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R Hołyst

Publications and source records attributed to R Hołyst.

14 recordsLinked to original sources
PubMed2005

Condensation of a vapor bubble in submicrometer container.

Condensation of a spherically symmetric submicrometer size vapor bubble is studied using diffuse interface hydrodynamic model supplemented by the van der Waals equation of state with parameters characteristic for argon. The bubble, surrounded by liquid, is held in a container of constant volume with temperature of the wall kept fixed. The condensation is triggered by a sudden rise of the wall temperature. We find that in the same container and subjected to a similar increase of the wall temperature the condensation process is totally different from the opposite process of droplet evaporation. In particular, the rapid change of the wall temperature excites the wave, which hits the interface and compresses the bubble, leading to a considerable increase of the temperature inside. The condensation of the submicrometer size bubble takes tens of nanoseconds, whereas evaporation of the same size droplet lasts roughly 50 times longer. In contrast to evaporation the condensation process is hardly quasistationary.

Journal Article↗
PubMed2005

Tiling a plane in a dynamical process and its applications to arrays of quantum dots, drums, and heat transfer.

We present a reaction-diffusion system consisting of N components. The evolution of the system leads to the partition of the plane into cells, each occupied by only one component. For large N, the stationary state becomes a periodic array of hexagonal cells. We present a functional of the densities of the components, which decreases monotonically during the evolution and attains its minimal value in the stationary state. This value is equal to the sum of the first Laplacian eigenvalues for all cells. Thus, the resulting partition of the plane is determined by minimization of the sum of the eigenvalues, and not by the minimization of the total perimeter of the cells as in the famous honeycomb problem.

Journal Article↗
PubMed2005

Hidden minima of the gibbs free energy revealed in a phase separation in polymer/surfactant/water mixture.

We observed a very unusual kinetic pathway in a separating C(12)E(6)/PEG/H(2)O ternary mixture. We let the mixture separate above the spinodal temperature (cloud point temperature) for some time and next cool it into a metastable region of a phase diagram, characterized by two minima of the Gibbs potential, one corresponding to the homogeneous mixture and one to the fully separated PEG-rich and C(12)E(6)-rich phases. Despite the fact that in the metastable region the thermodynamic equilibrium corresponds to the separated phases (global minimum of the Gibbs free energy), we observe perfect mixing of the initially separated phase. The homogeneous state, obtained in this way, does not separate, if left undisturbed. However, many cooling-heating cycles or full separation with visible meniscus above the cloud point temperature induce the phase separation in the metastable region. The metastable region can exist tens of degrees below the cloud point temperature. This effect is not observed in the binary mixture of C(12)E(6)/H(2)O.

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PubMed2005

Minimization of the Renyi entropy production in the space-partitioning process.

The spontaneous division of space in Fleming-Viot processes is studied in terms of non-extensive thermodynamics. We analyze a system of n different types of Brownian particles confined in a box. Particles of different types annihilate each other when they come into close contact. Each process of annihilation is accompanied by a simultaneous nucleation of a particle of the same type, so that the number of particles of each component remains constant. The system eventually reaches a stationary state, in which the available space is divided into n separate subregions, each occupied by particles of one type. Within each subregion, the particle density distribution minimizes the Renyi entropy production. We show that the sum of these entropy productions in the stationary state is also minimized, i.e., the resulting boundaries between different components adopt a configuration which minimizes the total entropy production. The evolution of the system leads to decreasing of the total entropy production monotonically in time, irrespective of the initial conditions. In some circumstances, the stationary state is not unique-the entropy production may have several local minima for different configurations. In the case of a rectangular box, the existence and stability of different stationary states are studied as a function of the aspect ratio of the rectangle.

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PubMed2005

Evaporation of a thin liquid film.

Evaporation of a thin (submicrometer size) liquid film confined between two solid substrates is studied using diffuse interface hydrodynamic model supplemented by the van der Waals equation of state. The time and space evolution of the basic thermodynamic quantities such as temperature, density, entropy, chemical potential, and entropy production is presented. The values of numerical parameters chosen correspond to those of argon. The time and space scales studied range from picoseconds to microseconds and from nanometers to micrometers correspondingly.

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PubMed2005

Global symmetry breaking in the nonconserved order parameter system during phase ordering.

We study global symmetry breaking in the 2D system of scalar nonconserved order parameter following a quench to zero temperature. We show that the instant of time when the symmetry is broken and the final morphology is chosen corresponds to the saturation of the order parameter inside the domains. There are three possible final morphologies: the positive and negative order parameter final morphology, and the state of the coexisting positive and negative order parameter subsystems with a flat interface between them. We find also that each type of the final morphology constitutes about 1/3 of all cases, what agrees with the results obtained recently by Spirin et al. [Phys. Rev. E 65, 016119 (2001)]. Our results are pertinent for the two dimensional systems, but we suspect that there is also a way to apply similar arguments for the three dimensional ones.

Computer Simulation↗
PubMed2004

Percolation-to-droplets transition during spinodal decomposition in polymer blends, morphology analysis.

Phase separation kinetics of the off-critical mixture of polystyrene and poly(methylphenylsiloxane) is studied by the time-resolved light scattering and optical microscopy. The results from the light scattering experiments are correlated with the images obtained by the optical microscopic observation in order to find characteristic features of the scattering intensity during the percolation-to-droplets morphology transition. At the beginning of the spinodal decomposition process only a bicontinuous network is present in the system and the light scattering intensity has only one peak. The network coarsens and at the same time small droplets appear in the system resulting in a growth of the scattering intensity at very small wave vectors. When the large network starts to break up into disjoint elongated domains a second peak in the scattering intensity appears. Finally, both peaks merge into a single peak at zero wave vector, indicating a complete transformation of elongated domains into spherical droplets of variable sizes. The comparison of the direct microscopic observations with the light scattering spectra shows that the process of breaking up of the bicontinuous network starts when the growth of the first peak, corresponding to the bicontinuous pattern, becomes very slow (essentially pinned down).

Journal Article↗
PubMed2004

Relaxation processes in mixtures of liquid crystals and polymers near phase boundaries and during phase separation.

We present experimental studies of the relaxation of concentration fluctuations in a semidilute solution of polystyrene (PS) (30% by weight) in 4-cyano-4'-n-octyl-biphenyl (8CB) (70% by weight) using the photon correlation spectroscopy (PCS). In the homogeneous phase there are two modes of relaxation. The slow one (typical time scale is taus = 0.001 s) is due to the diffusion of polymer chains (of molecular mass 65,000) in the LC matrix (of molecular mass 290), while the fast one has the time scale of the order of tauf approximately 0.00001 s. The amplitude of the fast mode is much weaker than the one for the slow mode. Moreover it does not depend on the scattering wave vector, q. The value of the diffusion coefficient, Dc = 1/(tausq2) for the slow mode decreases with temperature according to the Arhenius law until we reach the coexistence curve. Its value close to the coexistence is Dc = 4 x 10(5) nm2/s and the activation energy in the homogeneous mixture is Ec=127 kJ/mol. If we gradually undercool the mixture below the coexistence into the metastable two-phase region without inducing the phase separation we find unexpectedly that Dc does not change with temperature even 4 degrees below the coexistence curve. The characteristic time of the fast mode does not depend on the scattering wave vector indicating that it is related to the transient gel structure. We have shown that it is possible to measure the short time relaxation of concentration fluctuations during the phase separation in the mixture. At low temperature close to the isotropic-nematic phase transition we have observed that the relaxation is well separated in time from the typical time of the domain growth. This relaxation mode is characterized by the large diffusion coefficient D = 2 x 10(8) nm2/s. The mode probably comes from the coupling between the orientational dynamics of liquid crystals and the transient gel structure of polymers.

Journal Article↗
PubMed2003

Polymer domain growth in ordered liquid crystalline matrices.

The growth of polymer domains in the isotropic, nematic, and smectic matrices is studied by the light scattering. In the smectic and isotropic matrices the growth is diffusive, and in the nematic matrix it is influenced by the elastic forces. The scaling is obeyed. A crossover to the wetting fast-mode hydrodynamic regime is also observed at long times. In order to perform these measurements we had to eliminate the multiple scattering of light.

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PubMed2001

Periodic surfaces of simple and complex topology: comparison of scattering patterns.

We compute scattering patterns for six triply periodic minimal surfaces formed in oil/surfactant/water solutions: Three surfaces of a simple topology, Schwarz P (Im3m), Schwarz D-diamond (Pn3m), and Schoen G-gyroid (Ia3d), and three surfaces of a complex topology, SCN1 (Im3m), CD (Pn3m), and GX6 (Ia3d). We show that in the case of the complex structures, scattering intensity is shifted towards the higher hkl peaks. This might cause their misidentification and wrong estimates about the cell size of the structure.

Journal Article↗
PubMed2001

Mechanisms for facilitated target location and the optimal number of molecules in the diffusion search process.

We investigate the number N of molecules needed to perform independent diffusion in order to achieve bonding of a single molecule to a specific site in time t(0). For a certain range of values of t(0), an increase from N to kN molecules (k>1) results in the decrease of search time from t(0) to t(0)/k. In this regime, increasing the number of molecules is an effective way of speeding up the search process. However when N> or =N0 (optimal number of N) the reduction of time from t(0) to t(0)/k can be achieved only by an exponentially large increase in the number of molecules [from N to N exp(ck) for some c>0].

Binding Sites↗
PubMed2001

Scaling of the Euler characteristic, surface area, and curvatures in the phase separating or ordering systems.

We present robust scaling laws for the Euler characteristic and curvatures applicable to any symmetric system undergoing phase separating or ordering kinetics. We apply it to the phase ordering in a system of the nonconserved scalar order parameter and find three scaling regimes. The appearance of the preferred nonzero curvature of an interface separating +/- domains marks the crossover to the late stage regime characterized by the Lifshitz-Cahn-Allen scaling.

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PubMed1999

Diffusion on curved, periodic surfaces.

We present a simulation algorithm for a diffusion on a curved surface given by the equation phi(r)=0. The algorithm is tested against analytical results known for diffusion on a cylinder and a sphere, and applied to the diffusion on the P, D, and G periodic nodal surfaces. It should find application in an interpretation of two-dimensional exchange NMR spectroscopy data of diffusion on biological membranes.

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PubMed1999

Thinning transitions in free-standing liquid-crystal films as the successive formation of dislocation loops.

We describe a model for the layer-thinning transition in free-standing liquid-crystal films based on the successive, spontaneous formation of dislocation loops. As the film temperature increases and the smectic order and layer compressional modulus decrease, the condition for creating a dislocation loop of critical radius is met and a thinning is nucleated. The resulting equation for N, the number of smectic layers, as a function of temperature yields good fitting results to the thinning transitions obtained from several fluorinated compounds.

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