scholarly journals Probing the nanoscale: the first contact of an impacting drop

2015 ◽  
Vol 785 ◽  
Author(s):  
E. Q. Li ◽  
I. U. Vakarelski ◽  
S. T. Thoroddsen
Keyword(s):  
Solid Surface ◽  
High Speed ◽  
Water Drop ◽  
Triple Line ◽  
Immiscible Liquid ◽  
Initial Contact ◽  
High Speed Imaging ◽  
Left Behind ◽  
Drop Impacts ◽  
First Contact

When a drop impacts onto a solid surface, the lubrication pressure in the air deforms its bottom into a dimple. This makes the initial contact with the substrate occur not at a point but along a ring, thereby entrapping a central disc of air. We use ultra-high-speed imaging, with 200 ns time resolution, to observe the structure of this first contact between the liquid and a smooth solid surface. For a water drop impacting onto regular glass we observe a ring of microbubbles, due to multiple initial contacts just before the formation of the fully wetted outer section. These contacts are spaced by a few microns and quickly grow in size until they meet, thereby leaving behind a ring of microbubbles marking the original air-disc diameter. On the other hand, no microbubbles are left behind when the drop impacts onto molecularly smooth mica sheets. We thereby conclude that the localized contacts are due to nanometric roughness of the glass surface, and the presence of the microbubbles can therefore distinguish between glass with 10 nm roughness and perfectly smooth glass. We contrast this entrapment topology with the initial contact of a drop impacting onto a film of extremely viscous immiscible liquid, where the initial contact appears to be continuous along the ring. Here, an azimuthal instability occurs during the rapid contraction at the triple line, also leaving behind microbubbles. For low impact velocities the nature of the initial contact changes to one initiated by ruptures of a thin lubricating air film.

scholarly journals Rebound of self-lubricating compound drops

2020 ◽  
Vol 6 (11) ◽  
pp. eaay3499 ◽  
Author(s):  
Nathan Blanken ◽  
Muhammad Saeed Saleem ◽  
Carlo Antonini ◽  
Marie-Jean Thoraval
Keyword(s):  
Solid Surface ◽  
High Speed ◽  
Water Drop ◽  
Three Dimensional ◽  
Strong Impact ◽  
High Speed Imaging ◽  
Three Dimensional Printing ◽  
Compound Drops ◽  
The Impact ◽  
Dimensional Printing

Drop impact on solid surfaces is encountered in numerous natural and technological processes. Although the impact of single-phase drops has been widely explored, the impact of compound drops has received little attention. Here, we demonstrate a self-lubrication mechanism for water-in-oil compound drops impacting on a solid surface. Unexpectedly, the core water drop rebounds from the surface below a threshold impact velocity, irrespective of the substrate wettability. This is interpreted as the result of lubrication from the oil shell that prevents contact between the water core and the solid surface. We combine side and bottom view high-speed imaging to demonstrate the correlation between the water core rebound and the oil layer stability. A theoretical model is developed to explain the observed effect of compound drop geometry. This work sets the ground for precise complex drop deposition, with a strong impact on two- and three-dimensional printing technologies and liquid separation.

scholarly journals Drop impact entrapment of bubble rings

2013 ◽  
Vol 724 ◽  
pp. 234-258 ◽  
Author(s):  
M.-J. Thoraval ◽  
K. Takehara ◽  
T. G. Etoh ◽  
S. T. Thoroddsen
Keyword(s):  
High Speed ◽  
Strong Influence ◽  
Drop Size ◽  
Water Drop ◽  
High Impact ◽  
Initial Contact ◽  
Streamwise Vortices ◽  
Video Imaging ◽  
High Speed Video ◽  
First Contact

AbstractWe use ultra-high-speed video imaging to look at the initial contact of a drop impacting on a liquid layer. We observe experimentally the vortex street and the bubble-ring entrapments predicted numerically, for high impact velocities, by Thoraval et al. (Phys. Rev. Lett., vol. 108, 2012, article 264506). These dynamics mainly occur within $50~\mathrm{\mu} \mathrm{s} $ after the first contact, requiring imaging at 1 million f.p.s. For a water drop impacting on a thin layer of water, the entrapment of isolated bubbles starts through azimuthal instability, which forms at low impact velocities, in the neck connecting the drop and pool. For Reynolds number $Re$ above ${\sim }12\hspace{0.167em} 000$, up to 10 partial bubble rings have been observed at the base of the ejecta, starting when the contact is ${\sim }20\hspace{0.167em} \% $ of the drop size. More regular bubble rings are observed for a pool of ethanol or methanol. The video imaging shows rotation around some of these air cylinders, which can temporarily delay their breakup into micro-bubbles. The different refractive index in the pool liquid reveals the destabilization of the vortices and the formation of streamwise vortices and intricate vortex tangles. Fine-scale axisymmetry is thereby destroyed. We show also that the shape of the drop has a strong influence on these dynamics.

scholarly journals Air mediates the impact of a compliant hemisphere on a rigid smooth surface

Soft Matter ◽  
2021 ◽  
Author(s):  
Siqi Zheng ◽  
Sam Dillavou ◽  
John M. Kolinski
Keyword(s):  
Elastic Body ◽  
Elastic Properties ◽  
Impact Velocity ◽  
Solid Surface ◽  
High Speed ◽  
Smooth Surface ◽  
High Speed Imaging ◽  
The Impact ◽  
Rigid Smooth

When a soft elastic body impacts upon a smooth solid surface, the intervening air fails to drain, deforming the impactor. High-speed imaging with the VFT reveal rich dynamics and sensitivity to the impactor's elastic properties and the impact velocity.

Micro-splashing by drop impacts

2012 ◽  
Vol 706 ◽  
pp. 560-570 ◽  
Author(s):  
S. T. Thoroddsen ◽  
K. Takehara ◽  
T. G. Etoh
Keyword(s):  
Free Surface ◽  
Size Distribution ◽  
Solid Surface ◽  
High Speed ◽  
Solid Substrate ◽  
Liquid Sheet ◽  
Drop Surface ◽  
High Speed Video ◽  
Rain Drops ◽  
Drop Impacts

AbstractWe use ultra-high-speed video imaging to observe directly the earliest onset of prompt splashing when a drop impacts onto a smooth solid surface. We capture the start of the ejecta sheet travelling along the solid substrate and show how it breaks up immediately upon emergence from the underneath the drop. The resulting micro-droplets are much smaller and faster than previously reported and may have gone unobserved owing to their very small size and rapid ejection velocities, which approach 100 m s−1, for typical impact conditions of large rain drops. We propose a phenomenological mechanism which predicts the velocity and size distribution of the resulting microdroplets. We also observe azimuthal undulations which may help promote the earliest breakup of the ejecta. This instability occurs in the cusp in the free surface where the drop surface meets the radially ejected liquid sheet.

High‐speed photography of water drop impacts on sand and soil

2018 ◽  
Vol 70 (2) ◽  
pp. 245-256 ◽  
Author(s):  
N. Lardier ◽  
P. Roudier ◽  
B. Clothier ◽  
G. R. Willmott
Keyword(s):  
High Speed ◽  
Water Drop ◽  
High Speed Photography ◽  
Drop Impacts

Erosion Resistance and Its Mechanism for Flame-Hardened 12Cr Steel by High Speed Water Drop Impacts

2006 ◽  
pp. 179-184
Author(s):  
G.H. Kim ◽  
Min Ku Lee ◽  
G.M. Kim ◽  
Sung Mo Hong ◽  
Wheung Whoe Kim ◽  
...  
Keyword(s):  
High Speed ◽  
Erosion Resistance ◽  
Water Drop ◽  
Drop Impacts

scholarly journals Time-resolved imaging of a compressible air disc under a drop impacting on a solid surface

2015 ◽  
Vol 780 ◽  
pp. 636-648 ◽  
Author(s):  
E. Q. Li ◽  
S. T. Thoroddsen
Keyword(s):  
Solid Surface ◽  
High Speed ◽  
Theoretical Models ◽  
Adiabatic Compression ◽  
Time Resolved ◽  
Time Resolved Imaging ◽  
Rapid Deceleration ◽  
Drop Impacts ◽  
The Impact ◽  
Surface Minima

When a drop impacts on a solid surface, its rapid deceleration is cushioned by a thin layer of air, which leads to the entrapment of a bubble under its centre. For large impact velocities the lubrication pressure in this air layer becomes large enough to compress the air. Herein we use high-speed interferometry, with 200 ns time-resolution, to directly observe the thickness evolution of the air layer during the entire bubble entrapment process. The initial disc radius and thickness shows excellent agreement with available theoretical models, based on adiabatic compression. For the largest impact velocities the air is compressed by as much as a factor of 14. Immediately following the contact, the air disc shows rapid vertical expansion. The radial speed of the surface minima just before contact, can reach 50 times the impact velocity of the drop.

Erosion Resistance and Its Mechanism for Flame-Hardened 12Cr Steel by High Speed Water Drop Impacts

2006 ◽  
Vol 118 ◽  
pp. 179-184
Author(s):  
G.H. Kim ◽  
Min Ku Lee ◽  
G.M. Kim ◽  
Sung Mo Hong ◽  
Wheung Whoe Kim ◽  
...  
Keyword(s):  
Steady State ◽  
Incubation Period ◽  
High Speed ◽  
Erosion Resistance ◽  
Water Drop ◽  
Fatigue Cracks ◽  
Flame Hardening ◽  
Erosion Properties ◽  
Drop Impacts ◽  
Impact Erosion

In this study, the water drop impact erosion properties of 12Cr steel surface-hardened by the flame hardening process have been studied. For this, both the maximum erosion depth de,max and volume loss Ve with the number of cumulative impacts n have been investigated for the flame-hardened 12Cr steels with different hardnesses. Typically all the samples showed an erosion-time characteristic involving an incubation period initially followed by a steady state period. Compared to those for the as-received 12Cr steel, the flame-hardened ones showed an excellent erosion resistance to water drop impacts, showing a 2.2~2.8 times higher incubation time ti and 5~8 times lower erosion rate α. In the incubation period the as-received 12Cr steel was deformed by a ductile depression and ploughing, while the flame-hardened one by fatigue cracks and a brittle platelet deformation. In the steady state period the damage was progressed by a cleavage fracture for both the stages.

scholarly journals Collision of Bubbles with Solid Surface in the Presence of Specific Surfactants

Minerals ◽  
2021 ◽  
Vol 11 (5) ◽  
pp. 442
Author(s):  
Maria Zednikova ◽  
Jakub Crha ◽  
Lucie Vobecká ◽  
Pavlína Basařová ◽  
Jiri Vejrazka ◽  
...  
Keyword(s):  
Solid Surface ◽  
High Speed ◽  
Restitution Coefficient ◽  
Bubble Shape ◽  
High Speed Imaging ◽  
Viscous Forces ◽  
Three Phase ◽  
Surface Collision ◽  
Shape Oscillations ◽  
Bubble Rising

The present work is motivated by the effort to understand basic processes occurring in three-phase systems where small bubbles interact with large particles. The simplified system of a single bubble rising in a stagnant liquid and colliding with a solid surface is studied. The effect of two specific surfactants, α-Terpineol and n-Octanol, is investigated. Two independent measurements are combined: (i) bubble–solid surface collision experiments and (ii) the bubble shape oscillations induced by a movable capillary. Both experiments are based on high-speed imaging resulting in the evaluation of the restitution coefficient characterizing the collision process and the relative damping time characterizing the bubble shape oscillations in the presence of surfactants. It was observed that even for small concentrations of a surfactant, both the bubble shape oscillations and the bubble bouncing on the solid surface are significantly suppressed. Two predictions for the restitution coefficient are proposed. The equations include a term characterizing the suppression of the damping time in the presence of surfactants and a term balancing the inertia, capillary and viscous forces in the liquid film separating the bubble and the solid surface. The proposed equations successfully predict the restitution coefficient of bubble bouncing on the solid surface in liquids with the addition of specific surfactants.

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