Average Domain Size Research Articles

Domain growth kinetics in active binary mixtures.

We study motility-induced phase separation in symmetric and asymmetric active binary mixtures. We start with the coarse-grained run-and-tumble bacterial model that provides evolution equations for the density fields ρi(r⃗,t). Next, we study the phase separation dynamics by solving the evolution equations using the Euler discretization technique. We characterize the morphology of domains by calculating the equal-time correlation function C(r, t) and the structure factor S(k, t), both of which show dynamical scaling. The form of the scaling functions depends on the mixture composition and the relative activity of the species, Δ. For k → ∞, S(k, t) follows Porod's law: S(k, t) ∼ k-(d+1) and the average domain size L(t) shows a diffusive growth as L(t) ∼ t1/3 for all mixtures.

In situ study of microstructure evolution and α → ω phase transition in annealed and pre-deformed Zr under hydrostatic loading

The detailed study of the effect of the initial microstructure on its evolution under hydrostatic compression before, during, and after the irreversible α→ω phase transformation and during pressure release in Zr using in situ x-ray diffraction is presented. Two samples were studied: one is plastically pre-deformed Zr with saturated hardness and the other is annealed. Phase transformation α→ω initiates at lower pressure for a pre-deformed sample but for a volume fraction of ω Zr, c>0.7, a larger volume fraction is observed for the annealed sample. This implies that the proportionality between the athermal resistance to the transformation and the yield strength in the continuum phase transformation theory is invalid; an advanced version of the theory is outlined. Phenomenological plasticity theory under hydrostatic loading is outlined in terms of microstructural parameters, and plastic strain is estimated. During transformation, the first rule is suggested, i.e., the average domain size, microstrain, and dislocation density in ω Zr for c<0.8 are functions of the volume fraction, c of ω Zr only, which are independent of the plastic strain tensor prior to transformation and pressure. The microstructure is not inherited during phase transformation. Surprisingly, for the annealed sample, the final dislocation density and the average microstrain after pressure release in the ω phase are larger than for the severely pre-deformed sample. The results suggest that an extended experimental basis is required for the predictive models for the combined pressure-induced phase transformations and microstructure evolutions.

MoS2 synthesis on fluorine-terminated Si substrates prepared by SF6 mixed gas plasma

MoS2 synthesis methods with fewer grain boundaries are expected for device applications. To control the nucleation density and to increase the domain size of MoS2 on a Si substrate, MoS2 was synthesized on a fluorine-terminated Si substrate prepared by SF6 mixed gas plasma. The average domain size of monolayer MoS2 synthesized on a fluorine-terminated Si substrate was several times larger than that on a pristine Si substrate, and grain boundaries were reduced. The MoS2 synthesized on the fluorine-terminated substrate was found to have improved crystallinity based on the results of Raman and photoluminescence spectroscopy. XPS analysis showed that no residual fluoride was observed on the substrate surface after CVD, suggesting that fluorine atoms were volatilized together with Mo by chemical reaction during CVD. Fluorine-terminated surfaces prepared by SF6 mixed gas plasma contribute to increasing the domain size of MoS2, and it can be applied for selective growth in the subsequent CVD synthesis of MoS2.

Advancing piezoelectric properties of barium titanate ceramic through AC + DC field poling over Curie temperature

The significance of increased domain nucleation sites from smaller grain size (GS) of barium titanate (BT) ceramics on piezoelectric properties was analyzed for different types of poling, including conventional DC poling, modified DC poling, and AC plus DC poling, conducted at different poling temperatures. The AC plus DC poling conducted at 1.5 °C above the Curie temperature (T C) showed the highest piezoelectric constant (d 33) of 528 pC/N, with an average domain size of 100 nm observed after poling. The d 33 improvement was attributed to smaller domain size formation from field-induced phase transitions and homogenous distribution of point defects achieved by the AC field. Comparative analysis with larger grain BT ceramics under AC plus DC poling suggests that defects and volume fraction of grain boundaries in BT ceramics could have an effect on domain sizes.

Spatially-resolved in-situ/operando structural study of screen-printed BaTiO3/P(VDF-TrFE) flexible piezoelectric device

The incorporation of lead-free BaTiO3 particles into P(VDF-TrFE) provides a versatile way for tuning dielectric and piezoelectric properties. Screen-printing enables the easy production of flexible capacitors. To prevent particle aggregation, the BaTiO3 particles are functionalized with a surfactant. Initially, 60 % vol. BaTiO3 particles are deposited in the second layer out of three layers. After annealing and cooling, the particle distribution is successfully homogeneous in the whole film. After poling at 80 °C, the relative permittivity and the piezoelectric coefficient d33 significantly increase up to 159 and 8 pC/N respectively. In situ/operando spatially-resolved X-ray techniques allow exploring the structural evolution of the composite device during annealing and during an applied electric field. The application of an electric field leads to the quasi-disappearance of the P(VDF-TrFE) ferroelectric state. As a matter of fact, the interactions between the P(VDF-TrFE) and the surfactant may limit the rotation of P(VDF-TrFE) chains near the particles. Hence, paraelectric polymers could be chosen on a mechanical or economic basis for the matrix in piezoelectric composite devices. Regarding BaTiO3, the lattice strain evolves from an extrinsic strain at RT to an intrinsic strain after annealing and cooling. At the cooled state, the tetragonality c/a is higher than 1.01, leading to improved piezoelectric properties. The increase of the average domain size leads to the increase of the composite permittivity. Finally this knowledge facilitates the development of tailored flexible piezoelectric composite devices.

Interplay of phase segregation and chemical reaction: Crossover and effect on growth laws.

By combining the nonconserved spin-flip dynamics driving ferromagnetic ordering with the conserved Kawasaki-exchange dynamics driving phase segregation, we perform Monte Carlo simulations of the nearest-neighbor Ising model. This kind of mixed dynamics is found in a system consisting of a binary mixture of isomers, simultaneously undergoing a segregation and an interconversion reaction among themselves. Here, we study such a system following a quench from the high-temperature homogeneous phase to a temperature below the demixing transition. We monitor the growth of domains of both the winner; the isomer, which survives as the majority; and the loser, the isomer that perishes. Our results show a strong interplay of the two dynamics at early times, leading to a growth of the average domain size of both the winner and loser as ∼t^{1/7}, slower than a purely phase-segregating system. At later times, eventually the dynamics becomes reaction dominated and the winner exhibits a ∼t^{1/2} growth, expected for a system with purely nonconserved dynamics. On the other hand, the loser at first show a faster growth, albeit, slower than the winner, and then starts to decay before it almost vanishes. Further, we estimate the time τ_{s} marking the crossover from the early-time slow growth to the late-time reaction-dominated faster growth. As a function of the reaction probability p_{r}, we observe a power-law scaling τ_{s}∼p_{r}^{-x}, where x≈1.05, irrespective of the temperature. For a fixed value of p_{r} too, τ_{s} appears to be independent of the temperature.

Evolution Kinetics of Stabilizing Pickering Emulsion by Brush-Modified Janus Particles: DPD Simulation and Experimental Insights.

In the present study, we report the evolution of stabilizing Pickering emulsions using brush-modified Janus particles (JPs), utilizing the dissipative particle dynamics (DPD) simulation technique. Our results are subsequently corroborated with experimental findings. Each JP has one-half of the hydrophobic surface, with the other half embedded with hydrophilic polymer brushes grown via atom transfer radical polymerization (ATRP). Our generic simulation model analyzes the chemical kinetics of polymer brush growth on one-half of the initiator-embedded microparticle (MP) surface, resulting in the formation of JP. This involves evaluating monomer conversion and reaction rates. Our results exhibit a substantial influence of the number of JPs, grafted brush density, and brush length on oil-in-water emulsion stability. We studied the evolution kinetics and stability of emulsion formation by analyzing the growth of average domain size and corresponding scaling functions up to a late time limit. This study aims to clarify the connection between the size, quantity, and functionality of JPs and the stability of Pickering emulsions.

Nonuniversal aging during phase separation with long-range interaction.

Issues concerning the kinetics of phase transitions are not well established for the cases where the order parameter remains conserved with time, particularly when the interatomic interactions are long-range in nature.Here we present results on structure, growth, and aging from Monte Carlo simulations of the two-dimensional long-range Ising model. In our computer simulations, random initial configurations, for 50:50 compositions of up and down spins, mimicking high-temperature equilibrium states, have been quenched to temperatures inside the coexistence curve. Our analyses of the simulation data, for such a protocol, show interesting dependence of the aging exponent, λ, on σ, the parameter, within the Hamiltonian, that controls the range of interaction. These nonuniversal values of λ are compared with a theoretical result for lower bounds. For this purpose, we extracted information on relevant aspects of structural properties during the evolution. To estimate λ, as is necessary, we also calculated the average domain size and analyzed its time dependence to obtain the growth exponent α which also is nonuniversal. The trends in the values of λ and α, as well as an anomaly in structure, suggest that a crossover from the long-range to the short-range variety occurs at σ≃1. The location of this boundary and the nonuniversality provide a picture that is surprisingly different from that of the corresponding static critical phenomena. Furthermore, our results suggest an important scaling law combining α and λ.

3D microstructural and strain evolution during the early stages of tensile deformation

Dislocation patterning and self-organization during plastic deformation are associated with work hardening, but the exact mechanisms remain elusive. This is partly because studies of the structure and local strain during the initial stages of plastic deformation are a challenge. For this reason, literature data typically cover strains from 0.05-0.1 and higher. Here we use Dark Field X-ray Microscopy to generate 3D maps of embedded 350×900×72μm3 volumes within three pure Al single crystals. Tensile deformation was applied to true strains of 0.6%, 1.7%, and 3.5% along the [10 13 −10] direction. Orientation maps revealed the existence of two distinct types of planar dislocation boundaries both at 0.6% and 1.7% but no systematic patterning. At 3.5%, these boundaries have evolved into a well-defined checkerboard pattern, characteristic of Geometrically Necessary Boundaries, GNBs. The crystallographic alignment of the GNBs match that in polycrystals for grains of similar orientation. The GNB spacing measured perpendicular to the planesis ≈6μm and the misorientation ≈0.2°, in fair agreement with literature data for higher strains. By contrast to the sharp boundaries observed at higher strains, the boundaries are associated with a sinusoidal orientation gradient, showing that they are not yet fully formed. Maps of the elastic strain along the (111) direction exhibit strain variations of ±0.0002 with an average domain size of 3μm.

Communication—Texture and Bandgap Tuning of Phase Pure Cu2O Thin Films Grown by a Simple Potentiostatic Electrodeposition Technique

Highly textured phase pure Cu2O thin films have been grown by a simple electrodeposition technique with varying deposition voltages (−0.3 to −1.0 V). The surface morphology characterized by Scanning Electron Microscopy (SEM) revealed that the deposited thin films coherently carpet the underlying substrate and are composed of sharp faceted well-defined grains of 0.5–1.0 μm sizes. XRD analyses showed that all films are composed of polycrystalline cubic Cu2O phase only and have average crystalline domain size in the range of 30–73 nm. The preferred crystalline orientation of phase pure Cu2O films was found to be changing from (200) to (111) with increasing cathodic voltages and showed the highest (111) and (200) crystalline texture coefficient while growing at −1.0 and −0.8 V respectively. The optical bandgap of the as-grown samples was calculated in the range of 1.95–2.20 eV using UV–vis Transmission data. The performance of Cu2O/FTO photocathodes was tested by estimating LED “ON/OFF” modulated surface photovoltage into a photoelectrochemical cell at a zero bias.

Photomodulated phase-separation kinetics in block copolymer melts: a DPD simulation study

ABSTRACT We study phase-separation kinetics of symmetric diblock copolymer (BCP) melt in 3 d subjected to sequential light on/off cycles. The incompatible blocks of each BCP chain are connected by a photosensitive bond, which undergoes breakage during photo-illumination (on-cycle) and recombination during the off-cycle. We set a shorter fixed time limit for each on-cycles and focus on analysing how the much longer duration of the light off-cycles affects the segregation kinetics. We explore two scenarios for each off-cycle time variation: one with equal and another with increasing durations. For both cases, we determine the rate constants for bond formation and degradation reactions and assess their influence on the dynamical scaling functions and the growth scale of evolving morphologies. The average domain size typically exhibits diffusive growth ( R ( t ) ∼ t 1 / 3 ) for a couple of cycles in the beginning. However, the domain growth nearly freezes during the rest of the cycles, resulting in bicontinuous and nearly frozen isotropic morphologies.

Michael Addition Inducing Self-Assembly to Construct Mechanochromic BP Film.

Liquid crystalline blue phase (BP) with 3D cubic nanostructure has attracted much interest in the fields of photonic crystals due to their unique optical properties and the ability to control the flow of light. However, there remains a challenge for simultaneously achieving self-assembly and mechanochromic response of soft 3D cubic nanostructures. Herein, a scalable strategy for the preparation of soft 3D cubic nanostructured films using oligomerization of the Michael addition reaction, which can induce the assembly of double-twisted cylinders for collective replication, remodeling, recombination, and growth, with a phase transition from BPII to BPI, and to chiral nematic phase, is presented. The prepared BP patterns can be obtained by Michael addition oligomerization reaction and composite mask photopolymerization, which present distinct mechanochromic sensitive due to patterns derived from different BP state, and the pattern can be reversibly erased and recurred by mechanical force and temperature. The average domain size of BPII prepared using this strategy can achieve 96µm, which is 2.5 times larger than that obtained using the conventional cooling approach. This work provides new insights into the self-assembly and selective chemochromism of functional materials and devices.

Hierarchical structure growth across different length scales in the two-phase coexistence region of myristic acid Langmuir monolayers: correlation of static and dynamic heterogeneities.

We investigated the hierarchical structure growth of myristic acid monolayers at the air-water interface across different length scales in the two-phase coexistence region of the first order liquid expanded (LE)-liquid condensed (LC) phase transition. A combined study of surface pressure-area (π-A) isotherm measurements with Brewster angle microscopy (BAM) observations was done at different temperatures. At the nanometer scale, the analysis of the π-A isotherm by application of a thermodynamic cluster equation allowed us to obtain the π dependence of cluster size (cluster distribution) in the LE-LC coexistence region. The cluster distributions showed a peak at the midpoint pressure of the transition. At higher temperature the larger nanocluster size was obtained at the transition midpoint. At the micrometer scale, BAM showed that LC domains have characteristic textures depending on the temperature. At low temperature domain density was lower and the average size of circular domains was larger. A large number of circular domains revealed a virtual boojum texture from the initial to the late stage of the transition. At the final stage some circular domains coalesced to form larger circular stripe domains and others coalesced to each other without the formation of stripe domains, finally resulting in a uniform texture over the entire water surface. At high temperature the domain texture was predominantly uniform, and a small number of domains only included straight line defects from the intermediate to the late stage of the transition. All domains coalesced to each other without the development of any texture including the stripe, different from the case at low temperature. The phase boundary line tension is highly likely to play a key role for understanding the hierarchical growth and coarsening (coalescence) process in the LE-LC transition between the different length scales from the nanometer to the micrometer scale consistently together.

High‐Quality van der Waals Epitaxial CsPbBr3 Film Grown on Monolayer Graphene Covered TiO2 for High‐Performance Solar Cells

Two‐dimensional materials have been widely used to tune the growth and energy‐level alignment of perovskites. However, their incomplete passivation and chaotic usage amounts are not conducive to the preparation of high‐quality perovskite films. Herein, we succeeded in obtaining higher‐quality CsPbBr3 films by introducing large‐area monolayer graphene as a stable physical overlay on top of TiO2 substrates. Benefiting from the inert and atomic smooth graphene surface, the CsPbBr3 film grown on top by the van der Waal epitaxy has higher crystallinity, improved (100) orientation, and an average domain size of up to 1.22 μm. Meanwhile, a strong downward band bending is observed at the graphene/perovskite interface, improving the electron extraction to the electron transport layers (ETL). As a result, perovskite film grown on graphene has lower photoluminescence (PL) intensity, shorter carrier lifetime, and fewer defects. Finally, a photovoltaic device based on epitaxy CsPbBr3 film is fabricated, exhibiting power conversion efficiency (PCE) of up to 10.64% and stability over 2000 h in the air.

On the role of methyl groups in the molecular architectures of mesophase pitches

The role of methyl groups on the liquid–crystal structure of mesophase pitches was investigated by combining experimental characterizations and atomic-scale computational modeling, using three pitches synthesized from different precursors. Of the three pitches, C-9 alkyl benzene and naphthalene-based pitches have 13 and 7 methyl groups per average polyaromatic hydrocarbon, respectively. By contrast, mesophase produced from a coal-tar pitch has about one methyl group. The coal tar–based mesophase pitch is hydrogen deficient or more aromatic compared with C-9 alkyl benzene- and naphthalene-based pitches. Additionally, X-ray diffraction data showed that average coherent domain sizes of C-9 alkyl benzene (3.7 nm) and naphthalene-based (3.6 nm) pitches with more methyl groups are larger than that of coal tar–based mesophase (2.4 nm). Based on the identified features, the influence of the methyl group on the layering structures was investigated via molecular dynamics simulations. The results revealed that methyl groups are critical in mesophase layering in C-9 alkyl benzene- and naphthalene-based pitches, by reducing CH-π interaction. However, similar alignment could be achieved without the same degree of methyl substitutions for the coal tar-based pitch because of stronger π-π interaction than the other precursors. The insights from this study contribute to our understanding of the formation of conventional mesophase pitch and have implications for the processing of coal-derived materials. This knowledge is vital to produce valuable products like carbon fiber and graphite from pitches.

Domain statistics in the relaxation of the one-dimensional Ising model with strong long-range interactions

After a zero temperature quench, we study the kinetics of the one-dimensional Ising model with long-range interactions between spins at distance r decaying as r−α, with α≤1. As shown in our recent study (Corberi et al., 2021) that only a fraction of the non-equilibrium trajectories is characterised by the presence of coarsening domains while in the remaining ones the system is quickly driven towards a magnetised state. Restricting to realisations displaying coarsening we compute numerically the probability distribution of the size of the domains and find that it exhibits a scaling behaviour with an unusual α-dependent power-law decay. This peculiar behaviour is also related to the divergence of the average size of domains with system size at finite times. Such a scenario differs from the one observed when α>1, where the distribution decays exponentially. Finally, based on numerical results and on analytical calculations we argue that the average domain size grows asymptotically linearly in time.

Mechanical and morphological properties of PP/XNBR blends produced with rubber latex

In this work, polypropylene (PP)/carboxylated acrylonitrile butadiene rubber (XNBR) binary blends were prepared with the elastomer component dosed in its suspension (latex) form into the polymer matrix during melt compounding. For this purpose, samples containing 0-20 wt.% rubber were prepared using two different PP grades as matrices with lower and higher viscosity. Analogous reference samples with the same composition were also fabricated using traditional melt mixing by introducing the rubber in its dry, bulk form in order to analyze the efficiency of the latex route. Mechanical, thermomechanical and morphological analyses were used to investigate the structure-property relationships of the blends. Based on the SEM images the average domain size of the dispersed XNBR domains became markedly smaller when the rubber was introduced in its suspension form into the PP. Based on the Charpy impact tests and the tensile test results, the decreased rubber domain size led to improved ductility and toughness. The improvement was more prominent when the difference between the viscosity of the PP matrix and the XNBR rubber was higher.

On Water Growth of Continuous Thin Films of Two‐Dimensional Covalent Organic Frameworks with Large Single‐Crystal Domains

Comprehensive SummaryA core feature of two‐dimensional covalent organic frameworks is crystallinity, but it remains challenging to gain their thin films with high crystallinity. Here, we presented growth of thin films of two‐dimensional covalent organic frameworks with an average domain size of ~2.83 μm2 and maximum domain size of up to ~26.19 μm2 using amphiphilic glycine derivatives on water surface. We envisage that this work will inspire the growth of a wide variety of organic two‐dimensional materials with high crystallinity and boost their structure property investigations.

Melting domain size and recrystallization dynamics of ice revealed by time-resolved x-ray scattering

The phase transition between water and ice is ubiquitous and one of the most important phenomena in nature. Here, we performed time-resolved x-ray scattering experiments capturing the melting and recrystallization dynamics of ice. The ultrafast heating of ice I is induced by an IR laser pulse and probed with an intense x-ray pulse which provided us with direct structural information on different length scales. From the wide-angle x-ray scattering (WAXS) patterns, the molten fraction, as well as the corresponding temperature at each delay, were determined. The small-angle x-ray scattering (SAXS) patterns, together with the information extracted from the WAXS analysis, provided the time-dependent change of the size and the number of liquid domains. The results show partial melting (~13%) and superheating of ice occurring at around 20 ns. After 100 ns, the average size of the liquid domains grows from about 2.5 nm to 4.5 nm by the coalescence of approximately six adjacent domains. Subsequently, we capture the recrystallization of the liquid domains, which occurs on microsecond timescales due to the cooling by heat dissipation and results to a decrease of the average liquid domain size.

Large-Scale Formation of DNA Origami Lattices on Silicon

In recent years, hierarchical nanostructures have found applications in fields like diagnostics, medicine, nano-optics, and nanoelectronics, especially in challenging applications like the creation of metasurfaces with unique optical properties. One of the promising materials to fabricate such nanostructures has been DNA due to its robust self-assembly properties and plethora of different functionalization schemes. Here, we demonstrate the assembly of a two-dimensional fishnet-type lattice on a silicon substrate using cross-shaped DNA origami as the building block, i.e., tile. The effects of different environmental and structural factors are investigated under liquid atomic force microscopy (AFM) to optimize the lattice assembly. Furthermore, the arm-to-arm binding affinity of the tiles is analyzed, revealing preferential orientations. From the liquid AFM results, we develop a methodology to produce closely-spaced DNA origami lattices on silicon substrate, which allows further nanofabrication process steps, such as metallization. This formed polycrystalline lattice has high surface coverage and is extendable to the wafer scale with an average domain size of about a micrometer. Further studies are needed to increase the domain size toward a single-crystalline large-scale lattice.