Nucleation In Phase Transitions Research Articles

Investigating nucleation of phase transitions in rod-coil block copolymers

It is known that the nucleation of liquid crystal polymers with orientation interactions can reduce the energy barrier during the polymer crystallization. In this work, we combine the SCFT and string method to explore the nucleation and liquid crystal behavior of rod-coil block copolymers. By examining nucleation transitions from cylinders with different directions to lamellae, we obtain the information of critical nuclei for the first time, including the volume, shape and energy barrier. We further investigate the impacts of orientation interactions along different transition paths. The results show that if the cylinder and lamellae have inconsistent directions, the nucleation will occur with relatively longer transition path and multiple reorientations, and thus leading to higher energy barrier. Nucleation under different Flory-Huggins interactions and nucleation via precursory metastable structures are investigated, and compared with the classical nucleation theory. This work develops the nucleation studies for complex block copolymers with segment orientations, which is helpful for understanding the nucleation of liquid crystal polymers.

A First Glimpse of Nucleation of Phase Transitions in Living Cells

Prion formation and propagation involve the nucleation and growth of protein-based supramolecular assemblies. In this issue of Molecular Cell, Khan etal. (2018) report novel methods that enable quantitative, high-throughput analyses of nucleation of supramolecular assemblies by prion-forming proteins in living cells. Their approaches turn living cells into veritable test tubes for biophysical investigations.

Hypothesis on Phase Transition Nucleation and Propagation in Polycrystalline NiTi shape Memory Alloys under Nanoscale Compressive Loading

There is a need to clarify the phase transition nucleation and propagation phenomena in a polycrystalline NiTi shape memory alloy under extremely small-scale compressive loading. In the present study, the strain-stress indentation curves, temperature rise, phase transition volume, plastic volume and hardness of this smart material during static and dynamic loading are discussed and a hypothesis is proposed for the nucleation and propagation of phase transition volume underneath the stressed spot. According to the indentation curve, jagged loading/unloading stages are the evidences of discrete nucleation and propagation in the phase transformed zone.

Phase Transition at High Heating Rate and Strain Rate During Maraging Steel C250 Grinding

In this study, maraging steel kinetics of both diffusion-controlled and diffusionless phase transitions under thermo-mechanical conditions was predicted using a physics-based model via the investigation of heating rate, stain rate, and contact zone temperature during grinding. It was assumed that high heating rate and high strain rate will affect phase transition. The theory of phase transition nucleation was combined with analysis of heating rate, stain rate, and contact zone temperature to predict phase transition during the grinding. The effects of heating rate and strain rate on phase transition were verified through maraging steel grinding experiments, X-ray diffractometry, and regression analyses. The results of post-grinding phase volume fractions of martensite and ferrite were compared with the results predicted from the neural network model, and models without consideration of heating rate or strain rate. Validation tests proved that the proposed physics-based model successfully predicted the occurrence and extent of phase transition associated with heating rate and strain rate. This physics-based model can be used to reduce phase transition during grinding of maraging steel, or to cause a predefined phase transition by controlling the thermo-mechanical loading.

Magnesium vapor nucleation in phase transitions and condensation under vacuum conditions

Recent findings related to coagulable magnesium vapor nucleation and growth in vacuum were assessed critically, with emphasis on understanding these processes at a fundamental molecular level. The effects of magnesium vapor pressure, condensation temperature, and condensation zone temperature gradient on magnesium vapor nucleation in phase transitions and condensation from atomic collision and coacervation with collision under vacuum conditions were discussed. Magnesium powder and magnesium lump condensates were produced under different conditions and characterized by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). The right condensation zone temperature approach to the liquid transition primarily improved the magnesium vapor concentration rate. The gas–solid phase transition was primarily inhibited by setting a small condenser temperature gradient. Under the right condensation temperature and temperature gradients, increasing magnesium vapor partial pressure improved crystallization and reduced the oxidation rate.

A new methodology for the simulation of solid state phase transition kinetics by combination of nucleation and nuclei growth processes

A new methodology for the simulation of solid state phase transition kinetics has been developed by combining the influence of nucleation rate, nuclei growth rate and the power p characterizing the contact area between the growing particles. The equations used in this methodology were well known, and have been used previously for creating some of the most popular solid-state kinetic equations. The developed methodology made possible calculations of separate rate constants for two processes affecting the rate of phase transition—nucleation (described with K1) and nuclei growth (described with K2). Similar phase transitions were also approximated with the well-known single constant Avrami–Erofeev equation, but we successfully calculated both constants according to the new methodology, which allowed a separate evaluation of these two processes and explained the different induction periods. The effects of empirically adjusted constants on theoretically calculated kinetic curves were thus determined.

Electroweak phase transition nucleation with the MSSM and electromagnetic field creation

Using EW-MSSM field theory, so the EWPT is first order, we derive the equations of motion for the gauge fields. With an isospin ansatz we derive e.o.m. for the electrically charged W fields uncoupled from all other fields. These and the lepton currents serve as the current for the Maxwell-like e.o.m. for the electromagnetic field. The electromagnetic field arising during EWPT bubble nucleation without leptons is found. We then calculate the electron current contribution, which is seen to be quite large. This provides the basis for determinining the magnetic field created by EWPT bubble collisions, which could seed galactic and extra-galactic magnetic fields.

SELF-ORGANIZATION AND NONEQUILIBRIUM AGGREGATION PHENOMENA IN COLLOIDAL MATTER: WHY MICROGRAVITY MATTERS

The relevance of self-organization, nonlinear phenomena and nonequilibrium behavior in a wide range of problems in space science and microgravity research, calls for a concerted approach using the tools of statistical physics, thermodynamics, nonlinear dynamics, mathematical modeling and numerical simulation, in synergy with experimentally oriented work.The reason behind the ubiquity of such concepts is that in many instances of relevance in space science one witnesses an interplay between molecular and macroscopic-level entities and processes, such as nucleation in phase transitions or aggregation and self-assembly in materials science and biology. These phenomena are fundamentally dynamic in nature. We present two minimal models one dealing with issues of complex behavior at the microscopic level and the second referring to the strong nonlinear nature of macroscopic evolution, relevant to soft-condensed matter under observation both on the ground and in microgravity conditions.These investigations open the way to a whole class of unexpected situations whose proper characterization and control can only be expected in the framework of nonequilibrium physics and complexity theory.

Nonlinear kinetic theory and pulse interactions in phase transition

The kinetics of nucleation of phase transition is a phenomenal theory. Some new technologies of preparation of nanomaterials, for example, by shock wave and by electropulsing, are pulse interactions. Based on the known nonlinear theories of phase transition, the nonlinear kinetics of phase transition is discussed, and a soliton-like model is proposed. This mathematical method can not only explain the basic characteristics of pulse interactions and suddenness of phase transition, and possesses a consistency of mechanism for nucleation and growth.

Structure and transformation: Large molecular clusters as models of condensed matter.

This paper reviews investigations of homogeneous nucleation in phase transitions in large molecular clusters. The principal techniques brought to bear are electron diffraction analyses of transformations in clusters formed by condensation of vapor in supersonic expansions and computer simulations of spontaneous phase changes in clusters. Results obtained to date are contrasted with those of larger systems and interpreted in terms of nucleation theory. The review also refers to some unresolved aspects of nucleation theory.

Irreversibility of classical fluctuations studied in analogue electrical circuits

Fluctuations around some average or equilibrium state arise universally in physical systems. Large fluctuations — fluctuations that are much larger than average — occur only rarely but are responsible for many physical processes, such as nucleation in phase transitions, chemical reactions, mutations in DNA sequences, protein transport in cells and failure of electronic devices. They lie at the heart of many discussions1,2,3,4,5 of how the irreversible thermodynamic behaviour of bulk matter relates to the reversible (classical or quantum-mechanical) laws describing the constituent atoms and molecules. Large fluctuations can be described theoretically using hamiltonian6,7 and equivalent path-integral8,9,10,11,12 formulations, but these approaches remain largely untested experimentally, mainly because such fluctuations are rare and also because only recently was an appropriate statistical distribution function formulated11. It was shown recently, however, that experiments on fluctuations using analogue electronic circuits allow the phase-space trajectories of fluctuations in a dynamical system to be observed directly12. Here we show that this approach can be used to identify a fundamental distinction between two types of random motion: fluctuational motion, which takes the system away from a stable state, and relaxational motion back towards this state. We suggest that macroscopic irreversibility is related to temporal asymmetry of these two types of motion, which in turn implies a lack of detailed balance and corresponds to non-differentiability of the generalized nonequilibrium potential in which the motion takes place.

Nucleation Far from Equilibrium

Nucleation in phase transition is a classical problem. Close to the transition point, the critical radius is known to be much larger than the diffusion length. In this paper, we focus on the case far from the critical point, as it is the case in a supercooled liquid, or in the related context of excitable media. We show that the physics of nucleation is different from the classical case. The critical radius is of the order of the diffusion length (in 2-dimensions), and smaller than the diffusion length (in 1-dimension). As a result, diffusion first leads to a decrease in amplitude of the initial seed, before a propagating pulse (or front) is initiated. This results in different laws for the critical radius. The relevance of these effects to stimulation in biological tissues, such as cardiac muscle, is discussed.

Environment and time dependent hardness in zirconia

The microhardness of monoclinic ZrO2 single-crystals was measured in different environments: air, water, and toluene. An indentation creep process at room temperature was observed for the measurements in moist media pointing for a water-activated plastic relaxation mechanism. This effect is discussed employing the models previously proposed to explain similar behaviors in ZrO2 and other nonmetallic materials. A possible correlation with the conditions for the nucleation in phase transitions is proposed.

Late-phase-transition-induced fluctuations in the cosmic neutrino distribution and the formation of structure in the Universe.

We show that late-time (${T}_{c}\ensuremath{\le}1$ eV) cosmic vacuum phase transitions which induce separation of phases and which involve a discontinuity in neutrino properties (e.g., mass) across phase boundaries could give rise to spatial inhomogeneities in the distribution of neutrinos. The nucleation physics of the phase transition would determine the spatial scale of the fluctuations. These density perturbations would be born in the nonlinear regime and could have masses in the range of ${10}^{6}{M}_{\ensuremath{\bigodot}}\ensuremath{-}{10}^{13}{M}_{\ensuremath{\bigodot}}$. If the fluctuations are shells, as expected, and there is gravitational modification of the original phasetransition nucleation scale then the upper limit on their masses could be considerably larger ($\ensuremath{\approx}{10}^{18}{M}_{\ensuremath{\bigodot}}$), possibly encompassing the largest structures in the Universe. The motivation for this work stems, in part, from the possibility that future experiments (i.e., solar neutrino experiments) may suggest new, low-energy-scale weak-interaction phenomena, such as neutrino flavor mixing.

Theory of nucleation of phase transitions

Theory of nucleation of phase transitions

Nucleation in Phase Transitions.

Nucleation in Phase Transitions.