Intermolecular and surface forces in atomic-scale manufacturing

Atomic and close-to-atomic scale manufacturing(ACSM)aims to provide techniques for manufacturing in various fields,such as circuit manufacturing,high energy physics equipment,and medical devices and materials.The realization of atomic scale material manipulation depending on the theoretical system of classical mechanics faces great challenges.Understanding and using intermolecular and surface forces are the basis for better designing of ACSM.Transformation of atoms based on scanning tunneling microscopy or atomic force microscopy(AFM)is an essential process to regulate intermolecular interactions.Self-assemble process is a thermodynamic process involving complex intermolecular forces.The competition of these interaction determines structure assembly and packing geometry.For typical nanomachining processes including AFM nanomachining and chemical mechanical polishing,the coupling of chemistry and stress(tribochemistry)assists in the removal of surface atoms.Furthermore,based on the principle of triboelectrochemistry,we expect a further reduction of the potential barrier,and a potential application in high-efficiency atoms removal and fabricating functional coating.Future fundamental research is proposed for achieving high-efficiency and high-accuracy manufacturing with the aiding of external field.This review highlights the significant contribution of intermolecular and surface forces to ACSM,and may accelerate its progress in the in-depth investigation of fundamentals.

Study of ss-DNA Adsorption and Nano-mechanical Properties on Mica Substrate with Surface Forces Apparatus

Many DNA?based devices need to build stable and controllable DNA films on surfaces. However, the most com?monly used method of film characterization, namely, the probe?like microscopes which may destroy the sample and substrate. Surface Forces Apparatus(SFA) technique, specializing in surface interaction studies, is introduced to investigate the e ects of DNA concentration on the formation of single?stranded DNA(ss?DNA) film. The result demonstrates that 50 ng/μL is the lowest concentration that ss?DNA construct a dense layer on mica. Besides, it is also indicated that at di erent DNA concentrations, ss?DNA exhibit diverse morphology: lying flat on surface at 50 ng/μL while forming bilayer or cross?link at 100 ng/μL, and these ss?DNA structures are stable enough due to the repeatabil?ity even under the load of 15 mN/m. At the same time, an obvious adhesion force is measured:/m at 100 ng/μL, respectively, which is attributed to the ion?correlation e ect. M-6.5 mN/m at 50 ng/μL and-5.3 mNoreover, the atomic force microscopy(AFM) images reveal the entire surface is covered with wormlike ss?DNA and the measured surface roughness(1.8±0.2 nm) also matches well with the film thickness by SFA. The desorption behaviors of ss?DNA layer from mica surface occur by adding sodium salt into gap bu er, which is mainly ascribed to the decreased ion?ion cor?relation force. This paper employing SFA and AFM techniques to characterize the DNA film with flexibility and stable mechanical ability achieved by ion bridging method, is helpful to fabricate the DNA?based devices in nanoscale.

Mechanic model of water-based boundary lubricated contact based on surface force effects

In water-based boundary lubrication regime,the contact gaps(or boundary lubricated film thickness)and surface pressure distribution must be determined to really understand the boundary lubricated contact mechanism.However,the accurate determination of these parameters is limited.In this study,a mechanical model based on boundary lubricated contact involving surface force effects is developed.The surface force distribution characteristics,normal force vs.central film thickness curve,and macroscale water-based boundary lubricated contact are investigated numerically.The results show that hydration directly affects surface force interaction.The accurate boundary lubricated film thickness and surface pressure distribution can be obtained using this model in point contact.Furthermore,the mechanism of macroscale water-based liquid boundary lubricated contact is investigated,in which a water-based boundary lubricated film is formed under appropriate operating conditions based on surface force effects during running-in.This study can reveal the water-base boundary lubricated contact behavior and the carrying capacity of the surface force effect,and provides important design guidance for the surface force effect to achieve liquid superlubricity in water-based boundary lubricated contacts.

Numerical simulations of Atlantic meridional overturning circulation(AMOC)from OMIP experiments and its sensitivity to surface forcing

Atlantic meridional overturning circulation(AMOC)plays an important role in transporting heat meridionally in the Earth’s climate system and is also a key metrical tool to verify oceanic general circulation models.Two OMIP(Ocean Model Intercomparison Project phase 1 and 2)simulations with LICOM3(version 3 of the LASG/IAP Climate System Ocean Model)developed at the State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics(LASG),Institute of Atmospheric Physics(IAP),are compared in this study.Both simulations well reproduce the fundamental characteristics of the AMOC,but the OMIP1 simulation shows a significantly stronger AMOC than the OMIP2 simulation.Because the LICOM3 configurations are identical between these two experiments,any differences between them must be attributed to the surface forcing data.Further analysis suggests that sea surface salinity(SSS)differences should be mainly responsible for the enhanced AMOC in the OMIP1 simulation,but sea surface temperature(SST)also play an unignorable role in modulating AMOC.In the North Atlantic,where deep convection occurs,the SSS in OMIP1 is more saline than that in OMIP1.We find that in the major region of deep convection,the change of SSS has more significant effect on density than the change of SST.As a result,the SSS was more saline than that in OMIP2,leading to stronger deep convection and subsequently intensify the AMOC.We conduct a series of numerical experiments with LICOM3,and the results confirmed that the changes in SSS have more significant effect on the strength of AMOC than the changes in SST.

Probing the Interfacial Forces and Surface Interaction Mechanisms in Petroleum Production Processes

Despite the advances that have been made in renewable energy over the past decade,crude oil or petroleum remains one of the most important energy resources to the world.Petroleum production presents many challenging issues,such as the destabilization of complex oil-water emulsions,fouling phenomena on pipelines and other facilities,and water treatment.These problems are influenced by the molecular forces at the oil/water/solid/gas interfaces involved in relevant processes.Herein,we present an overview of recent advances on probing the interfacial forces in several petroleum production processes(e.g.,bitumen extraction,emulsion stabilization and destabilization,fouling and antifouling phenomena,and water treatment)by applying nanomechanical measurement technologies such as a surface forces apparatus(SFA)and an atomic force microscope(AFM).The interaction forces between bitumen and mineral solids or air bubbles in the surrounding fluid media determine the bitumen liberation and flotation efficiency in oil sands production.The stability of complex oil/water emulsions is governed by the forces between emulsion drops and particularly between interface-active species(e.g.,asphaltenes).Various oil components(e.g.,asphaltenes)and emulsion drops interact with different substrate surfaces(e.g.,pipelines or membranes),influencing fouling phenomena,oil-water separation,and wastewater treatment.Quantifying these intermolecular and interfacial forces has advanced the mechanistic understanding of these interfacial interactions,facilitating the development of advanced materials and technologies to solve relevant challenging issues and improve petroleum production processes.Remaining challenges and suggestions on future research directions in the field are also presented.

Intermolecular and Surface Interactions in Engineering Processes

Interactions involving chemical reagents,solid particles,gas bubbles,liquid droplets,and solid surfaces in complex fluids play a vital role in many engineering processes,such as froth flotation,emulsion and foam formation,adsorption,and fouling and anti-fouling phenomena.These interactions at the molecular,nano-,and micro scale significantly influence and determine the macroscopic performance and efficiency of related engineering processes.Understanding the intermolecular and surface interactions in engineering processes is of both fundamental and practical importance,which not only improves production technologies,but also provides valuable insights into the development of new materials.In this review,the typical intermolecular and surface interactions involved in various engineering processes,including Derjaguin–Landau–Verwey–Overbeek(DLVO)interactions(i.e.,van der Waals and electrical doublelayer interactions)and non-DLVO interactions,such as steric and hydrophobic interactions,are first introduced.Nanomechanical techniques such as atomic force microscopy and surface forces apparatus for quantifying the interaction forces of molecules and surfaces in complex fluids are briefly introduced.Our recent progress on characterizing the intermolecular and surface interactions in several engineering systems are reviewed,including mineral flotation,petroleum engineering,wastewater treatment,and energy storage materials.The correlation of these fundamental interaction mechanisms with practical applications in resolving engineering challenges and the perspectives of the research field have also been discussed.

Distinct Modes of Winter Arctic Sea Ice Motion and Their Associations with Surface Wind Variability

Using monthly mean sea ice velocity data obtained from the International Arctic Buoy Programme （IABP） for the period of 1979–1998 and the monthly mean NCEP/NCAR re-analysis dataset （1960–2002）, we investigated the spatiotemporal evolution of the leading sea ice motion mode （based on a complex correlation matrix constructed of normalized sea ice motion velocity） and their association with sea level pressure （SLP） and the predominant modes of surface wind field variability. The results indicate that the leading winter sea ice motion mode’s spatial evolution is characterized by two alternating and distinct sea ice modes, or their linear combination. One mode （M1） shows a nearly closed cyclonic or anti-cyclonic circulation anomaly in the Arctic Basin and its marginal seas, resembling to a large extent the response of sea ice motion to the Arctic Oscillation （AO）, as many previous studies have revealed. The other mode （M2） displays a coherent cyclonic or anti-cyclonic circulation anomaly with its center close to the Laptev Sea, which has not been identified in previous observational studies. In fact, M1 and M2 respectively reflect the responses of sea ice motion to two predominant modes of winter surface wind variability north of 70 ？ N, which well correspond, with slight differences, to the first two modes of EOF analysis of winter monthly mean SLP north of 70 ？ N. These slight differences in SLP anomalies lead to a difference of M2 from the response of sea ice motion to the dipole anomaly. Although the AO significantly influences sea ice motion, it is not crucial for the existence of M1. The new sea ice motion mode （M2） has the largest variance and clearly differs from the response of winter monthly mean sea ice motion to the dipole anomaly in SLP fields, and corresponding SLP anomalies also show differences compared to the dipole anomaly. This study indicates that in the Arctic Basin and its marginal seas, slight differences in SLP anomaly patterns can force distinctly different sea ice motion anomalies.

ATOMIC FORCE MICROSCOPY OBSERVATION OF MAGNETRON SPUTTERED ALUMINUM－SILICON ALLOY FILMS

wo different surface morphology characteristics of magnetron sputtered aluminumsilicon(Al-Si)alloy films deposited at 0 and 200℃ were observed by atomic force microscopy(AFM).One is irregularly shaped grains put togther on a plane.The other is irregularly shaped grains Piled up in space. Nanometer-sized particles with heights from 1.6 to 2.9 nm were first observed. On the basis of these observations the growth mechanism of magnetron sputtered films is discussed.

Exact mesh shape design of large cable-network antenna reflectors with flexible ring truss supports

An exact-designed mesh shape with favorable surface accuracy is of practical significance to the performance of large cable-network antenna reflectors. In this study, a novel design approach that could guide the generation of exact spatial parabolic mesh configurations of such reflector was proposed. By incorporating the traditional force density method with the standard finite element method, this proposed approach had taken the deformation effects of flexible ring truss supports into consideration, and searched for the desired mesh shapes that can satisfy the requirement that all the free nodes are exactly located on the objective paraboloid. Compared with the conventional design method,a remarkable improvement of surface accuracy in the obtained mesh shapes had been demonstrated by numerical examples. The present work would provide a helpful technical reference for the mesh shape design of such cable-network antenna reflector in engineering practice.

Experimental Study of Machinability in Millgrinding of SiCp/Al Composites

An attempt was made to investigate the machinability of Si Cp/Al composites based on the experimental study using mill-grinding processing method. The experiments were carried out on a high-speed CNC machining center using integrated abrasive cutting tool. The effects of combined machining parameters, e g, cutting speed（vs）, feed rate（vf）, and depth of cut（ap）, with the same change of material removal rate（MRR） on the mill-grinding force and surface roughness（Ra） were investigated. The formation mechanism of typical machined surface defects was analyzed by SEM. The experimental results reveal that with the same change of material removal rate, lower mill-grinding force values can be gained by increasing depth of cut and feed rate simultaneously at higher cutting speed. With the same change of MRR value, lower surface roughness values can be gained by increasing the feed rate at higher cutting speed, rather than just increasing the depth of cut, or increasing the feed rate and depth of cut simultaneously. The machined surface of Si Cp/Al composites reveals typical defects which can influence surface integrity.

An improved mathematical model to simulate mold filling process in high pressure die casting using CLSVOF method and CSF model

A 3D mathematical model was proposed to simulate the mold filling process in high-pressure die casting(HPDC) to improve accuracy considering the surface tension. Piecewise liner interface calculation(PLIC) and volume of fluid(VOF) methods were used to construct the pattern of the liquid interface. A coupled levelset and VOF method(CLSVOF) was proposed to capture the interface pattern and obtain its normal vector. A continuum surface force(CSF) model was used to consider the surface tension. Two water analogy experiments were carried out using the proposed model. Simulation and experimental results were analyzed and compared; and the effects of surface tension were also discussed. The simulation results agreed well with the experiments and the simulation accuracy was an improvement on interface geometries, liquid flows, and gas entrapments.

Study of main body element of crustal strain and its relationship with moderate-strong earthquakes

In this paper, progress in strain study of blocks and faults by GPS data are discussed, and the concept that active structures between blocks are the main body of crustal strain is clarified. By energy transfer principle of elastic mechanics, the relation between strain around faults and tectonic force on fault surfaces is set up and main body element model of crustal strain is constructed. Finally, the relation between mechanical evolution of model and seismogenic process of Kunlun earthquake （Ms=8.1） is discussed by continuous GPS data of datum stations. The result suggests that the relatively relaxed change under background of strong compressing and shearing may help to trigger moderate-strong earthquakes.

Why a mosquito leg possesses superior load-bearing capacity on water:Experimentals

Mosquitoes possess the striking ability to walk on water because each of their legs has a huge water supporting force（WSF） that is 23 times their body weight.Aiming at a full understanding of the origins of this extremely large force,in this study,we concentrate on two aspects of it：the intrinsic properties of the leg surface and the active control of the initial stepping angle of the whole leg.Using a measurement system that we developed ourselves,the WSFs for the original leg samples are compared with those whose surface wax and microstructures have been removed and with those of a different stiffness.The results show that leg f exibility plays a dominant role over surface wax and microstructures on the leg surface in creating the supporting force.Moreover,we discuss the dependence relationship between the maximum WSF and the initial stepping angle,which indicates that the mosquito can regulate this angle to increase or decrease the WSF during landing or takeoff.These finding are helpful for uncovering the locomotion mechanism of aquatic insects and for providing inspiration for the design of microfluids miniature boats,biomimetic robots,and microsensors.

Grinding behavior and surface appearance of(TiC_p+ TiB_w)/Ti-6Al-4V titanium matrix composites

（TiCp＋ TiBw）/Ti-6Al-4V titanium matrix composites（PTMCs） have broad application prospects in the aviation and nuclear field. However, it is a typical difficult-to-cut material due to high hardness of the reinforcements, high strength and low thermal conductivity of Ti-6Al-4V alloy matrix. Grinding experiments with vitrified CBN wheels were conducted to analyze comparatively the grinding performance of PTMCs and Ti-6Al-4V alloy. Grinding force and force ratios, specific grinding energy, grinding temperature, surface roughness, ground surface appearance were discussed. The results show that the normal grinding force and the force ratios of PTMCs are much larger than that of Ti-6Al-4V alloy. Low depth of cut and high workpiece speed are generally beneficial to achieve the precision ground surface for PTMCs. The hard reinforcements of PTMCs are mainly removed in the ductile mode during grinding. However, the removal phenomenon of the reinforcements due to brittle fracture still exists, which contributes to the lower specific grinding energy and grinding temperature of PTMCs than Ti-6Al-4V alloy.

Optimal machining conditions for turning Ti-6Al-4V using response surface methodology

Machining titanium is one of ever-increasing magnitude problems due to its characteristics such as low thermal conductivity, modulus of elasticity and work hardening. The efficient titanium alloy machining involves a proper selection of process parameters to minimize the tangential force （Fz） and surface roughness （Ra）. In the present work, the performance of PVD/TiA1N coated carbide inserts was investigated using response surface methodology （RSM） for turning Ti-6A1-4V. The effects of process parameters such as speed （v）, feed （/＇）, depth of cut （d） and back rake angle （Ty） on Fz and Ra were investi- gated. The experimental plan used for four factors and three levels was designed based on face centered, central composite design （CCD）. The experimental results indi- cated that Fz increased with the increase in d, f and decreased with the increase in v and yy, whereas Ra decreased with the increase in v and 7y, and increased with d and v. The goodness of fit of the regression equations and model fits （R2） for Fz and Ra were found to be 0.968 and 0.970, which demonstrated that it was an effective model. A confirmation test was also conducted in order to verify the correctness of the model.

IMPACTS OF SURFACE FRICTION AND OROGRAPHICAL FORCING ON THE EAST ASIA COASTAL CYCLOGENESIS

Some numerical simulations from real data were carried out to examine the impacts of surface friction and orographic forcing on the East Asia coastal cyclogenesis.The results show that the decreasing of the surface friction over the ocean is essential for the cyclone development and the mechanical forcing of Qinghai-Xizang Plateau acts a damping effect in the initial stage of the cyclone.

Distance dependence of atomic-resolution near-field imaging on α-Al2O3 （0001） surface with respect to surface photovoltage of silicon probe tip

Recently, we achieved atomic-resolution optical imaging with near-field scanning optical microscopy using photon-induced force detection. In this technique, the surface photovoltage of the silicon-tip apex induced by the optical near field on the surface is measured as the electrostatic force. We demonstrated atomicresolution imaging of the near field on the α-Al2O3 （0001） surface of a prism. We investigated the spatial distribution of the near field by scanning at different tip-sample distances and found that the atomic corrugation of the near-field signal was observed at greater distances than that of the atomic force microscopy signal. As the tip-sample distance increased, the normalized signal-to-noise ratio of the near field is in a gradual decline almost twice that of the frequency shift （Δf）.

PARTICLE PROPERTIES——PROMISE AND NEGLECT

We see two major trends in Particie Technology. First, the focus is shifted from unit operations towards functional products, i.e. towards product engineering. Second, modeling will become more and more important. Proc-esses cannot yet be designed from basie molecular understanding. Nanotechnology, however, begins to bridge this gap between molecules and particles and may thus open new ways not only for the production and handling of particulate matter but also for the engineered design of advanced material properties. Starting from the concept of product engineering we investigate the basie preconditions for tailoring nanoparticulate properties, i.e. the control of the particie in-teractions. Nanotechnology can only be transferred to industrial production if the interactions are effectively controlled.Material and particie properties are essential for predictive models. Although strong tools like MD, DEM or population balance models are available, these models are only predictive if realistic material and particie properties are available which is often not the case. We show for selected examples how particie properties can be obtained by studying the physically relevant elementary processes. The impact breakage behavior of many different materials is described by a master curve. Particie adhesion can be modeled if the roughness of particie and substrate and the Hamaker constant are known. The latter is obtained from adsorption studies.

Unlocking the secrets behind liquid superlubricity:A state-ofthe-art review on phenomena and mechanisms

Superlubricity,the state of ultralow friction between two sliding surfaces,has become a frontier subject in tribology.Here,a state-of-the-art review of the phenomena and mechanisms of liquid superlubricity are presented based on our ten-year research,to unlock the secrets behind liquid superlubricity,a major approach to achieve superlubricity.An overview of the discovery of liquid superlubricity materials is presented from five different categories,including water and acid-based solutions,hydrated materials,ionic liquids(ILs),two-dimensional(2D)materials as lubricant additives,and oil-based lubricants,to show the hydrodynamic and hydration contributions to liquid superlubricity.The review also discusses four methods to further expand superlubricity by solving the challenge of lubricants that have a high load-carrying capacity with a low shear resistance,including enhancing the hydration contribution by strengthening the hydration strength of lubricants,designing friction surfaces with higher negative surface charge densities,simultaneously combining hydration and hydrodynamic contribution,and using 2D materials(e.g.,graphene and black phosphorus)to separate the contact of asperities.Furthermore,uniform mechanisms of liquid superlubricity have been summarized for different liquid lubricants at the boundary,mixed,and hydrodynamic lubrication regimes.To the best of our knowledge,almost all the immense progresses of the exciting topic,superlubricity,since the first theoretical prediction in the early 1990s,focus on uniform superlubricity mechanisms.This review aims to guide the research direction of liquid superlubricity in the future and to further expand liquid superlubricity,whether in a theoretical research or engineering applications,ultimately enabling a sustainable state of ultra-low friction and ultra-low wear as well as transformative improvements in the efficiency of mechanical systems and human bodies.

Inter-and intramolecular adhesion mechanisms of mussel foot proteins

Mussel foot proteins(Mfps) secreted in the byssal plaque of marine mussels are widely researched for their relevance to mussel adhesion in water. As the abundant residue in the amino acid sequences of major adhesive proteins, 3,4-dihydroxyphenylalanine(Dopa) or its catecholic moiety plays a key role in both Mfp binding to surface and cohesive cross-linking of Mfps in byssal plaques. The binding performance of an Mfp significantly depends on the content and redox state of Dopa, whereas the types of interaction vary in line with different surface chemistries and p H conditions. Thorough understanding of mussel adhesion from a molecular perspective is crucial to promote the application of synthetic mussel-bionic adhesives. This article presents a brief review of the research progress on the adhesion mechanisms of Mfps, which further emphasizes the contributions of Dopamediated interactions and considers other amino acids and factors. The involved inter-and intramolecular interactions are responsible for not only the diverse adhesion capacities of an adhesive byssal plaque as mussel's adhesion precursor but also the formation and properties of the plaque structure.