Evaporation of Microdroplets of Ethanol−Water Mixtures on Gold Surfaces Modified with Self-Assembled Monolayers

Cheng, Alan K. H.; Soolaman, Dinah M.; Yu, Hua-Zhong

doi:10.1021/jp0572885

Cited by 84 publications

(112 citation statements)

References 33 publications

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“…Cheng et al (17) , although unable to take measurements during this phase because of the instabilities in contact line behaviour, postulate that the instabilities are driven by temperature gradients, citing the work of Hopkins and Reid (24) on temperature variations in evaporating aerosol drops of alcohol/water mixtures. We have used Infra-red thermography on our sessile drops (Fig.…”

Section: Drops Containing Ethanol Water Mixturesmentioning

confidence: 99%

“…With droplets formed from binary mixtures of an alcohol (methanol (15) , ethanol (16)(17)(18)(19) and 1-propanol (20) ) and water the behaviour is generally different from that of pure liquids, particularly for mixtures on the water-rich side of any binary azeotrope (20) . Depending on the wettability and smoothness of the surface there may be an initial phase during which the drop remains pinned and the contact angle decreases.…”

Section: Introductionmentioning

confidence: 99%

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The Flow Characteristics of an Evaporating Ethanol Water Mixture Droplet on a Glass Substrate

Hamamoto

Christy

Sefiane

2012

JTST

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Droplet evaporation has attracted much interest recently, being relevant to a wide range of biological and technological applications. The underlying mechanisms for this phenomenon are still poorly understood. We report on experimental results, from micro-Particle Image Velocimetry (µPIV), of the spatial and temporal velocity field within pure water and ethanol-water mixture droplets evaporating on a glass substrate. The drop profile, evaporation rate and surface temperature were also measured. For pure water droplets, the redial velocity is found to exhibit a maximum spatially towards the three-phase contact line and to increase dramatically towards the end of the drop lifetime. For ethanol-water droplets, three flow phases of (I) vortical flow, (II) transient flow and (III) radial flow were observed. Phase I has vortices, driven, we believe, by concentration differences arising during the preferential evaporation of ethanol. Phase II sees an exponential decay in vorticity with remaining vortices migrating towards the contact line, accompanied by the formation of one large toroidal vortex, possibly due to ethanol depletion at the apex of the drop leading to a surface tension instability. Phase III is characterized by radial flow towards the contact line, matching the evaporative flux and identical to the flow measured for pure water.

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Section: Drops Containing Ethanol Water Mixturesmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

The Flow Characteristics of an Evaporating Ethanol Water Mixture Droplet on a Glass Substrate

Hamamoto

Christy

Sefiane

2012

JTST

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“…Researchers agree on the observation that evaporation proceeds in distinct stages, a first stage where the more volatile component evaporates, a second stage which is a mixed stage and a last stage where the drop behaves as if it mainly consists of the less volatile component. These evaporation stages have been revealed through observations and measurements of the drop profile such as the angle, height, volume and base, Hopkins & Reid (2006), Cheng et al (2006). It is worth stressing that during the evaporation of binary mixture drops, additional physical mechanisms, which are absent in single component drops contribute to the observed behaviour.…”

Section: Introductionmentioning

confidence: 99%

Vortices, dissipation and flow transition in volatile binary drops

Bennacer

Sefiane

2014

J. Fluid Mech.

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(Received ?; revised ?; accepted ?. -To be entered by editorial office)Despite its fundamental and practical relevance, flow structure and evolution within volatile mixture drops remains largely unexplored. We study experimentally, using particle image velocimetry (PIV), the evolution of internal flow during the evaporation of ethanol-water mixture drops for different initial concentrations. The investigation revealed the existence of three stages in the evolving flow behaviour within these binary volatile drops. We propose an analysis of the nature of the flow and focus on understanding successive flow stages as well as transition from multiple vortices to a monotonous outward flow. We show that the existence of multiple vortices during the first stage is driven by local concentration gradients along the interface. When the more volatile component (in this case ethanol) is depleted, the intensity of this M arangoni flow abruptly declines. Towards the end of the first stage, ethanol is driven from the bulk of the drop to the interface to sustain weakening concentration gradients. Once these gradients are too weak, the solutal M arangoni number becomes sub-critical and the driving force for the flow switches off. The evolution of flow structure and transition between stages is found to be well correlated with the ratio of Marangoni and Reynolds numbers. Furthermore, we argue that whilst the observed vortices are driven by surface tension shear stress originating at the liquid/vapour interface, the transition in flow and its dynamics is entirely determined by viscous dissipation. The comparison between the analytical expression for vorticity decay based on viscous dissipation and the experimental data show a very good agreement. The analysis also shows that regardless of the initial concentration, for same size drops, the transition in flow follows exactly the same trend. This further supports the hypothesis of a viscous dissipation transition of the flow. The last stage is satisfactorily explained based on non-uniform evaporation and continuity driven flow.

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“…The overall wetting behavior was explained by the antagonistic effects of evaporation tending to increase contact angle and hydrodynamic flow tending to cause spreading. In addition, Cheng et al [12] studied the wetting and evaporation behaviors of ethanol-water mixtures of various concentrations on the gold surfaces modified with 1-decanethiolate self-assembled monolayers (SAMs). The changes in the contact angle, contact area, and volume of the mixture drops were monitored.…”

Section: Introductionmentioning

confidence: 99%

Wetting and evaporation behaviors of water–ethanol sessile drops on PTFE surfaces

Shi

Shen

Zhang

et al. 2009

Surface & Interface Analysis

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The wetting and evaporation behaviors of water-ethanol mixtures on polished poly(tetrafluoroethylene) (PTFE) surfaces were studied with an emphasis on the influence of concentration. Three representative stages: (i) constant contact diameter with decreasing contact angle and drop height; (ii) increase in contact angle and drop height with decreasing contact diameter; and (iii) simultaneous decrease in contact angle, drop height, and contact diameter, were identified in the wetting process under evaporation. In the initial stage, with increasing ethanol concentration, the wetting and evaporating behaviors of the mixture drops are close to those of pure ethanol, while in the final stage they are close to those of pure water, regardless of the concentration. The most significant difference between the pure substance and mixture drops is in the intermediate stage due to the different controlling mechanisms behind the de-pinning phenomenon. Moreover, the concrete wetting behavior is dependent on the composition of the mixture drops. For an evaporating sessile drop, the wetting should be evaluated using the combined parameters of contact angle, drop height, and contact diameter. Six representative modes are proposed to describe the wetting behaviors of the water-ethanol sessile drops on the PTFE surfaces under evaporation.

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Evaporation of Microdroplets of Ethanol−Water Mixtures on Gold Surfaces Modified with Self-Assembled Monolayers

Cited by 84 publications

References 33 publications

The Flow Characteristics of an Evaporating Ethanol Water Mixture Droplet on a Glass Substrate

The Flow Characteristics of an Evaporating Ethanol Water Mixture Droplet on a Glass Substrate

Vortices, dissipation and flow transition in volatile binary drops

Wetting and evaporation behaviors of water–ethanol sessile drops on PTFE surfaces

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