Experimental Study on Air Entrainment in Slot Die Coating of High-Viscosity, Shear-Thinning Fluids

Bhamidipati, Kanthi Latha; Didari, Sima; Harris, Tequila A. L.

doi:10.1016/j.ces.2012.06.033

Cited by 28 publications

(18 citation statements)

References 24 publications

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“…At this point, viscous forces pulling the liquid in the direction of substrate motion become dominant over surface tension forces acting in the opposite direction (Bhamidipati, Didari & Harris 2012), which results in an interfacial instability, causing the film liquid to entrain the air pocket from all sides (Severtson & Aidun 1996). When the substrate velocity (scaling with V 0 in our case) is increased, the viscous stresses also increase, enabling them to propagate upstream more quickly and causing the sawteeth to extend over a smaller area before pinch-off occurs (Bhamidipati et al 2012). This mechanism, which is dictated by the capillary number, results in the entrainment of smaller air bubbles as also noted in figure 5 (see figure caption).…”

Section: Qualitative Resultsmentioning

confidence: 99%

Cavitation structures formed during the collision of a sphere with an ultra-viscous wetted surface

et al. 2016

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We investigate the inception of cavitation and resulting structures when a sphere collides with a solid surface covered with a layer of non-Newtonian liquid having a kinematic viscosity of up to ν 0 = 20 000 000 cSt. We show the existence of shear-stress-induced cavitation during sphere approach towards the base wall (i.e. the pressurization stage) in ultra-viscous films using a synchronized dual-view high-speed imaging system. For the experimental parameters employed, liquids having viscoelastic properties of De O(1) are shown to enable sphere rebound without any prior contact with the solid wall. Cavitation by depressurization (i.e. during rebound) in such non-contact cases is observed to onset after a noticeable delay from when the minimum gap distance is reached. Also, the cavities created originate from remnant bubbles, being the remains of the primary bubble entrapment formed by the lubrication pressure of the air during film entry. Cases where physical contact occurs (contact cases) in 10 000 cSt ν 0 1000 000 cSt films produce cavities attached to the base wall, which extend into an hourglass shape. In contrast, strikingly different structures occur in the most viscous liquids due to the disproportionality in radial expansion and longitudinal extension along the cavity length. Horizontal shear rates calculated using particle image velocimetry (PIV) measurements show the apparent fluid viscosity to vary substantially as the sphere approaches and rebounds away from the base wall. A theoretical model based on the lubrication assumption is solved for the squeeze flow in the regime identified for shear-induced cavity events, to investigate the criterion for cavity inception in further detail.

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Section: Qualitative Resultsmentioning

confidence: 99%

Cavitation structures formed during the collision of a sphere with an ultra-viscous wetted surface

et al. 2016

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“…The capillary number can be related empirically to the non‐dimensional film thickness parameter at which defects such as air entrainment occur

\frac{h}{H} = f true(Ca true) .

…”

Section: Methodsmentioning

confidence: 99%

“…There is a constant demand to increase the processing speed of the thin film since the processing speed can increase the production output. At the same time, there is also a constant demand for maintaining low thicknesses of the film considering its applications in coating and polymer industry . However, if these two key factors are not balanced, the polymer film quality cannot be maintained properly.…”

Section: Introductionmentioning

confidence: 99%

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Does casting method matter in filtration membranes? A comparison in performance between doctor blade and slot‐die extruded polymeric membranes

Chede

Griffiths

Escobar

et al. 2017

J of Applied Polymer Sci

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Scaling up from a laboratory batch process to a continuous manufacturing process can result in unexpected changes in membrane morphology and performance. To understand how processing effects the structure and performance of cellulose acetate filtration membranes, membranes were produced using laboratory‐scale doctor blade and industrial/production‐scale slot die casting. Differences in morphology were seen because of the different casting method. However, filtration performance using bovine albumin serum and lipase showed no significant differences. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 45563.

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“…The OpenSCAD script allows for various design features to be incorporated into the design of the slot die following advanced geometries previously investigated [20][21][22][23][24][25][26]. Dimensional changes to the body of the die, along with the addition of internal features, create the potential for the fabrication of dual cavity slot dies.…”

Section: Slot Die Designmentioning

confidence: 99%

Open-source parametric 3-D printed slot die system for thin film semiconductor processing

Beeker

Pringle

Pearce

2018

Additive Manufacturing

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Slot die coating is growing in popularity because it is a low operational cost and easily scaled processing technique for depositing thin and uniform films rapidly, while minimizing material waste. The complex inner geometry of conventional slot dies require expensive machining that limits accessibility and experimentation. In order to overcome these issues this study follows an open hardware approach, which uses an open source 3-D printer to both fabricate the slot die and then to functionalize a 3-D slot die printing system. Polymer materials are tested and selected for compatibility with common solvents and used to fabricate a custom slot die head. This slot die is then integrated into a 3-D printer augmented with a syringe pump to form an additive manufacturing platform for thin film semiconductor devices. The full design of the slot die system is disclosed here using an open source license including software and operational protocols. This study demonstrates that functional lab-grade slot dies may be 3-D printed using low-cost open source hardware methods. A case study using NiO2 found an RMS value 0.486 nm, thickness of 17 to 49nm, and a maximum optical transmission of 99.1%, which shows this additive manufacturing approach to slot die depositions as well of fabrication is capable of producing viable layers of advanced electronic materials. Using this method, a cost savings of over 17,000% was obtained when compared to commercial slot die systems for laboratories.

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Experimental Study on Air Entrainment in Slot Die Coating of High-Viscosity, Shear-Thinning Fluids

Cited by 28 publications

References 24 publications

Cavitation structures formed during the collision of a sphere with an ultra-viscous wetted surface

Cavitation structures formed during the collision of a sphere with an ultra-viscous wetted surface

Does casting method matter in filtration membranes? A comparison in performance between doctor blade and slot‐die extruded polymeric membranes

Open-source parametric 3-D printed slot die system for thin film semiconductor processing

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