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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

High-resolution topographic images (PF mode) around the region indicated with a white arrow in Fig. 4 acquired at later times. The peak force was set to 220 pN for (a) and 660 pN for (b,c). The yellow arrow serves as a marker for comparison among the three panels. Scale bar, 70 nm. The images in (b,c) were acquired with the fast scan direction rotated 20° clockwise relative to that in (a); the row-like patterns could not be well resolved when the row orientation was parallel with the fast scan direction. Blue and green arrows are indicated in (b,c) for comparison of structural changes over time. Growth of more layers of ordered structures at the outer edges of the INB is evident in (c). The region outlined by a white dashed box in (b,c) highlights the growth of the ordered structures at a boundary of the INB.
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f5: High-resolution topographic images (PF mode) around the region indicated with a white arrow in Fig. 4 acquired at later times. The peak force was set to 220 pN for (a) and 660 pN for (b,c). The yellow arrow serves as a marker for comparison among the three panels. Scale bar, 70 nm. The images in (b,c) were acquired with the fast scan direction rotated 20° clockwise relative to that in (a); the row-like patterns could not be well resolved when the row orientation was parallel with the fast scan direction. Blue and green arrows are indicated in (b,c) for comparison of structural changes over time. Growth of more layers of ordered structures at the outer edges of the INB is evident in (c). The region outlined by a white dashed box in (b,c) highlights the growth of the ordered structures at a boundary of the INB.

Mentions: We acquired a higher-resolution topographic image around the cap-shaped structure indicated with a white arrow in Fig. 4 at t = 475 min (Fig. 5a). At this time point, the INB was already surrounded by several layers of ordered structures. When we scanned the INB at a higher peak force, the INB appeared as a depression surrounded by multi-layer ordered domains (Fig. 5b). We previously demonstrated that a higher peak force results in a lower surface profile of an INB because the tip penetrates more deeply into the fluid structure29. Figure 5b shows that only bare HOPG substrate, with no ordered structures, was present under the INB. The edges of the surrounding ordered structures were faceted and roughly hexagonal (Fig. 5b). The thickness of the ordered structures was larger at the perimeter of the INB than at other locations away from the INB, suggesting that the formation of ordered structures is more favourable next to a fluid structure. Images acquired at later times at this high peak force revealed the growth of the ordered structures at the outer boundaries of the INB (Fig. 5c) and clearly visualised strong confinement of the INB by the surrounding ordered structures.


Nucleation processes of nanobubbles at a solid/water interface.

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

High-resolution topographic images (PF mode) around the region indicated with a white arrow in Fig. 4 acquired at later times. The peak force was set to 220 pN for (a) and 660 pN for (b,c). The yellow arrow serves as a marker for comparison among the three panels. Scale bar, 70 nm. The images in (b,c) were acquired with the fast scan direction rotated 20° clockwise relative to that in (a); the row-like patterns could not be well resolved when the row orientation was parallel with the fast scan direction. Blue and green arrows are indicated in (b,c) for comparison of structural changes over time. Growth of more layers of ordered structures at the outer edges of the INB is evident in (c). The region outlined by a white dashed box in (b,c) highlights the growth of the ordered structures at a boundary of the INB.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f5: High-resolution topographic images (PF mode) around the region indicated with a white arrow in Fig. 4 acquired at later times. The peak force was set to 220 pN for (a) and 660 pN for (b,c). The yellow arrow serves as a marker for comparison among the three panels. Scale bar, 70 nm. The images in (b,c) were acquired with the fast scan direction rotated 20° clockwise relative to that in (a); the row-like patterns could not be well resolved when the row orientation was parallel with the fast scan direction. Blue and green arrows are indicated in (b,c) for comparison of structural changes over time. Growth of more layers of ordered structures at the outer edges of the INB is evident in (c). The region outlined by a white dashed box in (b,c) highlights the growth of the ordered structures at a boundary of the INB.
Mentions: We acquired a higher-resolution topographic image around the cap-shaped structure indicated with a white arrow in Fig. 4 at t = 475 min (Fig. 5a). At this time point, the INB was already surrounded by several layers of ordered structures. When we scanned the INB at a higher peak force, the INB appeared as a depression surrounded by multi-layer ordered domains (Fig. 5b). We previously demonstrated that a higher peak force results in a lower surface profile of an INB because the tip penetrates more deeply into the fluid structure29. Figure 5b shows that only bare HOPG substrate, with no ordered structures, was present under the INB. The edges of the surrounding ordered structures were faceted and roughly hexagonal (Fig. 5b). The thickness of the ordered structures was larger at the perimeter of the INB than at other locations away from the INB, suggesting that the formation of ordered structures is more favourable next to a fluid structure. Images acquired at later times at this high peak force revealed the growth of the ordered structures at the outer boundaries of the INB (Fig. 5c) and clearly visualised strong confinement of the INB by the surrounding ordered structures.

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