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Probing hydrophilic interface of solid/liquid-water by nanoultrasonics.

Mante PA, Chen CC, Wen YC, Chen HY, Yang SC, Huang YR, Chen IJ, Chen YW, Gusev V, Chen MJ, Kuo JL, Sheu JK, Sun CK - Sci Rep (2014)

Bottom Line: To answer this question, a complete picture of the distribution of the water molecule structure and molecular interactions has to be obtained in a non-invasive way and on an ultrafast time scale.We developed a new experimental technique that extends the classical acoustic technique to the molecular level.Moreover, we discuss the effect of the interfacial water structure on the abnormal thermal transport properties of solid/liquid interfaces.

View Article: PubMed Central - PubMed

Affiliation: Department of Electrical Engineering and Graduate Institute of Photonics and Optoelectronics, National Taiwan University, Taipei 10617, Taiwan.

ABSTRACT
Despite the numerous devoted studies, water at solid interfaces remains puzzling. An ongoing debate concerns the nature of interfacial water at a hydrophilic surface, whether it is more solid-like, ice-like, or liquid-like. To answer this question, a complete picture of the distribution of the water molecule structure and molecular interactions has to be obtained in a non-invasive way and on an ultrafast time scale. We developed a new experimental technique that extends the classical acoustic technique to the molecular level. Using nanoacoustic waves with a femtosecond pulsewidth and an ångström resolution to noninvasively diagnose the hydration structure distribution at ambient solid/water interface, we performed a complete mapping of the viscoelastic properties and of the density in the whole interfacial water region at hydrophilic surfaces. Our results suggest that water in the interfacial region possesses mixed properties and that the different pictures obtained up to now can be unified. Moreover, we discuss the effect of the interfacial water structure on the abnormal thermal transport properties of solid/liquid interfaces.

No MeSH data available.


Related in: MedlinePlus

(a) Schematic representation of the experimental configuration. (b) Photograph of the microfluidic channel. (c) X-ray photoelectron spectrum of the sample.
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f1: (a) Schematic representation of the experimental configuration. (b) Photograph of the microfluidic channel. (c) X-ray photoelectron spectrum of the sample.

Mentions: Nanoultrasonic experiments are based on the optical excitation of a piezoelectric semiconductor single quantum well (SQW) that launches a broadband nanoacoustic pulse. This pulse then travels within the sample, gets reflected by the multiple interfaces and finally is detected when it reaches the SQW again, as depicted in figure 1(a)1819. The spectrum of thus excited acoustic pulse range from few GHz to above THz, which has made this technique a powerful tool to image or characterize nanoscale materials. Indeed, in recent years, this method has not only been successfully applied to characterize the surface roughness of materials20, but also the acoustic attenuation up to 650 GHz in SiO221 and more recently we showed the possibility to measure the attenuation up to 1 THz.22 The nanoultrasonic technique allows generating nanoacoustic waves (NAW) with a pulsewidth of 3 nm and a ~10−4 peak intensity of strain, corresponding to a ~0.3-pm displacement, allowing the non-invasive characterization of the interface. In this pulse-and-echo scheme, the measured sub-picosecond temporal shape of acoustic echoes and thus transformed complex acoustic reflection spectrum of the solid-water interface, with an acoustic frequency bandwidth up to 1 THz, can unravel the interfacial structure of the water with a spatial resolution around half of the acoustic pulsewidth, which can be as fine as 3Å in liquid water due to its much reduced sound velocity (see supplementary information). Moreover, the penetration depth of the THz acoustic pulse in liquid water is only a few intermolecular distances (~2 nm), thus the acoustic reflection measurement has interface specificity and can be applied to diagnose solid/ambient water interface.


Probing hydrophilic interface of solid/liquid-water by nanoultrasonics.

Mante PA, Chen CC, Wen YC, Chen HY, Yang SC, Huang YR, Chen IJ, Chen YW, Gusev V, Chen MJ, Kuo JL, Sheu JK, Sun CK - Sci Rep (2014)

(a) Schematic representation of the experimental configuration. (b) Photograph of the microfluidic channel. (c) X-ray photoelectron spectrum of the sample.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4150100&req=5

f1: (a) Schematic representation of the experimental configuration. (b) Photograph of the microfluidic channel. (c) X-ray photoelectron spectrum of the sample.
Mentions: Nanoultrasonic experiments are based on the optical excitation of a piezoelectric semiconductor single quantum well (SQW) that launches a broadband nanoacoustic pulse. This pulse then travels within the sample, gets reflected by the multiple interfaces and finally is detected when it reaches the SQW again, as depicted in figure 1(a)1819. The spectrum of thus excited acoustic pulse range from few GHz to above THz, which has made this technique a powerful tool to image or characterize nanoscale materials. Indeed, in recent years, this method has not only been successfully applied to characterize the surface roughness of materials20, but also the acoustic attenuation up to 650 GHz in SiO221 and more recently we showed the possibility to measure the attenuation up to 1 THz.22 The nanoultrasonic technique allows generating nanoacoustic waves (NAW) with a pulsewidth of 3 nm and a ~10−4 peak intensity of strain, corresponding to a ~0.3-pm displacement, allowing the non-invasive characterization of the interface. In this pulse-and-echo scheme, the measured sub-picosecond temporal shape of acoustic echoes and thus transformed complex acoustic reflection spectrum of the solid-water interface, with an acoustic frequency bandwidth up to 1 THz, can unravel the interfacial structure of the water with a spatial resolution around half of the acoustic pulsewidth, which can be as fine as 3Å in liquid water due to its much reduced sound velocity (see supplementary information). Moreover, the penetration depth of the THz acoustic pulse in liquid water is only a few intermolecular distances (~2 nm), thus the acoustic reflection measurement has interface specificity and can be applied to diagnose solid/ambient water interface.

Bottom Line: To answer this question, a complete picture of the distribution of the water molecule structure and molecular interactions has to be obtained in a non-invasive way and on an ultrafast time scale.We developed a new experimental technique that extends the classical acoustic technique to the molecular level.Moreover, we discuss the effect of the interfacial water structure on the abnormal thermal transport properties of solid/liquid interfaces.

View Article: PubMed Central - PubMed

Affiliation: Department of Electrical Engineering and Graduate Institute of Photonics and Optoelectronics, National Taiwan University, Taipei 10617, Taiwan.

ABSTRACT
Despite the numerous devoted studies, water at solid interfaces remains puzzling. An ongoing debate concerns the nature of interfacial water at a hydrophilic surface, whether it is more solid-like, ice-like, or liquid-like. To answer this question, a complete picture of the distribution of the water molecule structure and molecular interactions has to be obtained in a non-invasive way and on an ultrafast time scale. We developed a new experimental technique that extends the classical acoustic technique to the molecular level. Using nanoacoustic waves with a femtosecond pulsewidth and an ångström resolution to noninvasively diagnose the hydration structure distribution at ambient solid/water interface, we performed a complete mapping of the viscoelastic properties and of the density in the whole interfacial water region at hydrophilic surfaces. Our results suggest that water in the interfacial region possesses mixed properties and that the different pictures obtained up to now can be unified. Moreover, we discuss the effect of the interfacial water structure on the abnormal thermal transport properties of solid/liquid interfaces.

No MeSH data available.


Related in: MedlinePlus