Flow Patterns Associated with the Steady Movement of a Solid/Liquid/Fluid Contact Line

Savelski, M.J.; Shetty, Sanat; Kolb, W. B.; Cerro, Ramón L.

doi:10.1006/jcis.1995.0015

Cited by 33 publications

(26 citation statements)

References 17 publications

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“…The flow field obtained from the 2D model agrees qualitatively with flow visualization from past dynamic wetting studies (Dussan V & Davis 1974;Savelski et al 1995). Results from the QP approach oppose our basic intuition that substrate drag should generate liquid flow which will contribute stresses that deform the fluid interface.…”

Section: Discussionsupporting

confidence: 60%

Delaying the onset of dynamic wetting failure through meniscus confinement

2012

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Dynamic wetting is crucial to processes where liquid displaces another fluid along a solid surface, such as the deposition of a coating liquid onto a moving substrate. Numerous studies report the failure of dynamic wetting past some critical process speed. However, the hydrodynamic factors that influence the transition to wetting failure remain poorly understood from an empirical and theoretical perspective. The objective of this investigation is to determine the effect of meniscus confinement on the onset of dynamic wetting failure. A novel experimental system is designed to simultaneously view confined and unconfined wetting systems as they approach wetting failure. The experimental apparatus consists of a scraped steel roll that rotates into a bath of glycerol. Confinement is imposed via a gap formed between a coating die and the roll surface. Flow visualization is used to record the critical roll speed at which wetting failure occurs. Comparison of the confined and unconfined data shows a clear increase in the relative critical speed as the meniscus becomes more confined. A hydrodynamic model for wetting failure is developed and analysed with (i) lubrication theory and (ii) a two-dimensional finite-element method (FEM). Both approaches do a remarkable job of matching the observed confinement trend, but only the two-dimensional model yields accurate estimates of the absolute values of the critical speeds due to the highly two-dimensional nature of the stress field in the displacing liquid. The overall success of the hydrodynamic model suggests a wetting failure mechanism primarily related to viscous bending of the meniscus.

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Section: Discussionsupporting

confidence: 60%

Delaying the onset of dynamic wetting failure through meniscus confinement

2012

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“…Although the slip model results in a flow akin to stagnation-point flow around the contact line, without a finite arrival time at the contact line of fluid particles along the interface, whereas pure rolling does result in such a finite arrival time, the confirmation by experiment of the velocity field in the inner region poses a formidable challenge. But the experiments of Savelski et al (1995) and Fuentes & Cerro (2005) show discrepancies with this hydrodynamic theory regarding the flow field even outside what would be expected to be the inner region. Also, in the numerical simulation of Sheng & Zhou (1992), a vortex is observed in the wedge near a contact line when applying free slip in the immediate vicinity of the contact line and no slip elsewhere.…”

Section: Flow Fieldmentioning

confidence: 76%

Validation and modification of asymptotic analysis of slow and rapid droplet spreading by numerical simulation

Sui

Spelt

2013

J. Fluid Mech.

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Using a slip-length based level-set approach with adaptive mesh refinement, we have simulated axisymmetric droplet spreading for a dimensionless slip length down to O(10 −4 ). The main purpose is to validate -and where necessary improve -the asymptotic analysis of Cox (1998) for rapid droplet spreading/dewetting, in terms of the detailed interface shape in various regions close to the moving contact line and the relation between the apparent angle and the capillary number based on the instantaneous contact line speed, Ca. Before presenting results for inertial spreading, simulation results are compared in detail with the theory of Hocking & Rivers (1982) for slow spreading, showing these to agree very well (and in detail) for such small slip length values, although limitations in the theoretically predicted interface shape are identified; a simple extension of the theory to viscous exterior fluids is also proposed and shown to yield similar excellent agreement. For rapid droplet spreading, it is found that, in principle, the theory of Cox (1998) can predict accurately the interface shapes in the intermediate viscous sublayer, although the inviscid sublayer can only be well presented when capillary-type waves are outside the contact line region. However, O(1) parameters taken to be unity in Cox (1998) must be specified and terms be corrected to Ca +1 in order to achieve good agreement between the theory and the simulation, both of which are undertaken here. We also find that the apparent angle from numerical simulation, obtained by extrapolating the interface shape from the macro region to the contact line, agrees reasonably well with the modified theory of Cox (1998). A simplified version of the inertial theory is proposed in the limit of negligible viscosity of the external fluid. Building on these results, we investigate the flow structure near the contact line, the shear stress and pressure along the wall, and the use of the analysis for droplet impact and rapid dewetting. Finally, we compare the modified theory of Cox (1998) with a recent experiment for rapid droplet spreading, the results of which suggest a spreading-velocity-dependent dynamic contact angle in the experiments. The paper is closed with a discussion of the outlook regarding the potential of using the present results in large-scale simulations wherein the contact-line region is not resolved down to the slip length, especially for inertial spreading.

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“…18,21 The role of contact angles in LB film deposition has been discussed. 22,23 Even though the specific contact angle values are slightly different, the general conclusion is that LB film deposition is possible if the dynamic contact angle is greater than 90 o during the down-stroke deposition or smaller than 90 o during the up-stroke deposition. In the current study, the measured contact angles of the hydrophilic substrate and Cu-Pc-C 8 LB film are 5 and 32 o , respectively.…”

Section: Resultsmentioning

confidence: 99%

Tetrapyrazinoindoloporphyrazine Langmuir-Blodgett films

2008

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We fabricated tetra(5-n-nonyl-8-tert-butyl-2,3-pyrazino[2,3-b]indolo)porphyrazinato copper(II) (Cu-Pc-C 8 ) Langmuir-Blodgett (LB) films. We further investigated the influence of arachidic acid (AA) as a transfer promoter, as well as the effect of dipping speed, on the deposition of the films on hydrophilic and hydrophobic substrates. In the case of pure Cu-Pc-C 8 LB deposition on a hydrophilic substrate, the transfer ratio was close to one for up-stroke depositions, but the previously deposited film was peeled off and re-spread onto water at down-stroke depositions. Whereas the stability of the Cu-Pc-C 8 LB films was not improved by AA addition on hydrophilic substrates, the deposition of Cu-Pc-C 8 was significantly improved by the presence of AA on a hydrophobic substrate. The AAassisted deposition had transfer ratio of close to 1 and was essentially stable up to 10-layer depositions. Comparison of the UV-visible spectrum of a Cu-Pc-C 8 /AA LB film with that of Cu-Pc-C 8 /AA solution in dichloroethane revealed that the Soret and Q bands for the Cu-Pc-C 8 /AA LB film were broadened and red-shifted due to the aggregation of phthalocyanines upon assembly in the LB film.

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Flow Patterns Associated with the Steady Movement of a Solid/Liquid/Fluid Contact Line

Cited by 33 publications

References 17 publications

Delaying the onset of dynamic wetting failure through meniscus confinement

Delaying the onset of dynamic wetting failure through meniscus confinement

Validation and modification of asymptotic analysis of slow and rapid droplet spreading by numerical simulation

Tetrapyrazinoindoloporphyrazine Langmuir-Blodgett films

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