Applied Shear Stress Research Articles

Effects of salinity and shear stress on clay deformation: A molecular dynamics study

The deformation of clay minerals is an important phenomenon that is relevant to many problems, particularly those that occur in subsurface geological formations. The salinity of the formations and external shear stress applied to them are two important factors that contribute to the deformation of such porous media. To gain a deeper understanding of such phenomena, we have carried out extensive molecular dynamics simulations using the Na-montmorillonite (Na-MMT) structure as the model of clay minerals and have studied the effect of salt concentration on its swelling. As the NaCl concentration increases, so also does the basal spacing. We demonstrate the effect of the coupling between the applied shear stress and NaCl salinity on the swelling behavior of Na-MMT, namely, deformation of the interlayer space that results in swelling. According to the results, the extent of Na-MMT deformation depends on both the brine salinity and the shear rate.

Abnormal interactions between high-speed edge dislocation and microvoid in BCC metals

The interaction between a high speed edge dislocation and a microvoid has been investigated by molecular dynamics (MD) simulations in BCC crystals of Ta, Fe, V and W in the present work. The focus is placed on the dynamic effect on the dislocation-microvoid interaction. Three interaction scenarios different from static cases, i.e., repeated dislocation oscillations around microvoids, dislocation depinning from microvoid like releasing an elastic slingshot, and formation of abnormal “pull forward” dislocation configuration, have been found for the first time. The “repeated oscillations” can be attributed to the dislocation line tension and dynamic effect, which is analogous to under-damped mechanical oscillator system. For the “releasing slingshot” case, the dislocation first bows out after breaking away from the microvoid, and then a stable “drag backward” dislocation configuration is formed. When further increasing the applied shear stress, the dislocation can accelerate to subsonic speed of roughly0.7CT, with CT being the transverse sound speed, leading to a stable “pull forward” configuration. These different dislocation configurations are closely related to the formation of superjog driven by the dislocation-microvoid interaction. By careful analysis, it is found that the variation of relative mobility between the original edge dislocation on the (110) plane and the superjog segments on the (112) plane with shear stresses perfectly coincides with the above three dislocation configurations. In fact, when the applied shear stress is high enough and the dislocation speed is subsonic, the friction stress on the superjog segments turns to be smaller than that of the original edge dislocation, resulting in the formation of abnormal “pull forward” configuration.

Red blood cells under flow show maximal ATP release for specific hematocrit

ATP release by red blood cells (RBCs) under shear stress (SS) plays a pivotal role in endothelial biochemical signaling cascades. The aim of this study is to investigate through numerical simulation how RBC spatiotemporal organization depends on flow and geometrical conditions to generate ATP patterns. Numerical simulations were conducted in a straight channel by considering both plasma and explicit presence of RBCs, their shape deformation and cell-cell interaction, and ATP release by RBCs. Two ATP release pathways through cell membrane are taken into account: pannexin 1 channel, sensitive to SS, and cystic fibrosis transmembrane conductance regulator, which responds to cell deformation. Several flow and hematocrit conditions are explored. The problem is solved by the lattice Boltzmann method. Application of SS to the RBC suspension triggers a nontrivial spatial RBC organization and ATP patterns. ATP localizes preferentially in the vicinity of the cell-free layer close to channel wall. Conditions for maximal ATP release per cell are identified, which depend on vessel size and hematocrit Ht. Increasing further Ht beyond optimum enhances the total ATP release but should degrade oxygen transport capacity, a compromise between an efficient ATP release and minimal blood dissipation. Moreover, ATP is boosted in capillaries, suggesting a vasomotor activity coordination throughout the resistance network.

Experimental study of rheological characteristics of MWCNT-Al2O3 (40:60) / SAE50 hybrid nano-lubricant to identify optimal lubrication conditions and post-processing of results using the response surface method

In this study, the rheological behavior of MWCNT-Al2O3 (40:60)/SAE50 hybrid nano-lubricant was studied to identify the maximum drop, the maximum increase in viscosity (μnf), as well as how the parameters of temperature, ϕ and shear rate (γ˙) affect the μnf. Various methods theoretically show that the nano-lubricant has a flow of pseudo-plastic non-Newtonian fluids. Statistical reports show that the highest increase and decrease in μnf of nano-lubricant compared to the base fluid in ϕ = 1%, T = 30 °C and γ=˙ 6665 s−1 (equivalent to high engine speed) and ϕ = 0.0625%, T = 25 °C and γ=˙ 3999 s−1 (equivalent to low engine speed) are occurred, which are equal to 38.76% and −5.14%, respectively. To predict the dependent variable data, a three-variable-quadratic model was presented with the RSM method with an R-Squared = 0.9997. The margin of deviation for data was determined in the range of −2.41% <MOD <3.13%. Using numerical simulation, it was found that with increasing the ϕ, the pressure drop of the flow and the applied shear stress to the wall of the pipe increase.

Polyanion-induced, microfluidic engineering of fragmented collagen microfibers for reconstituting extracellular environments of 3D hepatocyte culture

Artificial biological scaffolds made of extracellular matrix (ECM) components, such as type I collagen, provide ideal physicochemical cues to various cell culture platforms. However, it remains a challenge to fabricate micrometer-sized ECM materials with precisely controlled morphologies that could reconstitute the 3-dimensional (3D) microenvironments surrounding cells. In the present study, we proposed a unique process to fabricate fragmented collagen microfibers using a microfluidic laminar-flow system. The continuous flow of an acidic collagen solution was neutralized to generate solid fibers, which were subsequently fragmented by applying a gentle shear stress in a polyanion-containing phosphate buffer. The morphology of the fiber fragment was controllable in a wide range by changing the type and/or concentration of the polyanion and by tuning the applied shear stress. The biological benefits of the fragmented fibers were investigated through the formation of multicellular spheroids composed of primary rat hepatocytes and microfibers on non-cell-adhesive micro-vessels. The microfibers enhanced the survival and functions of the hepatocytes and reproduced proper cell polarity, because the fibers facilitated the formation of cell−cell and cell−matrix interactions while modulating the close packing of cells. These results clearly indicated that the microengineered fragmented collagen fibers have great potential to reconstitute extracellular microenvironments for hepatocytes in 3D culture, which will be of significant benefit for cell-based drug testing and bottom-up tissue engineering.

The Mass Settling Flux of Suspended Particulate Matter in Venice Lagoon, Italy

Amos, C.L.; Kassem, H.; Bergamasco, A.; Sutherland, T.F., and Cloutier, D., 2021. The mass settling flux of suspended particulate matter in Venice Lagoon, Italy. Journal of Coastal Research, 37(6), 1099–1116. Coconut Creek (Florida), ISSN 0749-0208. A multidisciplinary study of the stability of the tidal flats of Venice Lagoon has provided field and laboratory data on the factors influencing the mass settling rates of material in suspension. This work was performed using two in situ benthic flumes (Sea Carousel and Mini Flume) in association with a wide range of physical and biological measurements undertaken during the summer of 1998 and the subsequent winter. Also, controlled experiments on erosion/sedimentation of prepared beds were carried out using Lab Carousel, a laboratory equivalent of Sea Carousel. Particle size and mass settling rates were found to be largely independent of suspended sediment concentration but strongly controlled by the antecedent bed shear stresses that led to the suspension. Results between the three flume types differed because of differences in the induced stress history created in each case. Comparable results were obtained by normalizing mass settling rate to the mean friction velocity of the flow during settling, i.e. the Rouse parameter () , and by use of the mean dimensionless particle diameter (D*). Results fell in line with results on carbonate and silica sands of the inlets of the lagoon. The mean particle diameter (df) varied in proportion to the applied shear stress and shear rate (G) suggesting that the suspended particles were eroded aggregates not floccules. The effective density of these aggregates was least (∼16 kgm–3) at the largest sizes (df > 1 × 10–4 m) and greatest (∼160–1600 kgm–3) at the smallest sizes (df < 1 × 10–4 m). The lack of an increase in df at low shear rates suggests that flocculation was not taking place. The mean deposition threshold (all experiments) was 0.68 Pa, which is less than the mean erosion threshold from these sites (0.78 Pa).

Shear-Driven Mechanism of Temperature Gradient Formation in Microfluidic Nematic Devices: Theory and Numerical Studies

The purpose of this paper is to show some routes in describing the mechanism responsible for the formation of the temperature difference ΔT at the boundaries of the microfluidic hybrid aligned nematic (HAN) channel, initially equal to zero, if one sets up the stationary hydrodynamic flow vst or under the effect of an externally applied shear stress (SS) to the bounding surfaces. Calculations based on the nonlinear extension of the classical Ericksen–Leslie theory, supplemented by thermomechanical correction of the SS σzx and Rayleigh dissipation function while accounting for the entropy balance equation, show that the ΔT is proportional to the heat flux q across the HAN channel and grows by up to several degrees under the influence of the externally applied SS. The role of vst=ust(z)i^ with a sharp triangular profile ust(z) across the HAN in the production of the highest ΔT is also investigated.

Physiological Shear Stress Enhances Differentiation, Mucus-Formation and Structural 3D Organization of Intestinal Epithelial Cells In Vitro.

Gastrointestinal (GI) mucus plays a pivotal role in the tissue homoeostasis and functionality of the gut. However, due to the shortage of affordable, realistic in vitro GI models with a physiologically relevant mucus layer, studies with deeper insights into structural and compositional changes upon chemical or physical manipulation of the system are rare. To obtain an improved mucus-containing cell model, we developed easy-to-use, reusable culture chambers that facilitated the application of GI shear stresses (0.002–0.08 dyn∙cm−2) to cells on solid surfaces or membranes of cell culture inserts in bioreactor systems, thus making them readily accessible for subsequent analyses, e.g., by confocal microscopy or transepithelial electrical resistance (TEER) measurement. The human mucus-producing epithelial HT29-MTX cell-line exhibited superior reorganization into 3-dimensional villi-like structures with highly proliferative tips under dynamic culture conditions when compared to static culture (up to 180 vs. 80 µm in height). Additionally, the median mucus layer thickness was significantly increased under flow (50 ± 24 vs. 29 ± 14 µm (static)), with a simultaneous accelerated maturation of the cells into a goblet-like phenotype. We demonstrated the strong impact of culture conditions on the differentiation and reorganization of HT29-MTX cells. The results comprise valuable advances towards the improvement of existing GI and mucus models or the development of novel systems using our newly designed culture chambers.

An atomistic investigation of dislocation velocity in body-centered cubic FeCrAl alloys

Edge, screw, and mixed dislocation velocities in FeCrAl body-centered cubic alloy were investigated by classical molecular dynamics simulation at several temperatures for the 〈111〉{110} type slip system. For screw orientation, the dislocation velocity as a function of applied shear stress was found to be zero up to a threshold stress, beyond which the velocity increases with applied shear stress. For edge and mixed orientations, the dislocation velocity as a function of applied shear stress was found to have four regimes: zero value below a threshold stress, slow glide regime just above the threshold stress, a linear regime, and a final nonlinear regime past a certain velocity with a relatively lower slope. Two main features of the dislocation velocity were observed in FeCrAl alloys. First is that the rate of increase of the velocity with the applied shear stress decreases with chromium concentration and aluminum concentration, and that the dependence of the dislocation velocity on the angle between direction of the Burgers vector and the dislocation line direction shows a sinusoidal-like behavior.

Encapsulated Cell Dynamics in Droplet Microfluidic Devices with Sheath Flow

In this paper we study the dynamics of single cells encapsulated in water-in-oil emulsions in a microchannel. The flow field of a microfluidic channel is coupled to the internal flow field of a droplet through viscous traction at the interface, resulting in a rotational flow field inside the droplet. An encapsulated single cell being subjected to this flow field responds by undergoing multiple orbits, spins, and deformations that depend on its physical properties. Monitoring the cell dynamics, using a high-speed camera, can lead to the development of new label-free methods for the detection of rare cells, based on their biomechanical properties. A sheath flow microchannel was proposed to strengthen the rotational flow field inside droplets flowing in Poiseuille flow conditions. A numerical model was developed to investigate the effect of various parameters on the rotational flow field inside a droplet. The multi-phase flow model required the tracking of the fluid–fluid interface, which deforms over time due to the applied shear stresses. Experiments confirmed the significant effect of the sheath flow rate on the cell dynamics, where the speed of cell orbiting was doubled. Doubling the cell speed can double the amount of extracted biomechanical information from the encapsulated cell, while it remains within the field of view of the camera used.

Removing basal-dissociated [formula omitted] dislocations by [formula omitted] deformation twinning in magnesium alloys

Reactions of {101¯2} twin boundaries (TBs) with dislocations in a Mg alloy subjected to cyclic deformation were studied and modeled, based on atomic-resolution observations, theory of interfacial defects and molecular dynamics (MD) simulations. Atomic-resolution observations provide evidence for occurrence of reactions of {101¯2} TBs with basal 〈a60〉 and basal-dissociated 〈c+a〉 dislocations upon back and forth migration of {101¯2} TBs, respectively, during cyclic deformation. MD simulations show that immobile basal-dissociated 〈c+as〉, 〈c+a60〉 and 〈c〉 dislocations in Mg can be incorporated into {101¯2} TBs to produce steps which can move together with the TBs upon twinning/detwinning under low shear stresses. And such steps can usually emit 〈a60〉 dislocations under simultaneous application of shear and normal stresses. Importantly, the normal stresses required to transmute immobile basal-dissociated 〈c+a〉 dislocations to glissile 〈a60〉 dislocations are much lower than those required to transmute basal 〈a60〉 dislocations to 〈c+a〉 dislocations during {101¯2} deformation twinning. Our results may have implications for comprehensive understanding of the roles of deformation twinning, 〈c+a〉 dislocations, and their interactions/reactions in plastic deformation of Mg alloys.

Nanoparticle-driven self-assembling injectable hydrogels provide a multi-factorial approach for chronic wound treatment

Chronic wounds represent a major health burden and drain on medical system. Efficient wound repair is only possible if the dressing materials target simultaneously multiple factors involved in wound chronicity, such as deleterious proteolytic and oxidative enzymes and high bacterial load. Here we develop multifunctional hydrogels for chronic wound management through self-assembling of thiolated hyaluronic acid (HA-SH) and bioactive silver-lignin nanoparticles (Ag@Lig NPs). Dynamic and reversible interactions between the polymer and Ag@Lig NPs yield hybrid nanocomposite hydrogels with shear-thinning and self-healing properties, coupled to zero-order kinetics release of antimicrobial silver in response to infection-related hyalurodinase. The hydrogels inhibit the major enzymes myeloperoxidase and matrix metalloproteinases responsible for wound chronicity in a patient's wound exudate. Furthermore, the lignin-capped AgNPs provide the hydrogel with antioxidant properties and strong antibacterial activity against Staphylococcus aureus and Pseudomonas aeruginosa. The nanocomposite hydrogels are not toxic to human keratinocytes after 7 days of direct contact. Complete tissue remodeling and restoration of skin integrity is demonstrated in vivo in a diabetic mouse model. Hematological analysis reveals lack of wound inflammation due to bacterial infection or toxicity, confirming the potential of HA-SH/Ag@Lig NPs hydrogels for chronic wound management. Statement of significanceMultifunctional hydrogels are promising materials to promote healing of complex wounds. Herein, we report simple and versatile route to prepare biocompatible and multifunctional self-assembled hydrogels for efficient chronic wound treatment utilizing polymer-nanoparticle interactions. Hybrid silver-lignin nanoparticles (Ag@Lig NPs) played both: i) structural role, acting as crosslinking nodes in the hydrogel and endowing it with shear-thinning (ability to flow under applied shear stress) and self-healing properties, and ii) functional role, imparting strong antibacterial and antioxidant activity. Remarkably, the in situ self-assembling of thiolated hyaluronic acid and Ag@Lig NPs yields nanocomposite hydrogels able to simultaneously inhibits the major factors involved in wound chronicity, namely the overexpressed deleterious proteolytic and oxidative enzymes, and high bacterial load.

Studying dynamic stress effects on the behaviour of THP-1 cells by microfluidic channels

Atherosclerosis is a long-term disease process of the vascular system that is characterized by the formation of atherosclerotic plaques, which are inflammatory regions on medium and large-sized arteries. There are many factors contributing to plaque formation, such as changes in shear stress levels, rupture of endothelial cells, accumulation of lipids, and recruitment of leukocytes. Shear stress is one of the main factors that regulates the homeostasis of the circulatory system; therefore, sudden and chronic changes in shear stress may cause severe pathological conditions. In this study, microfluidic channels with cavitations were designed to mimic the shape of the atherosclerotic blood vessel, where the shear stress and pressure difference depend on design of the microchannels. Changes in the inflammatory-related molecules ICAM-1 and IL-8 were investigated in THP-1 cells in response to applied shear stresses in an continuous cycling system through microfluidic channels with periodic cavitations. ICAM-1 mRNA expression and IL-8 release were analyzed by qRT-PCR and ELISA, respectively. Additionally, the adhesion behavior of sheared THP-1 cells to endothelial cells was examined by fluorescence microscopy. The results showed that 15 Pa shear stress significantly increases expression of ICAM-1 gene and IL-8 release in THP-1 cells, whereas it decreases the adhesion between THP-1 cells and endothelial cells.

LDL and HDL Have Opposing Effects on VWF Self-Association

Von Willebrand Factor (VWF) is a large, multimeric plasma protein with roles in primary hemostasis and thrombosis. VWF unfolds in response to shear stress and self-associates into adhesive fibers that can capture and hold platelets at sites of vascular injury, initiating platelet plug formation. VWF has also been implicated in pathologies associated with microvascular dysfunction and occlusion, and dysregulation of VWF can produce the catastrophic microvascular thrombotic disorder thrombotic thrombocytopenic purpura. VWF self-association is regulated by several factors: it is enhanced by shear stress, it is decreased by regulatory cleavage by ADAMTS13 metalloprotease[Dong et al. Blood, 2002, 100:4033], and our group recently showed that high density lipoprotein (HDL) attenuates VWF self-association [Chung et al. Blood, 2016, 127:637]. High levels of HDL are associated with decreased risk of thrombosis, whereas high levels of low density lipoprotein (LDL) is a strong risk factor. This led us to investigate whether LDL also influences VWF self-association and fiber formation.We studied the effects of lipoproteins on VWF self-association by applying shear stress to VWF solutions by vortexing, which caused VWF loss from solution through a process of adsorption and self-association [Chung et al. Blood, 2016, 127:637]. We inhibited the ADAMTS13 in citrated-plasma with EDTA, sheared the treated plasma in the presence of exogenous HDL or LDL, and measured the VWF remaining in solution by sandwich ELISA. HDL attenuated VWF self-association in plasma, whereas LDL had the opposite effect, enhancing self-association. Using purified components, we sheared recombinant VWF in the presence of a fixed concentration of HDL that stabilized the VWF, and added increasing amounts of LDL to attain LDL/HDL ratios found in physiological and pathophysiological conditions. As the molar ratio of LDL/HDL particles increased from 0.17 to 0.67, VWF self-association also increased. When we repeated these assays with double the concentrations of both lipoproteins, the effect on VWF self-association was comparable. We tested EDTA-treated platelet-poor-plasma with known LDL and HDL concentrations and found that the LDL/HDL ratio regulated VWF self-association in a similar manner, but the effect was less pronounced than with the purified components.To further assess the effect of LDL and HDL on VWF self-association under shear, we perfused purified plasma VWF in a microcolumn impingement device [Herbig & Diamond JTH, 2015, 13:1699] at a wall shear rate of 10,000/s, in the presence of PBS buffer, LDL, HDL, and LDL/HDL molar ratios of 0.17 and 0.67. VWF fiber formation was monitored by differential interference contrast and immunofluorescence microscopy. The width of the bundles of VWF fibers were measured and total fluorescence was quantified using image analysis software. The presence of LDL dramatically enhanced the size of VWF fibers and the rate of formation and deposition on the microcolumn, indicating that LDL interacts directly with VWF to enhance self-association. Perfusing HDL with VWF had the opposite effect and attenuated self-association. When VWF was perfused with LDL and HDL together, the LDL/HDL ratio regulated the thickness and length of the VWF fibers formed. Our findings reveal a novel role by which LDL, by enhancing VWF self-association, may contribute to VWF-mediated thrombosis. DisclosuresNo relevant conflicts of interest to declare.

Passage dependent changes in nuclear and cytoskeleton structures of endothelial cells under laminar shear stress or cyclic stretch

&lt;p class="abstract"&gt;&lt;strong&gt;Background:&lt;/strong&gt; The ability of vascular endothelium to sense and respond to the mechanical stimuli generated by blood flow is pivotal in maintaining arterial homeostasis. A steady laminar flow tends to provide athero-protective effect via regulating endothelial functions, vascular tone, and further remodeling process. As arterial aging appeared to be an independent risk factor of cardiovascular diseases, it is critical to understand the effects of cell senescence on endothelial dysfunction under dynamic mechanical stimuli.&lt;/p&gt;&lt;p class="abstract"&gt;&lt;strong&gt;Methods:&lt;/strong&gt; In this study, we investigated the morphological responses of aortic endothelial cells toward laminar flow or cyclic stretch. Automated image recognition methods were applied to analyze image data to avoid bias. Differential patterns of morphological adaptations toward distinct mechanical stimuli were observed, and the shear-induced changes were found to be more associated with cell passages than that of cyclic strain. &lt;/p&gt;&lt;p class="abstract"&gt;&lt;strong&gt;Results:&lt;/strong&gt; Our results demonstrated that the cytoskeleton and nuclear structural adaptations in endothelial cells toward laminar flow were altered over prolonged culture, suggesting that the failure of senescent endothelial cells to adapt to the applied shear stress morphologically could be one of the contributors to endothelial dysfunctions during vascular aging.&lt;/p&gt;&lt;p class="abstract"&gt;&lt;strong&gt;Conclusions:&lt;/strong&gt; Results indicated that cells were able to adjust their cytoskeleton and nuclear alignment and nuclear shapes in response to the applied mechanical stimuli, and that the shear-induced changes were more dependent on PD levels, where cells with higher PDL were more responsive to external forces.&lt;/p&gt;

Phononic analyses of rectangular graphene and annular graphene under in-plane shear stress

In this work, the effects of in-plane shear stress on the thermal conductivities of two important kinds of graphene configurations (rectangular graphene and annular graphene) are investigated using molecular dynamics simulations. The various strain angles are set as θ = 0°, 3°, 5°, 10°, and 15° for rectangular graphene and θ = 0°, 3°, 5°, and 8° for annular graphene. A spectral energy density approach is applied to carry out phononic analyses of the two configurations under in-plane shear stress for the first time. It is found that for rectangular graphene, the thermal conductivity shows a significant decreasing trend from 239.6 to 79.1 W m−1 K−1 with the θ increasing from 0° to 15°. Besides, the application of shear stress can significantly widen the energy bands of branches, which indicates shorter phonon lifetimes. Further phononic analysis shows that most of the phonon scattering caused by in-plane shear stress emanates from the in-plane mode, which is an updated conclusion in this field. On the other hand, the thermal conductivity of annular graphene also shows a decreasing evolution with the increasing strain angles, but phonon transport in rectangular graphene is more susceptible to shear stress than in annular graphene due to a stronger phonon-boundary scattering in the latter configuration. In this work, the monotonically decreasing trends of the thermal conductivities of both graphene configurations with the increasing strain angle are different from the V-shape trend reported in the literature. Based on phononic analyses, it can be concluded that an abnormal increase of the thermal conductivities at a low shear stress can be attributed to the application of the AIREBO potential model in the literature.

Molecular tension in syndecan-1 is regulated by extracellular mechanical cues and fluidic shear stress

The endothelium plays a central role in regulating vascular homeostasis and is key in determining the response to materials implanted in the vascular system. Endothelial cells are uniquely sensitive to biophysical cues from applied forces and their local cellular microenvironment. The glycocalyx is a layer of proteoglycans, glycoproteins and glycosaminoglycans that lines the luminal surface of the vascular endothelium, interacting directly with the components of the blood and the forces of blood flow. In this work, we examined the changes in mechanical tension of syndecan-1, a cell surface proteoglycan that is an integral part of the glycocalyx, in response to substrate stiffness and fluidic shear stress. Our studies demonstrate that syndecan-1 has higher mechanical tension in regions of cell adhesion, on and in response to nanotopographical cues. In addition, we found that substrate stiffness also regulated the mechanical tension of syndecan-1 and altered its binding to actin, myosin iiB and signaling intermediates including Src, PKA and FAK. Application of fluidic shear stress created a gradient in tension in syndecan-1 and led to enhanced association with actin, Src, myosin IIb and other cytoskeleton related molecules. Overall, our studies support that syndecan-1 is responsive to the mechanical environment of the cells and alters its association with actin and signaling intermediates in response to mechanical stimuli.

Shear-Rolling Process for Unidirectionally and Perpendicularly Oriented Sub-10-nm Block Copolymer Patterns on the 4 in Scale.

Shear alignment of the block copolymer (BCP) thin film is one of the promising directed self-assembly (DSA) methodologies for the unidirectional alignment of sub-10 nm microdomains of BCPs for next-generation nanolithography and nanowire-grid polarizers. However, because of the differences in the surface/interfacial energies at the top surface/bottom interface, the shear-induced ordering of BCP nanopatterns has been restricted to BCPs with spherical and cylindrical nanopatterns and cannot be realized for high-aspect-ratio perpendicular lamellar structures, which is essential for practical application to semiconductor pattern processes. It is still a difficult challenge to fabricate the unidirectional alignment in a short time over a large area. In this study, we propose an approach for combining the shear-rolling process with the filtered plasma treatment of BCP films for the fabrication of unidirectionally aligned and perpendicularly oriented lamellar nanostructures. This approach enables fabrication within 1 min on a 4 in scale. We treated filtered plasma on the BCP film for perpendicular orientation and executed the hot-rolling process with different roller and stage speeds. Large-scale shear was generated only at the location where the BCP film was in contact with both the roller and stage, effectively applying shear stress to a large area of the BCP film within a short time. The repeated application of this shear-rolling process can achieve a higher level of unidirectional alignment. Our aligned BCP vertical lamellae were used to fabricate a high-aspect-ratio sub-10-nm-wide metallic nanowire array via dry/wet processes. In addition, shear-rolling with chemoepitaxy patterns can achieve higher orientational order and lower defectivity.

Atomic Origins of Friction Reduction in Metal Alloys

We present the results of large scale molecular dynamics simulations aimed at understanding the origins of high friction coefficients in pure metals, and their concomitant reduction in alloys and composites. We utilize a series of targeted simulations to demonstrate that different slip mechanisms are active in the two systems, leading to differing frictional behavior. Specifically, we show that in pure metals, sliding occurs along the crystallographic slip planes, whereas in alloys shear is accommodated by grain boundaries. In pure metals, there is significant grain growth induced by the applied shear stress and the slip planes are commensurate contacts with high friction. However, the presence of dissimilar atoms in alloys suppresses grain growth and stabilizes grain boundaries, leading to low friction via grain boundary sliding.Graphic Abstract

Effect of twin thickness-length ratio on twin-induced dynamic recrystallization of coarse-grained Mg alloys

In the current study, based on the disclination quadrupole, the thermodynamic process of the necklace-like TDRX structures with smooth and straight boundaries is theoretically modeled. The influence of the applied shear stress and the twin thickness-length ratio on the misorientation angle between TDRX and matrix grain and the volume ratio of TDRX to parent twin band are numerically analyzed and experimentally validated by the electron back-scatter diffraction characterization. The results show that: (1) the misorientation angle increases with increasing applied shear stress; (2) The greater the thickness-length ratio is, the lower the volume ratio of TDRX to parent twin is; (3) The elevation of the applied shear stress can clearly escalate the volume ratio of TDRX to parent twin. Based on the above results, some strategies regulating TDRX are given based on the control of the applied shear stress and twin thickness-length ratio.