Ribbing Instability in Coating Flows: Effect of Polymer Additives

Bauman, Therese M.; Sullivan, Tarah N.; Middleman, Stanley

doi:10.1080/00986448208911036

Cited by 32 publications

(27 citation statements)

References 19 publications

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“…This flow has been the most widely studied by previous researchers (Coyle et al 1990), and is one of the few such flows which has been investigated with viscoelastic liquids (Bauman et al 1982;Soules et al 1988;, Dontula et al 1996Grillet et al 1999). In addition, the theoretical dispersion relationship and critical conditions derived for Newtonian Hele-Shaw flows (Saffman & Taylor 1958) can be modified to analyse, as a first approximation, the stability of forward-roll coating due to the similarity in their flow fields.…”

Section: Resultsmentioning

confidence: 99%

“…As stated in the introduction, the increase in extensional viscosity due to the presence of a stagnation point/line on the free surface has often been identified as the main driving force for the onset of fingering instabilities in viscoelastic liquids (Bauman et al 1982). The DPIV technique is used to visualize the flow fields at various gap separations and to determine the location of the stagnation line(s) on the free surface.…”

Section: Resultsmentioning

confidence: 99%

“…The stability of polyacrylamide Boger fluids in the forward-roll coating and rollplate geometries has been investigated by Bauman, Sullivan & Middleman (1982) and later by Dontula et al (1996). Even for a liquid with a concentration of 10 p.p.m.…”

Section: Introductionmentioning

confidence: 99%

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Viscoelastic interfacial modes in a wetting layer

Bonn¹,

Wegdam²

1993

Phys. Rev. E

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We have investigated the role of liquid elasticity in the dynamics of air-liquid interfaces during immiscible fluid displacement flows. Our experimental studies of coating flows with gravity stabilization in an eccentric cylinder geometry for both a viscous Newtonian fluid and a series of elastic Boger fluids have uncovered two new elastically driven phenomena. First, elasticity is shown to create steady, two-dimensional 'sharp interfaces' under creeping flow conditions in forward-roll coating. Digital particle image velocimetry (DPIV) and DEVSS finite element techniques are applied to investigate the effect of gravity on both the flow field and the state of polymeric stresses near the free surface. Secondly, a new class of elastically driven stable substructures is shown to form and persist along the tip, i.e. the centre stagnation line, of the two-dimensional 'sharp interfaces' even after the onset of ribbing.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

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Viscoelastic interfacial modes in a wetting layer

Bonn¹,

Wegdam²

1993

Phys. Rev. E

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“…A commonly observed free surface interfacial instability is the ribbing or fingering instability [35,36]. At a critical value of Ca number, the interface develop ribs or fibrils that traverse across the spanwise direction.…”

Section: Interfacial Instabilities-a Discussion Of the Mechanismmentioning

confidence: 99%

“…At a critical value of Ca number, the interface develop ribs or fibrils that traverse across the spanwise direction. In experiments conducted with viscoelastic fluids, the critical conditions have been shown to reduce dramatically with the presence of elasticity [5,24,34,36]. In the case of Newtonian fluids, the mechanism of the fingering instability is well understood.…”

Section: Interfacial Instabilities-a Discussion Of the Mechanismmentioning

confidence: 99%

Influence of viscoelasticity on the interfacial dynamics of air displacing fluid flows—a computational study

Bhatara

Shaqfeh

Khomami

2004

Journal of Non-Newtonian Fluid Mechanics

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Template‐Free Scalable Fabrication of Linearly Periodic Microstructures by Controlling Ribbing Defects Phenomenon in Forward Roll Coating for Multifunctional Applications

Islam

Perera

Black

et al. 2022

Adv Materials Inter

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developing multifunctional surfaces with unique capabilities, including superhydrophobicity, [1,2] self-cleaning, [3,4] anti-icing, [3,5] anti-biofoulin, [6,7] biological sensors, [6] and radiative cooling. [6,8] For example, Namib Desert beetles use the superhydrophobicsuperhydrophilic micropatterned skin to harvest water from fog. [12][13][14] Plants such as lotus utilize microstructures on leaves to influence wetting behavior and enable self-cleaning. [12,15] Sharks' unique skin morphology augments the near-wall vorticity during turbulent flow. This augmentation reduces the skin friction and enables sharks to be one of the most efficient swimming species in the ocean. [16][17][18] These dragreducing microstructures are particularly interesting to the scientific community. Thus, researchers have focused on periodic microstructures aligned in the flow direction, similar to sharkskin. [19] In prior modeling and experimentation, researchers have decreased frictional drag by using different variations of linear periodic microstructures. For example, Xu et al. developed a series of linear microtrenches demonstrating a maximum drag reduction of ≈30% in high Reynolds number applications. [20] In addition, Park et al. studied the impact of grating parameters on drag reduction and demonstrated a max drag reduction of 75%. [21] Lithography is one of the standard processes for manufacturing superhydrophobic periodic microstructures. [20][21][22] Periodic micro/nanoscale structures from nature have inspired the scientific community to adopt surface design for various applications, including superhydrophobic drag reduction. One primary concern of practical applications of such periodic microstructures remains the scalability of conventional microfabrication technologies. This study demonstrates a simple template-free scalable manufacturing technique to fabricate periodic microstructures by controlling the ribbing defects in the forward roll coating. Viscoelastic composite coating materials are designed for roll-coating using carbon nanotubes (CNT) and polydimethylsiloxane (PDMS), which helps achieve a controllable ribbing with a periodicity of 114-700 µm. Depending on the process parameters, the patterned microstructures transition from the linear alignment to a random structure. The periodic microstructure enables hydrophobicity as the water contact angles of the samples ranged from 128° to 158°. When towed in a static water pool, a model boat coated with the microstructure film shows 7%-8% faster speed than the boat with a flat PDMS film. The CNT addition shows both mechanical and electrical properties improvement. In a mechanical scratch test, the cohesive failure of the CNT-PDMS film occurs in ≈90% higher force than bare PDMS. Moreover, the nonconductive bare PDMS shows sheet resistance of 747.84-22.66 Ω □ −1 with 0.5 to 2.5 wt% CNT inclusion.

show abstract

Ribbing Instability in Coating Flows: Effect of Polymer Additives

Abstract: Data are presented which show the effect of dilute addition of polymer on the ribbing instability in coating flows. A qualitative model which treats the growth of a disturbance as an extensional flow suggests that elasticity is a destabilizing factor, in agreement with the observations.

Cited by 32 publications

References 19 publications

Viscoelastic interfacial modes in a wetting layer

Viscoelastic interfacial modes in a wetting layer

Influence of viscoelasticity on the interfacial dynamics of air displacing fluid flows—a computational study

Template‐Free Scalable Fabrication of Linearly Periodic Microstructures by Controlling Ribbing Defects Phenomenon in Forward Roll Coating for Multifunctional Applications

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