Helical Dielectrophoretic Particle Separator Fabricated by Conformal Spindle Printing

This paper reports the fabrication and testing of a helical cell separator that uses insulator-based dielectrophoresis as the driving force of its separation. The helical channel shape’s main advantage is its constant curvature radius which generates a constant electric field gradient. The presented separator was fabricated by extruding a sacrificial ink on rotating spindles using a computer-controlled robot. After being assembled, connected to the reservoir and encapsulated in epoxy resin, the ink was removed to create a helical microchannel. The resulting device was tested by circulating polystyrene microbeads of 4 and 10 μm diameter through its channel using a voltage of 900 VDC. The particles were separated with efficiencies of 94.0% and 92.5%, respectively. However, roughness in some parts of the channel and connections that had larger diameters compared to the channel created local electric field gradients which, doubtless, hindered separation. It is a promising device that could lead the way toward portable and affordable medical devices.

Enhanced mechanical and thermal properties of two-dimensional SiC and GeC with temperature and size dependence

Two-dimensional materials with novel mechanical and thermal properties are available for sensors,photodetectors,thermoelectric,crystal diode and flexible nanodevices.In this investigation,the mechanical and thermal properties of pristine SiC and GeC are explored by molecular dynamics simulations.First,the fracture strength and fracture strain behaviors are addressed in the zigzag and armchair directions at 300 K.The excellent toughness of SiC and GeC is demonstrated by the maximal fracture strain of 0.43 and 0.47 in the zigzag direction,respectively.The temperature-tunable tensile strength of SiC and GeC is also investigated.Then,using non-equilibrium molecular dynamics(NEMD)calculations,the thermal performances of SiC and GeC are explored.In particular,the thermal conductivity of SiC and GeC shows a pronounced size dependence and reaches up to 85.67 W·m^(-1)-K^(-1)and 34.37 W·m^(-1)-K^(-1),respectively.The goal of our work is to provide a theoretical framework that can be used in the near future.This will enable us to design an efficient thermal management scheme for two-dimensional materials in electronics and optoelectronics.

Stress-assisted design of stiffened graphene electrode structure toward compact energy storage

The low spatial charge-storage density of porous carbons greatly limits volumetric performance in electrochemical capacitors.An increase of charge-storage density requires structural refinements to balance the trade-offs between the porosity and density of materials,but the limited mechanical properties of carbons usually fail to withstand effective densifying processes and obtain an ideal pore structure.Herein,we design the stiffened graphene of superior bending rigidity,enabling the fine adjustments of pore structure to maximize the volumetric capacitance for the graphene-based electrodes.The inplane crumples on graphene sheets are found to contribute largely to the bending rigidity,which is useful to control the structural evolution and maintain sufficient ion-accessible surface area during the assembling process.This makes the capacitance of stiffening activated graphene keep 98%when the electrode density increases by 769%to reach 1.13 g cm^(-3) after mechanical pressure,an excellent volumetric energy density of 98.7 Wh L^(-1) in an ionic-liquid electrolyte is achieved.Our results demonstrate the role of intrinsic material properties on the performance of carbon-based electrodes for capacitive energy storage.

Static and dynamic mechanics of cell monolayers:A multi-scale structural model

Epithelial monolayers act as a vital player in a variety of physiological activities,such as wound healing and embryonic development.The mechanical behavior of epithelial monolayers has been increasingly studied with the recent rapid development of techniques.Under dynamic loadings,the creep response of epithelial monolayers shows a power-law dependence on the time with an exponent larger than that of a single cell.Under static loadings,the elastic modulus of epithelial monolayers is nearly two orders of magnitude higher than that of a single cell.To date,there is a lack of a mechanical model that can describe both the dynamic and static mechanical responses of epithelial monolayers.Here,based on the structural features of cells,we establish a multi-scale structural model of cell monolayers.It is found that the proposed model can naturally capture the dynamic and static mechanical properties of cell monolayers.Further,we explore the effects of the cytoskeleton and the membrane moduli on the dynamical power-law rheological responses and static stress-strain relations of a single cell and cell monolayers,respectively.Our work lays the foundation for subsequent studies of the mechanical behavior of more complex epithelial tissues.

High energy barriers for edge dislocation motion in body-centered cubic high entropy alloys

Recent theory proposes that edge dislocations in random body-centered cubic(BCC)high entropy alloys have high barriers for motion,conveying high strengths up to high temperatures.Here,the energy barriers for edge motion are computed for two model alloys,NbTaV and MoNbTaW as represented by interatomic potentials,using the Nudged Elastic Band method and compared to theoretical predictions.The average magnitude of the barriers and the average spacing of the barriers along the glide direction agree well with the analytical theory,with no adjustable parameters.The evolution of the barriers versus applied stress is modeled,and the mean strength is in reasonable agreement with the predicted zero-temperature strength.These findings validate the analytic theory.A reduced analytic model based on solute misfit volumes is then applied to Hf-Mo-Nb-Ta-Ti-Zr and Mo-Nb-Ta-Ti-VW alloys,rationalizing the observed significant strength increases at room temperature and 1000℃upon addition of solutes with large misfit into a base alloy.The analytic theory for edge motion is thus a powerful validated tool for guiding alloy selection.

Insights into the dual effects of Ti on the grain refinement and mechanical properties of hypoeutectic Al-Si alloys

Hypoeutectic Al-Si alloys are becoming increasingly popular in automotive and aerospace engineering fields due to their excellent overall performance,and grain refinement is regarded as an important way to improve casting and mechanical properties.Titanium(Ti)is a basic element for grain refinement;thus,a certain amount of Ti is often included in Al-Si alloys.In the present work,the changes in the grain re-finement,mechanical,and casting properties of Al-Si alloys with different Ti concentration levels under various grain refinement conditions were systematically investigated.The specific roles of Ti in the het-erogeneous nucleation ofα-Al grains were summarized,and the formation mechanism of Ti-rich zones in Al-Si alloys was revealed.Excess Ti concentration could not efficiently reduce the grain size of Al-Si alloys and eventually resulted in inferior mechanical and casting qualities;hence,the recommended Ti concentration level for the aluminum alloy grades of A356 and A357 is≤0.1 wt%.Furthermore,an opti-mized technique for the grain refinement of hypoeutectic Al-Si alloys was presented.A small amount of an Al-TCB master alloy was introduced to achieve the best grain refinement and mechanical properties in a trace Ti environment.The addition of 0.5 wt%of the Al-TCB master alloy at the Ti concentration level of 0.06 wt%increased the ultimate tensile strength,elongation,and quality index of the Al-7Si-0.45Mg alloy to 328.8±5.0 MPa,14.4%±0.6%,and 970.7±33.1 MPa,respectively.

First-principles-based prediction of yield strength in the RhIrPdPtNiCu high-entropy alloy

High-entropy alloys are random alloys with five or more components,often near equi-composition,that often exhibit excellent mechanical properties.Guiding the design of new materials across the wide composition space requires an ability to compute necessary underlying material parameters via ab initio methods.Here,density functional theory is used to compute the elemental misfit volumes,alloy lattice constant,elastic constants,and stable stacking fault energy in the fcc noble metal RhIrPdPtNiCu.These properties are then used in a recent theory for the temperature and strain-rate dependent yield strength.The parameter-free prediction of 583 MPa is in excellent agreement with the measured value of 527 MPa.This quantitative connection between alloy composition and yield strength,without any experimental input,motivates this general density functional theory-based methodological path for exploring new potential high-strength high-entropy alloys,in this and other alloy classes,with the chemical accuracy of first-principles methods.

High throughput synthesis enabled exploration of CoCrFeNi-based high entropy alloys

To accelerate the exploration,screening,and discovery of structural high-entropy alloys with targeted properties,the newly developed High-Throughput Hot-Isostatic-Pressing based Micro-Synthesis Approach(HT-HIP-MSA)is employed to efficiently synthesize and characterize 85 combinatorial alloys in a 13-principal element alloying space.These Co Cr Fe Ni-based high entropy alloys span 1 quaternary,9 quinary,and 36 senary alloy systems,and their composition-structure-property relationships are characterized and analyzed experimentally and computationally.From the single-phase FCC CoCrFeNi alloy base,with Mn,Cu,Ti,Nb,Ta,Mo,W,Al,and Si as principal element alloying additions,we find(1)the extended Mn solubility in the single-phase FCC CoCrFeNi-Mn_(x) alloys,(2)the destabilizing behavior for most of the quinary and senary alloys,and(3)the distinctive solid-solution-strengthening effects in the alloys.In combining the computational methods,the HT-HIP-MSA can be systematic and economic to explore and refine the compositions,structures,and properties of structural high-entropy alloys.

Screw dislocation structure and mobility in body centered cubic Fe predicted by a Gaussian Approximation Potential

The plastic flow behavior of bcc transition metals up to moderate temperatures is dominated by the thermally activated glide of screw dislocations,which in turn is determined by the atomic-scale screw dislocation core structure and the associated kink-pair nucleation mechanism for glide.Modeling complex plasticity phenomena requires the simulation of many atoms and interacting dislocations and defects.These sizes are beyond the scope of first-principles methods and thus require empirical interatomic potentials.Especially for the technological important case of bcc Fe,existing empirical interatomic potentials yield spurious behavior.Here,the structure and motion of the screw dislocations in Fe are studied using a new Gaussian Approximation Potential(GAP)for bcc Fe,which has been shown to reproduce the potential energy surface predicted by density-functional theory(DFT)and many associated properties.The Fe GAP predicts a compact,non-degenerate core structure,a single-hump Peierls potential,and glide on{110},consistent with DFT results.The thermally activated motion at finite temperatures occurs by the expected kink-pair nucleation and propagation mechanism.The stress-dependent enthalpy barrier for screw motion,computed using the nudgedelastic-band method,follows closely a form predicted by standard theories with a zero-stress barrier of~1 eV,close to the experimental value of 0.84 eV,and a Peierls stress of~2 GPa consistent with DFT predictions of the Peierls potential.