Interfacial Energy Difference Research Articles

Selection and mechanical evaluation of γ/γ boundary in γ-TiAl alloy

Simulation of lamellar boundary (γ/γ) selection during the transformation of α2’→α2+γ in γ-TiAl alloy has been investigated using an improved 3D Phase Field (PF) model, and the mechanical properties of γ/γ boundaries are evaluated by Molecular Dynamics (MD) simulation. The effects of elastic strain energy and interfacial energy difference among different types of γ/γ interfaces on the occurrence frequencies of the three types of γ/γ boundaries (i.e., true twin (TT), pseudo-twin (PT) and ordered domain (OD)) have been studied. It is found that the boundary fraction of TT increases with increasing elastic strain energy or increasing interfacial energy difference among γ/γ interfaces. Besides TT, the elastic interaction also favors OD while PT is suppressed. The relative fractions of PT and OD could be effectively controlled by elastic strain energy. Furthermore, the frequency of PT or OD can also be adjusted by their interface energy ratio. The simulation results well explain the phenomenon that boundary frequencies via experimental statistics deviate from those under random distribution without interface selection. It can also be found that one-twin-dominant zones (OTDZ) can be induced by higher elastic strain energy and larger interface energy difference among different γ/γ boundaries through the merging of adjacent small clusters with the same γ/γ boundary type under the premise of correlated and sympathetic nucleation. Through MD simulation, it is found that the strengths of the configurations with true twin boundary (TTB) and ordered domain boundary (ODB) are almost the same, while the strength of that with pseudo-twin boundary (PTB) is relatively low. The order of plasticity of the configurations with three types of γ/γ interfaces is ODB > TTB > PTB.

Facet-Dependent in Situ Growth of Nanoparticles in Epitaxial Thin Films: The Role of Interfacial Energy.

Nucleation of nanoparticles using the exsolution phenomenon is a promising pathway to design durable and active materials for catalysis and renewable energy. Here, we focus on the impact of surface orientation of the host lattice on the nucleation dynamics to resolve questions with regards to "preferential nucleation sites". For this, we carried out a systematic model study on three differently oriented perovskite thin films. Remarkably, in contrast to the previous bulk powder-based study suggesting that the (110)-surface is a preferred plane for exsolution, we identify that other planes such as (001)- and (111)-facets also reveal vigorous exsolution. Moreover, particle size and surface coverage vary significantly depending on the surface orientation. Exsolution of (111)-oriented film produces the largest number of particles, the smallest particle size, the deepest embedment, and the smallest and most uniform interparticle distance among the oriented films. Based on classic nucleation theory, we elucidate that the differences in interfacial energies as a function of substrate orientation play a crucial role in controlling the distinct morphology and nucleation behavior of exsolved nanoparticles. Our finding suggests new design principles for tunable solid-state catalyst or nanoscale metal decoration.

Phenomenological Theory of First-Order Prefreezing.

Prefreezing is the prewetting of the crystalline phase at the interface of a melt to a solid substrate via a first-order phase transition. We present a phenomenological theory of prefreezing and analyze thermodynamic properties of the prefrozen crystalline layer. The theory enables a clear thermodynamic explanation of the abrupt formation of a mesoscopically thick crystalline layer during cooling and defines the corresponding transition temperature as a function of the interfacial free energies. It is shown that the interfacial energy difference γsm - ( γsc + γcm) acts as a driving force for prefreezing. The analytical results are congruent with recent experimental outcomes for poly(ε-caprolactone) crystallized on graphite via prefreezing. The calculated interfacial free energies take reasonable values being close to the experimental estimates.

Toward fast charge extraction in all-inorganic CsPbBr3 perovskite solar cells by setting intermediate energy levels

Perovskite-structured cesium lead bromide (CsPbBr3) halide is a rising light harvester for perovskite solar cell applications due to its high absorption coefficient and stability upon heat and humidity attacks. However, the serious electron-hole recombination arising from large interfacial energy differences has markedly limited charge extraction for enhanced photovoltaic performances. Herein, we systematically study fast charge extraction at TiO2/CsPbBr3 and CsPbBr3/carbon interfaces by setting intermediate energy levels with carbon quantum dots and red phosphorus quantum dots, respectively. The interfacial radiative or trap-dominant recombination can be significantly suppressed owing to the boosted charge transfer ability as well as the passivation effect by incorporating the carbon quantum dots and red phosphorus quantum dots into solar cells. Finally, the optimal perovskite solar cell device achieves a maximized power conversion efficiency of 8.20% under one sun illumination in comparison with 6.37% for quantum dots-free solar cell. Moreover, the efficiency is reduced by only 3% upon persistent attack with 80% relative humidity over 1000 h, suggesting a good environmental tolerance to boost the commercialization.

Alloy-Controlled Work Function for Enhanced Charge Extraction in All-Inorganic CsPbBr3 Perovskite Solar Cells.

All-inorganic CsPbX3 (X=I, Br) perovskite solar cells are regarded as cost-effective and stable alternatives for next-generation photovoltaics. However, sluggish charge extraction at CsPbX3 /charge-transporting material interfaces, which arises from large interfacial energy differences, have markedly limited the further enhancement of solar cell performance. In this work, the work function (WF) of the back electrode is tuned by doping alloyed PtNi nanowires in carbon ink to promote hole extraction from CsPbBr3 halides, while an intermediate energy by setting carbon quantum dots (CQDs) at TiO2 /CsPbBr3 interface bridges electron transportation. The preliminary results demonstrate that the matching WFs and intermediate energy level markedly reduce charge recombination. A power conversion efficiency of 7.17 % is achieved for the WF-tuned all-inorganic perovskite solar cell, in comparison with 6.10 % for the pristine device, and this is further increased to 7.86 % by simultaneously modifying with CQDs. The high efficiency and improved stability make WF-controlled all-inorganic perovskite solar cells promising to develop advanced photovoltaic platforms.

Effect of an ionic liquid/air Interface on the structure and dynamics of amphiphilic peptides

Ionic liquids (ILs) are well known to have significant impacts on the structure and dynamics of proteins and enzymes; however, there is still much to be done to understand the molecular scale mechanisms of these processes. Using classical molecular dynamics (MD) and metadynamics simulations, we have studied how multiple IL solutions change the structure and behavior of two short, model, leucine-lysine (LK) peptides at a vacuum/solvent interface. These peptides - LKα14 and LKβ15 - have been researched extensively through both experiments and simulations in pure water, but have not yet been examined when exposed to ILs. In our study, we found that the two 50% 1-butyl-3-methylimidazolium ([BMIM])-based solutions we tested had a substantial effect on both the interfacial adsorption affinity and secondary structure of our peptides when compared to water. Metadynamics simulations revealed a nearly 40kJ/mol difference in interfacial adsorption free energy for the same peptide when solvated in water versus in IL solution. Additionally, we saw IL solutions prevent LKβ15 from forming extended β-sheet structures that were found to form at the vacuum/water interface. In place of these β-sheet structures, we observed the formation of a structure similar to a left-handed helix for lone LKβ15 peptides at the interface. The presence of IL also had a subtle effect on LKα14's strong α-helical character, reducing it for peptides at the interface and increasing it for peptides in bulk solution. This work provides several new testable hypotheses about IL action on biomolecular structure that can be studied in detail using experimental surface-specific analysis techniques such as sum frequency generation (SFG) spectroscopy.

Interfacial Tension; a Stabilizing Factor for Janus Emulsions of Silicone Bixa Orellana Oils

AbstractThe destabilization process was investigated for a Janus emulsion of silicone and Bixa Orellana oils stabilized by polyoxyethylene sorbitan monooleate (Tw 80) and carboxymethyl cellulose. The emulsion stabilized with Tw 80 showed significant and fast creaming, a process that was prevented by the addition of the polymer. During the extensive coalescence of the emulsions stabilized by Tw 80, the Janus topology was retained for months of storage until, finally, separation of the oils occurred. This result strongly indicates an unexpected stabilizing action of the i nterfacial free energy. This conclusion was supported by a calculation for a realistic model system of the interfacial energy difference between two cases of coalescence. In the first case, the two coalescing Janus drops united into a larger Janus drop, while in the second case two drops formed, each with only one oil. The first case gave a spontaneous reaction (reduced interfacial energy), while the second one meant an increase of energy, i.e. it cannot happen without adding energy. The authors are aware that this stabilization is a new phenomenon in emulsion science with potential ramifications in future emulsion technology. However, it is essential to realize that the stabilization is of temporary occurrence in the destabilization process, and the free energy to give a final emulsion state with separated oils is overwhelmingly dominant. In short, Janus emulsions will, in the end, separate into layers of the liquids, like all emulsions.

Ice–Water Interfacial Free Energy for the TIP4P, TIP4P/2005, TIP4P/Ice, and mW Models As Obtained from the Mold Integration Technique

The freezing of water is greatly influenced by the ice–water interfacial free energy. Yet, no consistent experimental measures of this thermodynamic parameter can be found. In this work we provide estimates for the ice Ih–water interfacial free energy at the normal melting temperature for different crystal planes (basal, primary prismatic, and secondary prismatic) using some widely used water models: TIP4P, TIP4P/2005, TIP4P/Ice, and mW. To compute the interfacial free energy, we use the mold integration method. It consists in calculating the work needed to induce the formation of a crystal slab in the fluid at coexistence conditions with the aid of a mold of potential energy wells whose structure is that of the crystal plane under study. The basal plane has the lowest interfacial free energy in all models of the TIP4P family. For the mW model we could not resolve differences in interfacial free energy between different orientations. The interfacial free energies averaged over all crystal orientations we ...

Interface energetics in zinc phthalocyanine growth on Ag(100)

The nucleation and growth of zinc phthalocyanine (ZnPc) thin films on a Ag(100) surface are studied employing in situ, real-time low-energy electron microscopy and complementary density functional theory (DFT) calculation to elucidate the role of incorporation kinetics of planar molecules in phase selection during nucleation and apply this knowledge to the fabrication of highly crystalline ZnPc films. We show that the nucleation of crystalline ZnPc islands requires a large concentration of diffusing molecules. The required amount of nominal deposition to initiate the growth of monolayer (ML) high two-dimensional crystalline islands is dependent on both growth temperature and crystalline phase. At room temperature (RT) and slightly above (RT to \ensuremath{\sim}430 K), ZnPc crystalline islands have double-domain $R33.69$ structures with average domain sizes in the submicrometer range. At higher temperatures, a 5 \ifmmode\times\else\texttimes\fi{} 5 commensurate ZnPc structure nucleates. DFT calculations reveal significant differences in interfacial energies of an isolated ZnPc molecule on a substrate, depending on an adsorption site and azimuthal orientation of the molecule relative to the substrate atomic lattice. The observed delay in the onset of the nucleation of an island is caused by the existence of a large energy barrier for molecule incorporation into an island. At certain growth conditions it is possible to induce a structural transition from the 5 \ifmmode\times\else\texttimes\fi{} 5 to the $R33.69$ phase when the nominal coverage reaches 1 ML. The resulting film has excellent crystallinity with individual domains of hundreds of micrometers in size.

Structural Determinants of Raft Partitioning for Single-Pass Transmembrane Proteins

Transmembrane proteins (TMPs) comprise ∼30% of the mammalian proteome and mediate nearly all functions of the cell. The subcellular localization, trafficking, signalling, and enzymatic activity of many TMPs is regulated by their association with lipid-driven lateral membrane domains known as lipid rafts. However, the structural determinants of TMP partitioning to raft domains remain almost unknown. We hypothesized that structural features of the transmembrane domain (TMD) of single-pass TMPs would guide raft partitioning and raft-dependent sub-cellular trafficking. To explore TMD-dependent raft partitioning, we isolated plasma membranes as Giant Plasma Membrane Vesicles (GPMVs), a model system that allows direct observation of protein partitioning between raft/non-raft phases by fluorescence microscopy. We generated 96 different fluorescent mutants of a model TMP and quantified their partitioning as a function of TMD features, namely hydrophobic length and accessible surface area. Raft partitioning was related to TMD length, with longer TMDs imparting greater raft association, confirming previously untested predictions. Investigation of 74 mutants with constant TMD length revealed that raft partitioning was also inversely related to the TMD accessible surface area, with larger surface areas preferring the non-raft phase. To explain these results, we present a simple physical model wherein raft partitioning is driven by differences in interfacial energy between the TMD and its surrounding lipid matrix in raft and non-raft phases. This model is in quantitative agreement with experimental observations and provides first predictions of protein-lipid surface tensions differences between coexisting membrane phases. The model could successfully connect predicted raft partitioning with subcellular localization of single-pass TMPs in Eukaryota. These results point the way to a general rule for raft partitioning of TMPs and underline the central role of membrane domains in cellular traffic.

The Biophysics of Living Membranes: Protein Partitioning and Functional Differentiation in Ordered Plasma Membrane Domains

The lipid raft hypothesis posits that ordered, lateral membrane domains are important for the regulation of plasma membrane (PM) structure and function in eukaryotes. Giant Plasma Membrane Vesicles (GPMVs) are isolated plasma membranes that microscopically separate into coexisting ordered and disordered phases, facilitating experimental analysis of the composition and physical properties of ordered raft domains in biological membranes. In these studies, we analyze the biophysical and lipidomic differentiation of the plasma membrane in Mesenchymal Stem Cells (MSC) as the cells undergo differentiation into adipocytes and osteoblasts. During differentiation, dramatic remodeling the PM lipidome, including lipid acyl chain length and unsaturation, results inchanges to membrane order and phase separation. These observations elucidate the compositional determinants of biophysical properties in biological membranes, as well as identify lineage-specific PM features. These results facilitate rational remodeling of membrane phenotypes to direct differentiation, as supplementation with ꙍ-3 docosahexaneoic acid (DHA) promoted the osteoblastic PM phenotype and potentiated osteogenic differentiation. The differences in the physical properties of the coexisting domains lead to preferential protein partitioning between them. We evaluate the structural determinants of raft partitioning of a model transmembrane protein, and find that raft phase partitioning is related to features of the protein's transmembrane domain (TMD), namely the hydrophobic length and surface area of the TMD. Longer TMDs impart greater raft association while TMDs with larger, bulkier amino acid side chains prefer the non-raft phase. We present a simple physical model wherein raft partitioning is driven by phase-dependent differences in interfacial energy between the TMD and its surrounding lipid matrix, and find excellent quantitative agreement with observations that provide the first predictions of protein-lipid surface tension. These results point the way to a general rule for raft partitioning of transmembrane proteins.

Mapping Substrate Surface Field Propagation in Block Polymer Thin Films

We isolated the key substrate–polymer interactions responsible for the propagation of substrate surface field effects in block polymer (BP) thin films through a modified approach to the Owens and Wendt interfacial energy formalism. This modification captured the influence of long-range surface energy components on through-film nanostructure orientation in BP thin films, and it provides a framework for manipulating BP thin film behavior without the need for extensive parameter space exploration. Optical microscopy (OM) of gradient thickness films on chlorosilane-modified substrates provided a high-throughput approach for identifying the critical propagation depth of substrate–polymer interfacial energy effects. Atomic force microscopy (AFM) was combined with OM to verify changes in free surface nanostructure as a function of film thickness. Using a model poly(methyl methacrylate-b-n-butyl acrylate) BP thin films system, we mapped the critical propagation depth as a function of interfacial energy difference...

Metal Nanostructures Fabricated by the Difference of Interfacial Energy at a Dielectric/Metal Interface

Abstract Due to its high sensitivity to changes in the environmental dielectric constant, localized surface plasmon resonance (LSPR) is utilized for various sensing materials. However, because of this high sensitivity, it is difficult to detect a specific substance among mixed materials. Here, we enhanced the size selectivity using a metal nanostructure. By preparing a cup-like metal nanostructure that is the same size as a virus, this cup-like structure may be able to capture a virus, and thus the LSPR characteristics would change. This phenomenon would not occur for larger materials, such as animal cells, i.e., this cup-like structure may have selectivity for material size. In this paper, we fabricated metal nanocups out of two-dimensional colloidal crystals by exploiting the difference of interfacial energy at a dielectric/metal interface. The size selectivity and plasmon characteristics of the fabricated metal nanocups were investigated with model viruses, i.e., virus-like polystyrene (PSt) nanoparticles with almost the same dielectric constant and size as a virus. As a result, the transmission spectra show a 20-nm red shift in the visible light range before and after adsorption of the model virus. Field emission scanning electron microscopy (FE-SEM), optical microscopy, UV–vis spectrometry and contact angle measurement results are also discussed.

Nanoparticle Capture During Directional Solidification of Nano-Sized SiC Particle-Reinforced AZ91D Composites.

The capture/push behavior of a particle in front of a solidification interface was analyzed theoretically and experimentally in this work. Van der Waals force, viscous force, and force due to interfacial energy played important roles in the particle capture/push process. Directional solidification experiments were conducted with nano-sized SiC particle-reinforced AZ91D composites to observe the distribution of nanoparticles in different solidification morphologies under varied cooling rates. When the composite solidified with plane manner, the nanoparticles could be captured by the solidification front and distributed uniformly in the matrix. When solidified with columnar or equiaxial manners, the nanoparticles could be captured by the solidification front but distributed uniformly only in the grain boundary as a result of the difference in interfacial energy and wettability between SiC/α-Mg and SiC/eutectic phase. Theoretical prediction of particle capture was in agreement with the experiment results.

A Top Coat with Solvent Annealing Enables Perpendicular Orientation of Sub‐10 nm Microdomains in Si‐Containing Block Copolymer Thin Films

Achieving sub‐10 nm high‐aspect‐ratio patterns from diblock copolymer self‐assembly requires both a high interaction parameter (χ, which is determined by the incompatibility between the two blocks) and a perpendicular orientation of microdomains. However, these two conditions are extremely difficult to achieve simultaneously because the blocks in a high‐χ copolymer typically have very different surface energies, favoring in‐plane microdomain orientations. A fully perpendicular orientation of a high‐χ block copolymer, poly(styrene‐block‐dimethylsiloxane) (PS‐b‐PDMS) is realized here using partially hydrolyzed polyvinyl alcohol (PVA) top coats with a solvent annealing process, despite the large surface energy differences between PS and PDMS. The PVA top coat on the block copolymer films under a solvent vapor atmosphere significantly reduces the interfacial energy difference between two blocks at the top surface and provides sufficient solvent concentration gradient in the through‐thickness direction and appropriate solvent evaporation rates within the film to promote a perpendicular microdomain orientation. The effects of interfacial energy differences and the swellability of PVA top coats controlled by the degree of hydrolysis on the orientation of micro­domains are examined. The thickness of the BCP film and top coats also affects the orientation of the BCP film.

An Analytical Model for Solute Segregation at Liquid Metal/Solid Substrate Interface

In this paper, we present an analytical model for describing the equilibrium solute segregation at the interface between metallic liquid (an A–B solution, where A is solvent and B is solute) and a solid substrate (S) using approaches of thermodynamics and statistical mechanics. This analytical model suggests that the interfacial solute segregation is governed by the difference in interfacial energies between the pure B/S and pure A/S interfaces, the heat of mixing of the A–B solution and the difference in entropies of fusion between pure solute and solvent. The calculated solute segregations at the interface in the liquid Al-Ti/TiB2 and liquid Sn-Al/Al2O3 systems are in qualitative agreement with the experimental observations. It is demonstrated that the present analytical model can be used to predict the solute segregation at the liquid/substrate interface, at least qualitatively.

Destabilization of a dual emulsion to form a Janus emulsion

A vegetable oil (VO) was added to an emulsion of silicone oil in water (SO/W) with mixing limited to once turning the test tube upside down. Initially, the VO was dispersed into virtually centimeter-sized drops and the emulsion contained effectively no Janus drops, while after 1 h of agitation at a low level to prevent creaming, drops of 50–100-μm size of the two oils were observed: in addition to an insignificant number of Janus drops. The topology of the latter showed them to emanate from flocculated individual drops of the two oils, but with no discernible effect by the interfacial tension equilibrium on the drop topology. Continued gentle mixing gave increasing fraction of Janus drops of increased size with a topology gradually approaching the one expected from the interfacial equilibrium at the contact line. The spontaneous formation of Janus drops indicated a reduction of the interfacial free energy in the process and the interfacial energy difference between separate and Janus drops was calculated for an appropriate range of interfacial tensions and for all oil fractions. The calculations enabled a distinction of the decrease due to interfacial area changes from the reduction of interfacial tensions per se, with the latter only a minor fraction.

Aging characteristics and mechanical properties of 1600 MPa body-centered cubic Cu and B2-NiAl precipitation-strengthened ferritic steel

High-strength low-carbon ferritic steels attaining a maximum yield strength of 1600MPa by combined Cu and NiAl precipitation-strengthening were developed. The yield strength of the alloys increases monotonically with the total concentration of the principal alloying elements i.e. Mn, Cu, Ni and Al. At 12.40at.%, a 1600MPa yield strength is achieved after solution treatment at 950°C followed by aging at 550°C for 2h. For all three alloys investigated, the hardness reached a maximum after 1–2h aging at 500–550°C. At peak hardness, the combined precipitation of the body-centered cubic (bcc) Cu-alloy and B2-ordered NiAl-type intermetallic precipitates is observed by atom probe tomography (APT). The morphology, composition and structure of the Cu-alloy and NiAl-type precipitates were characterized using APT and transmission electron microscopy, as a function of aging time at 550°C. In peak hardness conditions, the equiaxed bcc Cu-alloyed precipitates contain substantial amounts of Fe and are enriched in Ni, Al and Mn. Ni and Mn segregate at the Cu-alloy precipitate/ferrite matrix interface. In addition to the segregation, B2 NiAl-type precipitates nucleate at the Cu-alloy precipitates. After aging for 2h, most Cu-alloy precipitates have a NiAl-type precipitate attached to their side. On subsequent further aging, the Cu-alloyed precipitates enrich progressively with Cu and elongate, indicating a transformation to the 9R or face centered cubic structure. The Cu-alloyed precipitates coarsen slower than the NiAl-type precipitates due to interfacial energy differences between the two types of precipitates, slower diffusion kinetics of Cu through the NiAl precipitates, different matrix equilibrium solubility and solute transfer from Cu-alloyed precipitates to NiAl-type precipitates. The relatively slow growth and coarsening of Cu-alloyed precipitates are consistent with the observation of an only modest decrease of hardness with extended aging.

Highly Porous Silicon Membranes Fabricated from Silicon Nitride/Silicon Stacks

Nanopore formation in silicon films has previously been demonstrated using rapid thermal crystallization of ultrathin (15 nm) amorphous Si films sandwiched between nm-thick SiO2 layers. In this work, the silicon dioxide barrier layers are replaced with silicon nitride, resulting in nanoporous silicon films with unprecedented pore density and novel morphology. Four different thin film stack systems including silicon nitride/silicon/silicon nitride (NSN), silicon dioxide/silicon/silicon nitride (OSN), silicon nitride/silicon/silicon dioxide (NSO), and silicon dioxide/silicon/silicon dioxide (OSO) are tested under different annealing temperatures. Generally the pore size, pore density, and porosity positively correlate with the annealing temperature for all four systems. The NSN system yields substantially higher porosity and pore density than the OSO system, with the OSN and NSO stack characteristics fallings between these extremes. The higher porosity of the Si membrane in the NSN stack is primarily due to the pore formation enhancement in the Si film. It is hypothesized that this could result from the interfacial energy difference between the silicon/silicon nitride and silicon/silicon dioxide, which influences the Si crystallization process.

Mineral scale control in polymer film heat exchangers

Single salt deposition of CaSO4 and CaCO3 is studied on various polymeric heat transfer surfaces to gain a sound basis for novel polymer film heat exchanger (PFHX) design. Even at high overall heat transfer conditions (possible due to small wall thickness) the scaling quantity was found to be very low compared to a stainless steel surface and strongly dependent on the interfacial energy difference between polymer surface and deposit. The comparatively low scaling quantity is explained by an investigation of the CaCO3-deposition kinetics, which reveals an activation energy that is 40% higher for the polyether ether ketone (PEEK) surface compared to stainless steel. The developed correlations for the quantity of crystallization fouling as a function of supersaturation and flow conditions can be applied in PFHX design and operation with regard to scaling mitigation. A breakup of the falling film results in significant crystallization fouling enhancement and should be avoided during heat transfer operation. The presented cleaning in place strategy for the PFHX concept is very promising and easily applicable, which contributes to the overall effectiveness of the apparatus concept.