UV-mediated coalescence and mixing of inkjet printed drops

Dongen, M.H.A. van; Loon, Annelies van; Vrancken, Robert J.; Bernards, J.P.C.; Dijksman, Joshua

doi:10.1007/s00348-014-1744-2

Cited by 6 publications

(4 citation statements)

References 25 publications

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“…In addition to the slow viscous regime discussed so far, the bridge height was observed to grow with a universal exponent of 2/3 for contact angle below 90 and an exponent of 1/2 for the contact angle of 90 in the inertial regime. [20][21][22] In contrast to Newtonian droplets discussed above, the coalescence of rheologically complex fluids rather remains obscure despite its wide application in droplet 3D printing, 23,24 emulsions, [25][26][27] and microfluidics. 28 Varma et al 29 highlighted the importance of viscoelasticity viscoelasticty and relaxation time on coalescence of polymeric droplets in a pendant-sessile configuration.…”

Section: Introductionmentioning

confidence: 99%

Elasticity can affect droplet coalescence

2022

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Coalescence of two droplets on a solid substrate is an interfacial phenomenon that imposes the challenges of capturing the complex contact line motion and energy interaction between the solid-liquid interface. Recent investigations on the coalescence of polymeric droplets on a solid substrate have reported strong disagreements; the heart of the issue is whether coalescence of polymeric drops is similar to that of Newtonian fluid and is independent of molecular relaxation, or whether the role of entanglement of polymeric chains leads to a transition kinetics different from that of Newtonian fluid. Via this article, we resolve the disagreements through a discussion on the effects of merging method on the dominant forces governing the coalescence process, i.e., inertia, dissipation, and relaxation. In this regard, two methods of merging have been identified, namely droplet spreading method (DSM) and volume filling method (VFM). Our study unveils that the coalescence dynamics of polymeric drops is not universal and in fact, is contingent of the method by which the coalescence is triggered. Additionally, we demonstrate the spatial features of the bridge at different time instants by a similarity analysis. We also theoretically obtain a universal bridge profile by employing the similarity parameter in a modified thin film lubrication equation for polymeric fluids.

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Section: Introductionmentioning

confidence: 99%

Elasticity can affect droplet coalescence

2022

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“…Coalescence of microscopic or macroscopic liquid drops has been one of the most widely researched multiphase problems owing to its significant role in a variety of phenomena like cloud formation and precipitation, oil spills, emulsions, additive manufacturing processes − such as aerosol jet printing, inkjet printing, syringe/extrusion printing, electrohydrodynamic (EHD) jet printing, etc. The effects of viscosity, surface tension, and surface wettability on the coalescence dynamics of Newtonian droplets on both solid surfaces and liquid films have been well studied. − Recently, a number of researchers have studied the coalescence dynamics of non-Newtonian polymeric droplets, − including the effect of impact velocity.…”

Section: Introductionmentioning

confidence: 99%

Numerical Study of the Coalescence and Mixing of Drops of Different Polymeric Materials

2022

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In this study, we employ direct numerical simulation (DNS) to investigate the solutal hydrodynamics dictating the three-dimensional coalescence of microscopic, identical-sized sessile drops of different but miscible shear-thinning polymeric liquids (namely, PVAc or polyvinyl acetate and PMMA or polymethylmethacrylate), with the drops being in partially wetted configuration. Despite the ubiquitousness of the interaction of different dissimilar droplets in a variety of engineering problems ranging from additive manufacturing to understanding the behavior of photonic crystals, coalescence of drops composed of different polymeric and non-Newtonian materials has not been significantly explored. Interaction of such dissimilar droplets often involves simultaneous drop spreading, coalescence, and mixing. The mixing dynamics of the dissimilar drops are governed by interphase diffusion, the residual kinetic energy of the drops stemming from the fact that coalescence starts before the spreading of the drops have been completed, and the solutal Marangoni convection. We provide the three-dimensional velocity fields and velocity vectors inside the completely miscible, dissimilar coalescing droplets. Our simulations explicate the relative influence of these different effects in determining the flow field at different locations and at different time instances and the consequent mixing behavior inside the interacting drops. We also show the non-monotonic (in terms of the direction of migration) propagation of the mixing front of the miscible coalescing drops over time. We also establish that the overall mixing (on either side of the mixing front) speeds up as the Marangoni effects dictate the mixing. We anticipate that our study will provide an important foundation for studying miscible multi-material liquid systems, which will be crucial for applications such as inkjet or aerosol jet printing, lab-on-a-chip, polymer processing, etc.

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“…Coalescence of liquid drops has been one of the most well-studied problems in the realm of capillary driven fluid flows. − The fundamental fluid mechanics issues associated with such coalescence that have received significant attention include the identification of different flow regimes and their effects on coalescence − as well as the identification of the effect of substrate wettability, axisymmetry, surrounding fluid, − drop surface tension, , and drop viscosity on the coalescence. Such fundamental knowledge on coalescence has implications in a large number of natural and engineering phenomena such as the formation of rain drops and thunderstorms, droplet-based 3D printing (e.g., inkjet printing , and aerosol jet (AJ) printing), stability of foams and emulsions, desalting of crude oil, and many more. The drop coalescence occurring with the drops either freely suspended inside another fluid medium or in a partially (dynamic) wetting state in contact with a solid has been equally explored.…”

Section: Introductionmentioning

confidence: 99%

“…However, a large number of applications require probing the drop dynamics and coalescence for polymeric, non-Newtonian liquid drops. Some such examples include the possible in-flight coalescence of polymeric drops as they are transported in a background carrier gas flow inside the printer nozzle during AJ printing (i.e., when the coalescence occurs with the drops being suspended entirely in another background fluid), , coalescence of polymeric drops (with and without in-situ curing) that have impacted the printing substrate (with a finite velocity) during inkjet printing and AJ printing (i.e., the coalescence event occurs with the drops being in a dynamic wetting state on a solid substrate), − the mechanisms dictating the dynamics of polymer blends, etc. Very recently, Varma et al presented one of the first studies on the coalescence of polymeric drops.…”

Section: Introductionmentioning

confidence: 99%

Coalescence of Microscopic Polymeric Drops: Effect of Drop Impact Velocities

et al. 2021

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In this paper, we employ the direct numerical simulation (DNS) method for probing three-dimensional, axisymmetric coalescence of microscale, power-law-obeying, and shear-thinning polymeric liquid drops of identical sizes impacting a solid, solvophilic substrate with a finite velocity. Unlike the cases of drop coalescence of Newtonian liquid drops, coalescence of non-Newtonian polymeric drops has received very little attention. Our study bridges this gap by providing (1) the time-dependent, three-dimensional (3D) velocity field and 3D velocity vectors inside two coalescing polymeric drops in the presence of a solid substrate and (2) the effect of the drop impact velocity (on the solid substrate), quantified by the Weber number (We), on the coalescence dynamics. Our simulations reveal that the drop coalescence is qualitatively similar for different We values, although the velocity magnitudes involved, the time required to attain different stages of coalescence, and the time needed to attain equilibrium vary drastically for finitely large We values. Finally, we provide detailed simulation-based, as well as physics-based, scaling laws describing the growth of the height and the width of the bridge (formed due to coalescence) dictating the 3D coalescence event. Our analyses reveal distinct scaling laws for the growth of bridge height and width for early and late stages of coalescence as a function of We. We also provide simulation-based coalescence results for the case of two unequal sized drops impacting on a substrate (nonaxisymmetric coalescence) as well as results for axisymmetric coalescence for drops of different rheology. We anticipate that our findings will be critical in better understanding events such as inkjet or aerosol jet polymer printing, dynamics of polymer blends, and many more.

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UV-mediated coalescence and mixing of inkjet printed drops

Cited by 6 publications

References 25 publications

Elasticity can affect droplet coalescence

Elasticity can affect droplet coalescence

Numerical Study of the Coalescence and Mixing of Drops of Different Polymeric Materials

Coalescence of Microscopic Polymeric Drops: Effect of Drop Impact Velocities

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