Domain Growth Dynamics Research Articles

Surface-directed spinodal decomposition of fluids confined in a cylindrical pore.

The surface-directed spinodal decomposition of a binary liquid confined inside a cylindrical pore is investigated using molecular dynamics simulations. One component of the liquid wets the pore surface while the other remains neutral. A variety of wetting conditions are studied. For the partial wetting case, after an initial period of phase separation, the domains organize themselves into pluglike structures and the system enters into a metastable state. Therefore, a complete phase separation is never achieved. Analysis of domain growth and the structure factor suggests a one-dimensional growth dynamics for the partial wetting case. As the wetting interaction is increased beyond a critical value, a transition from the pluglike to tubelike domain formation is observed, which corresponds to the full wetting morphology. Thus, a complete phase separation is achieved as the wetting species moves towards the pore surface and forms layers enclosing the nonwetting species residing around the axis of the cylinder. The coarsening dynamics of both the species are studied separately. The wetting species is found to follow a two-dimensional domain growth dynamics with a growth exponent 1/2 in the viscous hydrodynamic regime. This was substantiated by the Porod tail of the structure factor. On the other hand, the domain grows linearly with time for the nonwetting species. This suggests that the nonwetting species behaves akin to a three-dimensional bulk system. An appropriate reasoning is presented to justify the given observations.

Phase separation and ripening in a viscoelastic gel

The process of phase separation in elastic solids and viscous fluids is of fundamental importance to the stability and function of soft materials. We explore the dynamics of phase separation and domain growth in a viscoelastic material such as a polymer gel. Using analytical theory and Monte Carlo simulations, we report a domain growth regime in which the domain size increases algebraically with a ripening exponent [Formula: see text] that depends on the viscoelastic properties of the material. For a prototypical Maxwell material, we obtain [Formula: see text], which is markedly different from the well-known Ostwald ripening process with [Formula: see text]. We generalize our theory to systems with arbitrary power-law relaxation behavior and discuss our findings in the context of the long-term stability of materials as well as recent experimental results on phase separation in cross-linked networks and cytoskeleton.

General theory on the growth kinetics of topological domain structure in hexagonal manganites

Although the dynamics of domain growth has been a long-standing topic in ferroic systems, its science complexity and important guidance to practical applications cannot be overemphasized. Highly anisotropic systems with only domain-wall-type defects and roughly isotropic systems with only vortex-type defects have been extensively studied as two ideal and extreme examples in terms of domain growth dynamics. The domain growth processes in these two types of systems are believed to follow two different scaling laws. The driving forces behind are domain wall motion and vortex–antivortex annihilation, respectively. However, no realistic ferroic systems have ever been found to exhibit a domain growth process that strictly follows these scaling laws. Fortunately, we now have a realistic ferroic system, i.e., the ferroelectric hexagonal manganite family in which the aforementioned two types of defects coexist. This system supports a fascinating topological vortex–antivortex domain structure and is a unique platform for probing a generalized theory on the domain growth dynamics that covers the two extremes. In this work, we investigate this vortex–antivortex domain structure and its growth dynamics within the framework of the Landau theory using phase-field simulations. It is revealed that morphology of this domain structure can be controlled by a correlation length Lc that is different from the conventional correlation length. More importantly, this domain structure can be seen as an intermediate state between the two extremes in terms of domain growth dynamics. When Lc is very small, the domain growth process in this domain structure is driven by domain wall motion and follows the well-known Allen–Cahn scaling law. As Lc increases, vortex–antivortex annihilation will dominate the domain growth process and the scaling law will need a logarithmical correction. The present work provides a comprehensive understanding of the domain growth behavior in such a realistic ferroic system of much attention and represents a substantial extension of domain growth dynamics toward complicated multi-defect systems.

Ferroelectric Domain Reversal Dynamics in LiNbO3 Optical Superlattice Investigated with a Real-Time Monitoring System.

The optical superlattice structure derived from a periodic poling process endows ferroelectric crystals with tunable optical property regulation, which has become one of the most efficient strategies for fabricating high-efficiency optical devices. Achieving a precise superlattice structure has been the main barrier for preparation of specific optical applications due to the unclear dynamics of domain structure regulation. Herein, a real-time monitoring system for the in situ observation of periodic poling of lithium niobate is established to investigate ferroelectric domain reversal dynamics. The formation of reversed domain nuclei, growth, and expansion of the domain are monitored, which is highly related to domain growth dynamics. The nucleation and growth of domain are discussed combined with the monition of domain reversal and the variation of local electric field distribution along with finite element analysis. An electrode configuration with multiholes is proposed to use the local electric field more efficiently and controllably, which could achieve a higher domain nucleus density with high uniformity. Two-mm-thick periodically poled LiNbO3 crystals with high quality are achieved. A nonlinear light conversion from 1064.2 to 3402.4nm is realized by the single-resonance optical parameter oscillator with a nonlinear optical efficiency up to 26.2%.

Late Stage Domain Coarsening Dynamics of Lamellar Block Copolymers

Block copolymer (BCP) phase separation dynamics can be expected to differ significantly from that of the polymer blends due to the constraint of chain connectivity. BCP phase separation dynamics has been studied theoretically, but there has been little experimental evidence to confirm the BCP domain growth scaling laws put forward theoretically. Here, we investigate the dynamics of late-stage lamellar BCP domain coarsening and find that the scaling exponent for lamellar domain growth is ≈1/6 (0.17), irrespective of the annealing temperature, a value close to the scaling exponent of 0.2 predicted by theoretical studies. Furthermore, we show that the prefactors in the domain coarsening equation show Arrhenius dependence on temperature, indicating that the BCP domain growth dynamics is Arrhenius over the temperature range investigated.

An experiment-oriented analysis of 2D spin-glass dynamics: a twelve time-decades scaling study

Recent high precision experimental results on spin-glass films ask for a detailed understanding of the domain-growth dynamics of two-dimensional spin glasses. To achieve this goal, we numerically simulate the out-equilibrium dynamics of the Ising spin glass for a time that spans close to twelve orders of magnitude (from picoseconds to order of a second), in systems large enough to avoid finite-size effects. We find that the time-growth of the size of the glassy domains is excellently described by a single scaling function. A single time-scale controls the dynamics. diverges upon approaching the T = 0 critical point. The divergence of is Arrhenius-like, with a barrier height that depends very mildly on temperature. The growth of this barrier-height is best described by critical dynamics. As a side product we obtain an impressive confirmation of universality of the equilibrium behavior of two-dimensional spin-glasses.

Domain growth dynamics in PMN-PT ferroelectric thin films

Pb(Mg1/3Nb2/3)O3–PbTiO3 (PMN-PT) ferroelectric thin films have been widely used in many areas due to the outstanding piezoelectric and electromechanical properties. Although many studies have been operated on the properties and applications of PMN-PT films, few researches focused on the domain growth dynamics of these materials. In this paper, the domain growth dynamics of PMN-PT thin films were investigated using piezoelectric force microscopy. The shape and the size of the artificial domains were imaged and calculated to depict the relationship between the imposed pulse voltage and the domain behaviors. A linear relationship between the pulse voltage and the domain size could be obtained before the saturation of polarization. Meanwhile, the domain size and the duration show the logarithmic relationship, and such domain growth dynamics were explained according to previous theories.

Domain growth dynamics in (K, Na)NbO 3 ferroelectric thin films

(K,Na)NbO3 (KNN) based lead-free materials have gained great progress and drawn much attention recently, due to their attractive piezoelectric performance and the demand for environmental protection. As is known, domain motion is essential for piezoelectric output; however, there is limited understanding on this topic for KNN. In the present study, the domain growth process of the KNN thin film is studied by piezoresponse force microscopy (PFM). The domain size shows a linear dependence on the pulse voltage and a complex dependence, unlike the commonly accepted logarithmic relationship, on the pulse duration. Meanwhile, a power decay relationship between the domain wall velocity and the domain size is observed. The extremely low dynamical exponent proves that our sample is influenced by extremely strong pinning effects caused by defects, resulting in the uncommon pulse duration dependence of domain size.

Scaling laws of dipolar magnetic systems at finite temperature

We report theoretical and numerical results on scaling laws for systems with multiple time scales in the context of kinetic dynamics of domain growth. The theoretical method has been tested by Monte Carlo simulations of a planar magnetic Heisenberg model with long-range interactions. We show that the characteristic length of the domain growth behaves according to a Lisfshitz-Allen-Cahn law with logarithmic corrections, such that the exponent of the correction depends on the temperature.

Domain Dynamics in Nonequilibrium Random-Field Ising Models

We employ Monte Carlo simulations in order to study dynamics of the magnetization and domain growth processes in the random-field Ising models with uniform and Gaussian random field distributions of varying strengths. Domain sizes are determined directly using the Hoshen-Kopelman algorithm. For either case, both the magnetization and the largest domain growth dynamics are found to follow the power law with generally different exponents, which exponentially decay with the random field strength. Moreover, for relatively small random fields the relaxation is confirmed to comply with different regimes at early and later times. No significant differences were found between the results for the uniform and Gaussian distributions, in accordance with the universality assumption.

Charge gradient microscopy

Significance Polarization charges of ferroelectric materials are screened by an equal amount of surface charges with opposite polarity in ambient condition. Here we show that scraping, collecting, and quantifying the surface screen charges reveals the underlying polarization domain structure at high speed, a technique we call charge gradient microscopy. The scraped charge, measured as a current that scales with scraping rate, induces a charge gradient which leads to the immediate relocation or refill of the screen charges from the vicinity of the probe, making this method a reliable tool to study the complex dynamics of domain nucleation and growth induced by a biased tip in the absence of surface screen charges.

Investigation of the ferroelectric properties and dynamics of nanodomains in LiNbO3 thin films grown on Si (100) substrate by scanning probe microscopy techniques

In this work, scanning probe microscopy (SPM) in the so-called piezoresponse mode (PFM) is used to image the morphology, as-growth domain structure, domain wall motion and piezoelectric loop in lithium niobate thin films. A RF magnetron sputter system was used to deposit LiNbO3 thin films on (100)-oriented Si substrates with SiO2 layer. The surface of the sample shows small grains which diameter ranges from 30nm to 50nm and roughness is less than 8nm. Ferroelectric nanodomains were created in LiNbO3 thin films by applying a voltage to a sharp conducting tip of a PFM. Using the piezoresponse mode of the SPM to detect the out-of-plane and in-plane film polarization, the domain sizes were measured as a function of the applied writing voltage and the pulse time. The dynamics of domain growth is analyzed experimentally taking into account the strong inhomogeneity of the external electric field in the film and the influence of the Si substrate.

Domain growth and aggregation dynamics in photo-induced phase transition phenomena

We have studied domain growth dynamics in photo-induced phase transition phenomena on RbMn[Fe(CN)6] by measuring the time developments of the Raman peaks of the CN stretching modes, which are sensitive to the boundaries between high temperature and low temperature domains. Under the high excitation intensity, we observe abrupt increase and slow decrease of the boundary. This indicates creation of the small domains and subsequent growth process with domain aggregation. Experimental results are explained qualitatively by the mean field theory with the pair valence states of Fe and Mn pairs taking into account of instability of domain boundary.

An Ising-like model for monolayer-monolayer coupling in lipid bilayers

We have proposed the Ising bilayer model to study the domain growth dynamics in lipid bilayers. Interactions within and between layers are adopted from recent experimental and theoretical data. We investigate the effects of the mismatch area on the domain coarsening dynamics in both symmetric and asymmetric lipid bilayers. To explore domain coarsening, we used the Monte Carlo (MC) method with a standard Kawasaki dynamics to simulate the systems. The results show that domains on both layers grow following a power-law and that the domains grow slower when the mismatch areas are increased.

The intriguing ordering and compatibilizing performance of Janus nanoparticles with various shapes and different dividing surface designs in immiscible polymer blends

As a unique type of building blocks for directional self-assembly of superstructures as well as a novel class of stabilizers in polymer alloys, Janus nanoparticles if blended with immiscible homopolymers may not only open a route for fabrication of nanostructured materials with hierarchical order but also provide a means to stabilize immiscible homopolymers through formation of bicontinuous microemulsions. In this paper, by systematically investigating the phase behavior and phase dynamics of ternary systems composed of two immiscible homopolymers and Janus nanoparticles with various shapes and different dividing surface designs, we disclose the consequences and precise mechanism of varying the particle shape and the relevant dividing surface design on the ordering and compatibilizing performance of Janus nanoparticles for nanostructuring immiscible polymers. We demonstrate that a lamellar phase is only formed in systems with anisotropic “standing” Janus nanoparticles. This microphase ordering can go along with the lateral ordering of “standing” particles within lamellar layers and the exhibited in-layer arrangement is dependent on the particle shape. Moreover, the addition of Janus nanoparticles tremendously slows down the phase separation, and the compatibilizing performance is directly related to the total dividing surface area of Janus nanoparticles which is determined by the particle shapes and dividing surface designs. Particularly, the slow exponential domain growth dynamics at the late-time phase separation process follows a crossover scaling form regardless of the particle shapes and dividing surface designs, indicating that the phase separation dynamics of these systems is controlled by the same physical mechanism, that is, the interfacial aggregation of Janus nanoparticles reduces the interfacial tension to virtually zero.

Phase-separation of mixed surfactant monolayers: A comparison of film morphology at the solid–air and liquid–air interfaces

The morphologies of phase-separated monolayer films prepared from two different binary mixtures of perfluorocarbons and hydrocarbons have been examined and compared, for the first time, at the solid–air and liquid–air interfaces. Films were comprised of binary mixtures of arachidic acid (C19H39COOH) with perfluorotetradecanoic acid (C13F27COOH) and of palmitic acid (C15H31COOH) with perfluorooctadecanoic acid (C17F35COOH). For both mixed systems, Langmuir Blodgett films on mica substrates consisted of polygonal domains of one surfactant dispersed in a continuous matrix of the other (arachidic acid in perfluorotetradecanoic acid or perfluorooctadecanoic acid in palmitic acid, respectively), consistent with previous reports. Real-time imaging of the air–water interface via Brewster angle microscopy revealed that comparable film morphology was present at the air–water interface and the solid–air interface over a wide range of surface pressures, and that for the arachidic acid-based mixture, domain growth dynamics at the air–water interface is consistent with that inferred from sequential “static” atomic force microscope images collected at the solid–air interface.

Nanoscale Observation of Time‐Dependent Domain Wall Pinning as the Origin of Polarization Fatigue

AbstractThe microscopic mechanism of polarization fatigue (i.e., a loss of switchable polarization under electrical cycling) remains one of the most important long‐standing problems in ferroelectric communities. Although there are numerous proposed fatigue models, a consensus between the models and experimental results is not reached yet. By using modified‐piezoresponse force microscopy, nanoscale domain switching dynamics are visualized for different fatigue stages in epitaxial PbZr0.4Ti0.6O3 capacitors. Systematic time‐dependent studies of the domain nucleation and evolution reveal that domain wall pinning, rather than nucleation inhibition, is the primary origin of fatigue. In particular, the evolution of domain wall pinning process during electrical cycling, from the suppression of sideways domain growth in early fatigued stages to the blockage of forward domain growth in later stages, is directly observed. The pinning of forward growth results in a nucleation‐limited polarization switching and a significant slowdown of the switching time in the severely fatigued samples. The direct nanoscale observation of domain nucleation and growth dynamics elucidates the importance of evolution of the domain wall pinning process in the fatigue of ferroelectric materials.

Incoherence induced by phonon excitations in domain-growth dynamics: Role of the domain center-of-gravity motion

An ultrafast growth dynamics of a quantum domain after visible or near-infrared photoexcitation is discussed in a one-dimensional system that resides on the first-order phase boundary. Special emphasis is placed on the effects of phonon excitations that are expected to occur in the course of the dynamics. To treat such effects as transparently as possible, we incorporate phonon degrees of freedom into a domain model that consists of two fundamental domain degrees of freedom, namely the spatial extension and the center of gravity. An exact time-evolution calculation within a restricted Hilbert space that almost converges the results indicates that the phonon excitations provide appreciable incoherence to the domain growth especially via overall distributions of the domain center-of-gravity momentum over its nonzero values.

Revealing Local Dynamics of Domain Growth in a Ferroelectric Material by In-Situ STEM-SPM

Extended abstract of a paper presented at Microscopy and Microanalysis 2010 in Portland, Oregon, USA, August 1 – August 5, 2010.

Domain dynamics and fractal growth analysis in thin ferroelectric films

In this article we consider the nonlinear dynamics of domain growth and dynamics under the influence of an external electric field and an intrinsic pinning field due to disorder. The theoretical framework is based on a finite time-difference method as applied to a time-dependent Ginzburg–Landau–Devonshire equation. The domain growth is seen to be of fractal nature, the fractal dimension of which is in good agreement with experiments. When it comes to dynamics we compute the areal velocity of the domain growth as a function of the applied field and find different regions of the nonlinearities that are also in qualitative agreement with experiments.