arXiv subjects

Jiří Janek

Publications and source records attributed to Jiří Janek.

5 recordsLinked to original sources

arXiv2026

Beyond capillary condensation: Shear-induced bridging transitions in patterned slits

We study the equilibrium phase behavior of a fluid confined in a slit made from two patterned walls. Shearing the walls frustrates the fluid, due to a competition between capillary condensation and interface delocalization, forcing the formation of bridging phases with different pinning properties. This leads to an unusually rich phase diagram, displaying first-order and continuous phase transitions, depending sensitively on the slit width and shear. Generalized Kelvin equations determine the phase boundaries, while the bridging phases are characterized by large correlation lengths, predictions for which are tested using a microscopic density functional model.

cond-mat.soft↗

arXiv2026

Uniform distributions in nonuniform systems: Wall potentials generating constant density profiles in classical density functional theory

We study the inverse problem of classical density functional theory for inhomogeneous fluids: finding the wall potential that produces a constant equilibrium density profile, i.e., a perfectly flat density distribution in the accessible region adjacent to a substrate. Within Rosenfeld's fundamental measure theory, we solve this problem for a one-component fluid in planar, spherical, and cylindrical geometries, considering both a hard-sphere fluid and a fluid with an additional truncated Lennard-Jones attraction treated at the mean-field level. Explicit analytical expressions are obtained for planar walls, while spherical walls also admit an analytical treatment in a more cumbersome form. The cylindrical case is treated numerically. The construction provides an explicit microscopic realization of structure-cancelling wall fields, related to flat-profile conditions that occur under special matching conditions in interfacial theories of wetting and drying. The theory also yields a compact collection of formulae for weighted densities and one-body direct correlation functions in the three fundamental geometries, providing useful reference expressions for density-functional implementations. The resulting analytic wall potentials are validated in independent density functional calculations, which confirm that the prescribed flat profiles are recovered within numerical accuracy.

cond-mat.soft↗

arXiv2025

Complete Wetting and Drying at Sinusoidal Walls

We investigate complete wetting and drying at sinusoidally corrugated solid walls, focusing on the effects of wall geometry and interaction range. Two distinct interaction models are considered: one incorporating only short-ranged (SR) forces (applied to drying), and another including long-ranged (LR) van der Waals interactions (applied to wetting). The SR model is analyzed within the framework of nonlocal Hamiltonian theory by Parry et al., while the LR model is treated using a sharp-kink approximation. In both cases, we derive scaling relations that describe the dependence of the adsorbed layer's width and morphology on the wall's geometric parameters as the system approaches two-phase coexistence. We identify distinct scaling regimes determined by the degree of wall corrugation and highlight the contrasting effects of SR and LR interactions. Theoretical predictions are corroborated by numerical results from classical density functional theory.

cond-mat.soft↗

arXiv2025

Three types of condensation in open wedges

Condensation in linear wedges formed by semi-infinite walls is a well-established critical phenomenon characterized by the continuous growth of an adsorbed liquid layer as bulk two-phase coexistence is approached. In this study, we investigate condensation in finite-length wedges open at both ends, demonstrating that the process becomes first-order. The open boundaries and finite geometry induce a remarkably rich phase behavior of the confined fluid, exhibiting three distinct types of condensation, reentrant phenomena, and continuous higher-order transitions between condensation states. Through a detailed macroscopic analysis, we derive the conditions for each type of condensation, classify the global phase diagrams, and explore asymptotic behavior in specific limiting cases. The asymptotic predictions are confirmed by a detailed comparison with the numerical solutions of the governing equations.

cond-mat.soft↗

arXiv2024

Capillary condensation between non-parallel walls

We study the condensation of fluids confined by a pair of non-parallel plates of finite height $H$. We show that such a system experiences two types of condensation, termed single- and double-pinning, which can be characterized by one (single-pinning) or two (double-pinning) edge contact angles describing the shape of menisci pinned at the system edges. For both types of capillary condensation we formulate the Kelvin-like equation and determine the conditions under which the given type of condensation occurs. We construct the global phase diagram revealing a reentrant phenomenon pertinent to the change of the capillary condensation type upon varying the inclination of the walls. Asymptotic properties of the system are discussed and a link with related phase phenomena in different systems is made. Finally, we show that the change from a single- to a double-pinned state is a continuous transition, the character of which depends on the wetting properties of the walls.

cond-mat.mes-hall↗