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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

PF (220 pN) images of gas-containing structures at a HOPG/water interface after the deposition of chilled water.Top, middle, and bottom rows contain height, stiffness, and adhesion maps, respectively. Scale bar, 500 nm. The green arrow in (a) highlights a fluid layer that disappeared at a later time (b). The white, blue, and pink arrows indicate fluid regions that later transformed into a cap-shaped structure (e). Two blue arrows indicate fluid regions that were confined by two step edges, yielding rectangular gas structures (a–d). Note that the ordered domains exhibited less adhesion than the bare HOPG surface and the fluid structures. In (e), the entire interface (except for the INBs) was dark on the adhesion maps (bottom row) and bright on the stiffness maps (middle row), indicating that the interface was nearly completely covered by the ordered domains. The regions of the fluid structures can be distinguished easily in the stiffness maps because they exhibited less stiffness than the ordered domains and HOPG substrate. This AFM tip was relatively hydrophobic, yielding a penetration depth for the fluid regions that was larger than that obtained with the tips used to acquire the data in the other figures presented in this work. A cap-shaped structure is visible in a topographic image only when its height is larger than the tip penetration depth. In addition, it is difficult to distinguish between INBs and fluid layers from the stiffness and adhesion maps. Thus, the INBs may have formed well before we detected the cap-shaped structures in the topographic (height) maps.
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f4: PF (220 pN) images of gas-containing structures at a HOPG/water interface after the deposition of chilled water.Top, middle, and bottom rows contain height, stiffness, and adhesion maps, respectively. Scale bar, 500 nm. The green arrow in (a) highlights a fluid layer that disappeared at a later time (b). The white, blue, and pink arrows indicate fluid regions that later transformed into a cap-shaped structure (e). Two blue arrows indicate fluid regions that were confined by two step edges, yielding rectangular gas structures (a–d). Note that the ordered domains exhibited less adhesion than the bare HOPG surface and the fluid structures. In (e), the entire interface (except for the INBs) was dark on the adhesion maps (bottom row) and bright on the stiffness maps (middle row), indicating that the interface was nearly completely covered by the ordered domains. The regions of the fluid structures can be distinguished easily in the stiffness maps because they exhibited less stiffness than the ordered domains and HOPG substrate. This AFM tip was relatively hydrophobic, yielding a penetration depth for the fluid regions that was larger than that obtained with the tips used to acquire the data in the other figures presented in this work. A cap-shaped structure is visible in a topographic image only when its height is larger than the tip penetration depth. In addition, it is difficult to distinguish between INBs and fluid layers from the stiffness and adhesion maps. Thus, the INBs may have formed well before we detected the cap-shaped structures in the topographic (height) maps.

Mentions: We identified an interesting case of relatively fast nucleation and growth of the ordered domains (Fig. 4). Fluid layers (some indicated with coloured arrows in Fig. 4a) and low-coverage ordered domains appeared in the stiffness and adhesion maps at t = 8 min (Fig. 4a). Confinement of the fluid regions occurred at t = 12 min (Fig. 4b). The fluid regions seemed to be present at a lower height than the surrounding ordered domains and were barely distinguishable from the bare HOPG regions in the topographic images (Fig. 4a,b). Portions of the outer parts of the fluid regions transformed into ordered domains, decreasing the lateral size of the fluid regions (Fig. 4b–d). Cap-shaped protrusions were evident in the topographic images at t~50 min (data not shown). At t = 352 min, all regions highlighted by coloured arrows in Fig. 4 transformed into cap-shaped structures (Fig. 4e), with the exception of the region denoted by a green arrow in Fig. 4a.


Nucleation processes of nanobubbles at a solid/water interface.

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

PF (220 pN) images of gas-containing structures at a HOPG/water interface after the deposition of chilled water.Top, middle, and bottom rows contain height, stiffness, and adhesion maps, respectively. Scale bar, 500 nm. The green arrow in (a) highlights a fluid layer that disappeared at a later time (b). The white, blue, and pink arrows indicate fluid regions that later transformed into a cap-shaped structure (e). Two blue arrows indicate fluid regions that were confined by two step edges, yielding rectangular gas structures (a–d). Note that the ordered domains exhibited less adhesion than the bare HOPG surface and the fluid structures. In (e), the entire interface (except for the INBs) was dark on the adhesion maps (bottom row) and bright on the stiffness maps (middle row), indicating that the interface was nearly completely covered by the ordered domains. The regions of the fluid structures can be distinguished easily in the stiffness maps because they exhibited less stiffness than the ordered domains and HOPG substrate. This AFM tip was relatively hydrophobic, yielding a penetration depth for the fluid regions that was larger than that obtained with the tips used to acquire the data in the other figures presented in this work. A cap-shaped structure is visible in a topographic image only when its height is larger than the tip penetration depth. In addition, it is difficult to distinguish between INBs and fluid layers from the stiffness and adhesion maps. Thus, the INBs may have formed well before we detected the cap-shaped structures in the topographic (height) maps.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f4: PF (220 pN) images of gas-containing structures at a HOPG/water interface after the deposition of chilled water.Top, middle, and bottom rows contain height, stiffness, and adhesion maps, respectively. Scale bar, 500 nm. The green arrow in (a) highlights a fluid layer that disappeared at a later time (b). The white, blue, and pink arrows indicate fluid regions that later transformed into a cap-shaped structure (e). Two blue arrows indicate fluid regions that were confined by two step edges, yielding rectangular gas structures (a–d). Note that the ordered domains exhibited less adhesion than the bare HOPG surface and the fluid structures. In (e), the entire interface (except for the INBs) was dark on the adhesion maps (bottom row) and bright on the stiffness maps (middle row), indicating that the interface was nearly completely covered by the ordered domains. The regions of the fluid structures can be distinguished easily in the stiffness maps because they exhibited less stiffness than the ordered domains and HOPG substrate. This AFM tip was relatively hydrophobic, yielding a penetration depth for the fluid regions that was larger than that obtained with the tips used to acquire the data in the other figures presented in this work. A cap-shaped structure is visible in a topographic image only when its height is larger than the tip penetration depth. In addition, it is difficult to distinguish between INBs and fluid layers from the stiffness and adhesion maps. Thus, the INBs may have formed well before we detected the cap-shaped structures in the topographic (height) maps.
Mentions: We identified an interesting case of relatively fast nucleation and growth of the ordered domains (Fig. 4). Fluid layers (some indicated with coloured arrows in Fig. 4a) and low-coverage ordered domains appeared in the stiffness and adhesion maps at t = 8 min (Fig. 4a). Confinement of the fluid regions occurred at t = 12 min (Fig. 4b). The fluid regions seemed to be present at a lower height than the surrounding ordered domains and were barely distinguishable from the bare HOPG regions in the topographic images (Fig. 4a,b). Portions of the outer parts of the fluid regions transformed into ordered domains, decreasing the lateral size of the fluid regions (Fig. 4b–d). Cap-shaped protrusions were evident in the topographic images at t~50 min (data not shown). At t = 352 min, all regions highlighted by coloured arrows in Fig. 4 transformed into cap-shaped structures (Fig. 4e), with the exception of the region denoted by a green arrow in Fig. 4a.

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