Correlations in Interfaces with Surfactants

The existence or nonexistence of the bending coefficient in liquid interfaces, as well as the applicability of the Helfrich free energy, is examined by comparing correlations in the interfaces with or without a weak surfactant. In the latter case, the formation of a bilayer is studied and density–density correlations and height–height correlations are reported, analyzed, and compared with normal liquid interfaces. In particular, the role of lateral tension is discussed.     

Temperature Gradients Drive Bulk Flow Within Microchannel Lined by Fluid–Fluid Interfaces

Surface tension gradients induce Marangoni flow, which may be exploited for fluid transport. At the micrometer scale, these surface‐driven flows can be quite significant. By introducing fluid–fluid interfaces along the walls of microfluidic channels, bulk fluid flows driven by temperature gradients are observed. The temperature dependence of the fluid–fluid interfacial tension appears responsible for these flows. In this report, the design concept for a biocompatible microchannel capable of being powered by solar irradiation is provided. Using microscale particle image velocimetry, a bulk flow generated by apparent surface tension gradients along the walls is observed. The direction of flow relative to the imposed temperature gradient agrees with the expected surface tension gradient. The phenomenon's ability to replace bulky peripherals, like traditional syringe pumps, on a diagnostic microfluidic device that captures and detects leukocyte subpopulations within blood is demonstrated. Such microfluidic devices may be implemented for clinical assays at the point of care without the use of electricity.     

Nanoanalysis of Ceramic Composite Interfaces

Instrumentation requirements, particularly for small probes, for high resolution analytical electron microscopy are described. Analysis of structure and chemistry of interfaces in conventionally processed Si₃N₄/SiC(w) ceramic matrix composites (CMCs) and metal/(0001) 6H-SiC single crystal substrates are presented. All of these interfaces are characterized by a chemical and a structural width. In the CMCs, which were processed at high temperatures, the chemical widths formed by diffusion of sintering aids into the bulk microstructure and were always much larger than the corresponding structural widths. The metals on SiC were deposited near room temperature, where diffusion is slow. Significant chemical widths did not form, and microstructure was determined by crystallographic factors. Upon annealing, reaction zones with appreciable chemical widths did form, with interesting morphologies that separated naturally into two groups. For metals that formed stable silicides and carbides, e.g. Ti, all interfaces in the reaction zones remained nearly atomically flat over large distances. For metals that formed only stable silicides interfaces in the reaction zones were often curved, and sometimes formed closed surfaces, for relatively low annealing temperatures, suggesting that interface melting had occurred even at temperatures less than expected for Si-metal eutectics.     

How Coherent and Semi-Coherent Interfaces Govern Dislocation Nucleation in Lamellar TiAl Alloys

γ/γ interfaces drive plastic deformation in lamellar TiAl alloys. Due to the ordering and resulting tetragonal nature of γ phase, γ/γ twin interfaces exist as different variants, some of which exhibit coherency stresses or semicoherent interface structures. While geometric parameters, such as the lamella spacing and orientation, are explored extensively in experiments, the isolation of individual influence of different interfaces in a nanolamellar microstructure remains a challenge. Herein, the range of γ/γ interface states is modeled using bilayers of the coherent γ/γ_TrueTwin, and the coherent or semicoherent γ/γ_PseudoTwin, and their deformation behavior is compared. It is shown that residual coherency stresses arise due to misfit accommodation in coherent γ/γ_PT specimens, which causes early preferential nucleation in one γ layer. Similarly, semicoherent specimens show preferential nucleation from misfit dislocations at the interface, which obeys Schmid's rule. In contrast, coherent γ/γ_TT specimens show no preferential nucleation and therefore exhibit higher strength. Thus, it is demonstrated that the presence of rotational γ/γ interfaces with misfit is responsible for localized and early plasticity, that lowers the strength of a lamellar microstructure. The interface type, which considers the coherency state, is used as a criterion for alloy microstructure design in the future.     

Progress in Brain-Compatible Interfaces with Soft Nanomaterials

Neural interfaces facilitating communication between the brain and machines must be compatible with the soft, curvilinear, and elastic tissues of the brain and yet yield enough power to read and write information across a wide range of brain areas through high-throughput recordings or optogenetics. Biocompatible-material engineering has facilitated the development of brain-compatible neural interfaces to support built-in modulation of neural circuits and neurological disorders. Recent developments in brain-compatible neural interfaces that use soft nanomaterials more suitable for complex neural circuit analysis and modulation are reviewed. Preclinical tests of the compatibility and specificity of these interfaces in animal models are also discussed.     

Diluted Oxide Interfaces with Tunable Ground States

The metallic interface between two oxide insulators, such as LaAlO₃/SrTiO₃ (LAO/STO), provides new opportunities for electronics and spintronics. However, due to the presence of multiple orbital populations, tailoring the interfacial properties such as the ground state and metal‐insulator transitions remains challenging. Here, an unforeseen tunability of the phase diagram of LAO/STO is reported by alloying LAO with a ferromagnetic LaMnO₃ insulator without forming lattice disorder and at the same time without changing the polarity of the system. By increasing the Mn‐doping level, x, of LaAl_1?xMn_xO₃/STO (0 ≤ x ≤ 1), the interface undergoes a Lifshitz transition at x = 0.225 across a critical carrier density of n_c = 2.8 × 10¹³ cm^?2, where a peak T_SC ≈255 mK of superconducting transition temperature is observed. Moreover, the LaAl_1?xMn_xO₃ turns ferromagnetic at x ≥ 0.25. Remarkably, at x = 0.3, where the metallic interface is populated by only d_xy electrons and just before it becomes insulating, a same device with both signatures of superconductivity and clear anomalous Hall effect (7.6 × 10¹² cm^?2 < n_s ≤ 1.1 × 10¹³ cm^?2) is achieved reproducibly. This provides a unique and effective way to tailor oxide interfaces for designing on‐demand electronic and spintronic devices.     

Effect of Roughness Differences on the Unbinding of Interfaces

In recent years there has been considerable interest in the effect of disorder on the nature and universality of wetting transitions. One of the most frequently studied systems is that in which geometrical disorder is present in the form of substrate roughness. In 2D there is compelling evidence that the critical wetting transition found for a flat substrate may become first order when surface roughness is included. In particular, if the roughness exponent of the wall exceeds the anisotropy index of interface fluctuations in the bulk, then first-order wetting is found. Here we extend the investigation of roughness-induced effects to the situation in which we have unbinding of two fluctuating interfaces characterized by different roughness exponents ₁and ₂(e.g., a fluid membrane depinning from a liquid–vapor interface) in the absence of quenched disorder. In this case symmetry prevents a change in order of the unbinding transition as the roughnesses are varied; however, the critical behavior is again found to be controlled by the larger of ₁and ₂. In addition, our results depend quantitatively on a nonuniversal parameter related to the relative curvature of the two interfaces whenever ₁₂.     

学龄前儿童使用有形和多点触控界面的眼动研究

目的 比较有形用户界面(TUI)和多点触控界面(MTI)对学龄前儿童学习的影响。方法 开发“NUMBERS”学前数学游戏,通过对比实验分析学龄前儿童使用TUI和MTI完成任务时的任务绩效、眼动追踪数据、情绪问卷和访谈结果,以比较2种界面在认知、注意力、情绪等方面的影响。结果 当使用TUI版本时,参与者进行了更多的探索;使用TUI版本的参与者在操作卡片时注视时间较短;使用TUI版本的参与者的注意力主要在屏幕上的出题区域和答题区域之间转移;参与者对TUI版本的情绪问卷评分更高。结论 TUI相较于MTI来说,能够激发探索欲、降低认知负荷、促进注意力集中、提高愉悦度,进而对学龄前儿童的学习产生长远的积极影响。这些发现为TUI在学前教育中的应用提供了理论支持,同时也为眼动追踪法在这一领域的应用提供了可能。     

Measurement of the Diffusion Coefficient of Miscible Fluids Using Both Interferometry and Wiener's Method

Measurements of the diffusion coefficient of two miscible liquids are reported. The liquids are various combinations of pure silicone oils and those to which small amounts of solvents are added to control the difference in density between the fluids. The liquids were placed in a quartz cell such that the interface is initially horizontal. As the fluids diffuse, the profile of the index of refraction near the interface is time dependent and is related to the local concentration of the diffusing fluids. The concentration gradient profile was measured by a shearing interferometer incorporating a Wollaston prism, as well as Wiener's method. In the latter technique, a 45° light sheet was passed through the test cell, and the local deflection of the light beam was measured. The average diffusion coefficient was obtained by analysis of the measured concentration gradient profile, assuming that the diffusion process is one-dimensional and is characterized by a constant value of the diffusion coefficient.     

STO/BTO Modulated Superlattice Multilayer Structures with Atomically Sharp Interfaces

A comparative study is carried out investigating the microstructure and the electrical properties of Ba_xSr_1‐xTiO₃ films with x = (0.25, 0.5, 0.75) deposited as modulated superlattice (SL) multilayer structures by laser ablation on both LaAlO₃ and MgO substrates. The SL structures are examined using high‐resolution transmission electron microscopy and scanning transmission electron microscopy . Their interfaces and chemical composition are investigated using energy dispersive X‐ray spectroscopy, complemented with electron energy loss spectra analysis performed to give insight to the local chemistry, structure and bonding. It is found that all modulated SL samples consisted of continuous well defined 1 nm SrTiO₃ and 4 nm BaTiO₃ layers. When modulated SL multilayered structures are compared with their single target deposited equivalents, they exhibit similar electrical properties (e.g. dielectric constant and dielectric loss) but undergo phase transition in a broader temperature region. A very important observation is that the oxygen K‐edges in SrTiO₃ and BaTiO₃ layers are distinctive. Therefore it can be used as finger‐print signature for analysis of ultra‐thin SrTiO₃/BaTiO₃ layers and their interfaces. Finally it is demonstrated that by varying the modulation period it is possible to develop structures with engineered ferroelectric properties and improved thermal stability.     

Design of Active Interfaces Using Responsive Molecular Components

Responsive interfaces are interfaces that show a defined and reversible change in physical properties in response to external stimuli. Typically, responsive interfaces result from the immobilization of responsive molecular components at the interface that translate a nanoscale signal into a macroscopic effect. Responsive interfaces can also be obtained if the topology of the interface can be reversibly changed using an external stimulus. As the surface of any material is its connection to the environment, responsive interfaces provide opportunities for interactive materials which are not only able to change properties upon demand, but also sense their environment and act autonomously. The application of responsive molecular components at interfaces, however, requires chemical and physical compatibility with the material surface of interest, posing a challenge not least in the retention of the responsive functionality. The state of the art in “active” interfaces which display responsive wettability, permeability, or adhesion is discussed, with a particular emphasis on microscale and nanoscale patterning since patterned interfaces can give rise to unique material properties. Finally, perspectives in the development of responsive interfaces, as well as promising approaches for bypassing the most prominent challenges are discussed.     

Hierarchical Hydrogel Composite Interfaces with Robust Mechanical Properties for Biomedical Applications

Cells sense and respond to a wide range of external signals, including chemical signals, topography, and interface mechanics, via interactions with the extracellular matrix (ECM), triggering the regulation of behavior and function. The ECM can be considered a hierarchical multiphase porous matrix with various components. Highly porous hydrogel‐based biomaterials can mimic the critical ECM properties, to provide mechanical support for tissues and to regulate cellular behaviors, such as adhesion, proliferation, and differentiation. Herein, based on micro/nanoscale‐topography‐coupled mechanical action, recent advances in the fabrication and application of hydrogel composites with tunable mechanical properties and topography in biomedicine are summarized. In particular, recent findings showing that hydrogels with specifically designed structures not only influence a range of cellular processes and fit the needs of engineered tissues but also have pharmacological effects are emphasized.     

A Metal–Organic‐Framework‐Based Electrolyte with Nanowetted Interfaces for High‐Energy‐Density Solid‐State Lithium Battery

Solid‐state batteries (SSBs) are promising for safer energy storage, but their active loading and energy density have been limited by large interfacial impedance caused by the poor Li⁺ transport kinetics between the solid‐state electrolyte and the electrode materials. To address the interfacial issue and achieve higher energy density, herein, a novel solid‐like electrolyte (SLE) based on ionic‐liquid‐impregnated metal–organic framework nanocrystals (Li‐IL@MOF) is reported, which demonstrates excellent electrochemical properties, including a high room‐temperature ionic conductivity of 3.0 × 10^‐4 S cm^‐1, an improved Li⁺ transference number of 0.36, and good compatibilities against both Li metal and active electrodes with low interfacial resistances. The Li‐IL@MOF SLE is further integrated into a rechargeable Li|LiFePO₄ SSB with an unprecedented active loading of 25 mg cm^‐2, and the battery exhibits remarkable performance over a wide temperature range from ?20 up to 150 °C. Besides the intrinsically high ionic conductivity of Li‐IL@MOF, the unique interfacial contact between the SLE and the active electrodes owing to an interfacial wettability effect of the nanoconfined Li‐IL guests, which creates an effective 3D Li⁺ conductive network throughout the whole battery, is considered to be the key factor for the excellent performance of the SSB.     

Numerical Simulations of Convection Induced by Korteweg Stresses in a Miscible Polymer–Monomer System: Effects of Variable Transport Coefficients, Polymerization Rate and Volume Changes

We modeled a miscible polymer-monomer system with a sharp transition zone separating the two fluids to determine if convection analogous to Marangoni convection in immiscible fluids could occur because of thermal and concentration gradients. We considered three cases: with a temperature gradient along the transition zone, with a variable transition zone width, and one with a gradient in the conversion of polymerization. Using the Navier–Stokes equations with an additional term, the Korteweg stress term arising from non-local interactions in the fluid, we demonstrated with realistic parameters that measurable fluid flow would result in the absence of buoyancy-driven convection for all three cases. We show that even if the Korteweg stress is not a function of temperature, the increase in the diffusion coefficient with temperature can result in convection because a gradient in the transition zone width develops. We also examine the effects of a polymer viscosity that is not only a function of concentration but also temperature. We demonstrate that a constant flux of heat, as would be realistic for a heating element in contact with the side of the reactor, would produce a greater flow than a linear thermal gradient parallel to the transition zone. We demonstrate that qualitatively different flow patterns can be realized by using unusual initial conditions that could be realized with different masks for the photopolymerization. We also demonstrate that the volume change during polymerization and caused by side heating could not cause significant fluid flow that would confound the observation of Korteweg-stress induced flows. To avoid buoyancy-driven convection, the experiment would have to be performed in microgravity.     

氧气在 PVDF 片材中扩散的分子动力学模拟

目的研究气体在PVDF片材中的扩散。方法采用分子动力学模拟方法研究了氧气在其片材中的扩散行为,得到氧气在PVDF片材中的扩散系数,并讨论了时间、聚合度、温度及残余压力对扩散系数的影响。结果模拟时间太短对模拟结果不利,应以大于1000 fs为宜。当聚合度由400增加到800时,扩散系数由4.77×10-6cm2/s下降到1.78×10-6cm2/s;当温度从298 K提高到303 K时,扩散系数由1.06×10-6cm2/s增加到1.42×10-6cm2/s;当残余压力由60 kPa增大到100 kPa时,扩散系数由7.07×10-6cm2/s下降到3.06×10-6cm2/s。结论氧气在PVDF片层中的扩散系数随聚合度和残余压力的增大而变小,随温度的提高而变大。     

子结构界面连接刚度参数识别的一种直接方法

提出一种通过特征方程反问题识别子结构界面连接刚度参数的直接方法。新方法以动柔度矩阵特征方程为基础，建立通过界面位移求解界面内力的方程，由模态叠加法对可测自由度上不完全的振型拟合估计界面不可测自由度上的位移，适合于部分子结构不具备可测自由度的复杂组合结构。数值仿真算例和工程实例表明本方法具有良好的识别精度和数值稳定性。计算量和对计算机存贮量的要求也较小。