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Circulating tumor cell (CTC) and their isolation is one potential clinically useful target within a "liquid biopsy". Detection and characterization of CTCs provide a non-invasive approach for monitoring cancer therapy. In the present research, a magnet- deformability hybrid integrated microfluidic chip was designed to enumerate CTCs. Arrays of narrow gaps (patterned by micro-ellipse microposts) were designed to capture CTCs bonded with magnetic immune beads. Eleven samples, including Gastric of Colorectal, non-small-cell lung cancer (NSCLC), Ureter cancer, and Breast cancer, were used to validate the microfluidic device clinically. Clinical test results show a high capture efficiency (over 90% at 3ml/h) and high viability (96%) at high flow rate. Furthermore, comparisons of device performance with and without magnet beads were also conducted. This hybrid chip design demonstrated excellent performance in the clinical enumeration of CTCs, which is promising in the future cancer therapy evaluation. [ABSTRACT FROM AUTHOR]

The deformation of a loaded bike tire has been analyzed with a model consisting of a toroid of thin inextensible walls mounted on a central rim. If the tire radius is much smaller than the rim radius, the deflection, d, of the tire can be calculated as a function of the applied load, F. The solution can be approximated by a power law dependence F ∝ d 3 / 2 for small loads. The theoretical predictions compare well with the experiments carried out on two bicycle tires. [ABSTRACT FROM AUTHOR]

In this study, the dynamic characteristics of beam perveance under thermal deformation in a three-grid ion thruster are analyzed and discussed by a combination of theory and experiment. Beam extraction in the apertures of the grids is simulated by the particle-in-cell–Monte Carlo collision method. The influences of thermal deformation on ion density thresholds in underperveance and overperveance conditions are analyzed and calculated. Finally, a verification experiment is performed. The simulated and experimental results show the gradually increasing underperveance threshold but decreasing overperveance threshold with the grid gap widening. Unlike under normal perveance in the cold state, the extracted beam exhibits a local anomalous perveance under thermal deformation with overperveance or underperveance occuring in the middle or edge area, respectively. The simulation and experimental results agree well with a maximum relative error of less than 4.1%. This work offers a reference for uniformity of optimization of beam density for ion thrusters. [ABSTRACT FROM AUTHOR]

The stockwell transform (S transform) is used to conduct analysis and processing of the Acoustic Emission (AE) signal in the welding process. The multi dimension instantaneous frequency information of AE signal in the joint time frequency distribution is obtained to analyze and recognize the welding structure state. The changing paces of window functions under different parameters are analyzed, and the parameters of S transform are determined to realize the optimal adaptive multi resolution and time frequency clustering. The S transform is performed to analyze the time frequency characteristics of the collected AE signal in weldment tensile testing experiment. According to the analysis results of the weldment tensile AE signal, the time frequency distribution and the first-order moment of the AE signal are observed to identify and detect the elastic, plastic deformation, and crack in the welding restrictable experiment. The results indicate that the feature information of the AE signal obtained by S transform can present the welding structural state, which provides an effective method for online detection of welding crack. [ABSTRACT FROM AUTHOR]

Long-standing evidence suggests that plasticity in metals may proceed in an intermittent fashion. While the documentation of intermittency in plastically deforming materials has been achieved in several experimental settings, efforts to draw connections from dislocation motion and structure development to stress relaxation have been limited, especially in the bulk of deforming polycrystals. This work uses high energy x-ray diffraction measurements to build these links by characterizing plastic deformation events inside individual deforming grains in both the titanium alloy, Ti-7Al, and the magnesium alloy, AZ31. This analysis is performed by combining macroscopic stress relaxation data, complete grain stress states found using far-field high energy diffraction microscopy, and rapid x-ray diffraction spot measurements made using a Mixed-Mode Pixel Array Detector. Changes in the dislocation content within the deforming grains are monitored using the evolution of the full 3-D shapes of the diffraction spot intensity distributions in reciprocal space. The results for the Ti-7Al alloy show the presence of large stress fluctuations in contrast to AZ31, which shows a lesser degree of intermittent plastic flow. [ABSTRACT FROM AUTHOR]

Adding polyethylene greatly affects the rheological response of isotactic polypropylene (PP) under uniaxial elongational flow. Though strain hardening in the transient elongational viscosity barely appeared in pure PP, we induced strain hardening by adding low-density polyethylene (LDPE) to PP, even though the blends showed a phase-separated structure. During elongational flow, LDPE droplets dispersed in the PP were deformed in the flow direction. Because LDPE shows marked strain hardening in the elongational viscosity, the deformed LDPE droplets behaved as rigid fibers as the strain increased. Consequently, the PP between the fibrous LDPE droplets experienced excess localized deformation, which increased the apparent elongational viscosity. Furthermore, adding the high-density polyethylene (HDPE) increased the drawdown force—defined as the force required for uniaxial stretching of a molten polymer in the nonisothermal condition. This behavior comes from the rapid crystallization of HDPE, which causes the deformed HDPE particles to act as rigid fibers in the molten PP and enhances the PP crystallization, which increases the elongational stress. [ABSTRACT FROM AUTHOR]

We compare the predictions of the Vasquez–Cook–McKinley (VCM) [P. a. Vasquez et al., J. Non-Newton. Fluid. Mech. 144, 122–139 (2007)] model, which treats wormlike micelles as Hookean dumbbells that break at half-length to form two shorter dumbbells, to an analogous Brownian dynamics (BD) simulation of the same physical model. We find a discrepancy between VCM model predictions and trace it to the absence in the VCM model of the spatial position of the nascent breakage point in the long micelle, which is needed to satisfy microscopic reversibility of breakage and fusion. We incorporate microscopic reversibility in the VCM model by extending an ensemble-averaged bead-spring phase space model of Wiest et al. [J. Chem. Phys. 90, 587 (1989)] to include reversible scission of two-spring chains. The revision tracks the conformations of the two halves of the long micelle and transmits this information to the short micelles upon breakage and thereby recovers complete agreement with the BD results. A general method is offered for retaining this information in populations of micelles of many different lengths, represented by an ensemble of many-spring chains. The new model also offers the prospect of including additional physics, such as flow-enhanced micelle growth or breakage, and the ability to check the accuracy of closure approximations using parallel BD simulations. [ABSTRACT FROM AUTHOR]

We construct a numerical model for a liquid microlens formed by filling a microwell with two immiscible liquids, namely oil and water. The water–oil interface can be actuated as a tunable liquid lens because its curvature is well controlled by applying an external electric field. The contact angle of the oil droplet has the opposite tendency to that of a traditional water-filled microwell because of the repulsion force from the water phase. We study the dynamic interface deformation as functions of time and applied voltage, which typically within 10 ms is good enough as an imaging system for human eyes. In addition, using two different filling liquids provides more possibilities for tuning the focal length. [ABSTRACT FROM AUTHOR]

Diamond fly cutting (DFC) is a technique which can accurately and efficiently generate shapes in the micro & nanometer scale. However, the miniaturization of parts and the small depth of cut make the materials removal or deformation in the DFC different from the common machining technology. It is difficult to investigate materials deformation or failure by means of pure macroscopic or microscopic scale method. Multiscale method can study material behavior across different length & temporal scale simultaneously which is helpful about uncover important properties and materials response in DFC and thus being employed in this work. The results show that several slipping-dislocation systems are generated with feeding of the cutting tool while most of them extend along the rake angle of cutting tool. The plastic deformation is a discrete process in the atomic scale while it is generally considered as continuum process in the macroscopic scale. The first slipping-band becomes the boundary of the following slipping process which leads to the different generation mechanism of the following dislocation. The dislocation density, cross-slip and junction increase with the increasing of strain rate. The dislocation density is gradually decreased far away from materials surface which justifies that most of the dislocation ought to be generated by the surface defects than by the internal defects. The dislocation can also be regenerated by the complicated dynamic behavior of the existing dislocations without external loading which lead to the complexity of the deformation process. The slipping-band can be considered as the green-channel of stress relaxation as the maximum stress is originated at the tool-workpiece contact area and gradually decreased in the further area. [ABSTRACT FROM AUTHOR]

In this work, we have fabricated physiologically relevant polydimethylsiloxane microfluidic phantoms to investigate the fluid-structure interaction that arises from the interaction between a non-Newtonian fluid and the deformable wall. A shear thinning fluid (Xanthan gum solution) is used as the blood analog fluid. We have systematically analyzed the steady flow characteristics of the microfluidic phantom using pressure drop, deformation, and flow visualization using micro-PIV (Particle Image Velocimetry) to identify the intricate aspects of the pressure as well as the velocity field. A simple mathematical formulation is introduced to evaluate the flow induced deformation. These results will aid in the design and development of deformable microfluidic systems and provide a deeper understanding of the fluid-structure interaction in microchannels with special emphasis on biomimetic in-vitro models for lab-on-a-chip applications. [ABSTRACT FROM AUTHOR]

Elongational thinning is observed in model polypropylene/polystyrene (PS) blends filled with nanoparticles at nanoparticle loadings ≥ 3 vol.% and high strain rates, wherein the nanoparticle network that forms at rest is destroyed by the deformation. The elongational thinning is stronger in blends with hydrophilic silica surfaces than with hydrophobic silica, apparently due to stronger interaction within the hydrophilic silica network and between PS and hydrophilic silica. Moreover, the elongational deformation of droplets is not significantly altered by the addition of hydrophilic silica at lower silica loadings but nearly completely inhibited at higher loadings. In contrast, hydrophobic silica significantly boosts the deformation of droplets in elongation possibly because of the reduced interfacial tension due to the preferential distribution of hydrophobic silica at the droplet-matrix interface, relative to the hydrophilic silica which resides mostly in the PS matrix. [ABSTRACT FROM AUTHOR]

The traditional methods of parasitic mode excitation diagnosis in an X-band triaxial klystron amplifier (TKA) meet two difficulties: limited installation space and vacuum sealing. In order to solve these issues, a simple and compact coupler with good sealing performance, which can prevent air flow between the main and the auxiliary waveguides, is proposed and investigated experimentally. The coupler is designed with the aperture diffraction theory and the finite-different time-domain (FDTD) method. The designed coupler consists of a main coaxial waveguide (for microwave transmission) and a rectangular auxiliary waveguide (for parasitic mode diagnosis). The entire coupler structure has been fabricated by macromolecule polymer which is transparent to microwave signal in frequency range of X-band. The metal coating of about 200 microns has been performed through electroplating technique to ensure that the device operates well at high power. A small aperture is made in the metal coating. Hence, microwave can couple through the hole and the wave-transparent medium, whereas air flow is blocked by the wave-transparent medium. The coupling coefficient is analyzed and simulated with CST software. The coupler model is also included in particle-in-cell (PIC) simulation with CHIPIC software and the associated parasitic mode excitation is studied. A frequency component of 11.46 GHz is observed in the FFT of the electric field of the drift tube and its corresponding competition mode appears as TE61 mode according to the electric field distribution. Besides, a frequency component of 10.8 GHz is also observed in the FFT of the electric field. After optimization of TE61 mode suppression, an experiment of the TKA with the designed coupler is carried out and the parasitic mode excitation at 10.8 GHz is observed through the designed coupler. [ABSTRACT FROM AUTHOR]

An incremental wave superimposed on a pre-deformed hyper-elastic material perceives an elastic media with the instantaneous modulus of the current material. This offers a new route with a broad-band feature to control elastic waves by purposely creating finite deformation field. This study proves that the governing equation of a semi-linear material under a symmetric pre-deformation condition maintains the form invariance for longitudinal wave, so the longitudinal wave control can be made by transformation method without the constraint condition on principle stretches; however, this is not the case for shear waves. Therefore, pre-deforming a semi-linear material provides a potential method for treating longitudinal and shear waves differently. Examples with elastic wave control and band structure shift through pre-deforming a semi-linear material are provided to illustrate this finding. Finally, a one-dimensional spring lattice is proposed to mimic a semi-linear material, and the dispersion relation for longitudinal waves in a sandwich structure with such spring lattice is shown to be invariant during elongation, confirming the result found based on a homogeneous semi-linear material. These results may stimulate researches on designing new hyper-elastic microstructures as well as designing new devices based on pre-deformed hyper-elastic materials. [ABSTRACT FROM AUTHOR]

Particle-fluid based surface generation process has already become one of the most important materials processing technology for many advanced materials such as optical crystal, ceramics and so on. Most of the particle-fluid based surface generation technology involves two key process: chemical reaction which is responsible for surface softening; physical behavior which is responsible for materials removal/deformation. Presently, researchers cannot give a reasonable explanation about the complex process in the particle-fluid based surface generation technology because of the small temporal-spatial scale and the concurrent influence of physical-chemical process. Molecular dynamics (MD) method has already been proved to be a promising approach for constructing effective model of atomic scale phenomenon and can serve as a predicting simulation tool in analyzing the complex surface generation mechanism and is employed in this research to study the essence of surface generation. The deformation and piles of water molecule is induced with the feeding of abrasive particle which justifies the property mutation of water at nanometer scale. There are little silica molecule aggregation or materials removal because the water-layer greatly reduce the strength of mechanical interaction between particle and materials surface and minimize the stress concentration. Furthermore, chemical effect is also observed at the interface: stable chemical bond is generated between water and silica which lead to the formation of silconl and the reaction rate changes with the amount of water molecules in the local environment. Novel ring structure is observed in the silica surface and it is justified to be favored of chemical reaction with water molecule. The siloxane bond formation process quickly strengthened across the interface with the feeding of abrasive particle because of the compressive stress resulted by the impacting behavior. [ABSTRACT FROM AUTHOR]

Particles suspended in a less-wetting fluid can be aggregated by addition of a small quantity of an immiscible fluid that preferentially wets the particles. If the added wetting fluid is sufficiently dilute, the aggregates are composed of particles held together by pendular menisci of the wetting fluid. Such pendular aggregates can then percolate into a network which endows the suspension with a yield stress. We examine the yielding behavior of pendular networks at a particle volume fraction of 20%, with wetting fluid loadings ranging from 0:08% to 6:4%. Steady shear experiments give a dynamic yield stress that increases roughly linearly with wetting fluid loading within the pendular regime, and the shear stress vs shear rate behavior can be collapsed onto a mastercurve by simply normalizing the stress by the yield stress. Linear viscoelastic moduli are found to decrease if the suspensions are sheared at a high rate prior to the modulus measurement, but this decrease can be reversed by shearing at a low rate. Various measures of yielding--the limit of linear viscoelastic behavior, the crossover of the storage and loss moduli in large amplitude oscillatory shear experiments, and strain recoil after cessation of shear--all suggest that the networks yield at ~1% strain. This strain is much smaller than expected from the micromechanics of rupturing pendular menisci, and we suggest nonhomogeneous deformation of the networks as the reason for the discrepancy. [ABSTRACT FROM AUTHOR]

A framework for determining the first nonlinear relaxation modulus of a viscoelastic fluid from a medium-amplitude oscillatory shear (MAOS) deformation is constructed. Knowledge of this "MAOS relaxation modulus" allows one to predict the weakly nonlinear stress response of a material under an arbitrary transient deformation via a memory integral expansion. Our framework is demonstrated by explicitly determining the MAOS relaxation modulus for a dilute suspension of Brownian spheroids subject to a dual-frequency oscillatory shear flow. Specifically, we first calculate the second normal stress difference for such a deformation from a corotational memory integral expansion. Second, the microstructural stress response of the model system of Brownian spheroids is determined via a regular perturbation expansion of the orientation distribution function at small dimensionless strain-rate amplitude, or Weissenberg number. An analytical expression for the MAOS relaxation modulus is resolved by comparing the second normal stress difference results of the memory integral expansion and microstructural stress calculation. Finally, using the MAOS relaxation modulus, we reconstruct the stress response of the model system for the start-up and cessation of simple shear and uniaxial extension. In summary, our work offers an approach to utilizing medium (and large) amplitude oscillatory shear results to predict stress dynamics of viscoelastic fluids in other transient, nonlinear flows. [ABSTRACT FROM AUTHOR]

To explore the time-dependent dissipative behaviors of a circular dielectric elastomer membrane subject to force and voltage, a viscoelastic model is formulated based on the nonlinear theory for dissipative dielectrics. The circular membrane is attached centrally to a light rigid disk and then connected to a fixed rigid ring. When subject to force and voltage, the membrane deforms into an out-of plane shape, undergoing large deformation. The governing equations to describe the large deformation are derived by using energy variational principle while the viscoelasticity of the membrane is describe by a two-unit spring-dashpot model. The evolutions of the considered variables and the deformed shape are illustrated graphically. In calculation, the effects of the voltage and the pre-stretch on the electromechanical behaviors of the membrane are examined and the results show that they significantly influence the electromechanical behaviors of the membrane. It is expected that the present model may provide some guidelines in the design and application of such dielectric elastomer transducers. [ABSTRACT FROM AUTHOR]

The effects of contact states on polymer pattern deformation during demolding are investigated using a numerical simulation approach considering the relationship between the demolding force and demolding displacement. According to the difference of the contact states between the mold and polymer, the demolding model is divided into three kinds of contact types. It is shown that tearing of the residual layer and breaking of the polymer embossment have direct relations with the adhesion states of the contact surfaces at different positions. Among the three kinds of contact types, the sufficient contact type has the highest resolution, but it also has a large probability of defects. The incomplete contact type has the lowest defect rate, but it has a poor resolution. For the complete contact type, both the probability of defects and the resolution are better of the three kinds of contact types. [ABSTRACT FROM AUTHOR]

The dynamic compressive behavior of a hot pressed tungsten/zirconium (W/Zr) composite with a mass proportion of 34:64 (W:Zr) was experimentally investigated using a split Hopkinson pressure bar and a high-speed camera. The W/Zr composite has high strength but some brittle characteristics; when subjected to a strong enough impact loading, the sample is crushed, rapidly releasing high amounts of energy as a result. This impact-initiated reaction depends on the loading conditions, where a higher loading strain rate resulting a smaller fragment size. The Zr phase is involved in the reaction as the active component of the composite, and these fragments can be divided into small, medium, and large fragments with their reactions labeled as "fire ball," "spark," and "no react" respectively. A simple model is constructed to analyze the heat generated during plastic deformation based on yield stress, crack speed and the thermal properties of the brittle material. Our proposed model's prediction of temperature increase at initiation may reach several hundred degrees Celsius. [ABSTRACT FROM AUTHOR]

The belief that curved spacetime gravity cannot be simply and correctly presented results in such misleading presentations as elastic two-dimensional sheets deformed as they support heavy objects. This article attempts to show that the conceptual basis of curved spacetime gravity can be simply and correctly presented, and that the spatial curvature of a deformed elastic sheet is very different from the spacetime curvature underlying gravity. This article introduces the idea of a "splittable" spacetime that has spatial curvature, but is missing most of the manifestations of gravity. A section in which no mathematics is used is directed at students who have studied no more than introductory physics. A separate section, for students who have taken only an introductory course in general relativity, gives mathematical arguments centering on splittable spacetimes. [ABSTRACT FROM AUTHOR]

In this study, it is shown that under very weak dynamic and quasi-static deformation that is orders of magnitude below the yield deformation of the equivalent stress-strain curve (around 10-3), the elastic parameters of a civil engineering structure (resonance frequency and damping) exhibit nonlinear softening and recovery. These observations bridge the gap between laboratory and seismic scales where elastic nonlinear behavior has been previously observed. Under weak seismic or atmospheric loading, modal frequencies are modified by around 1% and damping by more than 100% for strain levels between 10-7 and 10-4. These observations support the concept of universal behavior of nonlinear elastic behavior in diverse systems, including granular materials and damaged solids that scale from millimeter dimensions to the scale of structures to fault dimensions in the Earth. [ABSTRACT FROM AUTHOR]

Compression-assisted magnetorheological (MR) fluid strengthening at the nonconfined conditions was studied with the Anton Paar Physica MCR300 magnetorheometer adapted for measurements of the storage modulus of magnetized MR fluid after its exposure to compressive strains as well as for measurements of the shear stress during build-up of compression at different mutual field/compression orientations. It was found that the compression significantly increases the linear viscoelastic region, suggesting an essential enhancement in the elastic properties of the tested material. An elevated elasticity of MR fluid compressed normal to the field is observed. Build-up of compression of magnetized MR fluid results in a dramatic increase in the shear stress and occurs in two phases. It is suggested that in the first phase, at the low compressive strains, the increase in the stress is associated with the elastic deformation of the initial structure formed by a magnetic field. Subsequent increase in the shear stress in the second phase is attributed to the compression-assisted MR fluid strengthening, which takes place when the compressive strain increases beyond the elastic region and the initial chain structure gradually transforms into a structure of a thick and strong columns. Compression normal to the field results in significantly higher shear stress increment than imposed along it. [ABSTRACT FROM AUTHOR]

Planar contraction flow of a nematic solution of poly-paraphenylene terephthalamide (PPTA) in sulphuric acid (H2SO4) was studied experimentally and compared with the flow of an isotropic model fluid, a poly-ethyleneglycol-poly-ethyleneoxide (PEG-PEO) Boger fluid, in the same geometry. The dimensions and deformation rates in our experiments are relevant for industrial polymer extrusion processes, such as fiber spinning. Under these conditions, viscoelastic lip vortices arise at the re-entrant corners in the nematic flow. The experimental results show that the vortex growth behavior in the nematic PPTA solution closely resembles that in isotropic viscoelastic fluids, such as the PEG-PEO Boger fluid that was used as a reference. The velocity field in the nematic flow is characteristic of Hele-Shaw flow of a shear-thinning power-law fluid, although locally, the influence of the nematic defect structure was observed, especially for the first minutes after starting the flow. Furthermore, the lateral movement of the extruded jet, downstream of the contraction, was shown to be coupled with velocity fluctuations in the upstream flow. Our experiments give detailed insight in the complex flow behavior of a nematic polymer solution under flow conditions that are relevant to practical applications. The results can be applied in the optimization of nematic polymer extrusion processes. [ABSTRACT FROM AUTHOR]

This work aims to examine whether or not interfacial failure can occur in a compatible polymer bilayer system under large shear and elongation deformations, as well as to probe the sensitivity of nonlinear transient rheology to the presence of interface/interphase at neighboring layers. For this, stress relaxation after a step strain and fast startup in simple shear and uniaxial extension experiments have been performed on healed and coextruded poly(methyl methacrylate)/poly(vinylidene fluoride) bilayers with the presence of a robust diffuse interphase as evaluated by energy dispersive X ray. For unhealed bilayers, interfacial failure occurred in shear flows at intermediate deformations, while for healed bilayers the interphase greatly delayed the onset of interfacial failure to larger deformation steps and to a higher deformation rate in the startup shear. Extensional rheology demonstrated that the presence of an interphase in the bilayers greatly enhanced the transient extensional viscosityηE+(t) as well as the tensile relaxation modulus E(t) of the structure, even though the entanglement density was relatively low. Moreover, models are presented to predict the nonlinear relaxation behavior of bilayers and to estimate the relaxation behavior of the interphase. Fitting of the tube model to the shear relaxation indicates a dilated tube diameter in the interphase, confirming its weak entanglement intensity and its readiness to flow-induced disentanglement under large external deformations. Finally, the physics of the interfacial failure was assessed based on some recent molecular dynamic theories. [ABSTRACT FROM AUTHOR]

A 13-month time series of Arctic Ocean noise from the marginal ice zone of the Eastern Beaufort Sea is analyzed to detect under-ice acoustic transients isolated from ambient noise with a dedicated algorithm. Noise transients due to ice cracking, fracturing, shearing, and ridging are sorted out into three categories: broadband impulses, frequency modulated (FM) tones, and high-frequency broadband noise. Their temporal and acoustic characteristics over the 8-month ice covered period, from November 2005 to mid-June 2006, are presented and their generation mechanisms are discussed. Correlations analyses showed that the occurrence of these ice transients responded to large-scale ice motion and deformation rates forced by meteorological events, often leading to opening of large-scale leads at main discontinuities in the ice cover. Such a sequence, resulting in the opening of a large lead, hundreds by tens of kilometers in size, along the margin of landfast ice and multiyear ice plume in the Beaufort-Chukchi seas is detailed. These ice transients largely contribute to the soundscape properties of the Arctic Ocean, for both its ambient and total noise components. Some FM tonal transients can be confounded with marine mammal songs, especially when they are repeated, with periods similar to wind generated waves. [ABSTRACT FROM AUTHOR]

Even inherently brittle hollow silicon nanoparticles (NPs) can withstand larger strain to failure than solid NPs. However, the influence of wall thickness on the mechanical behavior of hollow Si NPs is not fully understood. Using molecular dynamics simulations, we investigate the compressive behavior of hollow Si NPs. Three distinct failure mechanisms of hollow NPs are uncovered, and their strength and deformability are analyzed quantitatively. For extra-thick-walled NPs, dislocations will nucleate below the contact area and cut through the particles till failure. For mid-thick-walled NPs, however, dislocations will emit from the inner surface and slip towards the outer surface. For thin-walled NPs, elastic buckling is the cause of failure. Compared to solid NPs, hollow NPs with wall thickness being around half of its outer radius can achieve significant improvement in both strength and deformability. [ABSTRACT FROM AUTHOR]

Experimental data on homogeneous planar extension on well-characterized polymeric fluids are rare. As a result, the relationship between planar and uniaxial extensional viscosity is also unclear. We present measurements of the steady-state planar extensional viscosity of a well-characterized polymer solution with about 30 entanglements per chain. The measurements are made by modifying the filament stretching rheometer to enable the stretching of the sample in the shape of a cylindrical tube. When a constant strain rate is imposed on the sample, a well-defined steady-state in the planar extensional viscosity is observed in the experiments. Our experiments show that, within the range of strain rates used, the response of the entangled polymer solution in planar extensional flow is identical to that observed in uniaxial extensional flow. Such a finding, if found to be generally valid, facilitates the comparison between simulations and experimental data, since planar flows are easier to simulate than uniaxial flows. We also compare the predictions of a toy-version of the tube model that describes the flow properties of entangled polymer solutions with the experimental results. We find that the predictions of the model are in qualitative agreement with the experimental observations within the range of strain rates used in this study. [ABSTRACT FROM AUTHOR]

An anti-adhesion surface with a water contact angle of 167° was fabricated on aluminium samples of rubber plastic moulds by electrolysis plasma treatment using mixed electrolytes of C6H5O7(NH4)3 and Na2SO4, followed by fluorination. To optimise the fabrication conditions, several important processing parameters such as the discharge voltage, discharge time, concentrations of supporting electrolyte and stearic acid ethanol solution were examined systematically. Using scanning electron microscopy (SEM) to analyse surfaces morphology, micrometer scale pits, and protrusions were found on the surface, with numerous nanometer mastoids contained in the protrusions. These binary micro/nano-scale structures, which are similar to the micro-structures of soil-burrowing animals, play a critical role in achieving low adhesion properties. Otherwise, the anti-adhesion behaviours of the resulting samples were analysed by the atomic force microscope (AFM), Fourier-transform infrared spectrophotometer (FTIR), electrons probe micro-analyzer (EPMA), optical contact angle meter, digital Vickers microhardness (Hv) tester, and electronic universal testing. The results show that the electrolysis plasma treatment does not require complex processing parameters, using a simple device, and is an environment-friendly and effective method. Under the optimised conditions, the contact angle (CA) for the modified anti-adhesion surface is up to 167°, the sliding angle (SA) is less than 2°, roughness of the sample surface is only 0.409µm. Moreover, the adhesion force and Hv are 0. 9KN and 385, respectively. [ABSTRACT FROM AUTHOR]

Following recent work [e.g., J. Park et al., J. Rheol. 56, 1057-1082 (2012); T. Yaoita et al., Macromolecules 45, 2773-2782 (2012); and G. Ianniruberto et al., Macromolecules 45, 8058-8066 (2012)], we introduce the idea of a configuration dependent friction coefficient (CDFC) based on the relative orientation of Kuhn bonds of the test and surrounding matrix chains. We incorporate CDFC into the "toy" model of Mead et al. [Macromolecules 31, 7895-7914 (1998)] in a manner akin to Yaoita et al. [Nihon Reoroji Gakkaishi 42, 207-213 (2014)]. Additionally, we incorporate entanglement dynamics (ED) of discrete entanglement pairs into the new Mead-Banerjee-Park (MBP) model in a way similar to Ianniruberto and Marrucci [J. Rheol. 58, 89-102 (2014)]. The MBP model predicts a deformation dependent entanglement microstructure which is physically reflected in a reduced modulus that heals slowly following cessation of deformation. Incorporating ED into the model allows "shear modification" to be qualitatively captured. The MBP model is tested against experimental data in steady and transient extensional and shear flows. The MBP model captures the monotonic thinning of the extensional flow curve of entangled monodisperse polystyrene (PS) melts [A. Bach et al., Macromolecules 36, 5174-5179 (2003)] while simultaneously predicting the extension hardening found in PS semidilute solutions where CDFC is diluted out [P. K. Bhattacharjee et al., Macromolecules 35, 10131-10148 (2002)]. The simulation results also show that the rheological properties in nonlinear extensional flows of PS melts are sensitive to CDFC but not to convective constraint release (CCR) while those for shear flows are influenced more by CCR. The monodisperse MBP toy model is generalized to arbitrary polydispersity. [ABSTRACT FROM AUTHOR]

Deformation-based circulating tumor cell (CTC) microchips are a representative diagnostic device for early cancer detection. This type of device usually involves a process of CTC trapping in a confined microgeometry. Further understanding of the CTC flow regime, as well as the threshold passing-through pressure, is a key to the design of deformation-based CTC filtration devices. In the present numerical study, we investigate the transitional deformation and pressure signature from surface tension dominated flow to viscous shear stress dominated flow using a droplet model. Regarding whether CTC fully blocks the channel inlet, we observe two flow regimes: CTC squeezing and shearing regime. By studying the relation of CTC deformation at the exact critical pressure point for increasing inlet velocity, three different types of cell deformation are observed: (1) hemispherical front, (2) parabolic front, and (3) elongated CTC co-flowing with carrier media. Focusing on the circular channel, we observe a first increasing and then decreasing critical pressure change with increasing flow rate. By pressure analysis, the concept of optimum velocity is proposed to explain the behavior of CTC filtration and design optimization of CTC filter. Similar behavior is also observed in channels with symmetrical cross sections like square and triangular but not in rectangular channels which only results in decreasing critical pressure. [ABSTRACT FROM AUTHOR]

A series of large-scale molecular dynamics simulations were conducted to investigate the scaling laws and the related atomistic deformation mechanisms of Cu monocrystal samples containing randomly placed nanovoids under adiabatic uniaxial strain compression. At onset of yielding, plastic deformation is accommodated by dislocations emitted from void surfaces as shear loops. The collapse of voids are observed by continuous emissions of dislocations from void surfaces and their interactions with further plastic deformation. The simulation results also suggest that the effect modulus, the yield stress and the energy aborption density of samples under uniaxial strain are linearly proportional to the relative density p. Moreover, the yield stress, the average flow stress and the energy aborption density of samples with the same relative density show a strong dependence on the void diameter d, expressed by exponential relations with decay coefficients much higher than -1/2. The corresponding atomistic mechanisms for scaling laws of the relative density and the void diameter were also presented. The present results should provide insights for understanding deformation mechanisms of nanoporous metals under extreme conditions. [ABSTRACT FROM AUTHOR]

We have investigated the uniaxial elongation behavior of six different wormlike micelle systems covering a broad range of surfactant concentrations cs and salt/surfactant ratios R using the capillary breakup elongational rheometry (CaBER). In the fast-breaking limit (high cs and R), filament lifetime tfil is controlled by the equilibrium shear modulus G0 and the breakage time kbr obtained from small oscillatory shear according to tfil/G0 ∝ λlc2/3 and relaxation time ratios λe/λs ~ 1 are found. When reptation dominates (high cs, low R) λe/λs < 1 is observed similar as for solutions of covalently bound polymers. In this concentration regime, the micellar structure seems not to be affected by the strong elongational flow. In contrast, high filament lifetimes up to 1000 s and λe/λs values up to 10 are observed at low cs irrespective of R. This indicates the formation of elongation-induced structures (EISs). A minimum viscosity and a minimum initial diameter are required for creating EIS. Additional filament stretching experiments indicate that a critical total deformation has to be exceeded for structure build-up. Finally, our experiments reveal a distinct difference regarding the dependence between solutions of linear and branched micelles of filament lifetime on viscosity suggesting that CaBER is a versatile means to distinguish between these structures. [ABSTRACT FROM AUTHOR]

The influence of entanglement density on the constraint renewal time is studied experimentally in transitory nonequilibrium polymer melts. The entanglement density, as quantified by the rubber elasticity, increases as the linear polymer melt transforms into the equilibrium state. The relaxation modulus obtained from linear step-strain deformations, performed at different points during the equilibration, shows an increase in constraint renewal time as the entanglement density increases. The normalized relaxation modulus curves collapse onto a single curve by rescaling the time axis with a factor G'(t)0.9 (where G't) is the normalized instantaneous modulus). These findings suggest that, though the relaxation time increases with the increasing number of entanglements, the mechanism responsible for stress relaxation, after application of step-strain, is similar to that in a fully entangled melt. [ABSTRACT FROM AUTHOR]

This work reports experimental and theoretical studies of hydrodynamic behaviour of deformable objects such as droplets and cells in a microchannel. Effects of mechanical properties including size and viscosity of these objects on their deformability, mobility, and induced hydrodynamic resistance are investigated. The experimental results revealed that the deformability of droplets, which is quantified in terms of deformability index (D.I.), depends on the droplet-to-channel size ratio q and droplet-to-medium viscosity ratio λ. Using a large set of experimental data, for the first time, we provide a mathematical formula that correlates induced hydrodynamic resistance of a single droplet DRd with the droplet size q and viscosity λ. A simple theoretical model is developed to obtain closed form expressions for droplet mobility ø and ΓRd. The predictions of the theoretical model successfully confront the experimental results in terms of the droplet mobility ø and induced hydrodynamic resistance ΓRd. Numerical simulations are carried out using volume-of-fluid model to predict droplet generation and deformation of droplets of different size ratio q and viscosity ratio kλ, which compare well with that obtained from the experiments. In a novel effort, we performed experiments to measure the bulk induced hydrodynamic resistance DR of different biological cells (yeast, L6, and HEK 293). The results reveal that the bulk induced hydrodynamic resistance DR is related to the cell concentration and apparent viscosity of the cells. [ABSTRACT FROM AUTHOR]

The flow of a two-dimensional foam through a constriction is investigated numerically with the bubble model, and results are compared with existing experimental and numerical studies. We predict the dynamical behavior of the foam by measuring its flowrate as a function of the imposed pressure drop. We show that two flow regimes can be observed, with an affine relationship between flowrate and pressure drop. The model also shows that the flowrate increases with the width of the distribution of bubble sizes. The simulations exhibit a power law dependency of the flowrate in the width of the constriction. The local properties of the flow are also investigated by measuring the velocity field, the frequency and direction of plastic events, and main orientations of strain. We show that the main qualitative features of the plastic and strain tensors fit with existing experiments. Finally, we test a theoretical model that predicts a relationship among plasticity, deformation, and strain. [ABSTRACT FROM AUTHOR]

Internal degrees of freedom and periodic structure are critical requirements in the design of acoustic/elastic metamaterials since they can give rise to extraordinary properties like negative effective mass and stiffness. However, they are challenging to realize in three dimensions. Closed-cell, crystalline foams are a particularly advantageous basis to develop metamaterials as they intrinsically have a complex microstructure, exhibiting internal resonances. Recently self-assembly techniques have been implemented to produce such foams: a Kelvin (body centered cubic) foam, a face centered cubic foam, and a Weaire-Phelan structure. Numerical models are employed to demonstrate that such foams are superanisotropic, selectively behaving as a liquid or a solid, pentamode solids as a result of fluid--structure interaction, in addition to having regimes characterized by film resonances and high density of states. Microstructural deformations obtained from numerical models allow the derivation of equivalent mechanical models. [ABSTRACT FROM AUTHOR]

In this study, we simulated deformation and surfactant distribution on the interface of a surfactant-covered droplet using optical tweezers as an external source. Two optical forces attracted a single droplet from the center to both sides. This resulted in an elliptical shape deformation. The droplet deformation was characterized as the change of the magnitudes of surface tension and optical force. In this process, a non-linear relationship among deformation, surface tension, and optical forces was observed. The change in the local surfactant concentration resulting from the application of optical forces was also analyzed and compared with the concentration of surfactants subjected to an extensional flow. Under the optical force influence, the surfactant molecules were concentrated at the droplet equator, which is totally opposite to the surfactants behavior under extensional flow, where the molecules were concentrated at the poles. Lastly, the quasi-equilibrium surfactant distribution was obtained by combining the effects of the optical forces with the extensional flow. All simulations were executed by the lattice Boltzmann method which is a powerful tool for solving micro-scale problems. [ABSTRACT FROM AUTHOR]

Most investigations of large amplitude oscillatory shear (LAOS) rheometry to date have presumed uniform shear. The study of structured materials would especially benefit from LAOS rheometry but require the use of the larger gaps and roughened surfaces in parallel-plate and cylindrical-Couette geometries. However, in these geometries, the shear profiles are not homogeneous throughout the deformation field. For elastoviscoplastic materials undergoing LAOS in these geometries, both elastic and viscoplastic deformations may occur simultaneously, complicating the data analysis. By means of model simulations, we provide a comprehensive picture of a model elastoviscoplastic material undergoing oscillatory shear deformation in the parallel-plate and cylindrical-Couette geometries, and we compare the oscillatory signals to those obtained from a uniform-shear field. Both displacement-controlled and torque-controlled oscillatory flows were simulated. We show that using popular linear formulas for mapping displacement to strain and torque to stress results in strain and stress signals that deviate significantly from their uniform-shear counterparts. For some limited cases, specifically displacement-controlled parallel-plate and torque-controlled cylindrical-Couette oscillatory rheometry, the use of advanced mapping methods to improve the calculation of strain and stress signals was demonstrated. As an alternative, we suggest that analyzing LAOS signals via constitutive modeling provides a unifying approach. [ABSTRACT FROM AUTHOR]

Acoustically sensitive emulsions are a promising tool for medical applications such as localized drug delivery. The physical mechanisms underlying the ultrasound-triggered nucleation and subsequent vaporization of these phase-change emulsions are largely unexplored. Here, the acoustic vaporization of individual micron-sized perfluoropentane (PFP) droplets is studied at a nanoseconds timescale. Highly diluted emulsions of PFP-in-water and oil-in-PFP-in-water droplets, ranging from 3.5 to 11 μm in radius, were prepared and the nucleation and growth of the vapor bubbles was imaged at frame rates of up to 20 Mfps. The droplet vaporization dynamics was observed to have three distinct regimes: (1) prior to nucleation, a regime of droplet deformation and oscillatory translations within the surrounding fluid along the propagation direction of the applied ultrasound; (2) a regime characterized by the rapid growth of a vapor bubble enhanced by ultrasound-driven rectified heat transfer; and (3) a final phase characterized by a relatively slow expansion, after ultrasound stops, that is fully dominated by heat transfer. A method to measure the moment of inception of the nucleation event with respect to the phase of the ultrasound wave is proposed. A simple physical model captures quantitatively all of the features of the subsequent vapor bubble growth. [ABSTRACT FROM AUTHOR]

The discrete slip-link model (DSM) was developed to describe the dynamics of flexible polymer melts. The model is able to predict linear viscoelasticity of monodisperse linear, polydisperse linear, and branched systems. The model also shows good agreement with dielectric relaxation experiments, except for the single data set available for bidisperse linear systems with a small volume fraction of long chains. In this work, both shear and elongational flow predictions obtained using the DSM without parameter adjustment are shown. Model predictions for shear flow agree very well with experimental results. The DSM is able to capture the transient response as well as the steady-state viscosity. However, for elongational flow, agreement is unsatisfactory at large strains. The DSM captures the onset of strain hardening, but after a Hencky strain between 2 and 3, it predicts transient strain softening, whereas experiments show only monotonic growth. We explore a number of assumptions and approximations of the model and their effect on flow predictions. The approximations are related to the neglect of these phenomena, which are expected to be more sensitive in elongational flow: finite extensibility, convective constraint release, and deformation of dangling ends. We indeed find that shear flow predictions are insensitive to these approximations, but elongational flow is affected. However, none of these effects is able to bring prediction in line with experiments. We conclude that the currently accepted view of entanglement dynamics is incomplete. [ABSTRACT FROM AUTHOR]

Being able to model at what point a yield stress material starts to flow under its own weight is of great importance for many practical applications. However, describing the deformation of yield stress fluids under gravity is anything but a simple exercise due to the feedback between the shape of the deposited material and the locally acting stresses. In this article, we concentrate on a specific aspect of this problem: What is the maximum height of a pile of a yield stress fluid which can be obtained under gravity? For this purpose we use the example of liquid foams in which the yield stress is strongly coupled to the bubble size and the liquid fraction. We show that a good agreement between models and experiments is obtained over a wide parameter range in two limiting cases: When the yield stress is either higher or much lower than the normal stresses encountered in the material. [ABSTRACT FROM AUTHOR]

This work applied a particle-tracking velocimetric technique to observe the deformation field in the die entry pressure-driven extrusion, motivated by insights gained from previous studies of entangled melts in simple shear. Based on several styrene-butadiene rubbers and a polybutadiene melt, we show that shear yielding takes place to result in (shear banding-like) strain localization in the die entry. The degree of strain discontinuity is shown to grow with the level of chain entanglement. The critical pressure for shear yielding corresponds to a level of shear stress at a 45° inclined plane that is comparable to the melt plateau modulus, and therefore can be predicted based on our recent understanding of yielding and strain localization in startup shear. The unstable (i.e., time-dependent) shear strain localization in the die entry during continuous extrusion at a sufficiently high volumetric throughput or pressure results in extrudate distortion that is often also known as gross melt fracture. [ABSTRACT FROM AUTHOR]

This work reports four different modes of failure during startup uniaxial extension of entangled polymer melts: Capillary, tensile decohesion, shear-yielding-induced necking, and rupture. Emphasis is placed on the identification of the critical condition separating tensile failure from necking and the molecular mechanisms for each type of failures. When Weissenberg number Wi is not vanishingly small, a startup extension terminates in a rupture-like failure where nonuniform extension takes place in a sharply localized manner. This decohesion event reflects the tensile yielding of the entanglement network that occurs due to insufficient intermolecular gripping force to balance the growing intrachain elastic retraction force. At higher rates, the failure mode switches from the tensile decohesion to necking as the entangled melts experience a Cauchy stress level in excess of twice the elastic plateau modulus (2GN0). Since the minimum stress to produce shear yielding is on the order of GN0, in these high-rate extension tests the melts have the option to undergo shear yielding. Birefringence and particle-tracking velocimetric observations were carried out to reveal the first evidence for shear deformation as a precursor to the nonuniform extension: The necessarily localized shear yielding initiates nonuniformity of the stretched specimen sometimes termed 'necking.' [ABSTRACT FROM AUTHOR]

Using simultaneous rheometric and particle-tracking velocimetric measurements, we show that the long-time rheological states of well-entangled polymer solutions are not unique in simple shear. Shear banding emerges upon a sudden startup shear as well as during conventional large amplitude oscillatory shear at rates higher than the overall chain relaxation rate. However, shear homogeneity prevails when the final conditions of continuous shear and oscillatory shear are approached gradually from rates lower than the terminal relaxation rate. This suggests that the observed shear banding as nonlinear response to sudden large deformation is only metastable and not unique. [ABSTRACT FROM AUTHOR]

We have modified the full-chain stochastic tube (XDS) model developed by Xu et al. [J. Rheol. 50, 477-494 (2006)] to simulate the rheology of entangled melts and solutions of linear monodisperse polymers. The XDS model, which has a single adjustable parameter that is equivalent to the Rouse time, successfully describes steady and transient shear and normal stress data at low to moderate rates, but the results deviate systematically from experimental data at high rates. The algorithm for re-entanglement was revised, and a configuration-dependent friction coefficient (CDFC), as originally proposed by Giesekus, was incorporated to account for microstructural change of the tube away from equilibrium. The simulation results from the modified model significantly reduce the deviation from the experimental data in shear, and they also agree well with extensional data for entangled solutions, including an initial -0.5-power dependence of the steady extensional viscosity on extension rate. We also applied the CDFC to the molecular model developed by Mead et al. [Macromolecules 31, 7895-7914 (1998)] and obtained improved predictive performance at high deformation rates, reinforcing the idea that there is a structural change in the tube far from equilibrium that accelerates relaxation processes. Finally, noting that molecular models make fundamentally different assumptions about the effect of the deformation on the entanglement density but give essentially equivalent rheological predictions, we explored the effect of the dynamics of the entanglement density by changing the entanglement assumptions in the stochastic model. [ABSTRACT FROM AUTHOR]

It has recently been shown that the dynamics of complex interfaces can be treated by hyperelastic finite deformation, and the Cauchy stress tensor can be written as a tensor derivative of the interfacial energy. In the present study, the analytical nature of this tensor derivative was further explored, resulting in a more useful constitutive relation between the stress tensor and the Finger strain tensor. To accommodate the interfacial relaxation effects, an energy balance principle was adopted in developing a nonlinear relaxation model which was then used in a visco-hyperelastic formulation for stress determination. Case studies on this visco-hyperelastic model were performed, and validations against known results were attempted. While at small deformation rates, the new model agrees with the linear viscoelastic calculations, as well as Doi and Ohta's scaling predictions, high nonlinearity was observed at large deformation rates. [ABSTRACT FROM AUTHOR]

The effect of the interplay between surface tension and gravity on the sedimentation of objects in structured fluids is investigated by simulating the quasi-static motion of a spherical particle through an ordered foam. We describe the path which a sphere takes as it descends through bamboo (1,1,0), staircase (2,1,1), chiral (3,2,1), and double staircase (4,2,2) foams, and measure the degree of control of the sphere's motion that each foam offers. For an ordered foam contained within a vertical cylinder, the resulting sphere motion depends strongly on the structure itself, on how the films are deformed near the sphere, and on how the motion of the sphere deforms them further. For staircase and chiral foams, the distance that a sphere is pulled away from the center-line of the cylinder by the foam is found to depend on the Bond number with a power-law relation. By tilting the cylinder at an angle to the vertical, we show that there exists a critical tilt angle above which the sphere falls out of the foam. This angle is dependent on the choice of foam structure and the Bond number. For a sphere of given size and given Bond number in the ordered foams studied here, the greatest tilt can be imposed on the double staircase foam. [ABSTRACT FROM AUTHOR]

A comprehensive set of experiments on a two-dimensional constriction flow of a foam are described. Image analysis of the flow is used to ascertain bubble shape and flow dynamics. The bubble velocity, elongation (texture), stress, and deformation rate for a reference case are used to validate a quasistatic simulation. Changes to the constriction geometry, most especially in the rounding of the corners, have a significant effect on the response of the foam, captured in both experiment and simulation. On the other hand, foam properties such as bubble size have little impact on the rheological behavior of the foam in the range considered here. [ABSTRACT FROM AUTHOR]

The two-dimensional, regular, hexagonal foam is a common benchmark system for studies of foam rheology under imposed shear. Traditionally, the hexagonal foam has been studied under quasistatic shear deformations. Here, however, nonequilibrium systems are considered. Specifically, the hexagonal foam is assumed to depart from physicochemical equilibrium (surfactant coverage varies and hence surface tension varies between films), but to remain in static mechanical equilibrium (as a consequence, films in the hexagonal foam remain straight, simplifying the geometrical description considerably). Regardless of the mechanism for departing from equilibrium, topological transformations (during which certain films in the hexagonal structure shrink to zero, and bubbles exchange neighbors) tend to be postponed compared to an equilibrium foam. Even when the rate of imposed shear is small, significant departures from physicochemical equilibrium are still observed on the approach to and in the immediate aftermath of a topological transformation. The nature of the relaxation post-topological transformation depends on the variation of film tension with surfactant coverage. It may be almost entirely mechanical (in the case of weakly varying film tension) or almost entirely physicochemical (for a strongly varying film tension). As the imposed shear rate increases, models incorporating weak departures from physicochemical equilibrium prove inadequate to predict the criteria for topological transformation: far-from-equilibrium physicochemical properties must be considered also. [ABSTRACT FROM AUTHOR]

Using Brownian dynamics simulations, without excluded volume and hydrodynamic interactions, on single polymer molecules represented by bead-spring models with stiff Fraenkel springs mimicking a single Kuhn step, we find multiple nonlinear regimes of deformation in shear flows that are controlled by the Peclet number (Pe), which is the shear rate times the relaxation time of a Kuhn step. We observe that, for all chain lengths investigated, the average stretch in the flow direction initially increases with increasing Pe, followed by saturation in chain stretch, as observed in previous studies. At even higher Pe, the stretch begins to decrease with increasing shear rate, in accordance with similar simulations of Sendner and Netz, Eur. Phys. J. E 30, 75-81 (2009). At these rates, the trajectories reveal 'premature' recoiling of the chain before attaining a fully extended state during the phase of the 'tumbling orbit' in which the chain is stretching. An increasing stretch at even higher Pe is characterized by peculiar orientation 'locking' effects that may be sensitive to modeling details. We also show that the stretch predictions of coarse-grained springs agree well with those of the fine-grained chains until high shear rates are reached, where the flow perturbs the individual springs from equilibrium. [ABSTRACT FROM AUTHOR]