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Superconfinement tailors fluid flow at microscales.

Setu SA, Dullens RP, Hernández-Machado A, Pagonabarraga I, Aarts DG, Ledesma-Aguilar R - Nat Commun (2015)

Bottom Line: Understanding fluid dynamics under extreme confinement, where device and intrinsic fluid length scales become comparable, is essential to successfully develop the coming generations of fluidic devices.Henceforth, we present a theory that quantifies our experiments in terms of the relevant interfacial length scale, which in our system is the intrinsic contact-line slip length.Our findings show that length-scale overlap can be used as a new fluid-control mechanism in strongly confined systems.

View Article: PubMed Central - PubMed

Affiliation: 1] Department of Chemistry, Physical and Theoretical Chemistry Laboratory, University of Oxford, South Parks Road, Oxford OX1 3QZ, UK [2] Department of Chemistry, Faculty of Science, Universiti Teknologi Malaysia, Johor Bahru, Johor 81310, Malaysia.

ABSTRACT
Understanding fluid dynamics under extreme confinement, where device and intrinsic fluid length scales become comparable, is essential to successfully develop the coming generations of fluidic devices. Here we report measurements of advancing fluid fronts in such a regime, which we dub superconfinement. We find that the strong coupling between contact-line friction and geometric confinement gives rise to a new stability regime where the maximum speed for a stable moving front exhibits a distinctive response to changes in the bounding geometry. Unstable fronts develop into drop-emitting jets controlled by thermal fluctuations. Numerical simulations reveal that the dynamics in superconfined systems is dominated by interfacial forces. Henceforth, we present a theory that quantifies our experiments in terms of the relevant interfacial length scale, which in our system is the intrinsic contact-line slip length. Our findings show that length-scale overlap can be used as a new fluid-control mechanism in strongly confined systems.

No MeSH data available.


Related in: MedlinePlus

Jet formation and drop emission in superconfinement.(a) Periodic emission of drops above the onset of entrainment. (b) Volume of the jet, and of the emitted drops, as a function of the channel thickness. The larger jet volume value at H=14 μm reflects the long snap-off time of the neck at large H relative to the interface thickness. (c) The snap-off time increases algebraically with H. (d) Growth of a liquid jet from the contact line (top) and collapse to release a drop (bottom) at H=14 μm. (e) Stabilization of the emitted jet at H=17 μm. Scale bars in a,d,e, 50, 10 and 10 μm, respectively. Error bars correspond to the s.d. of the sample.
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f5: Jet formation and drop emission in superconfinement.(a) Periodic emission of drops above the onset of entrainment. (b) Volume of the jet, and of the emitted drops, as a function of the channel thickness. The larger jet volume value at H=14 μm reflects the long snap-off time of the neck at large H relative to the interface thickness. (c) The snap-off time increases algebraically with H. (d) Growth of a liquid jet from the contact line (top) and collapse to release a drop (bottom) at H=14 μm. (e) Stabilization of the emitted jet at H=17 μm. Scale bars in a,d,e, 50, 10 and 10 μm, respectively. Error bars correspond to the s.d. of the sample.

Mentions: Beyond the onset of entrainment, the interface also responds to changes in confinement. This is reflected in the periodic emission of drops shown in Fig. 5a and Supplementary Movie 2, whose size and rate of release can be controlled by choosing the channel thickness (Fig. 5b,c). Drop emission begins with the slow down of the contact line relative to the front, which triggers the growth of a liquid jet. For small H, when the jet and interface thicknesses are comparable, the jet develops a thinning neck that connects to a nascent drop, which is then released (Fig. 5d). Because the speed of the front is kept above the entrainment threshold, subsequent drops are emitted at a constant rate.


Superconfinement tailors fluid flow at microscales.

Setu SA, Dullens RP, Hernández-Machado A, Pagonabarraga I, Aarts DG, Ledesma-Aguilar R - Nat Commun (2015)

Jet formation and drop emission in superconfinement.(a) Periodic emission of drops above the onset of entrainment. (b) Volume of the jet, and of the emitted drops, as a function of the channel thickness. The larger jet volume value at H=14 μm reflects the long snap-off time of the neck at large H relative to the interface thickness. (c) The snap-off time increases algebraically with H. (d) Growth of a liquid jet from the contact line (top) and collapse to release a drop (bottom) at H=14 μm. (e) Stabilization of the emitted jet at H=17 μm. Scale bars in a,d,e, 50, 10 and 10 μm, respectively. Error bars correspond to the s.d. of the sample.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4490407&req=5

f5: Jet formation and drop emission in superconfinement.(a) Periodic emission of drops above the onset of entrainment. (b) Volume of the jet, and of the emitted drops, as a function of the channel thickness. The larger jet volume value at H=14 μm reflects the long snap-off time of the neck at large H relative to the interface thickness. (c) The snap-off time increases algebraically with H. (d) Growth of a liquid jet from the contact line (top) and collapse to release a drop (bottom) at H=14 μm. (e) Stabilization of the emitted jet at H=17 μm. Scale bars in a,d,e, 50, 10 and 10 μm, respectively. Error bars correspond to the s.d. of the sample.
Mentions: Beyond the onset of entrainment, the interface also responds to changes in confinement. This is reflected in the periodic emission of drops shown in Fig. 5a and Supplementary Movie 2, whose size and rate of release can be controlled by choosing the channel thickness (Fig. 5b,c). Drop emission begins with the slow down of the contact line relative to the front, which triggers the growth of a liquid jet. For small H, when the jet and interface thicknesses are comparable, the jet develops a thinning neck that connects to a nascent drop, which is then released (Fig. 5d). Because the speed of the front is kept above the entrainment threshold, subsequent drops are emitted at a constant rate.

Bottom Line: Understanding fluid dynamics under extreme confinement, where device and intrinsic fluid length scales become comparable, is essential to successfully develop the coming generations of fluidic devices.Henceforth, we present a theory that quantifies our experiments in terms of the relevant interfacial length scale, which in our system is the intrinsic contact-line slip length.Our findings show that length-scale overlap can be used as a new fluid-control mechanism in strongly confined systems.

View Article: PubMed Central - PubMed

Affiliation: 1] Department of Chemistry, Physical and Theoretical Chemistry Laboratory, University of Oxford, South Parks Road, Oxford OX1 3QZ, UK [2] Department of Chemistry, Faculty of Science, Universiti Teknologi Malaysia, Johor Bahru, Johor 81310, Malaysia.

ABSTRACT
Understanding fluid dynamics under extreme confinement, where device and intrinsic fluid length scales become comparable, is essential to successfully develop the coming generations of fluidic devices. Here we report measurements of advancing fluid fronts in such a regime, which we dub superconfinement. We find that the strong coupling between contact-line friction and geometric confinement gives rise to a new stability regime where the maximum speed for a stable moving front exhibits a distinctive response to changes in the bounding geometry. Unstable fronts develop into drop-emitting jets controlled by thermal fluctuations. Numerical simulations reveal that the dynamics in superconfined systems is dominated by interfacial forces. Henceforth, we present a theory that quantifies our experiments in terms of the relevant interfacial length scale, which in our system is the intrinsic contact-line slip length. Our findings show that length-scale overlap can be used as a new fluid-control mechanism in strongly confined systems.

No MeSH data available.


Related in: MedlinePlus