Significance Fluid flows, governed by nonlinear equations, permit formation of singularities. Often, singularities are artifacts neglecting physical effects. However, free-surface flows exhibit observable including filament pinch-off. As filaments thin, slightly (highly) viscous expected from theory to transition an inertial (viscous) regime where viscosity (density) is negligible inertial–viscous and effects important. Previous works show this either does not occur or occurs for radii well...

Whether a thin filament of liquid separates into two or more droplets eventually condenses lengthwise to form single larger drop depends on the liquid's density, viscosity, and surface tension initial dimensions filament. Surface drives competing processes, pinching-off shortening, relative time scales these, controlled by balance between capillary viscous forces, determine final outcome. Here we provide experimental evidence for conditions under which will break up drops, in terms wide...

Droplets splash when they impact dry, flat substrates above a critical velocity that depends on parameters such as droplet size, viscosity, and air pressure. By imaging ethanol drops impacting silicone gels of different stiffnesses, we show substrate stiffness also affects the splashing threshold. Splashing is reduced or even eliminated: droplets softest need over 70% more kinetic energy to than do rigid substrates. We this due losses caused by deformations soft during first few microseconds...

Abstract Whether a droplet splashes upon impact onto solid is known to depend not only on the fluid properties and its speed, but also substrate characteristics. Past research has shown that splashing heavily influenced by roughness. Indeed, in this manuscript, we demonstrate ruled surface roughness, ratio, dynamic contact angle. Experiments consist of water ethanol droplets impacting substrates with varying degrees High speed imaging used extract angle as function spreading for these...

Effective integration of molecular self-assembly and additive manufacturing would provide a technological leap in bioprinting. This article reports on biofabrication system based the hydrodynamically guided co-assembly peptide amphiphiles (PAs) with naturally occurring biomolecules proteins to generate hierarchical constructs tuneable composition structural control. The takes advantage droplet-on-demand inkjet printing exploit interfacial fluid forces guide into aligned or disordered...

In this Letter, we study the splashing behavior of droplets upon impact onto a variety substrates with different wetting properties, ranging from hydrophilic to superhydrophobic surfaces. particular, effects dynamic contact angle on splashing. The experimental approach uses high-speed imaging and image analysis recover apparent as function spreading speed. Our results show that neither Capillary number nor so-called parameter are appropriate characterize under these circumstances. However,...

Abstract Conventional polymer dispersed liquid crystal (PDLC) films have been successful as electrically‐switchable screens for privacy applications. However, spatial patterning of the so to generate a visually appealing design, logo, or image typically requires intricate fabrication processes, such use prefabricated photomasks that do not allow on‐demand designs. Herein is reported on and characterization spatially patterned PDLC “pixels” using drop‐on‐demand inkjet printing, it...

We present the results of a systematic study elucidating role that dynamic surface tension has on spreading and splashing dynamics surfactant-laden droplets during impact hydrophobic substrates. Using four different surfactants at various concentrations, we generated range solutions whose were characterized to submillisecond timescales using maximum bubble-pressure tensiometry. Impact these observed by high-speed imaging with subsequent quantitative image processing determine parameters...

• A VoF-time-splitting technique is described and released ( http://www.basilisk.fr ). The splashing of viscoelastic droplets on solid liquid substrates studied. Viscoelastic bulk effects are negligible in hard substrate. On substrate stresses alter the dynamic vortex shedding. We propose an adaptive numerical solver for study 2D two-phase flows using volume-of-fluid method. scheme uses robust log conformation tensor Fattal Kupferman (2004, 2005) [1,2] combined with time-split proposed by...

Significance Despite improvements in our ability to manipulate ever-smaller volumes, most workflows cell biology still use volumes of many microliters. We describe a method for creating microfluidic arrangements containing submicroliter volumes. It exploits interfacial forces dominant at the microscale confine liquids with fluid (not solid) walls. demonstrate basic manipulations required culture and some widely used downstream workflows. The eliminates problems associated fabrication...

Droplet impact onto liquid pools is a canonical scenario relevant to numerous natural phenomena and industrial processes. However, despite their ubiquity, multi-fluid systems with the drop pool consisting of different liquids are far less well understood. Our hypothesis that post-impact dynamics greatly depends on pool-to-droplet viscosity ratioμp/μd, which we explore over range six orders magnitude using combination experiments theoretical approaches (mathematical modelling direct numerical...

The coalescence and mixing of a sessile an impacting liquid droplet on solid surface are studied experimentally numerically in terms lateral separation speed. Two generators used to produce differently colored droplets. high-speed imaging systems investigate the impact droplets color from side view with simultaneous gray-scale below. Millimeter-sized were dynamical conditions, based Reynolds Weber numbers, relevant microfluidics commercial inkjet printing. Experimental measurements advancing...

Droplets impacting dry solid substrates often splash above a certain threshold impact velocity. We hypothesise that substrate curvature alters splashing thresholds due to modification the lift force acting on lamella at point of breakup. have undertaken high-speed imaging experiments millimetric droplets convex and concave surfaces establish dynamics across wide range geometries conditions. Our findings indicate tendency is proportional reciprocal substrate's radius curvature, independent...

The final stages of pinchoff and breakup dripping droplets near-inviscid Newtonian fluids are studied experimentally for pure water ethanol. High-speed imaging image analysis used to determine the angle minimum neck size cone-shaped extrema ligaments attached in microseconds before pinchoff. is shown steadily approach value 18.0 $\phantom{\rule{0.16em}{0ex}}\ifmmode\pm\else\textpm\fi{}\phantom{\rule{0.28em}{0ex}}{0.4}^{\ensuremath{\circ}}$, independently initial flow conditions or type...

From rain drops landing on the ocean to inkjet printing, impact of droplets onto moving liquid surfaces is a ubiquitous process in nature and industry. A rich range phenomena can arise. The behaviour depends inertia, properties relative speeds zone. While result ranges from tranquil coalescence violent splashing, intermediate regimes also occur, including partial complete bouncing even ‘surfing’ droplet. These are determined by ratio drop surface velocities properties. regime diagram be...

Microfluidics with fluid walls opens up the realm of reconfiguring cellular environments during assays.

Abstract Practical considerations on the measurement of dynamic contact angle and spreading diameter impacting droplets are discussed in this paper. The a liquid is commonly obtained either by polynomial or linear fitting to droplet profile around triple-phase point. Previous works have focused quasi-static sessile droplets, cases where inertia does not play major role dynamics. Here, we study effect shape, order domain, various stages following impact line moving. Our results, presented...

Abstract

The fate of a contracting liquid filament depends on the Ohnesorge number ( $Oh$ ), initial aspect ratio $\unicode[STIX]{x1D6E4}$ ) and surface perturbation. Generally, it is believed that there exists critical $\unicode[STIX]{x1D6E4}_{c}(Oh)$ such longer filaments break up shorter ones recoil into single drop. Through computational experimental studies, we report transitional regime for with broad range intermediate ratios, where exist multiple $\unicode[STIX]{x1D6E4}_{c}$ thresholds at...

The wrinkling of thin elastic objects provides a means generating regular patterning at small scales in applications ranging from photovoltaics to microfluidic devices. Static wrinkle patterns are known be governed by an energetic balance between the object's bending stiffness and effective substrate stiffness, which may originate true or tension curvature along wrinkles. Here, we investigate dynamic induced impact solid sphere onto ultrathin polymer sheet floating on water. vertical...

A liquid drop impacting onto a soft solid will entrap more air in the central disc than an equivalent rigid surface.

There is an unmet demand for microfluidics in biomedicine. This paper describes contactless fabrication of microfluidic circuits on standard Petri dishes using just a dispensing needle, syringe pump, three-way traverse, cell-culture media, and immiscible fluorocarbon (FC40). A submerged microjet FC40 projected through media onto the bottom dish, where it washes away to leave liquid walls pinned substrate by interfacial forces. Such fluid can be built into almost any imaginable 2D circuit...

When a fast droplet impacts pool of the same fluid, thin ejecta sheet that dominates early-time dynamics emerges within first few microseconds. Fluid and impact properties are known to affect its evolution; we experimentally reveal depth is critical factor too. Whilst sheets can remain separate subsequently fold inwards on deeper pools, they instead develop into outward-propagating lamellae sufficiently shallow undergoing transition delineate by comprehensively varying inertia depth. Aided...

This work presents a new method to generate droplets with diameters significantly smaller than the nozzle from which they emerge. The electrical waveform used produce jetting consists of single square negative pulse. edge pressure wave pulls meniscus in, overturning surface in such way that cavity is created. then forced collapse under action positive wave. violent produces thin jet eventually breaks up and droplets. Four droplet generator prototypes demonstrate capabilities this novel...