Effects of Substrate Heating and Wettability on Evaporation Dynamics and Deposition Patterns for a Sessile Water Droplet Containing Colloidal Particles

Patil, Nagesh D.; Bange, Prathamesh G.; Bhardwaj, Rajneesh; Sharma, Atul

doi:10.1021/acs.langmuir.6b02769

Cited by 119 publications

(174 citation statements)

References 41 publications

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“…The measured temperature is close to liquid-gas interface temperature because water is opaque to the infrared radiation. The calibration of the infrared camera was reported our previous study [26] and the uncertainty in the temperature response of IR camera is around ±1.0°C.…”

Section: Methodsmentioning

confidence: 99%

A combined computational and experimental investigation on evaporation of a sessile water droplet on a heated hydrophilic substrate

Kumar

Bhardwaj

2018

International Journal of Heat and Mass Transfer

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We numerically and experimentally investigate evaporation of a sessile droplet on a heated substrate. We develop a finite element (FE) model in two-dimensional axisymmetric coordinates to solve coupled transport of heat in the droplet and substrate, and of the mass of liquid vapor in surrounding ambient while assuming diffusion-limited, quasi-steady evaporation of the droplet.The two-way coupling is implemented using an iterative scheme and under-relaxation is used to ensure numerical stability. The FE model is validated against the published spatial profile of the evaporation mass flux and temperature of the liquid-gas interface. We discuss cases in which the two-way coupling is significantly accurate than the one-way coupling. In experiments, we visualized side view of an evaporating microliter water droplet using a high-speed camera at different substrate temperatures and recorded temperature of the liquid-gas interface from the top using an infrared camera. We examine the dependency of inversion of the temperature profile across the liquid-gas interface on the ratio of the substrate thickness to the wetted radius, the ratio of the thermal conductivity of the substrate to that of the droplet and contact angle. A regime map is plotted to demarcate the inversion of the temperature profile for a wide range of these variables.A comparison of measured evaporation mass rate with the computed values at different substrate temperature show that the evaporation mass rate increases non-linearly with respect to the substrate temperature, and FE model predicts these values close to the experimental data. Comparisons of time-averaged evaporation mass rate obtained by the previous and present models against the measurements suggest that the evaporative cooling at the interface and variation of diffusion coefficient with temperature should be taken into account in the model in order to accurately capture the measurements. We compare the measurements of time-varying droplet dimensions and of temperature profile across the liquid-gas interface with the numerical results and found good agreements. We quantify increase in the evaporation mass flux and evaporation mas rate by the substrate heating and present the combined effect of substrate heating, the ratio of the substrate thickness to the wetted radius, substrate-droplet thermal conductivity ratio and the contact angle on the evaporation mass rate.

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Section: Methodsmentioning

confidence: 99%

A combined computational and experimental investigation on evaporation of a sessile water droplet on a heated hydrophilic substrate

Kumar

Bhardwaj

2018

International Journal of Heat and Mass Transfer

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“…Due to these two factors, a thermal gradient appears across the liquid-gas interface. Consequently, it results in a surface tension gradient and a thermal Marangoni flow exists at the liquid-gas interface whose direction is from the contact line to the droplet apex [12][13][14]. Along with radially outward flow (bulk flow), it leads to an axisymmetric Marangoni recirculation inside the droplet that advects particles towards the inner region, as shown in For d = 0.1 μm, the ring width is wider on the TL side as compared to the TH side for all the cases of dT/dX as observed qualitatively in Figure 8 (a) and quantitatively in Figure 9 (a).…”

Section: Mechanism Of Formation Of the Depositsmentioning

confidence: 99%

“…In a follow-up study [25], they reported the suppression of dual ring at 84ºC due to the enhanced outward radial flow in comparison to the Marangoni flow. Patil et al [14] studied the deposition patterns of polystyrene particles on glass and silicon wafers heated from 27 ºC to 90ºC at different particles concentrations in an aqueous droplet. They reported the 5 thinning of the ring width with an increase in the substrate temperature.…”

Section: Introductionmentioning

confidence: 99%

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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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“…Once the factors deciding the dominance of capillary flow or Marangoni effect have been identified, it becomes possible to control the deposition pattern and choose whether a thin ring or a uniformly covered circular patch or a small spot at the center of the drop is desired. Besides physical and chemical properties of the fluid and substrate, manipulating the temperature distribution using heated/cooled substrates or microheaters has also been used to tailor the deposition pattern [119][120][121] for various applications. The effect of particle shape has also been found to play a role in the final desiccation pattern; ellipsoid-shaped particles suppress the coffee-ring effect as shown in several works [109,117].…”

Section: Evaporation Of a Suspension Of Micro-or Nanoparticlesmentioning

confidence: 99%

Droplet Drying Patterns on Solid Substrates: From Hydrophilic to Superhydrophobic Contact to Levitating Drops

Tarafdar

Tarasevich

Choudhury

et al. 2018

Advances in Condensed Matter Physics

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This review is devoted to the simple process of drying a multicomponent droplet of a complex fluid which may contain salt or other inclusions. These processes provide a fascinating subject for study. The explanation of the rich variety of patterns formed is not only an academic challenge but also a problem of practical importance, as applications are growing in medical diagnosis and improvement of coating/printing technology. The fundamental scientific problem is the study of the mechanism of microand nanoparticle self-organization in open systems. The specific fundamental problems to be solved, related to this system, are the investigation of the mass transfer processes, the formation and evolution of phase fronts, and the identification of mechanisms of pattern formation. The drops of liquid containing dissolved substances and suspended particles are assumed to be drying on a horizontal solid insoluble smooth substrate. The chemical composition and macroscopic properties of the complex fluid, the concentration and nature of the salt, the surface energy of the substrate, and the interaction between the fluid and substrate which determines the wetting all affect the final morphology of the dried film. The range of our study encompasses the fully wetting case with zero contact angle between the fluid and substrate to the case where the drop is levitated in space, so there is no contact with a substrate and angle of contact can be considered as 180 ∘ .

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Effects of Substrate Heating and Wettability on Evaporation Dynamics and Deposition Patterns for a Sessile Water Droplet Containing Colloidal Particles

Cited by 119 publications

References 41 publications

A combined computational and experimental investigation on evaporation of a sessile water droplet on a heated hydrophilic substrate

A combined computational and experimental investigation on evaporation of a sessile water droplet on a heated hydrophilic substrate

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

Droplet Drying Patterns on Solid Substrates: From Hydrophilic to Superhydrophobic Contact to Levitating Drops

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