Pattern formation in drying droplets of polyelectrolyte and salt

Kaya, Deniz; Белый, В. А.; Muthukumar, M.

doi:10.1063/1.3493687

Cited by 117 publications

(126 citation statements)

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“…They study the regime where drop arrays form via directed convective dewetting of the solvent before they subsequently dry out. A thin film model that produces rings is presented by Kaya et al 60 , however, there the contact line is shifted 'by hand' if a certain condition is met. A thin film description of an evaporating drop of a suspension may also be coupled to a full description of the diffusion of vapour in the gas phase.…”

Section: Introductionmentioning

confidence: 99%

Modelling the formation of structured deposits at receding contact lines of evaporating solutions and suspensions

2012

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When a film of a liquid suspension of nanoparticles or a polymer solution is deposited on a surface, it may dewet from the surface and as the solvent evaporates the solute particles/polymer can be deposited on the surface in regular line patterns. In this paper we explore a hydrodynamic model for the process that is based on a long-wave approximation that predicts the deposition of irregular and regular line patterns. This is due to a self-organised pinning-depinning cycle that resembles a stick-slip motion of the contact line. We present a detailed analysis of how the line pattern properties depend on quantities such as the evaporation rate, the solute concentration, the Péclet number, the chemical potential of the ambient vapour, the disjoining pressure, and the intrinsic viscosity. The results are related to several experiments and to depinning transitions in other soft matter systems.

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Section: Introductionmentioning

confidence: 99%

Modelling the formation of structured deposits at receding contact lines of evaporating solutions and suspensions

2012

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“…6,7 Mineral rings left on washed glassware or sweat stained clothes are convenient examples of physical systems displaying such a behavior. Understanding the formation of the ring-like patterns from a colloidal droplet is important for many applications such as printing, [8][9][10] genotyping, 11 and colloidal self-assembly, 12,13 for which the distribution of the solute during drying process has to be put under control.…”

Section: Introductionmentioning

confidence: 99%

Ring formation from a drying sessile colloidal droplet

Zhang

Long-Guang

et al. 2013

AIP Advances

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Ring formation from drying sessile colloidal droplets (∼1.0 mm in size) containing microparticles of silicon or polystyrene was investigated with video microscopy. Results show that ring formation begins at the pinned contact line with the growth of an annular nucleus in a line by line way, which recedes inward albeit only slightly, followed by stacking of particles when the flow velocity becomes sufficiently large. The central height of the droplet decreases linearly with evaporation time, which implies that in the early stage, the number of particles arriving at contact line increases with time in a power law N∝t3/(1 + λ), where the parameter λ, according to Deegan's evaporation model, is related to the contact angle via $\lambda = \frac{{\pi - 2\theta _c }}{{2\pi - 2\theta _c }}$λ=π−2θc2π−2θc. Experimental values of λ agree well with model calculation for small contact angles, but are relatively smaller in the case of large contact angles. ‘Amorphization’ mechanism for the deposit at different stages of evaporation is discussed. Marangoni flow in a droplet on heated substrate introduces a desorption path for particles along the liquid surface, which can partially resolve the ring. Residual particles floating on the liquid surface may leave behind a homogeneous monolayer coating inside the dried spot. A “jump” in the droplet surface area at later stage of evaporation seems inevitably to cause a depletion zone of particles next to the ring. These results may be helpful for the development of strategies towards suppression of coffee ring effect and/or obtaining homogeneous coatings from drying colloidal suspension.

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“…2(b)]. Notice that such patterns have also been observed in other evaporating systems [16]. The resulting frictional landscape exhibits areas of high friction separated by low friction "valleys."…”

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confidence: 63%

Artificial Tribotactic Microscopic Walkers: Walking Based on Friction Gradients

2014

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Friction, the resistive force between two surfaces sliding past each other, is at the core of a wide diversity of locomotion schemes. While such schemes are well described for homogeneous environments, locomotion based on friction in inhomogeneous environments has not received much attention. Here we introduce and demonstrate the concept of tribotaxis, a motion that is guided by gradients in the friction coefficient. Our system is composed of microwalkers that undergo an effective frictional interaction with biological receptors on the substrate, which is regulated by the density of such receptors. When actuated stochastically, microwalkers migrate to regions of higher friction, much like a chemotactic cell migrates to regions of higher chemoattractant concentration. Simulations and theory based on biased random walks are in excellent agreement with experiments. We foresee important implications for tribotaxis in artificial and natural locomotion in biological environments. DOI: 10.1103/PhysRevLett.113.178101 PACS numbers: 87.85.gj, 81.40.Pq, 87.16.Uv Tribotaxis is the process by which an active object, biotic or abiotic, detects differences in the effective local friction coefficient and moves to regions of higher or lower friction according to a given protocol. The local friction coefficient between an object and a surface is dictated by the effective interactions between both. If these interactions are directional in nature, the friction coefficient is anisotropic. A prominent example of this, being the skin of many animals which feels rough when stroked in one direction, yet soft in the other. The origin of this asymmetry is due to the directionality and ordering of hair or scales sticking out from the surface at a slanted angle, which helps in modulating the effective friction between the skin (or scales) of an animal and the surrounding fluid [1,2]. These types of materials are important in many other processes, such as regulating the flow of complex fluids [3], controlling the motion of cells [4], or even skiing up a mountain.While the motifs that give rise to these asymmetric friction coefficients are rather large, one can envision an alternative microscopic scenario. For example, one can think of exchanging the mechanical texture with a chemical texture in which friction is dominated by the strength and spatial density of reversible bonds between an object and a substrate [5,6]. Moreover, gradients in the spatial density of such ligands produce anisotropic friction coefficients. Live cells, for example, naturally detect surface ligand gradients and move accordingly [7]; this is one of the most important clues for locomotion since cells are constantly encountering surfaces in our bodies. Mimicking this behavior using biological ligand-receptor pairs can potentially allow one to "walk on" and sense different conditions in the vast amounts of interfaces in tissues and organs. In addition, chemically based tribotaxis can be used to locally sense friction in purely synthetic environments. Interestingly, ...

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Pattern formation in drying droplets of polyelectrolyte and salt

Cited by 117 publications

References 28 publications

Modelling the formation of structured deposits at receding contact lines of evaporating solutions and suspensions

Modelling the formation of structured deposits at receding contact lines of evaporating solutions and suspensions

Ring formation from a drying sessile colloidal droplet

Artificial Tribotactic Microscopic Walkers: Walking Based on Friction Gradients

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