Electrostatic Suppression of the “Coffee Stain Effect”

Wray, Alexander; Papageorgiou, Demetrios T.; Craster, Richard V.; Sefiane, Khellil; Matar, Omar

doi:10.1021/la500805d

Cited by 54 publications

(49 citation statements)

References 36 publications

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“…We note that, as viewed from the ‘outer' region, the interface is located at z =0+ O (). Dropping the tilde decoration, this ultimately leads to the governing equations26,…”

Section: Methodsmentioning

confidence: 99%

Dynamics and universal scaling law in geometrically-controlled sessile drop evaporation

et al. 2017

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The evaporation of a liquid drop on a solid substrate is a remarkably common phenomenon. Yet, the complexity of the underlying mechanisms has constrained previous studies to spherically symmetric configurations. Here we investigate well-defined, non-spherical evaporating drops of pure liquids and binary mixtures. We deduce a universal scaling law for the evaporation rate valid for any shape and demonstrate that more curved regions lead to preferential localized depositions in particle-laden drops. Furthermore, geometry induces well-defined flow structures within the drop that change according to the driving mechanism. In the case of binary mixtures, geometry dictates the spatial segregation of the more volatile component as it is depleted. Our results suggest that the drop geometry can be exploited to prescribe the particle deposition and evaporative dynamics of pure drops and the mixing characteristics of multicomponent drops, which may be of interest to a wide range of industrial and scientific applications.

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“…We note that, as viewed from the ‘outer' region, the interface is located at z =0+ O (). Dropping the tilde decoration, this ultimately leads to the governing equations26,…”

Section: Methodsmentioning

confidence: 99%

Dynamics and universal scaling law in geometrically-controlled sessile drop evaporation

et al. 2017

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“…the use of electric fields. [16][17][18][19] Nevertheless, the mechanisms through which surfactants affect the evaporation process are not well understood and have been a topic of debate. It has been suggested that surfactants can be responsible for suppressing the effect of thermal Marangoni flow by generating a counter gradient of surface tension driving liquid outwards.…”

mentioning

confidence: 99%

Evaporation of Sessile Droplets Laden with Particles and Insoluble Surfactants

2016

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We consider the flow dynamics of a thin evaporating droplet in the presence of an insoluble surfactant and non-interacting particles in the bulk. Based on lubrication theory, we derive a set of evolution equations for the film height, the interfacial surfactant and bulk particle concentrations, taking into account the dependence of the liquid viscosity on the local particle concentration. An important ingredient of our model is that it takes into account the fact that the surfactant adsorbed at the interface hinders evaporation. We perform a parametric study to investigate how the presence of surfactants affects the evaporation process as well as the flow dynamics with and without the presence of particles in the bulk. Our numerical calculations show that the droplet life-time is affected significantly by the balance between the ability of surfactant to * To whom correspondence should be addressed † Department of Chemical Engineering, University of Patras, Patras 26500, Greece ‡ Department of Chemical Engineering, Indian Institute of Technology Hyderabad, Sangareddy 502 285, Telangana, India ¶ Department of Chemical Engineering, Imperial College London, London SW7 2AZ, UK 1 enhance spreading suppressing the effect of thermal Marangoni stresses-induced motion and to hinder the evaporation flux through the reduction of effective interfacial are of evaporation, which tend to accelerate and decelerate the evaporation process, respectively. For particle-laden droplets and in the case of dilute solutions, the droplet life-time is found to be weakly-dependent on the initial particle concentration. We also show that the particle deposition patterns are influenced strongly by the direct effect of surfactant on the evaporative flux; in certain cases, the "coffee stain" effect is enhanced significantly. A discussion of the delicate interplay between the effects of capillary pressure, solutal and thermal Marangoni stresses, which drive the liquid flow inside the evaporating droplet giving rise to the observed results is provided herein.

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“…After balancing the conductive heat within the film with the heat dissipated through evaporation, we arrive at a scaling factor for

j', j^{*} = k' Δ T' / h_{0}^{'} L a'

, where

k'

is the thermal conductivity of the film and

L a'

is the latent heat of vaporization for the solvent. As have previous works, we assume that the film's thermal conductivity is independent of film composition . The dimensionless temperature boundary conditions for the film are:

\begin{matrix} T = 1 at z = h_{b}, \\ - T_{z} = j = T / K at z = h, \end{matrix}

where K is the rescaled constant for the one‐sided evaporation model in eq ,

K = K' / (h_{0}^{'} L a' / k')

.…”

Section: Mathematical Modelmentioning

confidence: 99%

Drying of multicomponent thin films on substrates with topography

Pham

Cheng

Kumar

2016

J Polym Sci B Polym Phys

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Drying of multicomponent thin liquid films is an important step in coating and printing processes. In many cases, the substrate on which the film rests may possess topography, either intended or unintended. We present a lubrication‐theory‐based model describing the fundamentals of drying on such substrates. The film consists of volatile solvent and additional nonvolatile components such as colloidal particles, surfactants, and nonvolatile solvents. A system of one‐dimensional partial differential equations accounting for the film height, depth‐averaged concentration of bulk nonvolatile components, and interfacial concentration of insoluble surfactant is derived. Evaporation is included using the well‐known one‐sided description, and the governing equations are solved with finite‐difference methods to study various limiting cases. The results highlight the influence of evaporation rate, and thermal, surfactant, and solutal Marangoni flows on the film thickness and colloidal particle distribution. We find that, in a realistic region of parameter space, the addition of a nonvolatile solvent yields a film that conforms to the substrate topography. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017, 55, 1681–1691

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Electrostatic Suppression of the “Coffee Stain Effect”

Cited by 54 publications

References 36 publications

Dynamics and universal scaling law in geometrically-controlled sessile drop evaporation

Dynamics and universal scaling law in geometrically-controlled sessile drop evaporation

Evaporation of Sessile Droplets Laden with Particles and Insoluble Surfactants

Drying of multicomponent thin films on substrates with topography

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