Evaporation-driven colloidal cluster assembly using droplets on superhydrophobic fractal-like structures

Seyfert, Carola; Berenschot, J.W.; Tas, Niels Roelof; Susarrey-Arce, Arturo; Marin, Alvaro

doi:10.1039/d0sm01346c

Cited by 21 publications

(23 citation statements)

References 56 publications

(76 reference statements)

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“…2 we can see that, during a first stage of the evaporation process, the droplet volume evolves in time just like pure water droplets (solid lines), regardless of their composition (symbols). This is fairly well described by a simple model valid for pure water solutions, and has recently been shown for colloidal solutions [33]. Thus we conclude that the early evaporation process is not affected by the composition of the droplet, no matter the relative humidity, just as suggested by our analytical model described below.…”

Section: Experimental Results With Respiratory-like Dropletssupporting

confidence: 83%

“…This is a surprising phenomenon since a quick calculation can show that the time scale for the Brownian motion of, for example, a sodium ion is much shorter than the evaporation time scale. However, it can be shown that a salt concentration gradient can form in an evaporating droplet due to the non-linear dynamics of the receding interface [17], and a similar phenomenon has been shown to occur with colloids, yielding core-shell structures [33]. Consequently, it is not surprising that mucin and surfactant accumulate at the interface forming a sort of film, which could wrap (and protect) any other non-volatile content.…”

Section: Droplet Dry-out and Resulting Structurementioning

confidence: 99%

“…(3) Besides the contact angle which we assume roughly constant during the evaporation process (θ ≈ 150 o in our experiments), an expression for the contact radius R c is required [33],…”

Section: Analytical Modelmentioning

confidence: 99%

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Stability of Respiratory-Like Droplets under Evaporation

Seyfert¹,

Rodríguez-Rodríguez²,

Lohse³

et al. 2021

Preprint

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Pathogens contained in airborne respiratory droplets have been seen to remain infectious for periods of time that depend on the ambient temperature and humidity. In particular, regarding the humidity, the empirically least favorable conditions for the survival of viral pathogens are found at intermediate humidities. However, the precise physico-chemical mechanisms that generate such least-favorable conditions are not understood yet. In this work, we analyze the evaporation dynamics of respiratory-like droplets in air, semi-levitating them on superhydrophobic substrates with minimal solid-liquid contact area. Our results reveal that, compared to pure water droplets, the salt dissolved in the droplets can significantly change the evaporation behaviour, especially for high humidities close to and above the deliquesence limit. Due to the hygroscopic properties of salt, water evaporation is inhibited once the salt concentration reaches a critical value that depends on the relative humidity. The salt concentration in a stable droplet reaches its maximum at around 75% relative humidity, generating conditions that might shorten the time in which pathogens remain infectious.

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Section: Experimental Results With Respiratory-like Dropletssupporting

confidence: 83%

Section: Droplet Dry-out and Resulting Structurementioning

confidence: 99%

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Stability of Respiratory-Like Droplets under Evaporation

Seyfert¹,

Rodríguez-Rodríguez²,

Lohse³

et al. 2021

Preprint

Self Cite

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“…In particular, it would be interesting to study the additional role of the ratio of volumes of oil and particles in determining the supraparticle shape, along the lines of Tan et al ., and how this ratio interferes with the effect of colloidal particle size. Furthermore, a question to be addressed is whether our findings can be generalized and applied to the production of supraparticles on other substrates, such as structured superhydrophobic surfaces or oil-coated surfaces, and whether the pinning can be avoided completely or for a major part of the evaporation process on structured surfaces. ,,− As the shape of the supraparticle has been leveraged for desirable functionality of the supraparticle in the extensive literature, − ,− it will also be exciting to explore the functionalities of these supraparticles in the future.…”

Section: Resultsmentioning

confidence: 99%

Particle Size Determines the Shape of Supraparticles in Self-Lubricating Ternary Droplets

et al. 2021

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Supraparticles are large clusters of much smaller colloidal particles. Controlling the shape and anisotropy of supraparticles can enhance their functionality, enabling applications in fields such as optics, magnetics, and medicine. The evaporation of self-lubricating colloidal ouzo droplets is an easy and efficient strategy to create supraparticles, overcoming the problem of the “coffee-stain effect” during drop evaporation. Yet, the parameters that control the shape of the supraparticles formed in such evaporating droplets are not fully understood. Here, we show that the size of the colloidal particles determines the shape of the supraparticle. We compared the shape of the supraparticles made of seven different sizes of spherical silica particles, namely from 20 to 1000 nm, and of the mixtures of small and large colloidal particles at different mixing ratios. Specifically, our in situ measurements revealed that the supraparticle formation proceeds via the formation of a flexible shell of colloidal particles at the rapidly moving interfaces of the evaporating droplet. The time t c0 when the shell ceases to shrink and loses its flexibility is closely related to the size of particles. A lower t c0 , as observed for smaller colloidal particles, leads to a flat pancake-like supraparticle, in contrast to a more curved American football-like supraparticle from larger colloidal particles. Furthermore, using a mixture of large and small colloidal particles, we obtained supraparticles that display a spatial variation in particle distribution, with small colloids forming the outer surface of the supraparticle. Our findings provide a guideline for controlling the supraparticle shape and the spatial distribution of the colloidal particles in supraparticles by simply self-lubricating ternary drops filled with colloidal particles.

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“…In the literature, the evaporation of colloidal suspensions has been extensively studied with the objective of directing the assembly of colloids over a surface. − When a drop containing a colloidal suspension is evaporated on a surface, the resulting deposited residue may exhibit typical edge rings. This so-called “coffee ring” effect is due to the pinning of the contact line of the drop with the surface .…”

Section: Introductionmentioning

confidence: 99%

Hierarchical Superhydrophobic Device to Concentrate and Precisely Localize Water-Soluble Analytes: A Route to Environmental Analysis

et al. 2022

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An efficient superhydrophobic concentrator is developed using a hierarchical superhydrophobic surface on which the evaporation of a sessile droplet (6 μL) drives the nonvolatile elements it contains on a predefined micrometric analytical surface (pedestal of 80 μm diameter). This hierarchical silicon surface exhibits a surface texture made of etched nanopillars and consists of micropillars and guiding lines, arranged in radial symmetry around the central pedestal. The guiding lines ensure the overall convergence of the sessile droplet toward the central pedestal during evaporation. The nanopillar texturing induced a delay in the Cassie−Baxter to Wenzel regime transition, until the edge of the droplet reaches the periphery of the pedestal. Experiments performed with polymer microparticles suspended in ultrapure water or with DNA molecules solubilized in ultrapure water at sub-fM concentrations demonstrated that the totality of the nonvolatile elements in the liquid microvolume is delivered on or close to the pedestal area, in a very reproducible manner. The very high concentration capacity of the device enabled the discrimination of the degree of purity of ultrapure water samples from different origins. The concentrator also turned out to be functional for raw water samples, opening possible applications to environmental analysis.

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Evaporation-driven colloidal cluster assembly using droplets on superhydrophobic fractal-like structures

Abstract: Evaporation of suspension droplets on superhydrophobic substrates reveals a dominant shape dependency of the resulting supraparticles on initial particle concentration.

Cited by 21 publications

References 56 publications

Stability of Respiratory-Like Droplets under Evaporation

Stability of Respiratory-Like Droplets under Evaporation

Particle Size Determines the Shape of Supraparticles in Self-Lubricating Ternary Droplets

Hierarchical Superhydrophobic Device to Concentrate and Precisely Localize Water-Soluble Analytes: A Route to Environmental Analysis

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