Direct printing of nanostructures by electrostatic autofocussing of ink nanodroplets

Galliker, Patrick; Schneider, Julian; Eghlidi, Hadi; Kress, Sascha; Sandoghdar, Vahid; Poulikakos, Dimos

doi:10.1038/ncomms1891

Cited by 341 publications

(410 citation statements)

References 35 publications

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“…However, if the objective is to form drops that may be airborne for a later use, such as in material forming processes, this type of microdripping is seldom useful. A recent use of electrohydrodynamics to generate nanodroplets for printing of nanostructures is that of Galliker et al [40], where micron-sized nozzles were used to eject monodisperse droplets, with diameters between 100 and 80 nm, of a colloidal suspension of gold nanoparticles. At landing on a substrate, the volatile solvent evaporated thus leaving a dense residue formed by a compact agglomeration of the gold nanoparticles.…”

Section: Introductionmentioning

confidence: 99%

Periodic emission of droplets from an oscillating electrified meniscus of a low-viscosity, highly conductive liquid

et al. 2015

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The generation of identical droplets of controllable size in the micrometer range is a problem of much interest owing to the numerous technological applications of such droplets. This work reports an investigation of the regime of periodic emission of droplets from an electrified oscillating meniscus of a liquid of low viscosity and high electrical conductivity attached to the end of a capillary tube, which may be used to produce droplets more than ten times smaller than the diameter of the tube. To attain this periodic microdripping regime, termed axial spray mode II by Juraschek and Röllgen [R. Juraschek and F. W. Röllgen, Int. J. Mass Spectrom. 177, 1 (1998)], liquid is continuously supplied through the tube at a given constant flow rate, while a dc voltage is applied between the tube and a nearby counter electrode. The resulting electric field induces a stress at the surface of the liquid that stretches the meniscus until, in certain ranges of voltage and flow rate, it develops a ligament that eventually detaches, forming a single droplet, in a process that repeats itself periodically. While it is being stretched, the ligament develops a conical tip that emits ultrafine droplets, but the total mass emitted is practically contained in the main droplet. In the parametrical domain studied, we find that the process depends on two main dimensionless parameters, the flow rate nondimensionalized with the diameter of the tube and the capillary time, q, and the electric Bond number B E , which is a nondimensional measure of the square of the applied voltage. The meniscus oscillation frequency made nondimensional with the capillary time, f , is of order unity for very small flow rates and tends to decrease as the inverse of the square root of q for larger values of this parameter. The product of the meniscus mean volume times the oscillation frequency is nearly constant. The characteristic length and width of the liquid ligament immediately before its detachment approximately scale as powers of the flow rate and depend only weakly on the applied voltage. The diameter of the main droplets nondimensionalized with the diameter of the tube satisfies d d ≈ (6/π ) 1/3 (q/f ) 1/3 , from mass conservation, while the electric charge of these droplets is about 1/4 of the Rayleigh charge. At the minimum flow rate compatible with the periodic regimen, the dimensionless diameter of the droplets is smaller than one-tenth, which presents a way to use electrohydrodynamic atomization to generate droplets of highly conducting liquids in the micron-size range, in marked contrast with the cone-jet electrospray whose typical droplet size is in the nanometric regime for these liquids. In contrast with other microdripping regimes where the mass is emitted upon the periodic formation of a narrow capillary jet, the present regime gives one single droplet per oscillation, except for the almost massless fine aerosol emitted in the form of an electrospray.

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Section: Introductionmentioning

confidence: 99%

Periodic emission of droplets from an oscillating electrified meniscus of a low-viscosity, highly conductive liquid

et al. 2015

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“…By using a simple model based on the interfacial temperature, and balancing adhesion with bending LETTERS stresses, we are able to define and capture the possible outcome regimes: bouncing (liquid or solid), sticking and self-peeling. We expect that this approach can be extended to other liquids [28][29][30] (water, wax, thermoplastics) and other freezing applications where adhesion must be controlled, such as powder metallurgy, inkjet printing and de-icing.…”

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confidence: 99%

Self-peeling of impacting droplets

2017

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Whether an impacting droplet 1 sticks or not to a solid surface has been conventionally controlled by functionalizing the target surface 2-8 or by using additives in the drop 9,10 . Here we report on an unexpected self-peeling phenomenon that can happen even on smooth untreated surfaces by taking advantage of the solidification of the impacting drop and the thermal properties of the substrate. We control this phenomenon by tuning the coupling of the shorttimescale fluid dynamics-leading to interfacial defects upon local freezing-and the longer-timescale thermo-mechanical stresses-leading to global deformation. We establish a regime map that predicts whether a molten metal drop impacting onto a colder substrate 11-14 will bounce, stick or self-peel. In many applications, avoiding adhesion of impacting droplets around designated target surfaces can be as crucial as bonding onto them to minimize waste or cleaning. These insights have broad applicability in processes ranging from thermal spraying 12,15 and additive manufacturing [16][17][18][19] to extreme ultraviolet lithography 20 .We release molten tin droplets of millimetric size (R = 0.95 ± 0.03 mm) from a nozzle, such that they hit a target surface with moderate velocity (v = 1.9 ± 0.1 m s −1 , see Methods). Figure 1a shows a comparison between the deposition and subsequent solidification of a droplet (initial temperature T d,0 = 240 • C) onto a silicon wafer (top) and a glass slide with ∼200 times lower thermal conductivity (bottom). While the solidified droplet (or splat) sticks to the glass surface, it unexpectedly detaches from the silicon surface: we call this phenomenon 'self-peeling' (see Fig. 1a(top) at 3 and 100 ms, the increasing air gap between droplet and surface being a manifestation of this self-peeling). Two main differences can be observed at this stage. First, interferometric profilometry (see Fig. 1b) confirms that the bottom of the droplet impacting on glass is perfectly flat, while it has a nearly spherical bending curvature κ = 16 m −1 when deposited on silicon.Second, both bottom interfaces show a texture 21 formed by annular regions spaced by air ridges (insets of Fig. 1b) that act as interfacial defects. Their number is much higher for silicon than for glass. The striking contrasts in bending and defect density suggest that a balance between thermally induced stress and adhesion determines whether or not a droplet can self-peel upon solidification.To unravel the competing phenomena, we study the dynamics of the impact using high-speed photography through a transparent surface (see Supplementary Movie 2). Immediately upon contact, micrometre-sized annular air ridges are being trapped. Along the splat radius, their height increases up to a few micrometres, and their width up to tens of micrometres (as measured by profilometry). We also extract the distance d between ridges and the contact line velocity v CL from Supplementary Movie 2, and find that the characteristic timescale τ = d/v CL to form these ridges increases radially. Figure 2a ...

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“…So far self-assembly is in its infancy but as a tool to control wettability 73 and adhesion 16 Dip-pen lithography (DPN) has been shown to offer an excellent selection of both organic and inorganic materials with sub-50 nm resolution. In the course of the development of this technology, the traditional cantilever structure has been replaced by cantilever-free systems and arrays of probes.…”

Section: Discussionmentioning

confidence: 99%