Interfacial and Confined Water

This special topic on the chemical physics of interfacial and confined water contains a collection of original research papers that showcase recent theoretical and.
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Comprehensive Coordination Chemistry II. Design and Precise Synthesis of Thermoresponsive Polyacrylamides. Modern Gold Catalyzed Synthesis. Practical Functional Group Synthesis. An Introduction to Dynamics of Colloids. Advances in Chemical Physics. Nanocomposites with Biodegradable Polymers. Physics at the Biomolecular Interface. Metal-Catalyzed Reactions in Water. Water in Biological and Chemical Processes. Enthalpy and Internal Energy.


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  • Macromolecules in Solution and Brownian Relativity (Interface Science and Technology);
  • Interfacial water and water-gas interfaces.

Proceedings of the Conference. Advances in Quantum Chemistry. Particles at Fluid Interfaces and Membranes. Phase Transitions in Polymers: The Role of Metastable States. Sensors for Everyday Life. Directed Selectivity in Organic Synthesis. Atomic and Molecular Manipulation. Fundamentals of Membrane Bioreactors. Electroanalysis in Biomedical and Pharmaceutical Sciences. Reagents for Radical and Radical Ion Chemistry. Oxide-based Systems at the Crossroads of Chemistry. Advances in Heterocyclic Chemistry. The Chemistry of Pincer Compounds. How to write a great review. The review must be at least 50 characters long.

The title should be at least 4 characters long. Your display name should be at least 2 characters long. At Kobo, we try to ensure that published reviews do not contain rude or profane language, spoilers, or any of our reviewer's personal information. You submitted the following rating and review. We'll publish them on our site once we've reviewed them. Item s unavailable for purchase. Some ions prefer the surface as shown by their effect on the surface tension Jones-Ray effect [ ] and bubble coalescence.

Certainly, the surface pH may be several pH units different from that of the the bulk pH [ ].

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Strong acids like HCl and particularly HNO 3 re-associate at the interface [ ], so allowing their evaporation. However weak acids, such as formic and acetic acids, have a strong surface preference but dissociate more rapidly when at the surface, so reducing evaporation [ ]. Thus the suface is more complex than that suggested by vibrational sum frequency generation see elsewhere for an hypothesis.

Charge transfer causes the surface to reflect the charge on the ions close to the surface [ ], usually anions. An additional effect is charge transfer where the outside water molecules contain more hydrogen-bond acceptors whereas the water molecules just to the inside of the slip-plane contain an excess of hydrogen-bond donors [ ]. Aqueous radicals also prefer to reside at such interfaces [ ], as do some molecular species that prefer to hydrogen bond on the outside of clathrate-like structures; superoxide c for example [ ].

The presence of radicals at the surface is further shown by their release when microbubbles collapse [ ]. Excess electrons have been found to be stable at the surface of ice for several minutes [ ]. Small cations kosmotropes , but see ion effects in foams are found away from the interface towards the bulk where their requirement for efficient hydration may be satisfied and as they cannot easily be stripped of the bound water by the interface.

Also, there is a very large electrostatic solvation free energy cost that prevents adsorption of low polarizability ions at hydrophobic interfaces such as oils or air [ ]. Such cations only approach the interface in response to the surface negative charge. In acid solutions, oxonium ions point away from the surface as they only poorly accept hydrogen bonds but strongly donate three , with their oxygen atom pointing at the surface [ ]. This encourages these ions to sit in the surface layer [ ] in the absence of competing anions such as OH - see interfacial ions and can lead to the charging of hydrophobic surfaces in acid solution [ ].


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Mostly however at neutral pHs, there is a lower concentration of hydrogen ions than anions at the surface. The zeta potential of the surface of water is considerable and changes markedly with solute concentration mV for deionized water [ ], mV for 0. This is due to a surface charge density varying from about an electron per nm 2 for pure water to about an electron per 10 nm 2 for 0.

The charge at the surface of deionized water with air is similar to that found on small oil droplets in water [ c]. The aerosol mists formed at waterfalls see left are found to be negatively charged [ ]. If a charge lies on the outside of the interface then its image charge is attractive in the liquid phase as shown at the bottom of the diagram.

Water coats all hydrophilic surfaces open to ambient atmospheres that are not dried and the first absorbent layer is generally held strongly. Importantly this layer will affect the properties of the surface including their electrical properties and can cause negative resistance [ ]. The viscosity of water at hydrophilic surfaces may be orders of magnitude greater than that in the bulk but may be reduced considerably by light nm [ ].

Disrupting the 'unstirred layer' next to a surface has pronounced effects on the surface charge and surface chemistry which can last for several minutes after the stirring has ceased [ ].

Preface: special topic on interfacial and confined water. - PubMed - NCBI

Therefore under flow conditions, all surfaces should be considered as dynamic including gas-liquid interfaces where there are continuous molecular evaporations and condensations. The reduced density and stronger hydrogen bonds within the surface will both contribute to the stabilization of water clusters; particularly that of ES over CS full and partial clustering. Small gas molecules bind to these surface clusters due to multiple van der Waals dispersion interactions plus the good fit between the gas molecules and the clusters. There is no possibly-negative influence caused by the necessary closure of the clusters within the bulk.

This offers an explanation for the greater solubility of the hydrophobic gases at the interface as they can occupy clathrate-type water dodecahedra. They are also thought important in clathrate hydrate formation at liquid-gas interfaces [ ]. This is also supported by the exceptionally small difference in surface density from the bulk density as shown by the abnormally large pressure coefficient of the surface tension.

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Interestingly, the air-water interface may give rise to chiral selectivity and recognition [ ]. The surface may, therefore, act as the isotropic bulk cannot. It presents a mechanism for the choice of chirality early in the formation of life's molecules; for example, the D-series of carbohydrates and the L-series of amino acids.

Even simple neutral organic pollutants such as phenol have been shown to significantly affect the interfacial water structure [ ]. Recently, it has been discovered that the charge on the interface affects the freezing point of supercooled water [ ]. On a surface with no electric field, water droplets were found to freeze at around Whether this strange behavior is due to the reversal of the charge of the natural negatively-charged surface destroying the water clustering has yet to be determined.

There is a recent review of the surface of ice [ ]. Hexagonal ice is a very soft material 1. There appears to be a weakening of the hydrogen-bonded structure of the outermost water corrugated layers on the basal face at K. This has been interpreted in terms of a stepwise change from one to two molten layers [ ]. Certainly, different protocols have given rise to a wide range of apparent thicknesses of this outermost liquid-like layer [ ].

It remains unclear what the surface of ice looks like. It has been proposed that the quasi-liquid layer is made up of two-phase types that exhibit different morphologies droplets and thin layers [ ]. The surfaces can be examined by laser confocal microscopy combined with differential interference contrast microscopy LCM-DIM , which can directly visualize the 0. The non-equilibrium growth of these layers seems to form by the deposition of critically supersaturated water vapor onto the ice surface rather than by the surface melting of the ice or the sublimation of ice caused by undersaturated water vapor [ ].

An alternative proposal is that the surface consists of two layers [ ]. In the outer part, both the proton and oxygen sublattices are melted whereas in the inner part only the proton sublattice is melted with the oxygen sublattice stable. Yet another alternative proposa, using surface-responsive sum-frequency generation spectroscopy, is that the surface layer behaves like supercooled water [ ].

As the surface of ice, near its melting point and exposed to the air, is partially melted, it is able to take up ions and organic molecules with ease. Dissolved materials lower the freezing point and so increase the thickness of the molten layer. Also, reactions take place within this liquid-like phase. Although ice is often perceived as 'slippery' for example, ice skating , it is also very 'sticky' for example, the difficulty in removing ice from car windscreens, the compaction of snow to form 'snowballs' and the ease with which two ice cubes stick together.

The underlying slipperiness of ice can be explained by the tetrahedral open structuring [ ] of the liquid water surface that aids the formation of a slipping plane on confinement, whereas its 'stickiness' is due to the refreezing of liquid water confined between ice surfaces. Capillary condensation of liquid water between a tungsten tip and a hydrophobic graphite surface using a friction force microscope has been proposed to form a sticky 'ice' at room temperature [ ].

This surface layer is easily melted further by frictional heating with the low thermal conductivity of ice reducing the loss of heat. Also, there is a deformation of the ice, on skating, due to the pressure and the ease that the ice may deform plowing. The trails behind the skates are due to both the melting and the plowing. At low skating speeds, the plowing dominates whilst at high speeds the friction in the water layer dominates [ ]. The oxygen atoms of water bind to metal atom surfaces whereas the hydrogen atoms hydrogen bond surface water [ ].

The surface of Pt is four coordinated allowing fully hydrogen-bonding water. The structures are often uncovered experimentally by use of scanning tunneling microscopy STM [ ]. The structure of the bound H 2 O has little change upon adsorption, where they preferentially lie flat on the surface due to metal atoms' interactions of their 1 b 1 p-like lone pair orbitals perpendicular to the plane of the water molecule to metal 4 d -orbitals [ ].

The surface of Pt is six coordinated not allowing fully hydrogen-bonding water. As an example, the face of a platinum crystal is four-coordinated allowing a hydrogen-bonded water sheet to form see right top [ ]. As this water layer is fully hydrogen-bonded it forms a surprisingly substantial hydrophobic barrier to further water adhesion. Any further water added forms spherical droplets on the surface and do not spread.

The interfacial water molecules can diffuse within layers and exchange with secondary hydrating water through hydrogen bond rearrangements and quantum tunneling.

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Due to the different binding of the face compared with the face, the relaxation times of water molecules adsorbed on the face are much faster [ ]. The hydrophobicity of a naturally hydrophilic Pt-surface depends on its curvature. Water dissociates at the more reactive stepped Pt surface. It has been found that nuclear quantum effects NQE are important to the partial dissociation of water due to their ability to make many strained conformations thermodynamically competitive [ ]. Low-temperature scanning tunneling microscopy and density functional theory have shown the possibility of many water nano-clusters forming on metallic Cu surfaces.

Most water models give negative surface potentials. Not all workers follow this convention. Static and dynamic aspects of surface potentials are discussed in [ ]. The zeta potential is positive if the potential increases from the bulk towards the surface. It is due to the apparent effective charge on a moving charged particle and determined from the electrophoretic mobility. Although often proposed to be due to the charge at the 'slipping plane', it probably lies well within the unstirred surface layer except when maximally moved by an electric field and several water diameters away from the actually charged surface.

It is likely to be close to, if numerically smaller than. Although its exact physical meaning is unclear, it does give an indication of the electrostatic interaction between particles. Zeta potential is easily determined from the movement of such particles in an electric field and depends on the relative permittivity dielectric constant and viscosity. It is calculated using the Smoluchowski equation. There is a problem distinguishing the zeta potential of similarly sized sub-micron bubbles and particles in solution; thus zeta potentials of such solutions would be mixed.

The zeta potential changes with pH and there will be a pH at which it is zero, the isoelectric point. Colloids are least stable at this isoelectric point and, generally, most stable at higher positive or negative zeta potentials found at more extreme pH. The charge on the surface of theoretically modeled water without dissociation gives a change in the charge across the surface that is dependent on the depth of the surface examined, as indicated opposite [ a]. Thus overall it is negative relative to a positive bulk but where the very outer layer of the interface next to the gas is more positive [ c].