Classical density functional study of wetting transitions on nanopatterned surfaces

Yatsyshin, Peter; Parry, A. O.; Rascón, C.; Kalliadasis, Serafim

doi:10.1088/1361-648x/aa4fd7

Cited by 16 publications

(24 citation statements)

References 45 publications

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“…We use the Barker-Henderson perturbation theory with the reference system given by the Carnahan-Starling EOS for the hard-sphere fluid [57,58] and the perturbative part given by the ten Wolde-Frenkel model (see appendix D), which is well-suited for the description of globular proteins [40]. The EOS allows us to obtain the equilibrium bulk densities at coexistence for a given temperature (e.g [53,58]), r ¥ ( ) c (vapor-like) and r ( ) 0 c (liquid-like). These values define the coexistence (saturation) curve of the fluid.…”

Section: Resultsmentioning

confidence: 99%

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General framework for nonclassical nucleation

et al. 2018

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A great deal of experimental evidence suggests that a wide spectrum of phase transitions occur in a multistage manner via the appearance and subsequent transformation of intermediate metastable states. Such multistage mechanisms cannot be explained within the realm of the classical nucleation framework. Hence, there is a strong need to develop new theoretical tools to explain the occurrence and nature of these ubiquitous intermediate phases. Here we outline a unified and self-consistent theoretical framework to describe both classical and nonclassical nucleation. Our framework provides a detailed explanation of the whole multistage nucleation pathway showing in particular that the pathway involves a single energy barrier and it passes through a dense phase, starting from a lowdensity initial phase, before reaching the final stable state. Moreover, we demonstrate that the kinetics of matter inside subcritical clusters favors the formation of nucleation clusters with an intermediate density, i.e. nucleation precursors. Remarkably, these nucleation precursors are not associated with a local minimum of the thermodynamic potential, as commonly assumed in previous phenomenological approaches. On the contrary, we find that they emerge due to the competition between thermodynamics and kinetics of cluster formation. Thus, the mechanism uncovered for the formation of intermediate phases can be used to explain recently reported experimental findings in crystallization: up to now such phases were assumed a consequence of some complex energy landscape with multiple energy minima. Using fundamental concepts from kinetics and thermodynamics, we provide a satisfactory explanation for the so-called nonclassical nucleation pathways observed in experiments.

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Section: Resultsmentioning

confidence: 99%

“…The equilibrium states are computed by minimization of Ω which is the state-of-the-art in classical density functional theory (e.g. [52,53]). Within the FH approach, the nucleation clusters are associated with the spatially localized fluctuations of density that are brought about by thermal noise.…”

Section: Formulationmentioning

confidence: 99%

General framework for nonclassical nucleation

et al. 2018

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“…This would allow us to evaluate the impact of the coupling between translational and rotational DoF on characteristic quantities, such as the nucleation barrier and rate. But also effects of walls [71,72] and confinement [73,[74][75][76][77], which in general should lead to definite orientation in the first particle layers near a solid substrate which in turn can induce anisotropy of both equilibrium and transport properties. Orientation coupled with layering can also cause formation of new phases in the fluid with the extreme form of the substrate-induced ordering being 'surface freezing', i.e.…”

Section: Discussionmentioning

confidence: 99%

General framework for fluctuating dynamic density functional theory

et al. 2017

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We introduce a versatile bottom-up derivation of a formal theoretical framework to describe (passive) soft-matter systems out of equilibrium subject to fluctuations. We provide a unique connection between the constituent-particle dynamics of real systems and the time evolution equation of their measurable (coarse-grained) quantities, such as local density and velocity. The starting point is the full Hamiltonian description of a system of colloidal particles immersed in a fluid of identical bath particles. Then, we average out the bath via Zwanzig's projection-operator techniques and obtain the stochastic Langevin equations governing the colloidal-particle dynamics. Introducing the appropriate definition of the local number and momentum density fields yields a generalisation of the Dean-Kawasaki (DK) model, which resembles the stochastic Navier-Stokes description of a fluid. Nevertheless, the DK equation still contains all the microscopic information and, for that reason, does not represent the dynamical law of observable quantities. We address this controversial feature of the DK description by carrying out a nonequilibrium ensemble average. Adopting a natural decomposition into local-equilibrium and nonequilibrium contribution, where the former is related to a generalised version of the canonical distribution, we finally obtain the fluctuating-hydrodynamic equation governing the time-evolution of the mesoscopic density and momentum fields. Along the way, we outline the connection between the ad hoc energy functional introduced in previous DK derivations and the free-energy functional from classical density-functional theory. The resultant equation has the structure of a dynamical densityfunctional theory (DDFT) with an additional fluctuating force coming from the random interactions with the bath. We show that our fluctuating DDFT formalism corresponds to a particular version of the fluctuating Navier-Stokes equations, originally derived by Landau and Lifshitz. Our framework thus provides the formal apparatus for ab initio derivations of fluctuating DDFT equations capable of describing the dynamics of soft-matter systems in and out of equilibrium.

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“…New transitions also arise for planar but chemically heterogeneous substrates in which the wall is a composite formed by materials with different wetting properties. These include studies of unbending transitions [19][20][21] involving the local condensation of liquid within a patterned region, and also complete pre-wetting (also called step-wetting) in which a nucleated liquid phase spreads out laterally across the substrate [22,23]. It is even possible to combine chemical patterning and substrate geometry to produces surfaces that are partially wet (i.e., have a finite contact angle) even though the materials involved only show complete wetting [24].…”

Section: Introductionmentioning

confidence: 99%

Scaling behavior of thin films on chemically heterogeneous walls

2017

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We study the adsorption of a fluid in the grand canonical ensemble occurring at a planar heterogeneous wall which is decorated with a chemical stripe of width L. We suppose that the material of the stripe strongly preferentially adsorbs the liquid in contrast to the outer material which is only partially wet. This competition leads to the nucleation of a droplet of liquid on the stripe, the height h m and shape of which (at bulk two-phase coexistence) has been predicted previously using mesoscopic interfacial Hamiltonian theory. We test these predictions using a microscopic Fundamental Measure Density Functional Theory which incorporates shortranged fluid-fluid and fully long-ranged wall-fluid interactions. Our model functional accurately describes packing effects not captured by the interfacial Hamiltonian but still we show that there is excellent agreement with the predictions h m ≈ L 1/2 and for the scaled circular shape of the drop even for L as small as 50 molecular diameters. For smaller stripes the droplet height is considerably lower than that predicted by the mesoscopic interfacial theory. Phase transitions for droplet configurations occurring on substrates with multiple stripes are also discussed.

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Classical density functional study of wetting transitions on nanopatterned surfaces

Cited by 16 publications

References 45 publications

General framework for nonclassical nucleation

General framework for nonclassical nucleation

General framework for fluctuating dynamic density functional theory

Scaling behavior of thin films on chemically heterogeneous walls

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