs by one and by two orders of magnitude, respectively, from its highest and lowest previously estimated values.

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Section: Discussionsupporting

confidence: 53%

Direct measurement of the viscoelectric effect in water

Jin

Hwang

Chai

et al. 2021

Proc. Natl. Acad. Sci. U.S.A.

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“…Actually, the structure, hydrogen bonding, diffusion, and viscosity of bulk water strongly depend on external electric fields. 1 The electric field can even change the wettability of the material interface. For example, a water droplet can spread on a hydrophobic solid surface by tuning a parallel electric field, 2 implying an electrowetting phenomenon.…”

Section: ■ Introductionmentioning

confidence: 99%

Promoting Electroosmotic Water Flow through a Carbon Nanotube by Weakening the Competition between Cations and Anions in a Lateral Electric Field

Zhang

Liu

2022

Langmuir

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Understanding the electroosmotic flow through a nanochannel is essential to the design of novel nanofluidic devices, ranging from desalination to nanometer water pumps. Nonetheless, the competition between cation and anion in electric fields inevitably leads to a limited pumping of water, and thus weakening their competition could be a new avenue for the fundamental control of water transport. In this work, through a series of molecular dynamics simulations, we find a surprising phenomenon in which under the drive of a traditional longitudinal electric field, an additional lateral electric field can significantly weaken the competitive transport of a cation and anion through a carbon nanotube, which spontaneously leads to a massive increase in electroosmotic water flux. Specifically, with the increase in the lateral electric field, the anion flux exhibits an almost linear reduction, and the cation flux is stable and can even be enhanced. As a result, the net water flux along the cation direction increases significantly. The key to this unexpected phenomenon lies in the size and mobility difference between the cation and anion. The anion is larger and has greater mobility and is thus more susceptible to the lateral electric field, which ultimately leads to the reduction of its flux. For different ion types and CNT lengths, we can observe similar electropumping phenomenon, where the friction force induced by the lateral electric field becomes nontrivial for long CNTs. Our results provide a new route to tune the competitive transport of cations and anions and should be useful for the design of novel electroosmotic pumps.

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“…This is because water is a typical polar molecule and thus its dipole orientation is sensitive to the electric field. The bulk water properties including diffusion, viscosity, and hydrogen bonding also depend on the electric field . Furthermore, inside nanochannels such as carbon nanotubes (CNTs), the electric field can strongly affect the hydrogen-bonding network of confined water, resulting in rich phase morphologies. , In particular, for sub-nanometer CNTs, the water molecules form a single-file arrangement, whose dynamics and thermodynamics are sensitive to both longitudinal and lateral electric fields.…”

Section: Introductionmentioning

confidence: 99%

Enhanced Ion Rejection in Carbon Nanotubes by a Lateral Electric Field

Zhang

2022

Langmuir

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Reverse osmosis membranes hold great promise for dealing with global water scarcity. However, the trade-off between ion selectivity and water permeability is a serious obstacle to desalination. Herein, we introduce an effective strategy to enhance the desalination performance of the membrane. A series of molecular dynamics simulations manifest that an additional lateral electric field significantly promotes ion rejection in carbon nanotubes (CNTs) under the drive of longitudinal pressure. Specifically, with the increase in the electric field, the ion flux shows a deep linear decay, while the water flux decreases only slightly, resulting in a linear increase in ion rejection. The energy barriers of ions around the CNT inlet are obtained by calculating the potentials of mean force to explain enhanced ion rejection. The lateral electric field uniformly raises the energy barriers of ions by pushing them away from the CNT inlet, corresponding to the enhanced ion velocity in the field direction. Furthermore, with the increase in CNT diameter, there is a significant increase in the flux of both ions and water; however, the lateral electric field can also obviously enhance the ion rejection in wider CNTs. Consequently, the enhancement of ion rejection by lateral electric fields should be universal for different CNT diameters, which opens a new avenue for selective permeation and may have broad implications for desalination devices with large pore sizes.

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Water in an electric field does not dance alone: The relation between equilibrium structure, time dependent viscosity and molecular motions

Cited by 21 publications

References 94 publications

Direct measurement of the viscoelectric effect in water

Direct measurement of the viscoelectric effect in water

Promoting Electroosmotic Water Flow through a Carbon Nanotube by Weakening the Competition between Cations and Anions in a Lateral Electric Field

Enhanced Ion Rejection in Carbon Nanotubes by a Lateral Electric Field

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