From coffee rings to coffee eyes

Li, Yanshen; Lv, Cunjing; Li, Zhaohan; Quéré, David; Zheng, Quanshui

doi:10.1039/c5sm00654f

Cited by 124 publications

(163 citation statements)

References 41 publications

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“…The temperature gradient detected by an infrared technique was shown to orient to the contact line for both the natural and heating conditions, in consistent to the temperature profiles obtained by Girard,et al 37 . Subjected to the same mechanism that the inward Marangoni flow is enhanced upon heating the solid surface, the deposited profile transferred from a single ring to a dual ring formed by polystyrene spheres in the study of Li, et al 26 .…”

Section: Introductionmentioning

confidence: 96%

Disk to dual ring deposition transformation in evaporating nanofluid droplets from substrate cooling to heating

Zhong

Duan

2016

Phys. Chem. Chem. Phys.

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Substrate temperature plays an important role in deposited morphologies formed after the evaporation of nanofluid droplets. The deposited patterns are shown to vary from a uniform disk-like profile to a dual ring from cooling to heating of the substrate. The droplet on the substrate with a relatively low temperature reveals three primary stages. Stage I features an outward transport of nanoparticles along the liquid-air interface near the droplet edge. Meanwhile some nanoparticles form sediment on the solid surface with a certain distance to the contact line. In the central region nanoparticles are dominated by Brownian motion so they fluctuate around their positions. Stage II is characterized by an increasing outward transport of nanoparticles in the bulk so the coffee ring is gradually enhanced. Most particles in Stages I and II are central-concentrated, leaving an annular gap sparsely covered adjacent to the outer ring. In Stage III, the pattern is homogenized by filling the gap with the arrival of the interior nanoparticles. Upon increasing the substrate temperature, the accompanied flow pattern exhibits a transition when the substrate still remains cooler than the atmosphere. It is resulted from the evaporative cooling at the droplet apex counteractive to the applied temperature gradient by substrate cooling. Above the transition temperature, the induced inward Marangoni flow takes place earlier at a higher substrate temperature, and in conjunction with the outward radial flow a dual ring pattern is formed.

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Section: Introductionmentioning

confidence: 96%

Disk to dual ring deposition transformation in evaporating nanofluid droplets from substrate cooling to heating

Zhong

Duan

2016

Phys. Chem. Chem. Phys.

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“…They reported that the temperature difference between the contact line and the droplet apex decreases with time. Regarding colloidal suspensions, Li et al [12] reported the deposits obtained after evaporation of an aqueous droplet containing 0.25% (v/v) polystyrene nanoparticles on a glass substrate, heated from 30ºC to 80ºC. They reported that the "coffeering" changes to a "coffee-eye" due to inward axisymmetric Marangoni flow.…”

Section: Introductionmentioning

confidence: 99%

Colloidal deposit of an evaporating sessile droplet on a non-uniformly heated substrate

Malla

Bhardwaj

Neild

2020

Colloids and Surfaces A: Physicochemical and Engineering Aspect

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2 AbstractThe pattern and profile of a dried colloidal deposit formed after evaporation of a sessile water droplet containing polystyrene particles on a non-uniformly heated glass are investigated experimentally. In particular, the effects of temperature gradient across the substrate and particles size are investigated. The temperature gradient was imposed using Peltier coolers, and side visualization, infrared thermography, optical microscopy, and optical profilometry were employed to collect the data. On a uniformly heated substrate, a ring with an inner deposit is obtained, which is attributed to axisymmetric Marangoni recirculation and consistent with previous reports. However, the dimensions of the ring formed on a non-uniformly heated substrate are significantly different on the hot and cold side of the substrate and are found to be a function of the temperature gradient and particles size. In the case of smaller particle size, the contact line on hot side depins and together with twin asymmetric Marangoni recirculations, it results in a larger ring width on the cold side as compared to the hot side. In contrast, the contact line remains pinned in case of larger particles, and the twin asymmetric Marangoni recirculations advect more particles on the hot side, resulting in a larger ring width at the hot side. A mechanistic model is employed to explain why the depinning is dependent on the particle size. A larger temperature gradient significantly increases or decreases the ring width depending on the particle size, due to a stronger intensity recirculation. A regime map is proposed for the deposit patterns on temperature gradient-particle size plane to classify the deposits. Movie S6: Video of IR thermography of the evaporating droplet for d = 0.1 μm at dT/dX = 4.2ºC/mm.

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“…[8][9][10]. Nearly all data sets show that the skewness of the deposit reduces with increasing additives, indicating that pillars become flatter.…”

Section: Discussionmentioning

confidence: 91%

“…One of the aims of ongoing research into drying sessile droplets is to control and Contribution to the Topical Issue "Wetting and Drying: Physics and Pattern Formation", edited by Duyang Zang, Ludovic Pauchard and Wei Shen. a e-mail: david.fairhurst@ntu.ac.uk prevent the formation of the coffee ring-stain as many commercial processes require a uniform deposit. Several mechanisms have been observed to achieve this goal including: non-spherical particles [4], capillary forces [5]; Marangoni flow induced by surface tension gradients [6]; electrowetting [7]; using droplets smaller than a critical size [8] and heated substrates [9]. Many of these effects are summarised in a recent review [10].…”

Section: Introductionmentioning

confidence: 99%

Controlling and characterising the deposits from polymer droplets containing microparticles and salt

et al. 2016

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Abstract.A coffee ring-stain is left behind when droplets containing a wide range of different suspended particles evaporate, caused by a pinned contact line generating a strong outwards capillary flow. Conversely, in the very peculiar case of evaporating droplets of poly(ethylene oxide) solutions, tall pillars are deposited in the centre of the droplet following a boot-strapping process in which the contact line recedes quickly, driven by a constricting collar of polymer crystallisation: no other polymer has been reported to produce these central pillars. Here we map out the phase behaviour seen when the specific pillar-forming polymer is combined with spherical microparticles, illustrating a range of final deposit shapes, including the standard particle ring-stain, polymer pillars and also flat deposits. The topologies of the deposits are measured using profile images and stylus profilometery, and characterised using the skewness of the profile as a simple analytic method for quantifying the shapes: pillars produce positive skew, flat deposits have zero skew and ring-stains have a negative value. We also demonstrate that pillar formation is even more effectively disrupted using potassium sulphate salt solutions, which change the water from a good solvent to a thetapoint solvent, consequently reducing the size and configuration of the polymer coils. This inhibits polymer crystallisation, interfering with the bootstrap process and ultimately prevents pillars from forming. Again, the deposit shapes are quantified using the skew parameter.

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From coffee rings to coffee eyes

Cited by 124 publications

References 41 publications

Disk to dual ring deposition transformation in evaporating nanofluid droplets from substrate cooling to heating

Disk to dual ring deposition transformation in evaporating nanofluid droplets from substrate cooling to heating

Colloidal deposit of an evaporating sessile droplet on a non-uniformly heated substrate

Controlling and characterising the deposits from polymer droplets containing microparticles and salt

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