Spinodal Transition Research Articles

Spinodal Decomposition of Filled Polymer Blends: The Role of the Osmotic Effect of Fillers.

The reported work addresses the effect of fillers on the thermodynamic stability and miscibility of compressible polymer blends. We calculate the spinodal transition temperature of a filled polymer blend as a function of the interaction energies between the blend species, as well as the blend composition, filler size, and filler volume fraction. The calculation method relies on the developed thermodynamic theory of filled compressible polymer blends. This theory makes it possible to obtain the excess pressure and chemical potential caused by the presence of fillers. As a main result of the reported work, we demonstrate that the presence of neutral (non-adsorbing) fillers can be used to enhance the stability of a polymer blend that shows low critical solution temperature (LCST) behavior. The obtained results highlight the importance of the osmotic effect of fillers on the miscibility of polymer blends. The demonstrated good agreement with the experiment proves that this effect alone can explain the observed filler-induced change in the LCST.

Optimally-Tailored Spinodal Architected Materials for Multiscale Design and Manufacturing.

Spinodal architected materials with tunable anisotropy unify optimal design and manufacturing of multiscale structures. By locally varying the spinodal class, orientation, and porosity during topology optimization, a large portion of the anisotropic material space is exploited such that material is efficiently placed along principal stress trajectories at the microscale. Additionally, the bicontinuous, nonperiodic, unstructured, and stochastic nature of spinodal architected materials promotes mechanical and biological functions not explicitly considered during optimization (e.g., insensitivity to imperfections, fluid transport conduits). Furthermore, in contrast to laminated composites or periodic, structured architected materials (e.g., lattices), the functional representation of spinodal architected materials leads to multiscale, optimized designs with clear physical interpretation that can be manufactured directly, without special treatment at spinodal transitions. Physical models of the optimized, spinodal-embedded parts are manufactured using a scalable, voxel-based strategy to communicate with a masked stereolithography (m-SLA) 3Dprinter.

Scattering Function and Spinodal Transition of Linear and Nonlinear Block Copolymers Based on a Unified Molecular Model

This work uses a block copolymer architecture [(A′B)nA2]m to unify the scattering function and spinodal transition of typical AB-type block copolymers. The key roles of block number, junction points and asymmetry ratios of block length are (1) to determine the form factor of each block copolymer at the molecular scale; (2) to affect the entropy loss across the spinodal transition and may result in deflection of spinodal curves. The common features are validated in typical linear and nonlinear block copolymers, including AB diblock, asymmetric A′BA triblock, miktoarm stars of ABn, AnBn, (AB)n, (A′B)nA, A′BAm, and multi-graft combs of (BnA2)m and [(A′B)nA2]m. The explicit scattering functions and form factors of various block copolymers can be directly applied in radiation experiments (i.e. neutron or X-ray scattering) to unravel the effect of molecular architecture in solution and microphase separation in disordered melt. The molecular model used in this study is also helpful to guide the chemical synthesis to explore more potentially interesting block copolymers.

Thermal and field-induced transitions in ferroquadrupolar Kondo systems

Recent experiments have examined the impact of a magnetic field on ferroquadrupolar orders in the intermetallic Kondo material PrTi$_2$Al$_{20}$. Motivated by this, we use extensive Monte Carlo simulations to study a diamond lattice XY model of non-Kramers pseudospin-$1/2$ Pr$^{3+}$ moments which crucially incorporates three-spin interactions. This model supports a thermal $Z_3$ Potts ordering transition upon cooling from the paramagnetic phase into the ferroquadrupolar phase. An applied magnetic field along the [110] direction leads to a thermal Ising transition out of the quadrupolar ordered phase. A magnetic field along the [001] direction leads to only thermal crossovers, but supports a spinodal transition out of metastable domains which could be strongly pinned by coupling to elastic lattice deformations. We propose noise measurements as a potential probe to "hear" the spinodal transition. Our work highlights the importance of multispin interactions in Kondo materials near the small-to-large Fermi surface transition.

INFLUENCE OF HEAT TREATMENT AND DEFORMATION ON THE MICROSTRUCTURE AND MECHANICAL PROPERTIES Cu-Ni-Sn ALLOY

This article present about studying on effect heat treatment and strain on mechanical properties of Cu-7Ni-7Sn alloy. This alloy is high elasticity alloy, advance characteristics of this alloy can obtain when associate heat treatment and deformation. The article ejected advance heat treatment and deformation behavior for its. Before processing hardness, strength, the elastic limit of this alloy have a small value. The hardness obtains about 90 – 95HB; the strength obtains about 200MPa; the elastic limit obtain about 100MPa.After heat treatment and deformation, hardness, strength, elastic limit of alloy ascend to multiple; the hardness obtains 294 – 302HB; the strength obtains 1000MPa; the elastic limit obtains 600 – 700MPa. This fact could explain by two mechanisms: deformation mechanism and spinodal transition. Deformation mechanism is to pull small grain lichen, increasing the strength of this alloy. Spinodal decomposition is a mechanism by which a solution of two or more components can separate into distinct regions (or phases) with distinctly different chemical compositions and physical properties. This mechanism differs from classical nucleation in that phase separation due to spinodal decomposition is much more subtle, and occurs uniformly throughout the material not just at discrete nucleation sites. The fineness of spinodal structures is characterized by the distance between regions of identical composition, which is of the order of 50 to 1000 Ao.

The coupled map lattice models of thin liquid film rupture

The dewetting of the spread of thin liquid films over lyophobic solid substrates is studied by means of coupled map lattice models. It is assumed that the dewetting process can be initiated by either nucleation events or a spinodal transition. The growth of the holes is modeled by the local rules describing the evolution of a single lattice cell. Different coupled map lattices based on the von Neumann and Moore neighborhoods as well as on simple and proportional liquid distributions among adjacent cells are applied. The simulation results are discussed in terms of the kinetics of the dewetting process and the mass distribution of droplets formed as the final product of the dewetting. The results show that the presented models produce different patterns formed by growing holes, including mother holes and satellites. The final droplet distribution varies from the regular to the chaotic Voronoi tessellation. The rate of dewetting can be described by means of the superposition of first and second order kinetic equations. The final surface coverage degree only slightly depends on the details of models applied.

Simulations of Cold Electroweak Baryogenesis: quench from portal coupling to new singlet field

We compute the baryon asymmetry generated from Cold Electroweak Baryogenesis, when a dynamical Beyond-the-Standard-Model scalar singlet field triggers the spinodal transition. Using a simple potential for this additional field, we match the speed of the quench to earlier simulations with a “by-hand” mass flip. We find that for the parameter subspace most similar to a by-hand transition, the final baryon asymmetry shows a similar dependence on quench time and is of the same magnitude. For more general parameter choices the Higgs-singlet dynamics can be very complicated, resulting in an enhancement of the final baryon asymmetry. Our results validate and generalise results of simulations in the literature and open up the Cold Electroweak Baryogenesis scenario to further model building.

Mixed-order phase transition in a two-step contagion model with a single infectious seed.

Percolation is known as one of the most robust continuous transitions, because its occupation rule is intrinsically local. As one of the ways to break the robustness, occupation is allowed to more than one species of particles and they occupy cooperatively. This generalized percolation model undergoes a discontinuous transition. Here we investigate an epidemic model with two contagion steps and characterize its phase transition analytically and numerically. We find that even though the order parameter jumps at a transition point r_{c}, then increases continuously, it does not exhibit any critical behavior: the fluctuations of the order parameter do not diverge at r_{c}. However, critical behavior appears in mean outbreak size, which diverges at the transition point in a manner that the ordinary percolation shows. Such a type of phase transition is regarded as a mixed-order phase transition. We also obtain scaling relations of cascade outbreak statistics when the order parameter jumps at r_{c}.

First-order phase transitions in outbreaks of co-infectious diseases and the extended general epidemic process

In co-infections, positive feedback between multiple diseases can accelerate outbreaks. In a recent letter Chen, Ghanbarnejad, Cai, and Grassberger (CGCG) introduced a spatially homogeneous mean-field model system for such co-infections, and studied this system numerically with focus on the possible existence of discontinuous phase transitions. We show that their model coincides in mean-field theory with the homogenous limit of the extended general epidemic process (EGEP). Studying the latter analytically, we argue that the discontinuous transition observed by CGCG is basically a spinodal phase transition and not a first-order transition with phase coexistence. We derive the conditions for this spinodal transition along with predictions for important quantities such as the magnitude of the discontinuity. We also shed light on a true first-order transition with phase coexistence by discussing the EGEP with spatial inhomogeneities.

Adsorbate layering in narrow-pore materials

The conditions of layering of adsorbate molecules in porous systems with characteristic sizes of from 1 to 50–100 nm are discussed. The porous systems contain both very narrow pores, in which interaction potentials of pore walls overlap, and comparatively broad pores without overlapping of surface potentials. Three pore size intervals are distinguished. In the first interval, no adsorbate layering occurs, the second interval is characterized by capillary condensation with critical parameters different from their volume values, and, in the third interval, capillary condensation conditions are almost the same as in the volume adsorbtive phase. Criteria of the characteristic pore sizes of different geometries are formulated; the criteria correspond to small volumes in which first-order phase transitions are absent. The boundary between the first and second pore size regions is observed experimentally as the disappearance/appearance of hysteresis loops in adsorption-desorption isotherms measured under strictly equilibrium conditions as the size of pores decreases/increases. A nonuniform distribution of the surface potential is shown to be responsible for the multiplicity of local regions in porous media with their own vapor-liquid coexisting phases. The spinodal transitions in adsorption-desorption in pores can occur between various local regions. An analysis is performed in terms of the lattice gas model with short-range Lennard-Jones interaction of adsorbate molecules with each other and adsorbent walls.

Small-Angle Neutron Scattering Study of Temperature-Induced Emulsion Gelation: the Role of Sticky Microgel Particles

In this work, small-angle neutron scattering (SANS) is used to probe the structural transformations that accompany temperature-induced gelation of emulsions stabilized by a temperature-responsive polymer. The latter is poly(NIPAM-co-PEGMa) (N-isopropylacrylamide and poly(ethyleneglycol) methacrylate) and contains 86 mol% NIPAM. Turbidity measurements revealed that poly(NIPAM-co-PEGMa) has a lower critical solution temperature (T(LCST)) of 36.5 degrees C in D(2)O. Aqueous polymer solutions were used to prepare perfluorodecalin-in-water emulsions (average droplet size of 6.9 mum). These emulsions formed gels at 50 degrees C. SANS measurements were performed on the poly(NIPAM-co-PEGMa) solutions and emulsions as a function of temperature. The emulsion was also prepared using a D2O/H2O mixture containing 72 vol% D2O in order to make scattering from the droplets negligible (on-contrast). The SANS data were analyzed using a combination of Porod and Ornstein-Zernike form factors. The results showed that the correlation length (xi) of the polymer scaled as xi approximately phi(p)(-0.68) at 32 degrees C, where phi(p) is the polymer volume fraction. The xi value increased for all systems as the temperature increased, which was attributed to a spinodal transition. At temperatures greater than T(LCST), the polymer solution changed to a polymer dispersion of poly(NIPAM-co-PEGMa) aggregates. The aggregates have features that are similar to microgel particles. The average size of these particles was estimated as 160-170 nm. The particles are "sticky" and are gel-forming. The on-contrast experiments performed using the emulsion indicated that the interfacial polymer chains condensed to give a relatively thick polymer layer at the perfluorodecalin-water interface at 50 degrees C. The gelled emulsions appear to consist of perfluorodecalin droplets with an encapsulating layer of collapsed polymer to which sticky microgel particles are adsorbed. The latter act as a "glue" between coated droplets in the emulsion gel.

Studies of Liquid−Vapor Equilibria, Criticality, and Spinodal Transitions in Nanopores by the Gauge Cell Monte Carlo Simulation Method

Liquid−vapor equilibrium, criticality, and spinodal transitions in nanopores are studied by the gauge cell Monte Carlo simulation method proposed recently (Neimark, A. V.; Vishnyakov, A. Phys. Rev. E 2000, 62, 4611). As an instructive example, we consider the capillary condensation of argon in cylindrical pores of different diameters (1.5−5.5 nm) representing typical pore channels in mesoporous molecular sieves. At the subcritical conditions, the gauge cell method allows one to construct continuous phase diagrams in the form of a van der Waals-type sigmoid isotherm. The sigmoid isotherm contains stable and metastable states on the adsorption and desorption branches connected by a backward trajectory of thermodynamically unstable states which cannot be observed experimentally yet can be stabilized in simulations. The phase equilibrium is determined by thermodynamic integration along the sigmoid trajectory using the Maxwell rule. The spinodals give the true limits of stability of vaporlike and liquidlike st...

Exponentially rapid coarsening and buckling in coherently self-stressed thin plates

The nonlinear equations that couple diffusion and stress are solved by computation for one-dimensional spinodal decomposition and coarsening in a thin plate. The vicinity of two critical values of the stress parameter are explored. At small values of elastic self-stresses, coarsening changes to exponentially fast from the exponentially slow dynamics expected for one-dimensions in the absence of stress. Coarsening is by rapid thickening of a single layer of a different phase from each of the two plate surfaces, leading to bending of the plate. Even though the diffusion equation is the same for bulk and thin plate and changes type at the coherent spinodal transition, in a thin plate the changes near this transition are gradual; the difference in behavior is due to the boundary conditions. Furthermore elasto-chemical equilibria through this transition are completely continuous. If the elastic term is large compared to the wetting term, surface wetting layers of phase of lower energy are found to disappear late in the coarsening.

Microphase Separation in Comb Copolymers

Microphase separation in comblike copolymers, in which the backbone is of one monomeric species and the teeth are of another species, is discussed. Within the random phase approximation of Leibler, we calculate the spinodal transition curve (χN) s as a function of composition fraction f of back bone monomers. The comb is assumed to have either evenly spaced grafting points or randomly placed grafting points. The evenly spaced copolymers have teeth symmetrically or asymmetrically placed on the backbone. In the evenly spaced copolymer melt, as the number of teeth (n t ) is increased in the comb, the spinodal curve changes toward a fixed form

Temperature dependence of probe diffusion in gels

We present a dynamic light scattering study of the temperature dependence of the dynamics of probe diffusion in polyacrylamide gels and pregel solutions as a function of crosslink content and scattering angle. Our results show that the spinodal transition in polyacrylamide gels affects the movement of the probe particles. The dynamical behaviour ranges from overdamped vibration of particles controlled by the gel elasticity (relaxational behaviour) at low temperatures to the free diffusion of particles controlled by the sol viscosity at higher temperature. The decay rate of the relaxational mode decreases upon approaching the spinodal temperature, and this decrease is even more pronounced than that of gels without probe particles. Our results suggest that the friction felt by the 50 nm probe particles as they move in the gel appears to diverge at the spinodal temperature, scaling as ≈( T− T s) −1.5. This behaviour is observed over the entire temperature range for probe diffusion in a well gelled sample, whereas in a sample closer to the gel threshold the strong temperature dependence is observed only at low temperatures, the higher temperature behaviour being the same as that in pre-gel solutions. We propose an interpretation of the experimental data in terms of a simple theory of Brownian particles harmonically bound to the gel network.

Correlations and alloy properties: Growth, vacancies, surface segregation

The properties of alloy semiconductors are influenced by the state of order of the materials. Some properties, such as the liquidus and solidus curves, are relative insensitive but others are strongly affected. We first demonstrate which aspects of bonding interaction mechanisms impact the correlation state. We then deduce the effect of the correlation state on liquids and solidus curves, on surface segregation, and on vacancy densities. Surface segregation is a concentration variation of the alloy constituents away from surfaces, and is driven by Schottky vacancy-free energy differences between the constituents in the bulk and on a surface. The segregation profile for alloys equilibrated above a critical spinodal transition temperature exhibits a monatomic variation decaying over a few atomic layers from the surface to the bulk value. However, long-range concentration oscillations are predicted below the critical temperature. These oscillations may account for the long-range order observed in some MBE- and MOCVD-grown alloys (e.g., InPSb). The total free energy of this new ordered phase lies between that of a homogeneous but highly correlated alloy and that of a spinodally decomposed alloy. The phase, if it exists, would be locked into its metastable state by the presence of the surface. Boundary conditions at the interface between the epitaxial layer and the substrate would also affect the results.

Instabilities of the deformation process in cold drawing of poly(ethylene terephthalate) and other polymers

AbstractThe relationship between drawing rate and drawing stress was studied for amorphous poly(ethylene terephthalate) (PET) under various experimental conditions. Three types of expriments were performed: simple drawing with necking at constant rate, drawing through a conical die, and drawing at constant stress. Under constant stress conditions a transition between two stable regimes of drawing can be observed. The transition occurs at a critical stress σc at which the rate of neck propagation changes by some orders of magnitude. Such a transition was found both below and above the glass transition of PET. With constant drawing rates instabilities of neck propagation were observed under certain experimental conditions. Such self‐oscillations, described by other authors, are not due to heat effects as has been proposed, but are related to the existence of the critical stres σc.Stress‐induced transitions in deformation behavior as in PET were observed for polypropylene and nylon 6 but not for polycarbonate. The results obtained by various methods including morphological studies do not support the assumption that the instabilities are caused by thermal effects due to the dissipation of deformation energy. Rather, a model is proposed which is based on the existence of a “spinodal transition” from the isotropic into the highly oriented state.

DECOMPOSITION KINETICS IN Al-6.8 AT % Zn

The decomposition after quench of the binary solid solution A1-6.8 at % Zn has been studied by transmission electron rnieroscopy and neutron small angle scattering. The kinetics of formation of the Guinier-Preston zones has been followed at various aging temperatures inside the miscibility gap. Although the rate of decomposition increases rapidly with the degree of super- saturation no sharp spinodal transition is observed. The results are finally compared with the classical theory and with recent microscopic models.