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Nucleation processes of nanobubbles at a solid/water interface.

Fang CK, Ko HC, Yang CW, Lu YH, Hwang IS - Sci Rep (2016)

Bottom Line: Experimental investigations of hydrophobic/water interfaces often return controversial results, possibly due to the unknown role of gas accumulation at the interfaces.These ordered domains may be the interfacial hydrophilic gas hydrates and/or the long-sought chemical surface heterogeneities responsible for contact line pinning and contact angle hysteresis.The gradual nucleation and growth of hydrophilic ordered domains renders the original homogeneous hydrophobic/water interface more heterogeneous over time, which would have great consequence for interfacial properties that affect diverse phenomena, including interactions in water, chemical reactions, and the self-assembly and function of biological molecules.

View Article: PubMed Central - PubMed

Affiliation: Institute of Physics, Academia Sinica, Nankang, Taipei 115, Taiwan.

ABSTRACT
Experimental investigations of hydrophobic/water interfaces often return controversial results, possibly due to the unknown role of gas accumulation at the interfaces. Here, during advanced atomic force microscopy of the initial evolution of gas-containing structures at a highly ordered pyrolytic graphite/water interface, a fluid phase first appeared as a circular wetting layer ~0.3 nm in thickness and was later transformed into a cap-shaped nanostructure (an interfacial nanobubble). Two-dimensional ordered domains were nucleated and grew over time outside or at the perimeter of the fluid regions, eventually confining growth of the fluid regions to the vertical direction. We determined that interfacial nanobubbles and fluid layers have very similar mechanical properties, suggesting low interfacial tension with water and a liquid-like nature, explaining their high stability and their roles in boundary slip and bubble nucleation. These ordered domains may be the interfacial hydrophilic gas hydrates and/or the long-sought chemical surface heterogeneities responsible for contact line pinning and contact angle hysteresis. The gradual nucleation and growth of hydrophilic ordered domains renders the original homogeneous hydrophobic/water interface more heterogeneous over time, which would have great consequence for interfacial properties that affect diverse phenomena, including interactions in water, chemical reactions, and the self-assembly and function of biological molecules.

No MeSH data available.


Related in: MedlinePlus

AFM images (PF mode, 250 pN) of the transition from a 2D fluid layer to a 3D structure.The scan area is 2 μm × 2 μm. Chilled water was rapidly heated to 45 °C and deposited on a freshly cleaved HOPG substrate. Images were acquired continuously with a scanning rate of ~3 min per image. The top, middle, and bottom rows of each panel depict the topographic, stiffness (Young’s modulus), and adhesion maps, respectively. Two fluid regions are highlighted with white and blue arrows.
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f2: AFM images (PF mode, 250 pN) of the transition from a 2D fluid layer to a 3D structure.The scan area is 2 μm × 2 μm. Chilled water was rapidly heated to 45 °C and deposited on a freshly cleaved HOPG substrate. Images were acquired continuously with a scanning rate of ~3 min per image. The top, middle, and bottom rows of each panel depict the topographic, stiffness (Young’s modulus), and adhesion maps, respectively. Two fluid regions are highlighted with white and blue arrows.

Mentions: We detected a different transformation process for smaller fluid regions when chilled water was rapidly heated to 45 °C before deposition (Fig. 2). At t = 20 min and t = 23 min, gas adsorption at the interface was evident in the stiffness and adsorption maps, but was barely detectable in the topographic images acquired in PF mode (white arrow, Fig. 2a,b). This difference occurred because the AFM tip usually penetrates into fluid structures to a certain depth that depends on the hydrophobicity of the tip30, in order to achieve a positive pre-set peak force due to the capillary force between the tip and the fluid structure29. When the fluid structure is too thin, the tip traces the profile of the underlying stiff structure (the substrate, in this case). At t = 26 min, the topographic image began to reveal the presence of a circular layer 0.4–0.5 nm in thickness (white arrow, Fig. 2c). At t = 28 min, the apparent height of the fluid layer continued to grow, and a small protrusion appeared near the centre of the layer (Fig. 2d). A cap-shaped INB eventually formed (Fig. 2f–l).


Nucleation processes of nanobubbles at a solid/water interface.

Fang CK, Ko HC, Yang CW, Lu YH, Hwang IS - Sci Rep (2016)

AFM images (PF mode, 250 pN) of the transition from a 2D fluid layer to a 3D structure.The scan area is 2 μm × 2 μm. Chilled water was rapidly heated to 45 °C and deposited on a freshly cleaved HOPG substrate. Images were acquired continuously with a scanning rate of ~3 min per image. The top, middle, and bottom rows of each panel depict the topographic, stiffness (Young’s modulus), and adhesion maps, respectively. Two fluid regions are highlighted with white and blue arrows.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4835695&req=5

f2: AFM images (PF mode, 250 pN) of the transition from a 2D fluid layer to a 3D structure.The scan area is 2 μm × 2 μm. Chilled water was rapidly heated to 45 °C and deposited on a freshly cleaved HOPG substrate. Images were acquired continuously with a scanning rate of ~3 min per image. The top, middle, and bottom rows of each panel depict the topographic, stiffness (Young’s modulus), and adhesion maps, respectively. Two fluid regions are highlighted with white and blue arrows.
Mentions: We detected a different transformation process for smaller fluid regions when chilled water was rapidly heated to 45 °C before deposition (Fig. 2). At t = 20 min and t = 23 min, gas adsorption at the interface was evident in the stiffness and adsorption maps, but was barely detectable in the topographic images acquired in PF mode (white arrow, Fig. 2a,b). This difference occurred because the AFM tip usually penetrates into fluid structures to a certain depth that depends on the hydrophobicity of the tip30, in order to achieve a positive pre-set peak force due to the capillary force between the tip and the fluid structure29. When the fluid structure is too thin, the tip traces the profile of the underlying stiff structure (the substrate, in this case). At t = 26 min, the topographic image began to reveal the presence of a circular layer 0.4–0.5 nm in thickness (white arrow, Fig. 2c). At t = 28 min, the apparent height of the fluid layer continued to grow, and a small protrusion appeared near the centre of the layer (Fig. 2d). A cap-shaped INB eventually formed (Fig. 2f–l).

Bottom Line: Experimental investigations of hydrophobic/water interfaces often return controversial results, possibly due to the unknown role of gas accumulation at the interfaces.These ordered domains may be the interfacial hydrophilic gas hydrates and/or the long-sought chemical surface heterogeneities responsible for contact line pinning and contact angle hysteresis.The gradual nucleation and growth of hydrophilic ordered domains renders the original homogeneous hydrophobic/water interface more heterogeneous over time, which would have great consequence for interfacial properties that affect diverse phenomena, including interactions in water, chemical reactions, and the self-assembly and function of biological molecules.

View Article: PubMed Central - PubMed

Affiliation: Institute of Physics, Academia Sinica, Nankang, Taipei 115, Taiwan.

ABSTRACT
Experimental investigations of hydrophobic/water interfaces often return controversial results, possibly due to the unknown role of gas accumulation at the interfaces. Here, during advanced atomic force microscopy of the initial evolution of gas-containing structures at a highly ordered pyrolytic graphite/water interface, a fluid phase first appeared as a circular wetting layer ~0.3 nm in thickness and was later transformed into a cap-shaped nanostructure (an interfacial nanobubble). Two-dimensional ordered domains were nucleated and grew over time outside or at the perimeter of the fluid regions, eventually confining growth of the fluid regions to the vertical direction. We determined that interfacial nanobubbles and fluid layers have very similar mechanical properties, suggesting low interfacial tension with water and a liquid-like nature, explaining their high stability and their roles in boundary slip and bubble nucleation. These ordered domains may be the interfacial hydrophilic gas hydrates and/or the long-sought chemical surface heterogeneities responsible for contact line pinning and contact angle hysteresis. The gradual nucleation and growth of hydrophilic ordered domains renders the original homogeneous hydrophobic/water interface more heterogeneous over time, which would have great consequence for interfacial properties that affect diverse phenomena, including interactions in water, chemical reactions, and the self-assembly and function of biological molecules.

No MeSH data available.


Related in: MedlinePlus