Changes In Macroscopic Properties Research Articles

Light‐Triggered Disassembly of Molecular Motor‐based Supramolecular Polymers Revealed by High‐Speed AFM

AbstractPhotoresponsive supramolecular polymers have a major potential for applications in responsive materials that are externally triggered by light with spatio‐temporal control of their polymerisation state. While changes in macroscopic properties revealed the adaptive nature of these materials, it remains challenging to capture the dynamic depolymerisation process at the molecular level, which requires fast observation techniques combined with in situ irradiation. By implementing in situ UV illumination into a High‐Speed Atomic Force Microscope (HS‐AFM) setup, we have been able to capture the disassembly of a light‐driven molecular motor‐based supramolecular polymer. The real‐time visualisation of the light‐triggered disassembly process not only reveals cooperative depolymerisation, it also shows that this process continues after illumination is halted. Combining the data with cryo‐electron microscopy and spectroscopy approaches, we obtain a molecular‐level description of the motor‐based polymer dynamics reminiscent of actin chain‐end depolymerisation. Our detailed understanding of supramolecular depolymerisation will drive the development of future responsive polymer systems.

Light-Triggered Disassembly of Molecular Motor-based Supramolecular Polymers Revealed by High-Speed AFM.

Photoresponsive supramolecular polymers have a major potential for applications in responsive materials that are externally triggered by light with spatio-temporal control of their polymerisation state. While changes in macroscopic properties revealed the adaptive nature of these materials, it remains challenging to capture the dynamic depolymerisation process at the molecular level, which requires fast observation techniques combined with in situ irradiation. By implementing in situ UV illumination into a High-Speed Atomic Force Microscope (HS-AFM) setup, we have been able to capture the disassembly of a light-driven molecular motor-based supramolecular polymer. The real-time visualisation of the light-triggered disassembly process not only reveals cooperative depolymerisation, it also shows that this process continues after illumination is halted. Combining the data with cryo-electron microscopy and spectroscopy approaches, we obtain a molecular-level description of the motor-based polymer dynamics reminiscent of actin chain-end depolymerisation. Our detailed understanding of supramolecular depolymerisation will drive the development of future responsive polymer systems.

Study on the Properties Changes of Reversible Invert Emulsion during the Process from O/W to W/O with Alkali.

The reversible emulsion drilling fluid system combines the advantages of both oil-based and water-based drilling fluids, which can achieve ideal results in different stages of drilling and completion, and the system can be reused to effectively reduce costs. However, the research on reversible emulsions mainly focuses on the development of new reversible emulsifiers, while the specific phase transformation mechanism of reversible emulsion systems is still unclear. In this paper, a stable reversible emulsion was prepared using the reversible emulsifier DMOB as a raw material, and the reversible emulsion performance of the alkali response from the O/W emulsion phase to the W/O emulsion was studied. The microstructure of reversible emulsions was studied by a microscope, a cryogenic transmission electron microscopy, and a laser particle size analyzer. The changes in macroscopic properties of reversible emulsions in the process of alkali conversion were studied by pH, conductivity, demulsification voltage, static stability, viscosity, rheology, and other indicators, and the conversion mechanism of reversible emulsions from O/W emulsion ⟶ bicontinuous structure ⟶ O/W/O emulsion ⟶ W/O emulsion was clarified. The details are as follows: in the first stage, when the amount of NaOH ≤ 0.43 vol.%, the overall particle size of the emulsion decreases first and then increases with the increase in NaOH dosage. In the second stage, when the amount of NaOH was 0.45 vol.%, a double continuous structure was formed inside the emulsion. In the third stage, when the amount of NaOH is 0.48 vol.%, the O/W/O emulsion is formed, and with the increase in stirring time, the internal oil droplets gradually accumulate and are discharged from the water droplets, and finally, the W/O emulsion is formed. In the fourth stage, when the dosage of 0.50 vol.% ≤ NaOH ≤ 5.00 vol.%, the W/O emulsion was formed, and with the increase of NaOH dosage, the structure and compactness between water droplets increased first and then decreased. In the whole process, with the increase in the amount of NaOH solution, the total particle size of the emulsion first decreased and then increased.

Experimental Study on Permeability Characteristics of Mudstone under High Temperature Overburden Condition

High-temperature treatment significantly impacts the permeability of mudstone. The permeability of mudstone after exposure to high temperatures is closely influenced by the temperature it experiences and the stress state it is subjected to. This study examines the change in macroscopic physico-mechanical properties of mudstone with temperature following high-temperature treatment. Additionally, we conducted experimental research on the gas and water seepage behavior of mudstone specimens from the top of the coal seam of Taiyuan Group–Shanxi Group in the Ordos Basin. The coal-rock mechanics-permeability test system TAWD-2000 was employed for this purpose. Subsequently, we analyzed the evolution of mudstone permeability after high-temperature treatment with consideration to temperature, axial pressure, and other influencing factors. The findings reveal that gas permeability of mudstone gradually increases with increasing temperature, while water permeability initially decreases and subsequently increases. Furthermore, both gas and water permeability of mudstone exhibit a trend of decreasing and then increasing with rising stress levels after undergoing the same high-temperature treatment. We constructed a quadratic mathematical model with a goodness of fit of 99.4% and 89.2% to describe the relationship between temperature–stress coupling and mudstone gas and water permeability. This model underscores the significance of temperature–stress coupling on mudstone permeability and provides valuable guidance for numerically calculating the gas–water transport law of peripheral rock in the underground coal gasification process and its practical application in engineering.

Mechanical properties of viscoelastic materials subjected to thermal‐oxidative aging: An experimental and theoretical study

AbstractViscoelastic materials (VEMs) made from rubber polymer will inevitably age due to the interactions with the harmful environment during service life, thus reducing the reliability of viscoelastic (VE) damping equipment installed in building structures. In order to understand and be able to predict the degradation of VE damping equipment, it is imperative to comprehensively study the influence of aging on the mechanical properties of VEMs. In this paper, a series of thermal‐oxidative (TO) aging tests and mechanical property tests are conducted on our previously developed VEMs to study effects of TO aging on the molecular chain structure and corresponding changes of macroscopic mechanical properties of VEMs. By classifying molecular chains of VEMS into elastic chains and free chains, the effects of different chemical reactions during TO aging on these two main chains and corresponding changes on macroscopic mechanical behaviors of VEMs are analyzed. This facilitates formulating a mathematical model that can characterize the mechanical behavior of TO aging VEMs. In conjunction with the experimental data, the accuracy and applicability of the proposed model are compared and verified. Sensitivity analyses of parameters involved in the proposed model are then performed. The experimental results demonstrate that the TO aging can degrade the deformation capability and harden the modulus of VEMs, which may adversely affect the performance of VE damping devices. The parameter analyses depict that the TO aging affects the macroscopic mechanical behavior of VEMs by altering the relative number and configuration of free chains and elastic chains as well as their respective contributions to the total stress of VEMs. The results point to the high accuracy of the proposed model in representing the strain–stress behavior of VEMs under different aging conditions.

Short‐term length change measurements and sorption isotherms for AAC compared to OPC

AbstractThe interaction of adsorbed water with the microstructure of cementitious materials leads to effects on macroscopic properties. However, precise quantitative correlation of adsorbed water with short‐term changes in macroscopic properties, such as dimensional changes, remains a challenge. We compare recent results from precise dual‐microscope‐based short‐term length change measurements and discuss differences in length‐change isotherms and adsorption isotherms arising from various cement types. Water vapor adsorption happens already at very low humidity in the interlayer space of the C‐S‐H gel. Adsorption and desorption on cement surfaces due to changing relative humidity induces strong forces in the cement gel, leading to detectable changes in dimensional stability for the hardened material. A significant hysteresis in the water desorption isotherm is often accompanied by hysteresis in dimensional change as well. For precise length change measurements, an optical method for tracking surface patterns on thin cement slices was applied. Short‐term length change results are compared to corresponding water vapor sorption isotherms and pore size measurements. Hypotheses and conclusions regarding microstructural changes and shrinkage mechanisms are discussed in order to understand the experimental data.

Direct tensile mechanical properties and damage fracture mechanisms of thermally damaged coal measures sandstone under high strain rate loading

The direct tensile mechanical properties of highly thermally damaged rock under high strain rate loads are a key basic mechanical problem that must be solved for the stability and effective control of surrounding rock stability in the combustion control area of an underground coal gasification project. In this paper, a two-dimensional equivalent grain-based model (GBM) unit and Split Hopkinson Tension Bar (SHTB) numerical model for thermally damaged coal-measures sandstone were constructed using particle flow code (PFC). The comparison with the experimental results shows that the numerical method can accurately describe the dynamic direct tensile behavior of thermally damaged sandstone. The following conclusions are drawn: The dynamic tensile strength of thermally damaged sandstone shows a significant strain rate-strengthening effect. With the increase in thermal damage temperature, the dynamic tensile strength of sandstone increases first and then decreases. The generation and development of hot cracks in a high-temperature environment is the fundamental reason for the change in macroscopic mechanical properties. The dynamic tensile failure process of thermally damaged sandstone can be divided into four stages: the dynamic damage initiation, the dynamic damage development, the damage crack penetration, and the sample dynamic fracture. With the increase in impact velocity, the initial kinetic energy, elastic strain energy, dissipated energy, and elastic strain energy ratio in the failure process of thermally damaged sandstone gradually increase. In contrast, the dissipated energy ratio gradually decreases. As the heat treatment temperature increases, the elastic strain energy and the ratio of elastic strain energy increase first and then decrease.

Determining glass transition in all-atom acrylic polymeric melt simulations using machine learning.

The functionality of many polymeric materials depends on their glass transition temperatures (Tg). In computer simulations, Tg is often calculated from the gradual change in macroscopic properties. Precise determination of this change depends on the fitting protocols. We previously proposed a robust data-driven approach to determine Tg from the molecular dynamics simulation data of a coarse-grained semiflexible polymer model. In contrast to the global macroscopic properties, our method relies on high-resolution microscopic details. Here, we demonstrate the generality of our approach by using various dimensionality reduction and clustering methods and apply it to an atomistic model of acrylic polymers. Our study reveals the explicit contribution of the side chain and backbone residues in influencing the determination of the glass transition temperature.

Structural insight into the cooperativity of spin crossover compounds.

Spin-crossover (SCO) compounds are promising materials for a wide variety of industrial applications. However, the fundamental understanding of their nature of transition and its effect on the physical properties are still being fervently explored; the microscopic knowledge of their transition is essential for tailoring their properties. Here an attempt is made to correlate the changes in macroscopic physical properties with microscopic structural changes in the orthorhombic and monoclinic polymorphs of the SCO compound Fe(PM-Bia)2(NCS)2 (PM = N-2'-pyridylmethylene and Bia = 4-aminobiphenyl) by employing single-crystal X-ray diffraction, magnetization and DSC measurements. The dependence of macroscopic properties on cooperativity, highlighting the role of hydrogen bonding, π-π and van der Waals interactions is discussed. Values of entropy, enthalpy and cooperativity are calculated numerically based on the Slichter-Drickamer model. The particle size dependence of the magnetic properties is probed along with the thermal exchange and the kinetic behavior of the two polymorphs based on the dependence of magnetization on temperature scan rate and a theoretical model is proposed for the calculation of the non-equilibrium spin-phase fraction. Also a scan-rate-dependent two-step behavior observed for the orthorhombic polymorph, which is absent for the monoclinic polymorph, is reported. Moreover, it is found that the radiation dose from synchrotron radiation affects the spin-crossover process and shifts the transition region to lower temperatures, implying that the spin crossover can be tuned with radiation damage.

In-situ investigation of damage mechanisms in duplex AlCoCrFeNi2.1 high entropy alloy

The AlCoCrFeNi2.1 eutectic high entropy alloy (EHEA) is a promising casting system with high strength, and numerous studies investigating the effects of various thermomechanical processing routes. However, the ductility of this alloy – especially in its cast state – limits its practical applicability. In this paper, damage evolution and microstrain partitioning behaviour is presented along with bulk mechanical performance of the as-cast and hot rolled AlCoCrFeNi2.1 EHEA to provide experimental reasoning behind observed changes in ductility and strength. Tensile testing coupled with in-situ micro-digital image correlation (μ-DIC) and x-ray computed tomography (XCT) were used to determine the damage and fracture mechanisms. Microstrain analysis documents the effect of phase co-deformation and microstructure morphology on crack formation, and the role of damage evolution is supplemented with XCT. These results suggest methods to improve crack resistance in this alloy system and corroborate macroscopic mechanical property changes.

Molecular Dynamics Simulation of the Effect of Low Temperature on the Properties of Lignocellulosic Amorphous Region

In this paper, a molecular model of cellulose amorphous region-water molecule was developed using Materials Studio software by applying the molecular dynamics method. The effect of low temperature on the properties of the lignocellulosic amorphous region, the main component of wood, was investigated in an attempt to explain the macroscopic property changes from a microscopic perspective and to provide a theoretical basis for the safe use of wood and wood products in low-temperature environments and other related areas of research. Dynamic simulations were carried out at 20 °C, 0 °C, −30 °C, −70 °C, −110 °C and −150 °C for the NPT combinations to obtain the energy, volume, density, and hydrogen bonding change trends of their models, respectively. The changes in the microstructure of the water molecule–cellulose amorphous region model were analyzed, and the mechanical properties were calculated. The results showed that the interaction between the amorphous cellulose region and water molecules was enhanced as the temperature decreased, the density of the models increased, and the volume decreased. The number of total hydrogen bonds and the number of hydrogen bonds between water molecule–cellulose chains increased for each model, and the decrease in temperature made the cellulose molecular activities weaker. The values of G, E, and K increased with the decrease in temperature, and K/G decreased with the decrease in temperature. It shows that the decrease in temperature is beneficial to enhance the mechanical properties of the amorphous region of cellulose and increases the stiffness of the material. However, the toughness and plasticity decrease when the temperature is too low.

The emerging field of block copolymer self-assembly-directed quantum materials

The area of functional materials derived from block copolymers (BCPs) as structure-directing agents for various inorganic materials has seen substantial growth as a result of the immense scientific as well as technological promise associated with such hybrid materials. The convergence of BCP self-assembly with the fast-growing field of quantum materials now promises solution-based synthetic approaches to classes of materials that to date are dominated by stringent high-vacuum physical deposition techniques and bulk solid state chemical reactions. Moreover, the ensuing periodic nano- and mesostructures, a characteristic of BCP self-assembly, offer a unique platform for manipulating quantum-level properties, in turn resulting in substantial changes of macroscopic properties. This article will make a case for, review the existing work of, and provide our perspectives on this emerging field of block copolymer self-assembly directed quantum materials.

Adding dry ice into ultra-high-performance concrete to enhance engineering performances and lower CO2 emissions

Developing low-carbon cement-based materials is crucial to address the pressing sustainability concerns the construction industry faces. This study elucidates the effect of adding dry ice on the micro-meso-macro properties of ultra-high-performance concrete (UHPC). The main original points of the method were summarized as follows: simple operation, low technical difficulty, no specific equipment required, and solving the problem that the carbonation curing method is difficult to use in low water-cement ratio concrete. The results show that adding dry ice generates microscopic CO2 bubbles that react with the carbonation of Ca(OH)2 and improve the later-stage strength and electrical resistivity. And adding dry ice reduces the heat of hydration and promotes ettringite formation. The results of microscopic analyses confirmed that increasing the dry ice content results in a decrease in Ca(OH)2; hence more calcium carbonate is formed. It was also observed that the carbon conversion effect became more apparent when the curing period was 28 days. And optical micrograph analysis showed that adding dry ice increased the total bubble content of the matrix and decreased the average bubble diameter, thus affecting the change in macroscopic properties. Moreover, as the addition of dry ice increased from 0 to 15%, the CO2 emission per unit strength decreased from 6.5 to 4.5 kg·CO2·m−3·MPa−1 (30% reduction in CO2 emission). Therefore, adding dry ice to UHPC is an effective way to utilize carbon and is crucial to achieving carbon neutrality in the concrete industry.

Utilization of tricalcium aluminate as modifier on phosphogypsum-based full solid-waste cementitious material

In this study, it was proposed to use tricalcium aluminate (C3A) as modifier to promote the working performance, early strength and volume stability of phosphogypsum-based full solid-waste cementitious material (PSC). The PSC was composed of 60 % β-hemihydrate phosphogypsum (β-HPG), 30 % ground blast-furnace slag (BFS) and 10 % steel slag (SS). Fluidity, setting time, hydration process and phases and volume shrinkage rate were discussed, and the mechanism behind was revealed. The results showed that the addition of 0.5–4 % C3A contributed to the transformation of the PSC from high fluid to fast molding by shortening the setting time of the PSC, increased both the early and late mechanical properties by optimizing hydration products and structures, and improved the volume stability by increasing the generation AFt and C-S-H gel. Especially when the C3A content was 4 %, the 2 h compressive strength of the system reached 2 MPa, the 1 d compressive strength increased by 60 % and the 60 d compressive strength increased by 20 % compared with the blank group; the setting time of the system was shortened by about 1 h; the volume shrinkage rate of the system was reduced by about 50 %. Based on these changes of macroscopic properties, the hydration products and hydration process of the PSC were further analyzed by means of XRD, TG-DTG, thermal analysis of hydration, scanning electron microscope, etc. The influence mechanism of C3A on the PSC was comprehensively discussed, and the environmental assessments were provided. The research content and results of this paper could provide a theoretical basis for the application of PSC in practical engineering.

Boosting the convergence of low-variance DSMC by GSIS

The low-variance direct simulation Monte Carlo (LVDSMC) is a powerful method to simulate low-speed rarefied gas flows. However, in the near-continuum flow regime, due to limitations on the time step and spatial cell size, it takes plenty of time to find the steady-state solution. Here we remove these deficiencies by coupling the LVDSMC with the general synthetic iterative scheme (GSIS) which permits the simulation at the hydrodynamic scale rather than the much smaller kinetic scale. As a proof of concept, we propose the stochastic-deterministic coupling method based on the Bhatnagar-Gross-Krook kinetic model. First, macroscopic synthetic equations are derived exactly from the kinetic equation, which not only contain the Navier-Stokes-Fourier constitutive relation, but also encompass the higher-order terms describing the rarefaction effects. Then, the high-order terms are extracted from LVDSMC and fed into synthetic equations to predict the macroscopic properties which are closer to the steady-state solution than LVDSMC. Finally, the state of simulation particles in LVDSMC is updated to reflect the change of macroscopic properties. As a result, the convergence to steady state is greatly accelerated, and the restrictions on cell size and the time step are removed. We conduct the Fourier stability analysis and simulate several canonical rarefied gas flows to demonstrate the advantages of LVDSMC-GSIS: when the Knudsen number is lower than 0.1, it can use the grid size about 10 times larger than that in traditional DSMC, and it can reduce the computational cost by two orders of magnitude in the flow regime.

Environmental filling materials based on phosphogypsum powder with municipal solid waste incineration ash

A new building filling materials (NBFM) using phosphogypsum and municipal solid waste incineration (MSWI) fly ash is prepared in this paper. The effects of MSWI fly ash dosage and MSWI fly ash water washing pretreatment on mechanical properties, setting time, metal leaching, hydration products and microstructure of NBFM are analyzed by a range of experimental studies. The results indicate that the mechanical properties, setting time and the density of micro interface of NBFM are optimal when the MSWI fly ash dosage is 3%. The mechanical properties of NBFM rise and the condensation time and leaching concentration of heavy metals decline after washing the MSWI fly ash. With the increase of the curing age, the metal element leaching of NBFM decreases, and when the curing age is 7 days, the solidification effect of NBFM on most metal elements meets the standard of Chinese code (GB5085.3-2007). The feasibility of MSWI fly ash and phosphogypsum as filling materials for building engineering is verified, and the change of macroscopic properties of NBFM is explained as well.

Lowering exposure pH for durability enhancement of glass fiber reinforcement polymer (GFRP) rebars

Glass fiber reinforced polymer (GFRP) rebars can be utilized as a substitute for steel reinforcements in concrete structures to eliminate possible steel corrosion. However, embedded GFRP rebars may also degrade with aging time due to the high concrete alkalinity (pH ∼ 13). Previous studies only focused on the GFRP degradation in extreme conditions (pH = 7 and 12.5 to 13.5), whereas little research covered pH down to 11, which could be achieved by modifying the cementitious binder. The purpose of this paper is to evaluate the GFRP durability under exposure to various pH levels (i.e., pH = 7, 11, 12 and 13). Experimental results showed that lowering pH from 13 to 11 could considerably reduce fiber/matrix defects induced by alkali attack, leading to a reduction in diffusion rate from 6.2 × 10-7 to 4.2 × 10-7 mm2/s at 60 °C. Further, a significant increase from 27.6% to 45.9% in GFRP rebar tensile strength retention after 12-month exposure to 60 °C was found when the exposure pH dropped from 13 to 11, but the flexural strength and inter-laminar shear strength were not affected. This change in macroscopic mechanical properties was attributed to the continuous ingress of external solution and the microstructural corrosion of fibers and matrix. The results of this study provide in-depth explanations of the alkali-induced degradation mechanism as well as comprehensive information on the durability performance of GFRP rebars for engineering applications.

Effects of natural ageing on macroscopic physical and mechanical properties, chemical components and microscopic cell wall structure of ancient timber members

The main objective of this study was to investigate the effects of natural ageing on macroscopic physical and mechanical properties, chemical components, and microscopic cell wall structure of larch (Larix principis-rupprechtii Mayr) and nanmu (Phoebe zhennan S. Lee) timber members in ancient architecture. In this work, aged larch and nanmu timber members were obtained from the restoration architecture and their ages were determined based on accelerated mass spectrometer 14C method. Macroscopic physical, mechanical properties and chemical components were tested and determined of each timber members; meanwhile, the microstructural changes of cell wall were observed by scanning electron microscope (SEM). Finally, Pearson’s correlation analysis was conducted to reveal the relationships among them. The results indicated that natural ageing has a significantly effect on the macroscopic physical and mechanical properties, chemical components, and microscopic cell wall structure. First, equilibrium moisture content (EMC), the coefficient of wet swelling coefficient (SW) and colour parameters considerably changed of larch and nanmu timber members with aging years. Mechanical property parameters of larch timber show a significant decrease, and the changes of chemical components and microstructure of cell structure of nanmu specimens indicates the mechanical property parameters decreased. Further, the relative contents of cellulose and hemicellulose were significantly reduced, obvious damage and deformation were observed in the cell wall of larch and nanmu timber specimens. The results explained the change of macroscopic physical and mechanical properties, especially negative effects on mechanical properties. It was concluded that the relative contents of cellulose and hemicellulose were decreased, and the microstructure was damaged under the natural ageing effect, resulting in a decrease in mechanical properties with an increase in colour properties and dimensional stability.

Impact of complex irradiation scenarios on the structure and the properties of the International Simple Glass

This study addresses the consequences of three irradiation scenarios on the structure and macroscopic properties of the ISG glass. The coupling effect between 2.5 MeV electron irradiation (simulating the effects of beta particles and gamma rays) and 7 MeV Au irradiation (simulating the nuclear collisions of the recoil nuclei of alpha decays) was studied by comparing two monobeam irradiations with a sequential double beam irradiation. Various experimental techniques were used to characterize the glass structure and properties, combining Raman, NMR, IR-ATR spectroscopies, hydrostatic weighing, He pycnometry, X-Ray Reflectivity, AFM, surface tension and Vickers microhardness measurements.Electron irradiation up to 3.25 GGy induces only small changes of ISG glass structure and macroscopic properties than Au irradiation. Moreover, the magnitude of the changes induced by the sequential irradiation scenario, i.e. electron followed by Au ions, are the same as the one induced by the monobeam irradiation by Au ions, except for the surface tension. Because the bulk damage state are similar, this work demonstrates that there is no coupling between the damage generated by the electron irradiation and the subsequent nuclear collision generated by Au ions. Finally, the hardness and density changes of ISG glass are very similar to those of SON68 glass when submitted to similar irradiation conditions by electron or nuclear collisions. Therefore ISG glass is found to be a good glass surrogate with respect to radiation ageing of the SON68 glass.

Magnetic field effect on nanoscaled water: Structural and optical investigations

The goal of this work is to investigate the magnetic field with different intensities on the water structure for studying water quality management and agricultural problems. The nanoscale feature is researched under magnetic field effect on normal water through three different intensities; 0.10, 0.15 and 0.20 T. It is known that molecules clustering structure and distribution variations are resulted of magnetic field leading to changes of water macroscopic properties. Magnetic treatment is an impetus for exploring energy gap. The nanoscaled water is characterized using field emission-scanning electron microscopy (FE-SEM). Also, it is analyzed via Fourier-transform infrared spectroscopy (FTIR) and photoluminescence (PL). In addition to investigate the absorption. The magnetized nanoscaled water has energetic properties.