Search results for "SPINODAL DECOMPOSITION"
showing 10 items of 76 documents
On the nature of phase separation in a commercial aluminium-lithium alloy
1996
Abstract The formation of lithium-rich precipitate particles, known as δ′ phase, is responsible for the particularly desirable mechanical properties which make aluminium-lithium alloys interesting for different industrial applications. The structure and the kinetics of the phase separation process are conveniently studied by small-angle X-ray scattering, though uncertainties remain on the actual shape of the phase diagram of the system, particularly in the region of interest. In this paper are reported small-angle X-ray scattering measurements on a commercial AlLi (8.49% Li atoms) both in the region of formation of the precipitate and during its successive growth. Modelling of the experime…
Coupling between criticality and gelation in "sticky" spheres: a structural analysis.
2018
We combine experiments and simulations to study the link between criticality and gelation in sticky spheres. We employ confocal microscopy to image colloid-polymer mixtures and Monte Carlo simulations of the square-well (SW) potential as a reference model. To this end, we map our experimental samples onto the SW model. We find an excellent structural agreement between experiments and simulations, both for locally favored structures at the single particle level and large-scale fluctuations at criticality. We follow in detail the rapid structural change in the critical fluid when approaching the gas-liquid binodal and highlight the role of critical density fluctuations for this structural cro…
Calculation of miscibility behavior of multinary polymer blends
1996
A method for the calculation of phase diagrams (tie lines and binodal, spinodal, critical points and their stability) based exclusively on the Gibbs energy of mixing, δG, is presented which does not require the calculation of the derivatives with respect to the composition. The method is demonstrated for ternary mixtures of two homopolymers and the corresponding copolymer, and for quaternary and quinternary blends of five polymers exhibiting a closed miscibility gap. The advantages of the presented method become most obvious in the mathematical description of measured phase diagrams, where complex composition dependencies of the interaction parameter are observed.
Liquid/Gas and Liquid/Liquid Phase Behavior of n-Butane/1,4-Polybutadiene versus n-Butane/1,2-Polybutadiene
2005
Solutions of 1,4-polybutadiene (1,4-PB, 98% cis) and of 1,2-polybutadiene (1,2-PB) in n-butane (n-C 4 ) were studied with respect to their vapor pressure and to their demixing into two liquid phases under isochoric conditions within the temperature range from 25 to 75 °C. 1,2-PB mixes homogeneously with n-C 4 at any ratio, in contrast to 1,4-PB, which exhibits a miscibility gap extending from practically pure solvent to approximately 40 wt % polymer. Corresponding to these solubility differences, the vapor pressures for the system n-C 4 /1,4-PB are considerably higher than for n-C 4 /1,2-PB at the same concentration and temperature. The experimental results are modeled accurately and consis…
Monte Carlo Simulations of Alloy Phase Transformations
1994
The use of Monte Carlo simulation methods for study of order-disorder phase transitions in lattice models of alloys is reviewed, with an emphasis on interfacial phenomena and the kinetics of ordering and/or phase separation. Topics discussed include the attempt to predict the phase diagram of Fe-Al alloys from recent measurements of effective interaction parameters, competition between magnetic and crystallographic ordering in such alloys, and the structure of their antiphase domain boundaries. Both an interfacial roughening transition of this domain wall and interfacial enrichment phenomena are predicted. Then simulations of alloy-vacuum surfaces are discussed, and it is shown that both ca…
Superfluid density in metastable 3He4He mixtures
1990
Abstract We havestudied superfluld 3He4He mixtures quenched into nonequilibrium states inside the miscibility gap by means of second sound . From the results for the second sound velocity we conclude that the superfluid density in the metastable state is well described by extrapolation from equilibrium values. The boundary of the metastable region, where nucleation processes set in rapidly, is reflected in a sharp increase of the second sound attenuation.
Simulation of Transport in Partially Miscible Binary Fluids: Combination of Semigrandcanonical Monte Carlo and Molecular Dynamics Methods
2004
Binary Fluids that exhibit a miscibility gap are ubiquitous in nature (glass melts, polymer solutions and blends, mixtures of molten metals, etc.) and exhibit a delicate interplay between static and dynamic properties. This is exemplified for a simple model system, the symmetrical AB Lennard-Jones mixture. It is shown how semigrandcanonical Monte Carlo methods, that include A→B (B→A) identity switches as Monte Carlo moves, can yield the phase diagram, the interfacial tension between coexisting phases, and various pair correlation functions and structure factors. In addition to the build-up of long-ranged concentration correlations near the critical point, unmixing is also accompanied by the…
Spinodal decomposition of polymer solutions: molecular dynamics simulations of the two-dimensional case.
2012
As a generic model system for phase separation in polymer solutions, a coarse-grained model for hexadecane/carbon dioxide mixtures has been studied in two-dimensional geometry. Both the phase diagram in equilibrium (obtained from a finite size scaling analysis of Monte Carlo data) and the kinetics of state changes caused by pressure jumps (studied by large scale molecular dynamics simulations) are presented. The results are compared to previous work where the same model was studied in three-dimensional geometry and under confinement in slit geometry. For deep quenches the characteristic length scale ℓ(t) of the formed domains grows with time t according to a power law close to [Formula: see…
Phase transitions in polymer blends and block copolymer melts: Some recent developments
2005
The classical concepts about unmixing of polymer blends (Flory-Huggins theory) and about mesophase ordering in block copolymers (Leibler's theory) are briefly reviewed and their validity is discussed in the light of recent experiments, computer simulations and other theoretical concepts. It is emphasized that close to the critical point of unmixing non-classical critical exponents of the Ising universality class are observed, in contrast to the classical mean-field exponents implied by the Flory-Huggins theory. The temperature range of this non-mean-field behavior can be understood by Ginzburg criteria. The latter are also useful to discuss the conditions under which the linearized (Cahn-li…
Spinodal Decomposition Kinetics of Colloid-Polymer Mixtures Including Hydrodynamic Interactions
2012
The phase separation dynamics of a model colloid-polymer mixture is studied by taking explicitly the hydrodynamic interactions caused by the solvent into account. Based on the studies on equilibrium phase behavior we perform a volume quench from the homogeneous region of the phase diagram deep into the region where colloid-rich and polymer-rich phases coexist. We demonstrate that the Multiparticle Collision Dynamics (MPCD) algorithm is well suited to study spinodal decomposition and present first results on the domain growth behavior of colloid-polymer mixtures in quasi two-dimensional confinement. On the one hand side we find that the boundary condition of the solvent with respect to the r…