Search results for "Wetting"
showing 10 items of 235 documents
Properties of the interface in the confined Ising magnet with competing surface fields
2007
Abstract A two-dimensional magnetic Ising system confined in an L × D geometry ( L ⪡ D ) in the presence of competing magnetic fields (h) acting at opposite walls along the D -direction, exhibits an interface between domains of different orientation that run parallel to the walls. In the limit L → ∞ , this interface undergoes a wetting transition that occurs at the critical curve T w ( h ) , so that for T T w ( h ) such an interface is bound to the walls, while for T w ( h ) ⩽ T T cb the interface is freely fluctuating around the center of the film, where T cb is the bulk critical temperature. By considering both short- and long-range magnetic fields acting at the walls, we study the diverg…
Interface localisation-delocalisation transition in a symmetric polymer blend: a finite-size scaling Monte Carlo study
2001
Using extensive Monte Carlo simulations we study the phase diagram of a symmetric binary (AB) polymer blend confined into a thin film as a function of the film thickness D. The monomer-wall interactions are short ranged and antisymmetric, i.e, the left wall attracts the A-component of the mixture with the same strength as the right wall the B-component, and give rise to a first order wetting transition in a semi-infinite geometry. The phase diagram and the crossover between different critical behaviors is explored. For large film thicknesses we find a first order interface localisation/delocalisation transition and the phase diagram comprises two critical points, which are the finite film w…
Study of the dynamical approach to the interface localization–delocalization transition of the confined Ising model
2004
Confined magnetic Ising films in a L ? D geometry (), with short-range competing magnetic fields?(h) acting at opposite walls along the D-direction, exhibit a slightly rounded localization?delocalization transition of the interface between domains of different orientations that runs parallel to the walls. This transition is the precursor of a wetting transition that occurs in the limit of infinite film thickness () at the critical curve Tw(h). For T Tw(h)) such an interface is bounded (unbounded) to the walls, while right at Tw(h) the interface is freely fluctuating around the centre of the film. Starting from disordered configurations, corresponding to , we quench to the wetting critical t…
Monte Carlo studies ofd= 2 Ising strips with long-range boundary fields
2000
A two-dimensional Ising model with nearest-neighbour ferromagnetic exchange confined in a strip of width L between two parallel boundaries is studied by Monte Carlo simulations. `Free' boundaries are considered with unchanged exchange interactions at the boundary but long-range boundary fields of the form H (n ) = ? h [n -3 - (L - n + 1) -3 ], where n = 1, 2, ... ,L labels the rows across the strip. In the case of competing fields and L , the system exhibits a critical wetting transition of a similar type as in the well studied case of short-range boundary fields. At finite L , this wetting transition is replaced by a (rounded) interface localization-delocalization transition at Tc (h , L )…
Wetting transitions near the bulk critical point: Monte Carlo simulations for the Ising model
1989
Critical, tricritical, and first-order wetting transitions are studied near the bulk critical point of a simple cubic nearest-neighbor Ising model by extensive Monte Carlo simulations. The model applies an exchange J in the bulk and exchange ${J}_{s}$ in the surface planes, where surface fields ${H}_{1}$ also act in addition to a possible bulk field H. Lattices in a thin-film geometry L\ifmmode\times\else\texttimes\fi{}L\ifmmode\times\else\texttimes\fi{}D are used, with two free L\ifmmode\times\else\texttimes\fi{}L surfaces (with L up to 256) and film thickness D up to 160, applying a very fast fully vectorizing multispin coding program. Our results present the first quantitative evidence f…
Suspensions of rod-like colloids and a depleting agent under confinement
2008
We present a computer simulation study of suspensions of rod-like colloids and a depletant in confinement to a slit-pore. Mixtures of hard spherocylinders and ideal spheres were studied by means of Monte Carlo simulations in the grand canonical ensemble. By use of finite size scaling analysis we determined the critical behaviour. In order to overcome large barriers in the free energy we applied the successive umbrella sampling method (Virnau and Muller 2004 J. Chem. Phys. 120 10925). We find that, under confinement, the critical point of gas–liquid demixing shifts to higher concentrations of rods and smaller concentrations of spheres due to the formation of an orientationally ordered surfac…
Character of the Phase Transition in Thin Ising Films with Competing Walls
1995
By extensive Monte Carlo simulations of a lattice gas model we have studied the controversial nature of the gas-liquid transition of a fluid confined between two parallel plates that exert competing surface fields. We find that the transition is shifted to a temperature just below the wetting transition of a semi-infinite fluid but belongs to the two-dimensional Ising universality class. In between this new type of critical point and bulk criticality, a response function ${x}_{\mathrm{nn}}^{max}$ varying exponentially with $D$ is observed, $\frac{2 \mathrm{ln}{\ensuremath{\chi}}_{\mathrm{nn}}^{max}}{D}={\ensuremath{\ell}}^{\ensuremath{-}1}$, where $\ensuremath{\ell}$ is a new length charact…
Study of the confined Ising magnet with long-range competing boundary fields
2005
We present extensive Monte Carlo simulations of the Ising film confined in an L × M geometry () in the presence of long-range competing magnetic fields h(n) = h1/n3(n = 1,2,...,L) which are applied at opposite walls along the M-direction. Due to the fields, an interface between domains of different orientations that runs parallel to the walls forms and can be located close to one of the two surfaces or fluctuate in the centre of the film (localization–delocalization transition). This transition is the precursor of the wetting phase transition that occurs in the limit of infinite film thickness () at the critical curve Tw(h1). For T<Tw(h1) (T≥Tw(h1)) such an interface is bound to (unbound fr…
Rounding of Phase Transitions in Cylindrical Pores
2010
Phase transitions of systems confined in long cylindrical pores (capillary condensation, wetting, crystallization, etc.) are intrinsically not sharply defined but rounded. The finite size of the cross section causes destruction of long range order along the pore axis by spontaneous nucleation of domain walls. This rounding is analyzed for two models (Ising/lattice gas and Asakura-Oosawa model for colloid-polymer mixtures) by Monte Carlo simulations and interpreted by a phenomenological theory. We show that characteristic differences between the behavior of pores of finite length and infinitely long pores occur. In pores of finite length a rounded transition occurs first, from phase coexiste…
Critical Wetting and Interface Localization—Delocalization Transition in a Double Wedge
2004
Using Monte Carlo simulations and finite-size scaling methods we study “wetting” in Ising systems in a L x L x L y pore with quadratic cross section. Antisymmetric surface fields H s act on the free L x L y surfaces of the opposing wedges, and periodic boundary conditions are applied along the y-direction. Our results represent the first simulational observation of fluctuation effects in three dimensional wetting phenomena and corroborate recent predictions on wedge filling. In the limit L → ∞ L y /L 3 = const the system exhibits a new type of phase transition, which is the analog of the “filling transition” that occurs in a single wedge. It is characterized by critical exponents α = 3/4, β…