Scaling behavior of thin films on chemically heterogeneous walls

Malijevský, Alexandr; Parry, A. O.; Pospíšil, Martin

doi:10.1103/physreve.96.032801

Cited by 15 publications

(18 citation statements)

References 31 publications

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“…The properties of liquid drops on heterogeneous walls have been studied previously [43][44][45][46][47][48] at the bulk fluid coexistence in two [45][46][47] and three [43,44,48] dimensions. Systems involving only short-range forces have been shown to exhibit conformal invariance which allows to predict the explicit form of the droplet height for a number of different domain shapes [43]; this is no more the case of systems with the longrange forces which, however, still exhibit some scale invariance for the shape of the drop and its height which scales with the width of the stripe as m ∝ √ L [48]. The purpose of this work is to extend these studies by considering the growth of the drop as the saturation is approached from below.…”

Section: Introductionmentioning

confidence: 99%

Height of a liquid drop on a wetting stripe

Malijevský

2020

Phys. Rev. E

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Adsorption of liquid on a planar wall decorated by a hydrophilic stripe of width L is considered. Under the condition, that the wall is only partially wet (or dry) while the stripe tends to be wet completely, a liquid drop is formed above the stripe. The maximum height m(δµ) of the drop depends on the stripe width L and the chemical potential departure from saturation δµ where it adopts the value 0 = m(0). Assuming a long-range potential of van der Waals type exerted by the stripe, the interfacial Hamiltonian model is used to show that 0 is approached linearly with δµ with a slope which scales as L 2 over the region satisfying L ξ , where ξ is the parallel correlation function pertinent to the stripe. This suggests that near the saturation there exists a universal curve m(δµ) to which the adsorption isotherms corresponding to different values of L all collapse when appropriately rescaled. Although the series expansion based on the interfacial Hamiltonian model can be formed by considering higher order terms, a more appropriate approximation in the form of a rational function based on scaling arguments is proposed. The approximation is based on exact asymptotic results, namely that m ∼ δµ −1/3 for L → ∞ and that m obeys the correct δµ → 0 behaviour in line with the results of the interfacial Hamiltonian model. All the predictions are verified by the comparison with a microscopic density functional theory (DFT) and, in particular, the rational function approximation-even in its simplest form-is shown to be in a very reasonable agreement with DFT for a broad range of both δµ and L.

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Section: Introductionmentioning

confidence: 99%

Height of a liquid drop on a wetting stripe

Malijevský

2020

Phys. Rev. E

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“…In the grand canonical ensemble, that is when the volume of liquid is not constrained, morphological transitions do not occur since the fluid density profile must have the same symmetry as the confining external field induced by the wall. However in their place are a number of phase transitions including the possibility of the formation of liquid bridges that span between different striped regions when the gaps between them are sufficiently small [26]. These are similar to bridging transitions, that is the local condensation of liquid, between nano-particles (spheres, cylinders etc.)…”

Section: Introductionmentioning

confidence: 99%

Bridging of liquid drops at chemically structured walls

2019

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Using mesoscopic interfacial models and microscopic density functional theory we study fluid adsorption at a dry wall decorated with three completely wet stripes of width L separated by distances D1 and D2. The stripes interact with the fluid with long-range forces inducing a large finite-size contribution to the surface free-energy. We show that this non-extensive free-energy contribution scales with ln L and drives different types of bridging transition corresponding to the merging of liquid drops adsorbed at neighbouring wetting stripes when the separation between them is molecularly small. We determine the surface phase diagram and show that this exhibits two triple points, where isolated drops, double drops and triple drops coexist. For the symmetric case, D1 = D2 ≡ D, our results also confirm that the equilbrium droplet configuration always has the symmetry of the substrate corresponding to either three isolated drops when D is large or a single triple drop when D is small; however, symmetry broken configurations do occur in a metastable part of the phase diagram which lies very close to the equilibrium bridging phase boundary. Implications for phase transitions on other types of patterned surface are considered. arXiv:1905.00308v1 [cond-mat.stat-mech] 1 May 2019

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“…This, in turn, invoked theoretical and computational efforts for a description of liquid adsorption on chemically heterogenous surfaces by considering further aspects, additional to the surface tension arguments, such as the relevance of microscopic forces, packing effects, thermal fluctuations, line tension etc., all ignored within the original description of Cassie. These include molecular based simulations [15][16][17][18][19][20][21][22], stability analysis of liquid structures at microchannels [6,[23][24][25][26][27], exact statistical-mechanical arguments [28,29], various modifications of the effective Hamiltonian model [30][31][32][33], as well as studies using den- sity functional theory (DFT) approach [34][35][36][37][38][39][40][41][42][43].…”

Section: Introductionmentioning

confidence: 99%

Symmetry-breaking morphological transitions at chemically nanopatterned walls

Pospíšil¹,

Láska²,

Malijevský³

2019

Phys. Rev. E

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We study the structure and morphological changes of fluids that are in contact with solid composites formed by alternating and microscopically wide stripes of two different materials. One type of the stripes interacts with the fluid via long-ranged Lennard-Jones-like potential and tends to be completely wet, while the other type is purely repulsive and thus tends to be completely dry. We consider closed systems with a fixed number of particles that allows for stabilization of fluid configurations breaking the lateral symmetry of the wall potential. These include liquid morphologies corresponding to a sessile drop that is formed by a sequence of bridging transitions that connect neighboring wet regions adsorbed at the attractive stripes. We study the character of the transitions depending on the wall composition, stripes width, and system size. Using a (classical) nonlocal density functional theory (DFT), we show that the transitions between different liquid morphologies are typically weakly first-order but become rounded if the wavelength of the system is lower than a certain critical value Lc. We also argue that in the thermodynamic limit, i.e., for macroscopically large systems, the wall becomes wet via an infinite sequence of first-order bridging transitions that are, however, getting rapidly weaker and weaker and eventually become indistinguishable from a continuous process as the size of the bridging drop increases. Finally, we construct the global phase diagram and study the density dependence of the contact angle of the bridging drops using DFT density profiles and a simple macroscopic theory. arXiv:1912.12111v1 [cond-mat.stat-mech]

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Scaling behavior of thin films on chemically heterogeneous walls

Cited by 15 publications

References 31 publications

Height of a liquid drop on a wetting stripe

Height of a liquid drop on a wetting stripe

Bridging of liquid drops at chemically structured walls

Symmetry-breaking morphological transitions at chemically nanopatterned walls

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