Porous micropillar structures for retaining low surface tension liquids

Agonafer, Damena; Lee, Hyoungsoon; Vasquez, Pablo A.S.; Won, Yoonjin; Jung, Kwonil; Lingamneni, Srilakshmi; Ma, Binjian; Li, Shan; Shuai, Shuai; Du, Zichen; Maitra, Tanmoy; Palko, James W.; Goodson, Kenneth E.

doi:10.1016/j.jcis.2017.12.011

Cited by 29 publications

(24 citation statements)

References 38 publications

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“…If the pinhole is circular, the curvature of the meniscus increases by increasing the apparent contact angle θ app between the hydrophobic film surface and the meniscus liquid–vapor interface. The Laplace pressure difference across the interface can be expressed as p L = 2γ sin (θ app )/ R d , where γ is the surface tension of the condensate liquid–vapor interface. The meniscus will pin until θ app reaches the intrinsic advancing contact angle of water (θ a ) on the top of the CF x film.…”

Section: Resultsmentioning

confidence: 99%

Condensation Induced Delamination of Nanoscale Hydrophobic Films

Cha

Kim

et al. 2019

Adv Funct Materials

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Vapor condensation is a crucial phenomenon governing the efficiency of many processes. In particular, dropwise condensation on hydrophobic thin films (≈100 nm-thick) has the potential to achieve remarkable heat transfer. However, the lack of durability of these thin films has limited applications for a century. Although degradation due to steam condensation has been described as "blistering," no satisfactory insight exists capable of elucidating the driving force for film delamination. Here, it is shown that nanoscale pinholes in hydrophobic films are the source of blister formation. By creating artificial pinholes via nanoindentation on thin (30 to 500 nm-thick) fluorinated hydrophobic films, it is demostrated that water blisters can be initiated at the pinholes during condensation. It is experimentally demonstrated that vapor is transferred to the blister through the nanoscale pinhole, and the driving force for delamination is capillary pressure generated at the pinhole by the pinned liquid-vapor interface. The techniques and insights presented here will inform future work on polymeric thin film and enable their durable design for a variety of applications.

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Section: Resultsmentioning

confidence: 99%

Condensation Induced Delamination of Nanoscale Hydrophobic Films

Cha

Kim

et al. 2019

Adv Funct Materials

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“…For instance, such dynamical effects have been studied in a variety of porous structures. 25 , 27 , 28 Throughout, we nondimensionalize the Laplace pressure so that Δ P r = Δ P /(2γ lv / R 1 ). For convenience, we also nondimensionalize all radii with respect to R 1 , so that for example R ′ = R / R 1 and R 2 ′ = R 2 / R 1 .…”

Section: Theorymentioning

confidence: 99%

“… 15 , 19 − 21 Furthermore, substantial progress has been made in calculating the maximum Laplace pressures for liquid entering physically textured surfaces (see, for example, refs ( 22 and 23 )) as well as liquid exiting physically textured surfaces of axisymmetric and nonaxisymmetric cross sections. 24 , 25 However, the enclosed geometry, efficacy at preventing back-flow, and the impact of chemical patterning have never been discussed.…”

Section: Introductionmentioning

confidence: 99%

Critical Pressure Asymmetry in the Enclosed Fluid Diode

2020

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Joint physically and chemically pattered surfaces can provide efficient and passive manipulation of fluid flow. The ability of many of these surfaces to allow only unidirectional flow means they are often termed fluid diodes. Synthetic analogues of these are enabling technologies from sustainable water collection via fog harvesting to improved wound dressings. One key fluid diode geometry features a pore sandwiched between two absorbent substrates—an important design for applications that require liquid capture while preventing back-flow. However, the enclosed pore is particularly challenging to design as an effective fluid diode due to the need for both a low Laplace pressure for liquid entering the pore and a high Laplace pressure to liquid leaving. Here, we calculate the Laplace pressure for fluid traveling in both directions on a range of conical pore designs with a chemical gradient. We show that this chemical gradient is in general required to achieve the largest critical pressure differences between incoming and outgoing liquids. Finally, we discuss the optimization strategy to maximize this critical pressure asymmetry.

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“…This spherical cap model also implies we treat the fluid configurations as static; the impact of fluid velocity on burst pressures can also be important, but is outside the scope of the current work. For instance, such dynamical effects have been studied in a variety of porous structures [25,27,28]. Throughout, we nondimensionalise the Laplace pressure so that ∆P r = ∆P/(2γ lv /R 1 ).…”

Section: Absorbent Substratementioning

confidence: 99%

“…Conical pores, or pores with a variation in cross-sectional width have been shown in microfluidic fields to enable effective passive regulation of fluid flow, with a key application being the capillary burst valve [15,19,20,21]. Furthermore, substantial progress has been made in calculating the maximum Laplace pressures for liquid entering physically textured surfaces, see for example [22,23], as well as liquid exiting physically textured surfaces of axisymmetric and non-axisymmetric cross sections [24,25]. However, the enclosed geometry, efficacy at preventing back-flow, and the impact of chemical patterning have never been discussed.…”

Section: Introductionmentioning

confidence: 99%

Critical pressure asymmetry in the enclosed fluid diode

Panter¹,

Gizaw²,

Kusumaatmaja³

2020

Preprint

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Joint physically and chemically pattered surfaces can provide efficient and passive manipulation of fluid flow. The ability of many of these surfaces to allow only unidirectional flow mean they are often referred to as fluid diodes. Synthetic analogues of these are enabling technologies from sustainable water collection via fog harvesting, to improved wound dressings. One key fluid diode geometry features a pore sandwiched between two absorbent substrates, an important design for applications which require liquid capture while preventing back-flow. However, the enclosed pore is particularly challenging to design as an effective fluid diode, due to the need for both a low Laplace pressure for liquid entering the pore, and a high Laplace pressure to liquid leaving. Here, we calculate the Laplace pressure for fluid travelling in both directions on a range of conical pore designs with a chemical gradient. We show that this chemical gradient is in general required to achieve the largest critical pressure differences between incoming and outgoing liquids. Finally, we discuss the optimisation strategy to maximise this critical pressure asymmetry.

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Porous micropillar structures for retaining low surface tension liquids

Cited by 29 publications

References 38 publications

Condensation Induced Delamination of Nanoscale Hydrophobic Films

Condensation Induced Delamination of Nanoscale Hydrophobic Films

Critical Pressure Asymmetry in the Enclosed Fluid Diode

Critical pressure asymmetry in the enclosed fluid diode

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