Macroscopic Force Research Articles

Enhancing Mechanophore Activation through Polymer Crystallization.

In the field of polymer mechanochemistry, the activation of mechanophores within linear polymers in the bulk state is often limited by low activation rates. Herein, we demonstrate that the crystallization of polymers can significantly enhance the activation of mechanophores. Employing rhodamine-containing poly(lactic acid) (PLA) and polycaprolactone (PCL) as representative examples, our study reveals that the micromechanical force generated by crystallization is more effective in activating mechanophores than the macroscopic mechanical force induced by compression and ultrasonication, which is particularly pronounced for polymers with low molecular weights. Furthermore, the activation of the mechanophore is found to be positively correlated with the degree of crystallinity and polymer molecular weight, whereas the chirality of polymers does not influence the activation. This study offers new insights into mechanochemical reactions induced by polymer crystallization and provides a novel approach to enhancing mechanochemical reactivity.

Mesoscopic shear evolution characteristics of frozen soil-concrete interface

The mechanical properties of frozen-concrete interfaces affect the stability and durability of engineering structures in cold regions. To investigate these properties, laboratory tests and numerical simulations were conducted to study the mesoscopic evolution of the shear stress-displacement relationship and the shearing process at the interface. The direct shear tests were performed at different environmental temperatures (−2 °C, −5 °C, and −10 °C) and normal stresses (100 kPa, 200 kPa, and 300 kPa) on the frozen soil-concrete interface, and Particle Flow Code (PFC) model of direct shear was developed. The mesoscopic parameters (particle displacement, rotation, force chain, stress, coordination number, porosity, fabric, etc.) of the interface during shearing were simulated using the PFC model. Moreover, the relationship among the interface temperature, cohesion, and friction coefficient was determined based on experimental data, and the accuracy of the PFC model was verified using previous experimental data. The results of the PFC shear model aligned well with those of the laboratory test, and the formation of shear bands was simulated well. The displacement of the soil particles on the upper layer outside the shear zone was uniform, and the direction was the same, whereas the particles inside the shear zone showed significant differences in the dislocation and rotation of the soil particles. The force chain, stress field, coordination number, and porosity were similar in the shear process and showed a concentrated distribution in the opposite direction of the shear motion, which reflected the consistency of the microcosmic response of the particles under the action of macroscopic external forces. The regression equations for the temperature, cohesion, and friction coefficient in this study can be used to simulate the shear behavior of frozen soil-concrete interfaces under different temperatures and normal stresses.

Fermionic Casimir energy in Horava–Lifshitz scenario

In this work, we investigate the violation of Lorentz symmetry through the Casimir effect, one of the most intriguing phenomena in modern physics. The Casimir effect, which represents a macroscopic quantum force between two neutral conducting surfaces, is widely regarded as a triumph of Quantum Field Theory. In this study, we present new results for the Casimir effect, focusing on the contribution of mass associated with fermionic quantum fields confined between two large parallel plates, in the context of Lorentz symmetry violation within the Horava–Lifshitz formalism. To calculate the Casimir energy and pressure, we impose a MIT bag boundary condition on the two plates, compatible with the higher-order derivative term in the modified Dirac equation. Our results reveal a strong influence of Lorentz violation on the Casimir effect. We observe that the Casimir energy is significantly affected, both in intensity and sign, potentially resulting in a repulsive or attractive force between the plates, depending on the critical exponent associated with the Horava–Lifshitz formalism.

Anisotropic mechanism of monocrystalline silicon on surface quality in precision diamond wire saw cutting

The surface quality of wire-saw cut monocrystalline silicon is affected by its anisotropy. This work investigates the effect of anisotropy on the surface quality of monocrystalline silicon (100), (110), and (111) crystalline surfaces in wire-saw cutting processing. The material properties of monocrystalline silicon in different crystal directions are analyzed, and the expressions of elastic modulus of monocrystalline silicon (100), (110), and (111) crystal surfaces are derived, and the influences of material properties and process parameters on macroscopic sawing force and material removal are investigated. The single abrasive grains scratching the surface of monocrystalline silicon and the wire saw cutting and processing process were simulated, and the diamond wire saw cutting and processing of monocrystalline silicon experiment was carried out. The experiment results show that: When the wire saw cuts and processes the (100), (110), and (111) crystal surfaces, the cutting angle with better sawing performance is 30°. The macroscopic normal and tangential average sawing forces on the crystalline surface of monocrystalline silicon (110) differed by 7.22N and 2.54N. The average error between the experiment value of surface warpage and the simulation value is 5.47 %, which indicates the accuracy of the surface morphology prediction model.

Measuring line tension: Thermodynamic integration during detachment of a molecular dynamics droplet

The contact line (CL) is where solid, liquid, and vapor phases meet, and Young’s equation describes the macroscopic force balance of the interfacial tensions between these three phases. These interfacial tensions are related to the nanoscale stress inhomogeneity appearing around the interface, and for curved CLs, e.g., a three-dimensional droplet, another force known as the line tension must be included in Young’s equation. The line tension has units of force, acting parallel to the CL, and is required to incorporate the extra stress inhomogeneity around the CL into the force balance. Considering this feature, Bey et al. [J. Chem. Phys. 152, 094707 (2020)] reported a mechanical approach to extract the value of line tension τℓ from molecular dynamics (MD) simulations. In this study, we show a novel thermodynamics interpretation of the line tension as the free energy per CL length, and based on this interpretation, through MD simulations of a quasi-static detachment process of a quasi-two-dimensional droplet from a solid surface, we obtained the value τℓ as a function of the contact angle. The simulation scheme is considered to be an extension of a thermodynamic integration method, previously used to calculate the solid–liquid and solid–vapor interfacial tensions through a detachment process, extended here to the three-phase system. The obtained value agreed well with the result by Bey et al. and showed the validity of thermodynamic integration at the three-phase interface.

On macroscopic residual QCD force of electrodynamics

We explore a connection between virtual particles of quantum electrodynamics and quantum chromodynamics (QCD) which is predicted to give rise to a residual attractive interaction measurable as a macroscopic force. We calculate the asymptotic behavior of relevant scattering amplitudes, perform their resummation, and analyze the sign of the resulting interaction. Then, we calculate the primary experimentally observable consequences of this Standard Model force. We discuss the impact of this force at terrestrial scales and at astrophysical scales. In particular, we quantify the impact of this force on the warm ionized medium present in galaxies and the intracluster medium present in cluster of galaxies.

Transformative learning at the community-university-land interface: A political ecology of knowledge, education and health

As awareness grows of the catastrophic implications of global environmental change, multiple scholarly fields addressing health-environment relationships have advocated 'transformative' educational strategies. Holistic Indigenous health-environment models inspire and inform many such efforts, but related land-based learning initiatives involving universities are often impeded by the competitive processes of academia. In this article we report on a community-university partnership – Pedagogy for the Anthropocene (P4A) – aimed at developing transformative educational responses to pressing global crises, inspired by land-based approaches. We integrate political ecologies of health, education, and knowledge to understand the troubled production of pedagogical knowledge in P4A, participant experiences in the resulting educational programs and the role of health and bodies in both. We first trace the production of knowledge as shaped by macroscopic and localized institutional forces; organizational and occupational dynamics; interacting knowledges and individuals; and material factors. Next, we explore participant experiences in the resulting educational programming. In both steps, affect-laden bodies of academics, trainees and community members reveal entanglements with human communities and more-than-human elements, shaped in variable ways by institutional forces such as settler colonialism and university neoliberalization. One key finding involves the role of universities in relation to land dispossession at home and abroad; another includes the challenges of pursuing transformational community-university research within contemporary universities. Tracing such entanglements yields implications for future land-based learning efforts in university settings, and broader praxis for environmental justice in the shadow of higher education's complicity with settler colonialism and globally extractive neoliberal capitalism.

Rapid and Mechanically Robust Immobilization of Proteins on Silica Studied at the Single-Molecule Level by Force Spectroscopy and Verified at the Macroscopic Level.

Typical methods for stable immobilization of proteins often involve time-consuming surface modification of silicon-based materials to enable specific binding, while the nonspecific adsorption method is faster but usually unstable. Herein, we fused a silica-binding protein, Si-tag, to target proteins so that the target proteins could attach directly to silica substrates in a single step, markedly streamlining the immobilization process. The adhesion force between the Si-tag and glass substrates was determined to be approximately 400-600 pN at the single-molecule level by atomic force microscopy, which is greater than the unfolding force of most proteins. The adhesion force of the Si-tag exhibits a slight increase when pulled from the C-terminus compared to that from the N-terminus. Furthermore, the Si-tag's adhesion force on a glass surface is marginally higher than that on a silicon nitride probe. The binding properties of the Si-tag are not obviously affected by environmental factors, including pH, salt concentration, and temperature. In addition, the macroscopic adhesion force between the Si-tag-coated hydrogel and glass substrates was ∼40 times higher than that of unmodified hydrogels. Therefore, the Si-tag, with its strong silica substrate binding ability, provides a useful tool as an excellent fusion tag for the rapid and mechanically robust immobilization of proteins on silica and for the surface coating of silica-binding materials.

Three-dimensional spiral model of the wicking effect for continuous polyester filaments

The wicking effect constitutes a pivotal determinant in facilitating the ingress and transference of liquid water within yarns and fabrics. Its significance looms prominently in the context of subsequent product processing, particularly concerning the immersion and interface bonding of textile matrix composites. The twist exerts profound influence over the fiber disposition and density within yarns, as well as the yarn and the wicking pathways for liquid water. We use a mathematical model grounded in the three-dimensional helical capillary permeation mechanism, inherently linked to the twist factor. This model operates under the assumption that the yarn's fibers exhibit uniform diameters and arrangements. Leveraging the macroscopic force equilibrium method, a function of liquid capillary rise with wicking time was deduced. and the dynamic progression of liquid water ascent within the yarn was simulated using the COMSOL platform. Subsequently, a series of wicking experiments were executed on polyester filament yarns, each characterized by varying twist levels. The results revealed that the experimental data coincided well with the theoretical prediction, thus affirming the model's accuracy.

Fifth Forces from QCD Axions Scale Differently.

We reexamine the low-energy potential for a macroscopic fifth force generated from the exchange of two axions. The shift symmetry of the linear axion interactions leads to a potential falling off as V(r)∼1/r^{5}. We find that in the case of the QCD axion higher-order terms in the Lagrangian break the shift symmetry and lead to the dominant contribution to the potential scaling as V(r)∼1/r^{3}. These terms are generated by the same physics responsible for the axion mass, and therefore the new contributions to the potential induce a different force for external nucleons and leptons. We demonstrate how this result affects the sensitivity of searches for new long-range forces.

A new approach to transformation of micro analysis into macro analysis of forces to study the dynamic behaviour of riverbank morphology

ABSTRACT Due to complex nature of the riverbank erosion and owing to action of wide variety of forces on the particles, it is an uphill task for the researchers to find a general approach to riverbank failure mechanism. Here, a planar failure-block of right-angled trapezoidal shape spanning to the tension crack has been considered. Transformation of inter-particle microscopic forces into macroscopic forces has been made to analyse the stability of the block. Stability of the failure block is a function of the bank erosion rate in terms of the escape velocity. Moreover, varying free surface water level has been investigated to study the dynamic behaviour of the bank. With the increasing number of base particles in the tension crack from 10 to 100, escape velocity increases by 8.47% as the water level rises and 10.74% as it falls. Similarly, the increase in escape velocity with free surface water level height from 0 to full height of the tension crack is 39.4% as the water level rises and is 48.4% as water level falls. Rising water level increases hydrostatic confining pressure force, which is a resistive force. This increases the escape velocity continuously leading to greater stability of the mass.

Micro-scratches generation mechanism by copper oxides adhered on silica abrasive in copper chemical mechanical polishing

Chemical mechanical polishing (CMP) may introduce micro-scratches on the copper surface, posing a substantial challenge for developing advanced technology nodes. This study used macroscopic CMP and microscopic atomic force microscopy to investigate the micro-scratches generation mechanism in copper CMP from the perspective of abrasive particles. In the near-neutral slurry containing a low concentration of H2O2, copper can be oxidized to cuprous oxide and/or cupric oxide, forming a fragile oxide layer that can be removed by silica abrasive particles. The removed copper oxides can be adhered on the silica abrasive particles through electrostatic attraction, modifying the surface state. The adhered copper oxides possess irregularities and high hardness, likely inducing high contact stress locally and resulting in micro-scratches on the copper surface.

Modulating Transition Metal Reactivity with Force

AbstractThe reactivity and selectivity of a transition metal catalyst is intimately related to its ligand‐sphere geometry, and, in many cases, the ideal ligand geometry for one step of a catalytic cycle is poorly matched to the ideal ligand geometry for another. For this reason, methods for reversibly modulating ligand geometry on the time scale of catalytic turnover or monomer enchainment are highly desirable. Mechanical force represents a heretofore untapped approach to modulate catalyst geometry and/or reactivity, with the potential to do so on the timescale of catalytic turnover or monomer enchainment. Macroscopic mechanical forces are large, directional and localized to an extent that differentiates them from other forms of energy input such as heat or light. In this Concept, we describe our efforts to address the fundamental challenges associated with force‐modulated transition metal catalysis by employing molecular force probe ligands comprising a stiff stilbene photoswitch tethered to rotationally flexible biaryl bisphosphine ligand. Our efforts to date include the modulation of catalytic activity through force‐mediated ligand perturbations, quantification of the force‐coupled ligand effects on the energetics of elementary organometallic transformations, and evaluation of the mechanisms of force transduction in these systems.

Multi‐Length Scale Communication Effects in Catalysis: Thinking Big and Acting Small

AbstractThe use of hierarchically structured materials as catalysts has been finding increasing application in the past years. For these catalytic systems, not only the nano‐scale matters: a high degree of order across multiple length scales, along with its control and analytical assessment, is of paramount importance to obtain innovative properties that can find application in catalysis. Most reviews dealing with hierarchically structured materials are concerned with the “bottom‐up” transfer of structural information along the different length scales, with special emphasis on the transmission of chirality. Due to their mesoscale size together with their complex behaviour, these systems are often susceptible to feel the effects of macroscopic forces, that can exert a “top‐down” control of their catalytic properties, so that an external stimulus, acting at the level of the supramolecular architecture of the catalyst, can ultimately determine the outcome of the catalyzed reaction at the molecular level. We review in this paper some recent reports that deal with the experimental implementation of this concept, either by using a mechanical force in a full range direct transmission to the reaction coordinate, or by means of a stepwise relay transmission from the macroscopic level (purely supramolecular chirality) to the nanoscopic one. We focus in this review on these multi‐length scale communication control effects, identifying the different mechanisms that are affecting the catalytic activity.

Statistical field theory of mechanical stresses in Coulomb fluids: general covariant approach vs Noether’s theorem

In this paper, we introduce a statistical field theory that describes the macroscopic mechanical forces in inhomogeneous Coulomb fluids. Our approach employs the generalization of Noether’s first theorem for the case of a fluctuating order parameter to calculate the stress tensor for Coulomb fluids. This tensor encompasses the mean-field stress tensor and fluctuation corrections derived through the one-loop approximation. The correction for fluctuations includes a term that accounts for the thermal fluctuations of the local electrostatic potential and field in the vicinity of the mean-field configuration. This correlation stress tensor determines how electrostatic correlation affects local stresses in a nonuniform Coulomb fluid. We also use a previously formulated general covariant methodology (Brandyshev and Budkov 2023 J. Chem. Phys. 158 174114) in conjunction with a functional Legendre transformation method and derive within it the same total stress tensor. We would like to emphasize that our general approaches are applicable not only to Coulomb fluids but also to nonionic simple or complex fluids, for which the field-theoretic Hamiltonian is known as a function of the relevant scalar order parameters.

Variational field theory of macroscopic forces in coulomb fluids.

Based on the variational field theory framework, we extend our previous mean-field formalism [Y. A. Budkov and A. L. Kolesnikov, JStatMech 2022, 053205.2022], taking into account the electrostatic correlations of the ions. We employ a general covariant approach and derive a total stress tensor that considers the electrostatic correlations of ions. This is accomplished through an additional term that depends on the autocorrelation function of the local electric field fluctuations. Utilizing the derived total stress tensor and applying the mechanical equilibrium condition, we establish a general expression for the disjoining pressure of the Coulomb fluids, confined in a pore with a slit-like geometry. Using this equation, we derive an asymptotic expression for the disjoining pressure in a slit-like pore with non-electrified conductive walls. Present theory is the basis for future modeling of the mechanical stresses that occur in electrode pores with conductive charged walls, immersed in liquid phase electrolytes beyond the mean-field theory.

A 3D-Printed Dual Driving Forces Scaffold with Self-Promoted Cell Absorption for Spinal Cord Injury Repair.

Stem cells play critical roles in cell therapies and tissue engineering for nerve repair. However, achieving effective delivery of high cell density remains a challenge. Here, a novel cell delivery platform termed the hyper expansion scaffold (HES) is developed to enable high cell loading. HES facilitated self-promoted and efficient cell absorption via a dual driving force model. In vitro tests revealed that the HES rapidly expanded 80-fold in size upon absorbing 2.6 million human amniotic epithelial stem cells (hAESCs) within 2min, representing over a 400% increase in loading capacity versus controls. This enhanced uptake benefited from macroscopic swelling forces as well as microscale capillary action. In spinal cord injury (SCI) rats, HES-hAESCs promoted functional recovery and axonal projection by reducing neuroinflammation and improving the neurotrophic microenvironment surrounding the lesions. In summary, the dual driving forces model provides a new rationale for engineering hydrogel scaffolds to facilitate self-promoted cell absorption. The HES platform demonstrates great potential as a powerful and efficient vehicle for delivering high densities of hAESCs to promote clinical treatment and repair of SCI.

Macroscopic model for generalised Newtonian inertial two-phase flow in porous media

A closed macroscopic model for quasi-steady, inertial, incompressible, two-phase generalised Newtonian flow in rigid and homogeneous porous media is formally derived. The model consists of macroscopic equations for mass and momentum balance as well as an expression for the macroscopic pressure difference between the two fluid phases. The model is obtained by upscaling the pore-scale equations, employing a methodology based on volume averaging, the adjoint method and Green's formulation, only assuming the existence of a representative elementary volume and the separation of scales between the microscale and the macroscale. The average mass equations coincide with those for Newtonian flow. The macroscopic momentum balance equation in each phase expresses the seepage velocity in terms of a dominant and a coupling Darcy-like term, a contribution from interfacial tension effects and another one from interfacial inertia. Finally, the expression of the macroscopic pressure difference is obtained in terms of the macroscopic pressure gradient and body force in each phase, and interfacial terms that account for capillary effects and inertia, if present when the interface is not stationary. All terms involved in the macroscale equations are predicted from the solution of adjoint closure problems in periodic representative domains. Numerical predictions from the upscaled models are compared with direct numerical simulations for two-dimensional configurations, considering flow of a Newtonian non-wetting fluid and a Carreau wetting fluid. Excellent agreement between the two approaches confirms the pertinence of the macroscopic models derived here.

Preferential Mechanochemical Activation of Short Chains in Bidisperse Triblock Elastomers.

Polymer mechanochemistry offers attractive opportunities for using macroscopic forces to drive molecular-scale chemical transformations, but achieving efficient activation in bulk polymeric materials has remained challenging. Understanding how the structure and topology of polymer networks impact molecular-scale force distributions is critical for addressing this problem. Here we show that in block copolymer elastomers the molecular-scale force distributions and mechanochemical activation yields are strongly impacted by the molecular weight distribution of the polymers. We prepare bidisperse triblock copolymer elastomers with spiropyran mechanophores placed in either the short chains, the long chains, or both and show that the overall mechanochemical activation of the materials is dominated by the short chains. Molecular dynamics simulations reveal that this preferential activation occurs because pinning of the ends of the elastically effective midblocks to the glassy/rubbery interface forces early extension of the short chains. These results suggest that microphase segregation and network strand dispersity play a critical role in determining molecular-scale force distributions and suggest that selective placement of mechanophores in microphase-segregated polymers is a promising design strategy for efficient mechanochemical activation in bulk materials.

An experimental study of triboelectrostatic particle charging behavior and its associated fundamentals

Triboelectrostatic separation is a unique dry particle separation process that has been applied to many industrial applications. However, little attention has been directed to the process of charge transfer during the particle collision and friction which is critical for the success of triboelectrostatic separation. The present study has been conducted to quantify the effects of particle size, collision speed, contact mode (collision or friction), etc. on the charge density, surface potential, morphology, etc. of quartz particles based on macroscopic triboelectrostatic charge measurements and microscopic atomic force microscopy (AFM) characterization. The macroscopic charging performance results showed that the charge to mass ratio of quartz particles depended on process parameters such as feed rate and charger rotation speed and the highest charge to mass ratio reached −56.21 μC/g. The microscopic AFM characterization data reveals that the increase in particle size and collision velocity fundamentally enhanced the triboelectrostatic charging process. The surface potential of quartz increased from −60.60 mV to −477.15 mV with increasing PVC particle size from 280 μm to 1250 μm and similar behavior was observed with increasing the collision velocity from 0.99 m/s to 2.62 m/s. The change in contact mode only changed the magnitude of charge transfer but did not change the polarity of charged particle. The process of charge transfer was accompanied with the change of surface morphology and the degree of change in surface morphology was not directly related to the amount of charge transfer.