Thermal Conductance of Hydrophilic and Hydrophobic Interfaces

Ge, Zhong; Cahill, David G.; Braun, Paul V.

doi:10.1103/physrevlett.96.186101

Cited by 401 publications

(400 citation statements)

References 34 publications

(48 reference statements)

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“…The absence of signal from the liquid confirms that the signal observed in ice is not affected by unwanted contributions such as interferences between pump and probe light on the photodiode or optical effects on the cell windows. Thermoreflectance (22,23) does not contribute to our signal because of the absence of highly reflecting interfaces, and its transient signal would, however, be concluded in ∼1 ns. The transmission loss due to scattering at ice/water interfaces has been used to detect the freezing of water into ice VII under multiple-shock experiments (6,24), using white light.…”

Section: Resultsmentioning

confidence: 99%

Melting dynamics of ice in the mesoscopic regime

Citroni

Fanetti

Falsini³

et al. 2017

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

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How does a crystal melt? How long does it take for melt nuclei to grow? The melting mechanisms have been addressed by several theoretical and experimental works, covering a subnanosecond time window with sample sizes of tens of nanometers and thus suitable to determine the onset of the process but unable to unveil the following dynamics. On the other hand, macroscopic observations of phase transitions, with millisecond or longer time resolution, account for processes occurring at surfaces and time limited by thermal contact with the environment. Here, we fill the gap between these two extremes, investigating the melting of ice in the entire mesoscopic regime. A bulk ice I h or ice VI sample is homogeneously heated by a picosecond infrared pulse, which delivers all of the energy necessary for complete melting. The evolution of melt/ice interfaces thereafter is monitored by Mie scattering with nanosecond resolution, for all of the time needed for the sample to reequilibrate. The growth of the liquid domains, over distances of micrometers, takes hundreds of nanoseconds, a time orders of magnitude larger than expected from simple H-bond dynamics.Mie scattering | temperature jump | superheating | laser heating | anvil cell M elting of ice is one of the most common occurrences on our planet, from polar ices to glaciers, to the morning frost and the preparation of our drinks. Ices are present as well in extraterrestrial environments, planetary and intersellar, going through extremely different pressure and temperature conditions, where many phase boundaries are encountered. The molecular mechanisms of melting and the characteristic timescales of the process are not well elucidated, as for any other phase transition. In fact, great effort is presently being made with state of the art experimental techniques to understand the intrinsic kinetics of structural transformations, particularly under dynamic compression, by which phase-transition boundaries up to extreme pressures (P) and temperatures (T) can be accessed (1-6). Melting is the least hindered of phase transitions, requiring the disruption of the crystalline order and the achievement of the local structure of the liquid phase.The dynamics of melting have been studied up to the present in the picosecond timescale, observing structural changes on a length scale of few nanometers, in the attempt to explain the fundamental mechanisms of the transition onset. In both simulations and experiments, micrometric-or submicrometric-sized crystals can be rapidly heated above the melting temperature (Tm ), into a superheated state where melting occurs. Metals and water ice have been the test systems. Simulations have revealed a nucleation and growth mechanism (7-11), and nucleation has been especially addressed, in trying to determine the minimum number of atoms/molecules needed to form a critical nucleus for the transitions, the solid/melt interfacial energy, the transient local structures achieved during the transformation, and the role of defects and surfaces. Experimentally...

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Section: Resultsmentioning

confidence: 99%

Melting dynamics of ice in the mesoscopic regime

Citroni

Fanetti

Falsini³

et al. 2017

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

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“…Physically, this continuum hydrodynamic model is closely related to the so-called model "H" which was originally devised to describe the critical dynamics of thermal fluctuations [41,42]. Supplemented with the hydrodynamic boundary conditions derived in our previous works [22,25], this model can be used to fully take into account the various physical processes involved in the contact line dynamics, including phase transition (evaporation or condensation) and capillary flow in the bulk fluid region [26,27], boundary slip of fluid [25,39,40,43], temperature slip across the fluid-solid interface [44,45], and mechanical-thermal cross coupling at the fluid-solid interface [46]. Due to the use of diffuse-interface method, the stress and thermal singularities are resolved automatically.…”

Section: Introductionmentioning

confidence: 99%

Thermal singularity and droplet motion in one-component fluids on solid substrates with thermal gradients

Qian

2012

Phys. Rev. E

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Using a continuum model capable of describing the one-component liquid-gas hydrodynamics down to the contact line scale, we carry out numerical simulation and physical analysis for the droplet motion driven by thermal singularity. For liquid droplets in one-component fluids on heated or cooled substrates, the liquid-gas interface is nearly isothermal. Consequently, a thermal singularity occurs at the contact line and the Marangoni effect due to temperature gradient is suppressed. Through evaporation or condensation in the vicinity of the contact line, the thermal singularity makes the contact angle increase with the increasing substrate temperature. This effect on the contact angle can be used to move the droplets on substrates with thermal gradients. Our numerical results for this kind of droplet motion are explained by a simple fluid dynamical model at the droplet length scale. Since the mechanism for droplet motion is based on the change of contact angle, a separation of length scales is exhibited through a comparison between the droplet motion induced by a wettability gradient and that by a thermal gradient. It is shown that the flow field at the droplet length scale is independent of the statics or dynamics at the contact line scale.

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“…Although a number of experimental tools including X-ray (27)(28)(29)(30)(31) and neutron reflectivity (32,33), ellipsometry (34), and thermal conductivity (35) have been used to probe the width of the ''depletion layer'' at a hydrophobic surface, a clear picture has not yet emerged from these measurements (42). Fig.…”

mentioning

confidence: 99%

“…The lack of a correlation between water density and hydrophobicity reflects the complexities present in realistic systems arising from different molecular topologies and different head group water interactions. It also highlights and probably rationalizes the difficulty in obtaining unambiguous conclusions from experiments regarding wetting/dewetting of realistic hydrophobic interfaces (27)(28)(29)(30)(31)(32)(33)(34)(35).…”

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confidence: 99%

Characterizing hydrophobicity of interfaces by using cavity formation, solute binding, and water correlations

Godawat

Jamadagni

Garde

2009

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

328

396

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Hydrophobicity is often characterized macroscopically by the droplet contact angle. Molecular signatures of hydrophobicity have, however, remained elusive. Successful theories predict a drying transition leading to a vapor-like region near large hard-sphere solutes and interfaces. Adding attractions wets the interface with local density increasing with attractions. Here we present extensive molecular simulation studies of hydration of realistic surfaces with a wide range of chemistries from hydrophobic (؊CF 3, ؊CH3) to hydrophilic (؊OH, ؊CONH 2). We show that the water density near weakly attractive hydrophobic surfaces (e.g., ؊CF 3) can be bulk-like or larger, and provides a poor quantification of surface hydrophobicity. In contrast, the probability of cavity formation or the free energy of binding of hydrophobic solutes to interfaces correlates quantitatively with the macroscopic wetting properties and serves as an excellent signature of hydrophobicity. Specifically, the probability of cavity formation is enhanced in the vicinity of hydrophobic surfaces, and water-water correlations correspondingly display characteristics similar to those near a vapor-liquid interface. Hydrophilic surfaces suppress cavity formation and reduce the water-water correlation length. Our results suggest a potentially robust approach for characterizing hydrophobicity of more complex and heterogeneous surfaces of proteins and biomolecules, and other nanoscopic objects.hydration ͉ hydrophilic ͉ hydrophobic ͉ wetting ͉ fluctuations H ydrophobicity, reflected in the low solubility of nonpolar solutes or in their tendency to aggregate in water, is known to play an important role in many biological and colloidal self-assembly processes (1-4). Yet defining it precisely is challenging, and its molecular signatures remain unclear. Macroscopically, hydrophobicity is often characterized by measuring the droplet contact angle, with surfaces showing angles greater than 90°termed hydrophobic. Water beads up into droplets on hydrophobic surfaces and spreads on hydrophilic ones. Translating these ideas into the molecular domain presents special challenges. In a recent perspective, Granick and Bae (5) highlight the ambiguity in defining hydrophobicity at molecular length scales, such as near proteins or nanotubes, where droplet contact angle measurements are not possible.At the molecular level, hard-sphere solutes have served as excellent models for studies of hydrophobicity, with their hydration thermodynamics capturing the solubility of noble gases as a function of temperature (6, 7), pressure (8), and salt addition (9, 10). With increasing solute length scale, the elegant theory by Lum, Chandler, and Weeks (11) as well as computer simulations (12, 13) predict a gradual dewetting of the solute. Near large solutes or a hard-wall, water density is small and vapor-like, and the wall-water interface resembles a water vapor-liquid interface (14).Realistic solutes exert van der Waals and/or electrostatic interactions and pull the water interface closer, ...

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Thermal Conductance of Hydrophilic and Hydrophobic Interfaces

Cited by 401 publications

References 34 publications

Melting dynamics of ice in the mesoscopic regime

Melting dynamics of ice in the mesoscopic regime

Thermal singularity and droplet motion in one-component fluids on solid substrates with thermal gradients

Characterizing hydrophobicity of interfaces by using cavity formation, solute binding, and water correlations

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