Charge transfer as a ubiquitous mechanism in determining the negative charge at hydrophobic interfaces

  title={Charge transfer as a ubiquitous mechanism in determining the negative charge at hydrophobic interfaces},
  author={Emiliano Poli and Kwang Hyok Jong and Ali A Hassanali},
  journal={Nature Communications},
The origin of the apparent negative charge at hydrophobic–water interfaces has fueled debates in the physical chemistry community for decades. The most common interpretation given to explain this observation is that negatively charged hydroxide ions (OH – ) bind strongly to the interfaces. Using first principles calculations of extended air–water and oil–water interfaces, we unravel a mechanism that does not require the presence of OH – . Small amounts of charge transfer along hydrogen bonds… Expand
19 Citations
Electrification at water–hydrophobe interfaces
The origins of the excess positive charges incurred on water droplets that are dispensed from capillaries made of polypropylene, perfluorodecyltrichlorosilane-coated glass, and polytetrafluoroethylene are investigated and it is deduced that common hydrophobic materials possess surface-bound negative charge. Expand
Nanomolar surface-active charged impurities account for the zeta potential of hydrophobic surfaces.
It is shown that the interfacial adsorption and repulsion of small inorganic ions such as H3O+, OH-, HCO3-, and CO32- cannot account for the ζ potential observed in experiments because the surface affinities of these ions are too small. Expand
Interaction Energy Analysis of Monovalent Inorganic Anions in Bulk Water Versus Air/Water Interface
Soft anions exhibit surface activity at the air/water interface that can be probed using surface-sensitive vibrational spectroscopy, yet the statistical mechanics behind this surface activity remainsExpand
How Low Can You Go? Molecular Details of Low-Charge Nanoemulsion Surfaces.
This work describes the preparation and characterization of bare low-charge nanoemulsions (LCNEs), nanosized droplets of oil-absent emulsifiers, and shows that interfacial water bonds more strongly to the oil phase on the droplet surface compared to similar planar interfaces. Expand
On the stability and necessary electrophoretic mobility of bare oil nanodroplets in water.
It is shown that the cleaning procedure of glassware has no influence on the electrophoretic mobility of the droplets and that oil droplets with near-zero charge are unstable, and an alternative possible explanation for the observations involving glass surface chemistry is provided. Expand
Experimental Data Contributing to the Elusive Surface Charge of Inert Materials in Contact with Aqueous Media
We studied the charging of inert surfaces (polytetrafluoroethylene, i.e., PTFE; graphite; graphene; and hydrophobic silica) using classical colloid chemistry approaches. Potentiometric titrationsExpand
Electrification of water interface
  • Y. Uematsu
  • Physics, Medicine
  • Journal of physics. Condensed matter : an Institute of Physics journal
  • 2021
Experimental methods to characterize the surface charge densities developed so far are summarized, physical ion adsorption and chemical electrification as examples of electrification mechanisms are elucidated, and novel effects on surface electrification are discussed in detail. Expand
Electrowetting‐Assisted Generation of Ultrastable High Charge Densities in Composite Silicon Oxide–Fluoropolymer Electret Samples for Electric Nanogenerators
Electric nanogenerators that directly convert the energy of moving drops into electrical signals require hydrophobic substrates with a high density of static electric charge that is stable in “harshExpand
Intrinsic water layering next to soft, solid, hydrophobic, and hydrophilic substrates.
A layer-by-layer exfoliation method to identify physically meaningful water layers upon a substrate through molecular dynamics simulations under ambient conditions shows a qualitatively consistent long-ranged layer- by-layer propagation of the atomic structure, irrespective of whether the substrate is soft, solid, hydrophobic, or hydrophilic. Expand
Interactions between a responsive microgel monolayer and a rigid colloid: from soft to hard interfaces.
This work explores the interactions between microgel monolayers at the air-water interface and a hard colloid in the water and shows that the temperature-dependent swelling of the microgel fractions in the aqueous phase strongly influences the interaction with the probe. Expand


An explanation for the charge on water's surface.
A Hamaker-like force on the hydroxide ion is shown that attracts it to regions where dipole-moment fluctuations are smaller than in bulk water, in other words, to regions of low relative permittivity. Expand
Orientation-Induced Adsorption of Hydrated Protons at the Air-Water Interface.
This work calculates surface tensions and ionic surface propensities at air-water interfaces from classical, thermodynamically consistent molecular dynamics simulations and concludes that NaOH, HCl, and NaCl solutions show outstanding quantitative agreement with experiment. Expand
The excess proton at the air-water interface: The role of instantaneous liquid interfaces.
Using ab initio molecular dynamics simulations, this work revisits the propensity of the excess proton for the air-water interface with a particular focus on the role of instantaneous liquid interfaces and finds a more pronounced presence for the proton to be at the air -water interface. Expand
Charge Transfer between Water Molecules As the Possible Origin of the Observed Charging at the Surface of Pure Water
Classical molecular dynamics simulations point to an anisotropy of water–water hydrogen bonding at the water surface. Approaching from the gas phase, a region of primarily dangling hydrogens isExpand
Charge transfer effects of ions at the liquid water/vapor interface.
The effect of CT on ion adsorption to the water liquid-vapor interface is examined and CT is seen to have only minor effects on the overall free energy profiles, however, the long-ranged effects of ions are highlighted by the CT model. Expand
Propensity of Hydrated Excess Protons and Hydroxide Anions for the Air-Water Interface.
New and statistically conclusive molecular-scale results on the affinity of the hydrated excess proton and hydroxide anion for the air-water interface are presented and the fluctuation in the coordination number around water sheds new light on the observed entropic trends for both ions. Expand
Exploring the behaviour of the hydrated excess proton at hydrophobic interfaces.
The application of energy decomposition schemes to multiconfigurational simulations and the resulting consequences realized for the excess proton at hydrophobic interfaces are discussed. Expand
Central Role of Bicarbonate Anions in Charging Water/Hydrophobic Interfaces.
This work reports on two series of independent experimental studies that demonstrate that in the pH 5-10 range the negative interfacial charge of the colloids mostly stems from bicarbonate ions, whereas at lower and higher pH, protons and hydroxide ions contribute to the interfacial charging. Expand
Hydrated proton and hydroxide charge transfer at the liquid/vapor interface of water.
The hydrated proton and hydroxide affect water's liquid/vapor interface in a manner similar to monatomic ions, in that they induce a hydrogen-bonding imbalance at the surface, which results in charged surface waters, which persists until the ion is at least 10 Å away from the interface. Expand
Brønsted basicity of the air–water interface
By detecting RCOO−, experiments show the presence of OH− on the aerial side of on pH > 2 water exposed to RCOOH(g), and infer that the outer surface of water is Brønsted neutral at pH ∼3 (rather than at pH 7 as bulk water), a value that matches the isoelectric point of bubbles and oil droplets in independent electrophoretic experiments. Expand