Pinning and wicking in regular pillar arrays

Semprebon, Ciro; Forsberg, Pontus; Priest, Craig; Brinkmann, Martin

doi:10.1039/c4sm00684d

Cited by 55 publications

(63 citation statements)

References 30 publications

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“…Experimental results are shown for water on quartz pillar cuvettes exposed to a laboratory environment or, in selected cases, hydrophobization ( Figure 2c,d). The results are in qualitative agreement with Semprebon et al 26 Pinning lowers the critical contact angle below the thermodynamic prediction (eq 2). Experimental results in Figure 2c,d shows that filling of cuvettes with ϕ = 0.05 and h ∼ 12 μm would be less reliable than the other arrays studied because the material contact angle must be less than ∼20°for wicking to occur.…”

Section: ■ Theorysupporting

confidence: 92%

Pillar Cuvettes: Capillary-Filled, Microliter Quartz Cuvettes with Microscale Path Lengths for Optical Spectroscopy

2015

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The goal of most analytical techniques is to reduce the lower limit of detection; however, it is sometimes necessary to do the opposite. High sample concentrations or samples with high molar absorptivity (e.g., dyes and metal complexes) often require multiple dilution steps or laborious sample preparation prior to spectroscopic analysis. Here, we demonstrate dilution-free, one-step UV-vis spectroscopic analysis of high concentrations of platinum(IV) hexachloride in a micropillar array, that is, "pillar cuvette". The cuvette is spontaneously filled by wicking of the liquid sample into the micropillar array. The pillar height (thus, the film thickness) defines the optical path length, which was reduced to between 10 and 20 μm in this study (3 orders of magnitude smaller than in a typical cuvette). Only one small droplet (∼2 μL) of sample is required, and the dispensed volume need not be precise or even known to the analyst for accurate spectroscopy measurements. For opaque pillars, we show that absorbance is linearly related to platinum concentration (the Beer-Lambert Law). For fully transparent or semitransparent pillars, the measured absorbance was successfully corrected for the fractional surface coverage of the pillars and the transmittance of the pillars and reference. Thus, both opaque and transparent pillars can be applied to absorbance spectroscopy of high absorptivity, microliter samples. It is also shown here that the pillar array has a useful secondary function as an integrated (in-cuvette) filter for particulates. For pillar cuvette measurements of platinum solutions spiked with 6 μm diameter polystyrene spheres, filtered and unfiltered samples gave identical spectra.

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Section: ■ Theorysupporting

confidence: 92%

Pillar Cuvettes: Capillary-Filled, Microliter Quartz Cuvettes with Microscale Path Lengths for Optical Spectroscopy

2015

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“…The dynamic behaviors of the fringe in our experiments are consistent with the previous numerical simulations. 26 The dynamic processes of droplets with different viscosities spreading on micropillar-arrayed surfaces are shown in Fig. 5.…”

Section: A Experimental Resultsmentioning

confidence: 99%

“…12 Recently, Semprebon et al did elegant experiments and simulations to study the pinning and wicking of a liquid meniscus in a square array of pillars, and proposed a criteria for spontaneous film formation. 26 When liquid spreads on a smooth solid, a mesoscale intermediate region of size L is used to connect the macroscale and microscale region as shown in Fig. 1.…”

Section: -3mentioning

confidence: 99%

Dynamic spreading on pillar-arrayed surfaces: Viscous resistance versus molecular friction

2014

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The dynamic spreading of a liquid droplet on micropillar-arrayed surfaces is experimentally investigated. A theoretical model is proposed to include energy dissipations raised from both the viscous resistance at mesoscale and the molecular friction at microscale in the triple-phase region. The scaling laws and spreading shape of the droplet change with the variation of the liquid viscosity because of the competition between these two mechanisms of energy dissipations at the moving contact line. The Laplace pressures at the interior corner and at the wavy contact line are the answers to the excess driving energy and the superwetting on pillar-arrayed surfaces. The formation and evolution of the bulk and the fringe are also analyzed in detail. Our results may help to understand the wetting dynamics on microtextured surfaces and assist the future design of engineered surfaces in practical applications. C 2014 AIP Publishing LLC. [http://dx

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“…4(a), promising perspectives are to better understand the role of pillar-scale effects and to capture them into our dropscale model. For instance, of particular interest is the effect of pinning on wicking [31], as well as the influence of the fine details of front dynamics (including the zipping mechanism) on the macroscale front propagation dynamics [13,32,33]. We also hope that our work will stimulate more applied research aiming to improve heat transfer, self-assembly of soft structures, or deposition technologies.…”

Section: -P6mentioning

confidence: 99%

Evaporation dynamics of completely wetting drops on geometrically textured surfaces

Mekhitarian¹,

Sobac²,

Dehaeck³

et al. 2017

EPL

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-This study deals with the evaporation dynamics of completely wetting and highly volatile drops deposited on geometrically textured but chemically homogeneous surfaces. The texturation consists in a cylindrical pillars array with a square pitch. The triple line dynamics and the drop shape are characterized by an interferometric method. A parametric study is realized by varying the radius and the height of the pillars (at fixed interpillar distance), allowing to distinguish three types of dynamics: i) an evaporation-dominated regime with a receding triple line; ii) a spreading-dominated regime with an initially advancing triple line; iii) a cross-over region with strong pinning effects. The overall picture is in qualitative agreement with a mathematical model showing that the selected regime mostly depends on the value of a dimensionless parameter comparing the time scales for evaporation and spreading into the substrate texture. Introduction. -Wetting and evaporation of liquid drops on solid surfaces are of prime importance for a wide range of applications, from biomedicine and operation of DNA chips to painting and design of self-cleaning and antifouling surfaces. On the other hand, the recent development of small-scale fabrication techniques enables producing surfaces with well-defined chemical and/or geometrical textures, in the micron-range or even at the nanoscale. This offers a large range of new research possibilities, aiming in particular to improve the fundamental knowledge of wetting and evaporation/condensation of liquids on textured surfaces. In turn, a very promising outcome of such improved basic understanding could be the targeted manufacturing of novel hierarchical structures with potential applications in photovoltaics, substrates for engineered cell growth or other smart materials [1].In this work, we focus on surfaces geometrically textured by an array of cylindrical pillars with controlled dimensions (typically tens of microns). Previous studies have shown how such large-scale "roughness" influences the wetting of a drop deposited on the surface [2-4] by enhancing its wettability or non-wettability (i.e., by affecting its apparent contact angle and wetting surface). These works in particular highlighted that, in partial wetting situations, a part of the liquid can invade the surface

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Pinning and wicking in regular pillar arrays

Cited by 55 publications

References 30 publications

Pillar Cuvettes: Capillary-Filled, Microliter Quartz Cuvettes with Microscale Path Lengths for Optical Spectroscopy

Pillar Cuvettes: Capillary-Filled, Microliter Quartz Cuvettes with Microscale Path Lengths for Optical Spectroscopy

Dynamic spreading on pillar-arrayed surfaces: Viscous resistance versus molecular friction

Evaporation dynamics of completely wetting drops on geometrically textured surfaces

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