Condensation Phase Transition Research Articles

Condensation phase transitions of symmetric conserved-mass aggregation model on complex networks

We investigate condensation phase transitions of the symmetric conserved-mass aggregation (SCA) model on random networks (RNs) and scale-free networks (SFNs) with degree distribution P(k) approximately k(-gamma). In the SCA model, masses diffuse with unit rate, and unit mass chips off from mass with rate omega. The dynamics conserves total mass density rho. In the steady state, on RNs and SFNs with gamma > 3 for omega is not equal to infinity, we numerically show that the SCA model undergoes the same type of condensation transitions as those on regular lattices. However, the critical line rho(c)(omega) depends on network structures. On SFNs with gamma < or = 3, the fluid phase of exponential mass distribution completely disappears and no phase transitions occurs. Instead, the condensation with exponentially decaying background mass distribution always takes place for any nonzero density. For the existence of the condensed phase for gamma < or = 3 at the zero density limit, we investigate one lamb-lion problem on RNs and SFNs. We numerically show that a lamb survives indefinitely with finite survival probability on RNs and SFNs with gamma > 3, and dies out exponentially on SFNs with gamma< or = 3. The finite lifetime of a lamb on SFNs with gamma < or = 3 ensures the existence of the condensation at the zero density limit on SFNs with gamma < or = 3, at which direct numerical simulations are practically impossible. At omega = infinity, we numerically confirm that complete condensation takes place for any rho > 0 on RNs. Together with the recent study on SFNs, the complete condensation always occurs on both RNs and SFNs in zero range process with constant hopping rate.

Thermodynamics of the Liquid Expanded to Condensed Phase Transition of Poly(l-lactic acid) in Langmuir Monolayers

Surface pressure-area per monomer (pi-A) isotherms show that poly(L-lactic acid) (PLLA) Langmuir monolayers exhibit a liquid expanded-to-condensed (LE/LC) phase transition at low surface pressure. Brewster angle microscopy images show circular domains where the LC phase is surrounded by the LE phase during phase coexistence. Morphology studies via atomic force microscopy show that well-ordered patterns are only observed for Langmuir-Blodgett films prepared in the LC phase, while no ordered features are observed in the LE phase. The morphological differences confirm that during the LE/LC phase transition PLLA molecules form well-ordered structures at the air/water interface. Analysis by the two-dimensional Clausius-Clapeyron equation is used to predict the critical parameters (X(c)). Both critical parameters, the critical temperature (T(c)) and the critical pressure (pi(c)), increase with increasing number average molar mass (M(n)) as X(c) = X(c,infinity) - KM(n)(-1), where X(c,infinity) is the value of the critical parameter at infinite molar mass and K is a constant. For PLLA T(c,infinity) = 36.2 +/- 0.3 degrees C and pi(c,infinity) = 4.53 +/- 0.06 mN x m(-1). This study provides a model polymer system for examining critical behavior in two dimensions.

Kinetic Appearance of First-Order Gas−Liquid Expanded and Liquid Expanded−Liquid Condensed Phase Transitions below the Triple Point

Phase diagram of Gibbs monolayers of mixtures containing n-hexadecyl phosphate (n-HDP) and L-arginine (L-arg) at a molar ratio of 1:2 has been constructed by measuring surface-pressure-time (pi-t) isotherms with film balance and by observing monolayer morphology with Brewster angle microscopy (BAM). This phase diagram shows a triple point for gas (G), liquid expanded (LE), and liquid condensed (LC) phases at around 6.7 degrees C. Above this triple point, a first-order G-LE phase transition occurring at 0 surface pressure is followed by another first-order LE-LC phase transition taking place at a certain higher surface pressure that depends upon temperature. The BAM observation supports these results. Below the triple point, the pi-t measurements show only one first-order phase transition that should be G-LC. All of these findings are in agreement with the general phase diagram of the spread monolayers. However, the BAM observation at a temperature below the triple point shows that the thermodynamically allowed G-LC phase transition is, in fact, a combination of the G-LE and LE-LC phase transitions. The latter two-phase transitions are separated by time and not by the surface pressure, indicating that the G-LC phase transition is kinetically separated into these two-phase transitions. The position of the LE phase below the triple point in the phase diagram is along the phase boundary between the G and LC phases.

Atomic Gases at Negative Kinetic Temperature

We show that thermalization of the motion of atoms at negative temperature is possible in an optical lattice, for conditions that are feasible in current experiments. We present a method for reversibly inverting the temperature of a trapped gas. Moreover, a negative-temperature ensemble can be cooled (reducing |T|) by evaporation of the lowest-energy particles. This enables the attainment of the Bose-Einstein condensation phase transition at negative temperature.

Mixing behavior of 10-(perfluorohexyl)-decanol and DPPC

Fluorocarbon alcohol such as 10-(perfluorohexyl)-decanol are of interest for novel pulmonary drug delivery approaches. The purpose of this study was to investigate the mixing behavior of 10-(perfluorohexyl)-decanol with dipalmitoylphosphatidylcholine (DPPC), the major component of lung surfactant as an aid in assessing usefulness for this and other biomedical applications. The impact of 10-(perfluorohexyl)-decanol on the phase transitions of DPPC bilayers fully hydrated with a 0.15 M sodium chloride solution were studied using differential scanning calorimetry (DSC). No peak corresponding to excess alcohol was observed. The fluorinated alcohol caused DPPC peak broadening, especially below X DPPC < 0.95, and elimination of the pretransition of DPPC at X DPPC ∼ 0.91. The onset of the main phase transition remains constant down to X DPPC ∼ 0.91, suggesting limited miscibility in the gel phase. Hydration of the 10-(perfluorohexyl)-decanol–DPPC mixtures with calcium chloride (2 mM) in place of sodium chloride did not alter the macroscopic phase behavior. In addition to the thermal properties, the miscibility of 10-(perfluorohexyl)-decanol in DPPC in monolayers at the air water interface was investigated on water, sodium chloride (0.15 M), calcium chloride (2 mM) or hydrochloric acid (pH 1.9) subphases. The concentration dependence of the onset pressure of the liquid-expanded to liquid condensed phase transition of DPPC showed a slight change with increasing mole fraction on all four subphases. The surface area-mole fraction diagrams of 10-(perfluorohexyl)-decanol and DPPC on water, sodium chloride and calcium chloride showed near ideal behavior with slight negative deviations at higher surface pressure. A more significant negative deviation was observed for the hydrochloric acid subphase. Overall, both the DSC and the monolayer studies suggest that 10-(perfluorohexyl)-decanol and DPPC are partially miscible in biological mono- and bilayers. The macroscopic phase behavior 10-(perfluorohexyl)-decanol–DPPC system is significantly different from the analogous hydrocarbon system, which is attributed to a less favorable packing of the partially fluorinated hydrophobic tails in the mono- and bilayer.

Confined Water in Mesoporous MCM-41 and Nanoporous AlPO4-5: Structure and Dynamics

Confined water presents unusual properties in comparison with other sorbate species. First of all, the sorption isotherm is of type III, even in the microporous confinement range (O < 20 A). Whatever the pore diameter, water sorption phenomenon looks like the so-called capillary condensation phase transition. Our results clearly valid such an expected behaviour in the mesoporous confinement range (20 A < O < 40 A). The water confined phase is a liquid phase characterized by a short range order and a high translational molecular mobility. The confinement induces a strong displacement towards the low temperature of the water confined liquid solidification Tsol. (for instance, Tsol. = 230 K for D2O confined liquid in MCM-41 (O = 24 A). We have determined the structure of the water confined solid phase observed below Tsol.. It looks like those of the cubic ice structure affected by strong quasi-isotropic finite size effects induced by the confinement. Such a quasi-(1d) solid appears as a polycrystalline column rather than a single crystalline nanofiber. Concerning water confinement in the microporous range (as for example, AlPO4-5 zeolite (O = 7.3 A)), our results are more surprising. Type III sorption isotherm is the signature of a crystallization phenomenon at room temperature (T = 300 K). The confined water crystallizes in two helices that are commensurate with the AlPO4-5 micropore structure. The confined ice has a density of 1.2 g⋅ cm− 3.

Bose–Einstein condensation and chiral phase transition in linear sigma model

With the linear sigma model, we have studied Bose–Einstein condensation and the chiral phase transition in the chiral limit for an interacting pion system. A μ–T phase diagram including these two phenomena is presented. It is found that the phase plane has been divided into three areas: the Bose–Einstein condensation area, the chiral symmetry broken phase area and the chiral symmetry restored phase area. Bose–Einstein condensation can occur either from the chiral symmetry broken phase or from the restored phase. We show that the onset of the chiral phase transition is restricted in the area where there is no Bose–Einstein condensation.

The interaction between DNA and cationic lipid films at the air–water interface

The interaction between DNA and positively charged dioctadecyldimethylammonium bromide (DODAB) and DODAB/disteroylphosphatidylcholine (DSPC) monolayers at the air–aqueous interface was studied by a combination of the surface film balance and Brewster angle microscopy. In presence of DNA, the Π– A isotherm of the cationic monolayer shifts to larger mean molecular areas due to the electrostatic interaction with DNA while the typical liquid expanded–liquid condensed phase transition for DODAB monolayers disappear and the monolayer remains to be in the liquid expanded phase. Furthermore, the morphology of the film dramatically changes, where the large dendritic-like condensed aggregates observed for DODAB monolayers vanish. The charge density of the monolayer was varied by using mixed monolayers with the zwitterionic DSPC and no large effect was observed on the interaction with DNA. By modeling the electrostatic interactions with the linearized Poisson–Boltzmann equation using the finite-element method and taking into account the assumption in the dielectric constants of the system, it was possible to corroborate the expansion of the cationic monolayer upon interaction with DNA as well as the fact that DNA does not seem to penetrate into the monolayer.

Condensation phase transitions in bidisperse colloids

Condensation phase transitions in polydisperse colloids are studied theoretically. For maximal simplification of calculations, a bidisperse model of the system, consisting of relatively big and small particles, is considered. Direct van der Waals interactions between big particles as well as depletion forces between them due to small particles are taken into account. The diagrams of “gas–liquid”, “gas–solid” and “liquid–solid” phase transitions in an ensemble of the big particles are constructed. The influence of size and concentration of small particles on the phase transitions is studied. Our results show that increase in concentration of small particles leads to increase in the initial temperature of the phase transition, i.e., the presence of small particles stimulates the separation of the colloidal system into two phases with different concentration of the big particles. On the other hand, concentration of big particles, needed for the phase transition, increases with the total concentration of small particles. This factor makes realization of this phenomenon more difficult.

Development of a fluid functionalized lipidic matrix applied to direct in situ polynucleotide detection

This work presents a new approach for direct detection of polyelectrolytes at the air–water interface, based on the investigation of the interfacial properties of an active lipidic matrix especially designed for polynucleotide immobilization. A synthetic lipid with a cationic spermine headgroup, DiOctadecylamidoGlycylSpermine (DOGS), was spread at the interface to form a distortable film able to capture polynucleotides. The control of the organization state of this functionalized monolayer upon compression was achieved by recording surface pressure–area ( π– A) isotherm diagrams, presenting a specific shape with a typical liquid expanded–liquid condensed phase transition on a pure water subphase. In the presence of various dsDNA concentrations in the subphase, the isotherms were markedly modified in a time and concentration-dependent manner. The main modifications, corresponding to a large shift towards higher molecular areas and a clear fading of the phase transition, were corroborated by the fine analysis of the monolayer compressibility profile, thus suggesting a characteristic change in the monolayer fluidity as a function of both time and DNA concentration. Moreover, an ATR-Fourier transform infrared (ATR-FTIR) characterization showed evidences for the adsorption of DNA strands onto the lipidic matrix. The direct observation of the mixed monolayer morphology by Brewster angle microscopy (BAM) strongly suggests that DNA adsorption induces a reorganization of lipids at the interface, as evidenced by the change in the condensed lipidic domains morphology in the presence of DNA in the subphase. The immobilization of various polynucleotidic probes of 4000, 400 and 22 base length, confirmed by fluorescence microscopy, had similar effects on DOGS interfacial properties. Preliminary studies are finally presented to explore the possibility of using this system for the study of hybridization between complementary strands. Hence, this study demonstrates this functionalized matrix behaves as a fluid support where polynucleotide immobilization induces interfacial properties modifications, which could be further exploited through the experimental characterization of Faraday instabilities sensitive to visco-elasticity variations.

Condensation phase transitions in ferrofluids

We present the results of theoretical study of a new scenario of condensation phase transitions in ensemble of particles in ferrofluids. In this scenario the phase transition begins with the formation of linear chainlike clusters which collapse into dense globules when a number of particles in the chain exceeds a certain magnitude n c . These globules serve as nuclei of a new dense phase. Final (equilibrium) stage of the phase transition is also considered. Our estimates show that for actual parameters of ferrofluid without magnetic field n c is about 50–90. Calculated magnetic volume concentration of particles in dense phase after separation is about 0.2; initial susceptibility of the dense phase is 70–140. These results are in agreement with known computer and laboratory experiments.

On the Theory of Structural Transformations in Magnetic Fluids

Results of studying a new scenario of condensation phase transition in the ensemble of ferrofluid particles are reported. Phase transition in this ensemble starts with the formation of chain clusters. Chains whose length exceeds a certain critical value dependent on temperature and magnetic field undergo collapse and are transformed into very dense globules. The globule evolution leads to the separation of ferrofluid into two phases with different particle density. Initial (chain collapse) and final (equilibrium) stages of phase transition are investigated. Calculations of the critical length of a chain corresponding to its collapse, as well as the characteristics of dense phase at the final separation stage are in good agreement with the results of known experiments.

Molecular polarizability as a single-parameter predictor of vapour pressures and octanol–air partitioning coefficients of non-polar compounds: a priori approach and results

Abstract We present a one-parameter quantitative structure–property relationship (QSPR) which relates the vapour pressures, PL, and octanol–air partition coefficients, KOA, of a series of chlorinated organic compounds to their molecular polarizabilities. Polarizabilities, dipole moments and quadrupole moments were calculated for the complete set of chlorobenzenes, the mono-, di-, and tri-substituted chloronaphthalenes, the mono-, di-, tri-, and tetra-substituted chlorobiphenyls, and the chloroalkanes with one, two and three carbons using Density Functional Theory methods at the B3LYP/6-311G(d, p) level. Only the molecular polarizability was found to be significantly correlated with log P L and log K OA . The regression coefficients for plots of experimental values of log P L and log K OA as a function of molecular polarizability are approximately 0.98, indicating that non-specific intermolecular forces are dominant in governing the gas–condensed phase transition in these molecules. The predictive ability of the single-parameter QSPR is suggested by near-identical values of the residual sum of squares and PRESS parameters. We suggest that the QSPRs derived here could be used more generally.

Distribution kinetics of Ostwald ripening at large volume fraction and with coalescence

Condensation phase transitions from metastable fluids occur by nucleation with accompanying particle growth and eventual Ostwald ripening. During ripening the subcritical particles dissolve spontaneously while larger particles grow and possibly coalesce if their volume fraction is large enough. The classical diffusion-influenced rates are also affected by large particle concentrations and are here described by mass-dependent rates. We represent the kinetics of ripening through growth, dissolution, and biparticle coalescence by a new population dynamics equation for the particle size distribution (PSD). Numerical solutions of the scaled governing equations show that coalescence plays a major role in influencing the PSD when the scaled mass concentration (volume fraction) or number concentration is relatively large. The solution describes the time range from initial conditions to the final narrowing of polydispersity. We show that the time dependence of the average particle mass in the asymptotic period of ripening has a power-law increase dependent on rate expressions for particle growth and coalescence at large values of volume fraction.

2D Crystal Shapes, Droplet Condensation, and Exponential Slowing Down in Simulations of First-Order Phase Transitions

Multicanonical ensemble simulations for the simulation of first-order phase transitions suffer from exponential slowing down. Monte Carlo autocorrelation times diverge exponentially with free energy barriers ΔF, which in L d boxes grow as L d−1. We exemplify the situation in a study of the 2D Ising-model at temperature T/T c =0.63 for two different lattice manifolds, toroidal lattices, and surfaces of cubes. For both geometries the effect is caused by discontinuous droplet shape transitions between various classical crystal shapes obeying geometrical constraints. We use classical droplet theory and numerical simulations to calculate transition points and barrier heights. On toroidal lattices we determine finite size corrections to the droplet free energy, which are given by a linear combination of Gibbs–Thomson corrections, capillary wave fluctuation corrections, constant terms, and logarithmic terms in the droplet volume. Tolman corrections are absent. In addition, we study the finite size effects on the condensation phase transition, which occurs in infinite systems at the Onsager value of the magnetization. We find that this transition is of discontinuous order also. A combination of classical droplet theory and Gibbs–Thomson corrections yields a fair description for the transition point and for the droplet size discontinuity for large droplets. We also estimate the nucleation barrier that has to be surmounted in the formation of the stable droplet at coexistence.

Spontaneous Bose coherence of excitons and polaritons.

In the past decade, there has been an increasing number of experiments on spontaneous Bose coherence of excitons and polaritons. Four major areas of research are reviewed here: three-dimensional excitons in the bulk semiconductor Cu2O, two-dimensional excitons in coupled quantum wells, Coulomb drag experiments in coupled two-dimensional electron gases, and polaritons in semiconductor microcavities. The unifying theory of all these experiments is the effect of spontaneous symmetry breaking in the Bose-Einstein condensation phase transition.

To the theory of phase transitions in layered ferrofluids

Equilibrium thermodynamical characteristics of ferrosmectics are estimated under the conditions when both magnetic and steric interparticle interactions are taken into account. Deformation and condensation phase transitions in these systems are studied.

Transition from nucleation and growth to Ostwald ripening

Condensation phase transitions from metastable fluids occur by nucleation with accompanying cluster growth and eventual Ostwald ripening. In closed batch systems the supersaturation declines as clusters nucleate and grow, causing an increase in the stable critical nucleus size. During ripening the subcritical clusters are considered to dissolve spontaneously, so that their mass is released to contribute to further growth of remaining clusters. A model based on the dynamics of cluster size distributions (CSDs) represents this sequence of phenomena in terms of four-dimensionless parameters: initial supersaturation, power on the cluster-mass expression for the growth rate coefficient, and parameters for nucleation rate and Gibbs–Thomson effect. A numerical solution of the scaled governing equations for CSD and supersaturation shows the transition from nucleation and growth to ripening, which can occur over a relatively long time period, thus separating the stages. The asymptotic ripening stage shows a power law increase in average cluster mass as the CSD evolves to (minimum) polydispersity index of unity.

A simple model for ordering in adsorbed layers

Order-disorder phase transitions in adsorbed and confined fluids with directional interactions are studied using lattice density functional theory. A new model is developed that is capable of predicting both order-disorder and condensation phase transitions. For systems with weak interactions, the results of this model are compared with both lattice Monte Carlo simulation data and simple isotherm theories that are commonly used to fit experimental data. The results show that these simple isotherms are incapable of duplicating complex behaviour exhibited by anisotropic molecules. When sufficiently strong interactions are present, confined fluids with directional interactions may spontaneously form ordered structures. It is shown that the ordering predicted by this model can result in the assembly of long chains. Such ordering has been observed experimentally in magnetorheological fluids in a magnetic field. It is shown that the orientation of the chains predicted by this model can be controlled by adjusting the molecule-surface interaction. It may be possible to create nanoscale devices that exploit this type of molecular switching.

Effects of condensed-phase transitions in congruently vaporizing systems

When a binary system A xB(1−x) vaporizes congruently, the composition of the equilibrium vapor is such that the atom fractions of the elements entering the vapor are the same as those in the condensed phase. With temperature, the congruently vaporizing composition may vary continuously or may change discontinuously when a condensed-phase transition occurs. Such variations in the congruently vaporizing composition can be detected by monitoring the composition of the vapor phase. Condensed-phase transitions can cause anomalous vaporization behavior such as inverse dependence of vapor pressure on temperature or even increase in vapor pressure at constant temperature, as well as drastic changes in the composition of the vapor with temperature. However, such occurrences might be missed or dismissed as spurious if consideration be given only to data which follow Clausius–Clapeyron straight lines. This paper illustrates these points with results reported in the literature for three binary systems Ga/S, Ga/Se, and Mn/Te. Certain effects associated with phase transitions in these systems are discussed in detail. Other systems in which anomalous effects might occur are discussed in brief. The potential of high-temperature mass spectrometry for the study of such effects is highlighted.