Macroscopic Work Research Articles

Mechanisms of interface electrostatic potential induced asphalt-aggregate adhesion

The electrostatic potential at the interface of the asphalt molecular and aggregate oxides is the primary factor generating the adhesion between the asphalt-aggregate contact surfaces. However, the route of electrostatic potential affecting the asphalt-aggregate adhesion is yet to be determined at the molecular level. This study proposed that the electron accumulation at the interface of the asphalt molecular and aggregate oxides generates a significant electrostatic potential hence to induce the adhesion between the asphalt and aggregate in asphalt pavement. A microscopic molecular dynamics (MD) simulation incorporated with macroscopic adhesion work experiments is conducted to analyze the interface adhesive performance between the asphalt and aggregate. The adhesion work experiment demonstrated the effect of aggregate surface oxides on asphalt adhesion at the macro level and further verified the simulation results. The result demonstrated that a notable electron accumulation can be observed by MD at the interface of asphalt molecular and multiple oxides which generates the electrostatic potential. The strong electrostatic attractions and hydrogen bonds between alkaline oxides (MgO, CaO, CaCO3) and asphalt molecules enhance the relative concentration distribution, diffusion coefficient, and adhesion of asphalt on the aggregate surface. The significant electrostatic potential difference at the interface of the asphalt molecular and the oxide enables a strong adhesion between them due to the near-surface failure potential. Besides, the negative charge accumulation on both the benzene ring structure and oxygen atoms in the asphalt molecules results in poor adhesion at the interface of asphalt molecules and multiple oxides. It was found that a high correlation exists between the MD prediction and experimental testing results. Thus, this research provides a valuable tool for guiding the pairing and selection of asphalt with various minerals for pavement design, construction, and maintenance agencies.

Study on the modification mechanism of recycled brick-concrete aggregate concrete based on water glass solution immersion method

Recycling construction waste into concrete through the process of crushing and screening is a vital method of resource conservation. Recycled aggregates often contain imperfections such as micro-cracks, necessitating modification to produce high-performance concrete. Water glass, an economical modifier, addresses this need. However, recycled aggregates often contain concrete and brick aggregates and are difficult to completely separate. At present, there are few studies on the modification of recycled brick aggregates, and there is a lack of comprehensive and systematic research from the aggregate modification mechanism to the macroscopic working performance and mechanical properties of recycled concrete. Based on the above problems, the modification effect and modification mechanism of water glass solution on recycled brick aggregate and recycled concrete aggregate were studied by basic physical properties, SEM, and XRD tests. The relationship between macroscopic mechanical properties and the microstructure of modified recycled brick-concrete aggregate concrete was studied by compressive, flexural, and splitting tensile tests, XRD, NMR, and SEM. The results showed: (1) The best modification scheme for recycled brick aggregate and recycled concrete aggregate is the concentration of water glass solution at 4 % with a soaking time of 5 h; (2) the mechanical properties of recycled brick-concrete aggregate concrete are the best when the brick-concrete ratio is 5:5, and the compressive strength, flexural strength, and splitting tensile strength are increased by 10.84 %, 11.61 %, and 15.08 %, respectively; and (3) the water glass solution improved the pore structure and interfacial transition zone of recycled aggregate. The proportion of harmless pores and less harmful pores increased by 5.66 % and 13.3 %, respectively, and the proportion of harmful pores and more harmful pores decreased by 6.25 % and 12.7 %, respectively. The research results can promote the resource utilization of construction waste.

Densification of nanoporous metals during nanoindentation: The role of structural and mechanical properties

The analysis of the densification behavior of nanoporous metals in nanoindentation is challenging in simulations and experiments. A deeper understanding of the densification behavior provides valuable information about the different deformation mechanisms in nanoindentation and compression experiments. The developed two-scale model allows for predicting the densification field for variable microstructure and elastic–plastic behavior. It could be shown that the penetration depth of the densification field is mainly controlled by the ratio of the macroscopic work hardening rate to yield stress. The shape as well as the value at characteristic isolines of densification depend mainly on the macroscopic plastic response of the nanoporous material. This could be confirmed by nanoindentation experiments, where the densification under the indenter was measured for ligament sizes from 35 to 150 nm. Although the depth of the densification field was underpredicted by the simulations, the experiments confirmed the predicted trends.Graphical abstract

Controlling dynamics in extended molecular frameworks.

Molecular machines are essential dynamic components for fuel production, cargo delivery, information storage and processing in living systems. Scientists have demonstrated that they can design and synthesize artificial molecular machines that operate efficiently in isolation - for example, at high dilution in solution - fuelled by chemicals, electricity or light. To organize the spatial arrangement and motion of these machines within close proximity to one another in solid frameworks, such that useful macroscopic work can be performed, remains a challenge in both chemical and materials science. In this Review, we summarize the progress that has been made during the past decade in organizing dynamic molecular entities in such solid frameworks. Emerging applications of these dynamic smart materials in the contexts of molecular recognition, optoelectronics, drug delivery, photodynamic therapy and water desalination are highlighted. Finally, we review recent work on a new non-equilibrium adsorption phenomenon for which we have coined the term mechanisorption. The ability to use external energy to drive directional processes in mechanized extended frameworks augurs well for the future development of artificial molecular factories.

Analytical prediction of yield stress and strain hardening in a strain gradient plasticity material reinforced by small elastic particles

The influence on macroscopic work hardening of small, spherical, elastic particles dispersed within a matrix is studied using an isotropic strain gradient plasticity framework. An analytical solution for strain hardening, i.e. the flow stress as a function of plastic strain, based on a recently developed model for initial yield strength is proposed. The model accounts for random variations in particle size and elastic properties, and is numerically validated against FE solutions in 2D/3D unit cell models. Excellent agreement is found as long as the typical particle radius is much smaller than the material length scale, given that the particle volume fraction is not too large (<10%) and that the particle/matrix elastic mismatch is within a realistic range. Finally, the model is augmented to account for strengthening contribution from shearable particles using classic line tension models and successfully calibrated against experimental tensile data on an Al−2.8wt%Mg−0.16wt%Sc alloy.

Optimal power and efficiency of odd engines.

Odd materials feature antisymmetric response to perturbations. This anomalous property can stem from the nonequilibrium activity of their components, which is sustained by an external energy supply. These materials open the door to designing innovative engines which extract work by applying cyclic deformations, without any equivalent in equilibrium. Here, we reveal that the efficiency of such energy conversion, from local activity to macroscopic work, can be arbitrarily close to unity when the cycles of deformation are properly designed. We illustrate these principles in some canonical viscoelastic materials, which leads us to identify strategies for optimizing power and efficiency according to material properties and to delineate guidelines for the design of more complex odd engines.

A new method of stiffness prediction for composite plate structures with in-plane periodicity

This paper proposes an equivalence principle of macroscopic internal virtual work and microscopic internal virtual work, and uses it to predict the effective stiffnesses of composite plate structures with in-plane periodicity. The macroscopic internal virtual work is produced by internal forces acting on generalized virtual strains, and the microscopic internal virtual work is produced by microscopic stresses acting on microscopic virtual strains. The microscopic virtual strains consist of macroscopic strains and perturbed strains solved from the self-equilibrium equation of a unit cell. According to the equivalence principle, the effective stiffness matrix of periodic heterogeneous plates is presented in a product form of microscopic stresses and microscopic strains. To determine the unique solution of the self-equilibrium equation, five normalization conditions are given and elaborated physically. Moreover, standard finite element formulations for calculating the perturbed displacements are derived with the principle of virtual work. The present method of predicting the effective stiffnesses of composite plates can be easily implemented in the commercial software COMSOL Multiphysics. Finally, numerical comparisons with the results in literature validate the effectiveness and accuracy of the proposed method.

Electroless Plating of Metal Nanomaterials

AbstractElectroless plating is commonly associated with metallizing macroscopic work pieces, but also represents a surprisingly powerful nanomanufacturing tool. This review details the technique's use for creating nanomaterials of arbitrary dimensionality, ranging from nanoparticles over nanotubes, nanowires, and ultrathin films to nanostructured lattices, focusing on the solution chemistry and mechanistic aspects. The synthesis of defined nanostructures serves as overarching perspective, which is enriched by drawing connections to and insights from related fields. Strategies for controlling the size, shape, crystallinity, porosity, composition, and arrangement of electrolessly plated nanostructures are outlined, including templating (which harnesses the method's exceptional conformality to guide and limit deposit formation), the complementary approach of selective growth, tailored seeding, and bath design. Being able to strike convincing compromises between material quality and ease of preparation, electroless nanoplating has a distinct potential to facilitate the application of metal nanomaterials.

Deformation mechanisms and differential work hardening behavior of AZ31 magnesium alloy during biaxial deformation

Magnesium alloys are frequently subjected to biaxial stress during manufacturing process, however, the work hardening behavior under such circumstance are not well understood. In this study, the deformation mechanisms and differential work hardening behavior of rolled AZ31 magnesium alloy sheets under biaxial loading are investigated. The change of plastic work contours with increasing plastic strain indicates the differential work hardening behavior of AZ31 magnesium alloy under biaxial stress state, resulting in higher macroscopic work hardening rates of biaxial loading than uniaxial loading, with the elastic-plastic transition part of work hardening extended and stage III hardly emerged. Electron backscatter diffraction and Schmid factor analysis confirm the low activation of non-basal 〈a〉 slip during biaxial loading tests. While the thickness strain is primarily accommodated by pyramidal 〈 c + a 〉 slip at the initial stage of biaxial deformation, {10–11} contraction twinning is activated at larger plastic strain. The low activation of non-basal 〈a〉 slip also retards the dynamic recovery and cross-slip of basal and prismatic 〈a〉 slips, leading to the differential work hardening behavior of AZ31 magnesium alloy under biaxial stress state.

Diphenylarsinic acid sorption mechanisms in soils using batch experiments and EXAFS spectroscopy

Diphenylarsinic acid (DPAA) is a phenyl arsenic compound derived from chemical warfare weapons. Macroscopic and microscopic work on DPAA sorption will provide useful information in predicting the partitioning and mobility of DPAA in the soil-water environment. Here, batch experiments and extended X-ray absorption fine structure (EXAFS) spectroscopy were used to investigate the sorption mechanisms of DPAA. The DPAA sorption data from 11 soil types was found to fit the Freundlich equation, and the sorption capacity, Kf, was significantly and positively correlated with oxalate-extractable Fe2O3. The Kf values of eight of the 11 untreated soils (1.51–113.04) significantly decreased upon removal of amorphous metal (hydr)oxides (0.51–13.37). When both amorphous and crystalline metal (hydr)oxides were removed from the untreated soils, the Kf values either decreased or slightly increased (0.65–3.09). Subsequent removal of soil organic matter from these amorphous and crystalline metal (hydr)oxide-depleted samples led to further decreases in Kf to 0.02–1.38, with only one exception (Sulfic Aquic-Orthic Halosols). These findings strongly suggest that ligand exchange reactions with amorphous metal (hydr)oxides contribute most to DPAA sorption on soils. EXAFS data provide further evidence that DPAA primarily formed bidentate binuclear (2C) and monodentate mononuclear (1V) coring-sharing complexes with As-Fe distances of 3.34 and 3.66 Å, respectively, on Fe (hydr)oxides. Comparison of these results with earlier studies suggests that 2C and 1V complexes of DPAA may be favored under low and high surface coverages, respectively, with the formation of 1V bonds possibly conserving the sorption sites or decreasing the steric hindrance derived from phenyl substituents.

Molecular Springs: Integration of Complex Dynamic Architectures into Functional Devices.

Molecular/supramolecular springs are artificial nanoscale objects possessing well-defined structures and tunable physicochemical properties. Like a macroscopic spring, supramolecular springs are capable of switching their nanoscale conformation as a response to external stimuli by undergoing mechanical spring-like motions. This dynamic action offers intriguing opportunities for engineering molecular nanomachines by translating the stimuli-responsive nanoscopic motions into macroscopic work. These nanoscopic objects are reversible dynamic multifunctional architectures which can express a variety of novel properties and behave as adaptive nanoscopic systems. In this Minireview, we focus on the design and structure-property relationships of supramolecular springs and their (self-)assembly as a prerequisite towards the generation of novel dynamic materials featuring controlled movements to be readily integrated into macroscopic devices for applications in sensing, robotics, and the internet of things.

Molecular Springs: Integration of Complex Dynamic Architectures into Functional Devices

AbstractMolecular/supramolecular springs are artificial nanoscale objects possessing well‐defined structures and tunable physicochemical properties. Like a macroscopic spring, supramolecular springs are capable of switching their nanoscale conformation as a response to external stimuli by undergoing mechanical spring‐like motions. This dynamic action offers intriguing opportunities for engineering molecular nanomachines by translating the stimuli‐responsive nanoscopic motions into macroscopic work. These nanoscopic objects are reversible dynamic multifunctional architectures which can express a variety of novel properties and behave as adaptive nanoscopic systems. In this Minireview, we focus on the design and structure–property relationships of supramolecular springs and their (self‐)assembly as a prerequisite towards the generation of novel dynamic materials featuring controlled movements to be readily integrated into macroscopic devices for applications in sensing, robotics, and the internet of things.

Schools of skyrmions with electrically tunable elastic interactions

Coexistence of order and fluidity in soft matter often mimics that in biology, allowing for complex dynamics and applications-like displays. In active soft matter, emergent order can arise because of such dynamics. Powered by local energy conversion, this behavior resembles motions in living systems, like schooling of fish. Similar dynamics at cellular levels drive biological processes and generate macroscopic work. Inanimate particles capable of such emergent behavior could power nanomachines, but most active systems have biological origins. Here we show that thousands-to-millions of topological solitons, dubbed “skyrmions”, while each converting macroscopically-supplied electric energy, exhibit collective motions along spontaneously-chosen directions uncorrelated with the direction of electric field. Within these “schools” of skyrmions, we uncover polar ordering, reconfigurable multi-skyrmion clustering and large-scale cohesion mediated by out-of-equilibrium elastic interactions. Remarkably, this behavior arises under conditions similar to those in liquid crystal displays and may enable dynamic materials with strong emergent electro-optic responses.

Azo-MOFs showing controllable framework flexibility and consequently fine-tuned photomechanical crystal motion

Photo-response molecular-scale movement has been well developed in azobenzene photochromic molecules. However, material capable of converting this molecular-scale movement to macroscopic work remains a formidable challenge. Here, we describe an exquisite photomechanical effect observed in an azobenzene-Gd(III) MOF. The single crystal of this material displays complex motion including walking, rolling, self-rotating, swing, and finally popping, dependent on the exposed time under UV and the size of the crystals. Consequently, this functional material gives the direct and impressive evidence to support the potential of MOF material in photomechanical motion.

Relationships between surface chemistry, nanotopography, wettability and ice adhesion in epoxy and SU-8 modified with fluoroalkylsilanes from the vapor phase

The objective of this work was to elucidate how ice adhesion to solid substrates is related to surface wettability, which, in turn, results from surface chemical composition and nanotopography. The study was carried out using microscopically smooth surfaces of epoxy and SU-8, a negative epoxy-based photoresist. Epoxy resins are known for their outstanding physicochemical properties. They are often used as surface coatings for outdoor devices and can face harsh environmental conditions, such as icing. SU-8 is extensively used in microfabrication of surface topographical structures. Some of these structures are designed to be superhydrophobic and, in some cases, icephobic. In the present study, we focused on the role of surface physicochemical modifications of these materials in controlling their wetting and icing properties. A homologous series of fluoroalkyl silanes (FAS), which contained 3, 8, 10, and 12 carbon atoms in a molecule, was used to make epoxy and SU-8 surfaces hydrophobic. The FAS deposition process was carried out from vapor phase at atmospheric pressure (AP-VPD). The modified substrates exhibited a significantly increased surface nanoroughness, as a result of etching in oxygen radio frequency (RF) plasma and subsequent silanization. The coatings obtained by the AP-VPD contribute to surface roughness because the FAS vapors and atmospheric water are abundant during deposition processes. Such conditions favor vertical polymerization and formation of clustered deposits. The resulting nanoroughness was shown to affect wettability of modified surfaces. The influence of FAS backbone chain length on resulting surface nanotopography and how it affects surface wettability was investigated. Finally, the relationship between wettability and ice adhesion was examined. The strength of adhesion between frozen sessile droplets and modified substrates was investigated in tensile mode. A linear correlation between the ice-substrate adhesion strength and the macroscopic work of water-substrate adhesion was found.

Trans-scale Nanofabrication with Nanopositioning and Nanomeasuring Machines

Nanofabrication in macroscopic working areas addresses the manipulation with nanometer precision in large scale working areas of several hundred millimeters. In order to reduce the fabrication time of large objects, high dynamic position tracking is required. The position and orientation of the nanopositioning and nanomeasuring machine have to be controlled permanently to compensate external disturbances like ground motion, sound waves, et cetera. Many applications have strict demands on following the track, e.g. to reduce the line roughness. High performant data and signal processing and efficient control algorithms are required to overcome these challenges. This work presents the nanopositioning and measuring machine as well as the utilized control system. Several scanning and fabrication experiments have been carried out in order to demonstrate the performance of the setup.

Towards alternative 3D nanofabrication in macroscopic working volumes

This paper gives an overview of the research carried out at TU Ilmenau towards the development and application of tip- and laser-based nanofabrication on flat and curved surfaces in extended macroscopic working areas. It is shown that sub-10 nm structures can be fabricated by scanning probe lithography (SPL). The use of soft stamps has revealed their suitability for nanoimprinting on curved surfaces. Laser-based methods for a maskless exposure of resist on curved surfaces utilising 405 nm laser diodes have already been tested successfully. Furthermore, the current work deals with two-photon polymerisation, which has great potential with regard to the fabrication of sub-wavelength structures. At present, the methods mentioned have all been applied only in working ranges <100 × 100 μm2 in the plane and <10 μm in height. To overcome these limitations, the nanofabrication techniques are now being integrated in the nanopositioning and measuring machines (NPMMs) developed at TU Ilmenau. They offer working volumes of up to 200 × 200 × 25 mm3 with a positioning resolution of 20 pm. To provide access to any geometry elements in the 3D space with nanometre precision, the machine concepts as well as the metrological concepts are further developed. Due to the increased demands of lowest trajectory deviations within the fabrication process, new real-time controllers for probing and fabrication systems are investigated, as well as interactions in combined force and positioning sensors. Further important research is carried out into interference lithography, to enable an exposure of non-planar substrates and to improve the lateral structure resolution at the same time. A mix-and-match combination of such methods that allows the simultaneous exposure of large substrate regions with nanofabrication methods such as SPL becomes possible on the basis of the NPMMs, and is another area of great potential with regard to the research work presented in this paper.

Development and characterization of electrochemical flow cells for hydrodynamic scanning electrochemical microscopy

In the frame of this contribution, two electrochemical flow cells developed for scanning electrochemical microscopy (SECM) are presented. Forced convection was generated by a flow of the mediator solution through the flow cells. A description of the mandatory design aspects of the experimental flow cell setups is included. Using a macroscopic working electrode as a substrate electrode, forced convection leads to the formation of a stable diffusion layer during amperometric experiments in contrast to a growing diffusion layer in quiescent solution. To characterize the effects of forced convection, the diffusion layer around a platinum substrate electrode integrated into the cells was investigated utilizing chronoamperometric measurements and hydrodynamic SECM imaging in amperometric substrate generation-tip collection (SG/TC) mode. Both methods proved the stability and the time-independency of the diffusion layer. Mathematical simulations using COMSOL Multiphysics were computed to investigate the flow profile generated by the flowing mediator solution in the relevant region close to the substrate electrode. In summary, two different electrochemical flow cells for SECM were developed and characterized. Both cell designs enabled steady-state diffusion layer characteristics at a macroscopic substrate electrode offering interesting possibilities such as time-independent measurements in the context of the SG/TC mode.

Evaluation of Actuating Properties using Photoresponsive Polyimide Gel having Azobenzene Moiety

The development of intelligent materials which can produce spontaneously different deformation under some external stimuli (such as temperature, electricity, light, magnetic field and so on) provides promising substances for materials chemistry and biomimetic engineering. Among them, azobenzene is attractive molecular transducer for light driven devices and optical switches due to the large reversible changes in molecular shape that occur upon isomerization. Light-driven applications are facilitated by the distinct absorption bands of the cis and trans isomers that allow for selective conversion and are robust even after multiple photocycles. Photoresponsive gels having azobenzene units in a rigid aromatic backbone are expected as a next generation actuator that offers direct energy conversion from light to macroscopic work. Since it is not necessary electric wiring, possible to be operated remotely with light. And its operation principle is based on the movement of molecular scale, so it could be miniaturized. In this study, we synthesized photoresponsive polyimide (PI) gels which are hardly hydrolyzed and decomposed as compared with precursor photoresponsive poly (amide acid) (PAA) gels. Conventional polyimide gels obtained by crosslinking bifunctional oligomers having azobenzene moiety with tetrafunctional amine showed no reversible photoresponsiveness. However, by using N,N’-bis(3,5-diaminobenzoyl)-4,4’-diaminoazobenzene (BDA-Azo) as a tetrafunctional crosslinking agent which azobenzene is introduced, a centimeter-long cantilever made up of the photoresponsive PI gel exhibited reversible bending motions which were faster than the precursor PAA gel upon blue (402 nm) and visible light (532 nm) irradiation. Therefore, in order to elucidate the influence of chemical structure on bending behavior, we investigated various physical properties of the novel PI gel composed of BDA-Azo, conventional PI gel and their precursor by using UV-vis spectrum measurement, Raman scattering measurement, etc. and discussed relationships between photoisomerization and bending behavior.

Revolving supramolecular chiral structures powered by light in nanomotor-doped liquid crystals.

Molecular machines operated by light have been recently shown to be able to produce oriented motion at the molecular scale1,2 as well as do macroscopic work when embedded in supramolecular structures3-5. However, any supramolecular movement irremediably ceases as soon as the concentration of the interconverting molecular motors or switches reaches a photo-stationary state6,7. To circumvent this limitation, researchers have typically relied on establishing oscillating illumination conditions-either by modulating the source intensity8,9 or by using bespoke illumination arrangements10-13. In contrast, here we report a supramolecular system in which the emergence of oscillating patterns is encoded at the molecular level. Our system comprises chiral liquid crystal structures that revolve continuously when illuminated, under the action of embedded light-driven molecular motors. The rotation at the supramolecular level is sustained by the diffusion of the motors away from a localized illumination area. Above a critical irradiation power, we observe a spontaneous symmetry breaking that dictates the directionality of the supramolecular rotation. The interplay between the twist of the supramolecular structure and the diffusion 14 of the chiral molecular motors creates continuous, regular and unidirectional rotation of the liquid crystal structure under non-equilibrium conditions.