Irreversible phase transitions induced by an oscillatory input

A novel kind of irreversible phase transitions (IPT's) driven by an oscillatory input parameter is studied by means of computer simulations. Second order IPT's showing scale invariance in relevant dynamic critical properties are found to belong to the universality class of directed percolation. In contrast, the absence of universality is observed for first order IPT's.Comment: 18 pages (Revtex); 8 figures (.ps); submitted to Europhysics Letters, December 9th, 199

Phase diagram of polymer blends in confined geometry

Within self-consistent field theory we study the phase behavior of a symmetrical binary AB polymer blend confined into a thin film. The film surfaces interact with the monomers via short range potentials. One surface attracts the A component and the corresponding semi-infinite system exhibits a first order wetting transition. The surface interaction of the opposite surface is varied as to study the crossover from capillary condensation for symmetric surface fields to the interface localization/delocalization transition for antisymmetric surface fields. In the former case the phase diagram has a single critical point close to the bulk critical point. In the latter case the phase diagram exhibits two critical points which correspond to the prewetting critical points of the semi-infinite system. Only below a triple point there is a single two phase coexistence region. The crossover between these qualitatively different limiting behaviors occurs gradually, however, the critical temperature and the critical composition exhibit a non-monotonic dependence on the surface field. The dependence of the phase behavior for antisymmetric boundaries is studied as a function of the film thickness and the strength of the surface interactions. Upon reducing the film thickness or decreasing the strength of the surface interactions we can change the order of the interface localization/delocalization transition from first to second. The role of fluctuations is explored via Monte Carlo simulations of a coarse grained lattice model. Close to the (prewetting) critical points we observe 2D Ising critical behavior. At lower temperatures capillary waves of the AB interface lead to a pronounced dependence of the effective interface potential on the lateral system size.Comment: submitted to the Journal of Molecular Liquids and Condensed Matter Physic

Study of the one-dimensional off-lattice hot-monomer reaction model

Hot monomers are particles having a transient mobility (a ballistic flight) prior to being definitely absorbed on a surface. After arriving at a surface, the excess energy coming from the kinetic energy in the gas phase is dissipated through degrees of freedom parallel to the surface plane. In this paper we study the hot monomer-monomer adsorption-reaction process on a continuum (off-lattice) one-dimensional space by means of Monte Carlo simulations. The system exhibits second-order irreversible phase transition between a reactive and saturated (absorbing) phases which belong to the directed percolation (DP) universality class. This result is interpreted by means of a coarse-grained Langevin description which allows as to extend the DP conjecture to transitions occurring in continuous media.Comment: 13 pages, 5 figures, final version to appear in J. Phys.

A Novel Predictive Tool in Nanoengineering: Straightforward Estimation of Superconformal Filling Efficiency

It is shown that the superconformal filling (SCF) efficiency ($\epsilon_{SCF}$) of nano-scale cavities can be rationalized in terms of relevant physical and geometric parameters. Based on extensive numerical simulations and using the dynamic scaling theory of interface growth, it is concluded that the relevant quantity for the evaluation of $\epsilon_{SCF}$ is the so-called "physical" aspect ratio $S_{P} = L/M^{\beta/\alpha}$, where $\alpha$ ($\beta$) is the roughness (growth) exponent that governs the dynamic evolution of the system and $L$ ($M$) is the typical depth (width) of the cavity. The theoretical predictions are in excellent agreement with recently reported experimental data for the SCF of electrodeposited copper and chemically deposited silver in confined geometries, thus giving the basis of a new tool to manage nanoengineering-related problems not completely resolved so far.Comment: 3 pages, 2 figure

Critical behavior of a non-equilibrium interacting particle system driven by an oscillatory field

First- and second-order temperature driven transitions are studied, in a lattice gas driven by an oscillatory field. The short time dynamics study provides upper and lower bounds for the first-order transition points obtained using standard simulations. The difference between upper and lower bounds is a measure for the strength of the first-order transition and becomes negligible small for densities close to one half. In addition, we give strong evidence on the existence of multicritical points and a critical temperature gap, the latter induced by the anisotropy introduced by the driving field.Comment: 12 pages, 4 figures; to appear in Europhys. Let

Critical Behavior of an Ising System on the Sierpinski Carpet: A Short-Time Dynamics Study

The short-time dynamic evolution of an Ising model embedded in an infinitely ramified fractal structure with noninteger Hausdorff dimension was studied using Monte Carlo simulations. Completely ordered and disordered spin configurations were used as initial states for the dynamic simulations. In both cases, the evolution of the physical observables follows a power-law behavior. Based on this fact, the complete set of critical exponents characteristic of a second-order phase transition was evaluated. Also, the dynamic exponent $\theta$ of the critical initial increase in magnetization, as well as the critical temperature, were computed. The exponent $\theta$ exhibits a weak dependence on the initial (small) magnetization. On the other hand, the dynamic exponent $z$ shows a systematic decrease when the segmentation step is increased, i.e., when the system size becomes larger. Our results suggest that the effective noninteger dimension for the second-order phase transition is noticeably smaller than the Hausdorff dimension. Even when the behavior of the magnetization (in the case of the ordered initial state) and the autocorrelation (in the case of the disordered initial state) with time are very well fitted by power laws, the precision of our simulations allows us to detect the presence of a soft oscillation of the same type in both magnitudes that we attribute to the topological details of the generating cell at any scale.Comment: 10 figures, 4 tables and 14 page