Interfacial properties of the brine + carbon dioxide + oil + silica system.

Molecular dynamics simulations of the H2O + CO2 + aromatic hydrocarbon and H2O + CO2 + benzene + silica (hydrophilic) systems are performed to gain insights into CO2-enhanced oil recovery (EOR) processes. For comparison purposes, an overview of the previous simulation studies of the interfacial properties of the brine + CO2 + alkane + silica system is also presented. In general, the water contact angle (CA) of the H2O + CO2 + silica (hydrophilic) system increased with pressure and decreased with temperature. The CAs of the H2O + hydrocarbon + silica (hydrophilic) system are not significantly affected by temperature and pressure. The simulated CAs were in the ranges of about 58°-77° and 81°-93° for the H2O + hexane + silica (hydrophilic) and the H2O + aromatic hydrocarbon + silica (hydrophilic) systems, respectively. In general, these CAs were not significantly influenced by the addition of CO2. The simulated CAs were in the ranges of about 51.4°-95.0°, 69.1°-86.0°, and 72.0°-87.9° for the brine + CO2 + silica (hydrophilic), brine + hexane + silica (hydrophilic), and brine + CO2 + hexane + silica (hydrophilic) systems, respectively. All these CAs increased with increasing NaCl concentration. The adhesion tension of the brine + silica (hydrophilic) system in the presence of CO2 and/or hexane decreased with increasing salt concentration. The simulated CAs were in the range of about 117°-139° for the H2O + alkane + silica (hydrophobic) system. These CAs are increased by the addition of CO2. At high pressures, the distributions of H2O normal to the silica (hydrophobic) surface in the droplet region of the H2O + silica system were found to be strongly affected by the presence of CO2. These insights might be key for optimizing the performance of the miscible CO2 water-alternating-gas injection schemes widely used for EOR.

Mechanical improvement of boron nitride nanosheet-reinforced cement paste by multiscale modeling.

Representative volume (RVE) models are constructed to mimic the microstructural characteristics of boron nitride nanosheet (BNNS)-reinforced cement paste. The interfacial properties between BNNSs and cement paste are described by the cohesive zone model (CZM) developed by molecular dynamics (MD) simulations. Based on the RVE models and the MD-based CZM, the mechanical properties of the macroscale cement paste are obtained by finite element analysis (FEA). To validate the accuracy of the MD-based CZM, the tensile strength and compressive strength of BNNS-reinforced cement paste from the FEA are compared with those from measurements. The FEA shows that the compressive strength of BNNS-reinforced cement paste is close to that of the measurements. The discrepancy of the tensile strength of BNNS-reinforced cement paste between the FEA and the measurements is distributed to the load transfer at the BNNS-tobermorite interface through the inclined BNNSs.

Advanced Self-Healing Asphalt Reinforced by Graphene Structures: An Atomistic Insight.

Graphene can improve the self-healing properties of asphalt with high durability. However, the self-healing behaviors of graphene-modified asphalt nanocomposite and the role of incorporated graphene are still unclear at this stage. In this study, the self-healing properties of pure asphalt and graphene-modified asphalt are investigated through molecular dynamics simulations. Asphalt bulks with two crack widths and locations for graphene are introduced, and the molecular interactions among asphalt components and the graphene sheet are analyzed. The results show that the location of graphene significantly affects the self-healing behaviors of asphalt. Graphene near the crack surface can greatly accelerate the self-healing process by interacting with the aromatic molecules through π-π stacking, while graphene at the top area of the crack tip has a minor impact on the process. The self-healing process of asphalt goes through the reorientation of asphaltene, polar aromatic, and naphthene aromatic molecules, and the bridging of saturate molecules between crack surfaces. This in-depth understanding of the self-healing mechanism contributes to the knowledge of the enhancement for self-healing properties, which will help to develop durable asphalt pavements.

Correction: Antibody-coated microstructures for selective isolation of immune cells in blood.

Correction for 'Antibody-coated microstructures for selective isolation of immune cells in blood' by Jiyu Li et al., Lab Chip, 2020, 20, 1072-1082, DOI: 10.1039/D0LC00078G.

Deterioration Mechanisms and Advanced Inspection Technologies of Aluminum Windows.

Aluminum windows are crucial components of building envelopes since they connect the indoor space to the external environment. Various external causes degrade or harm the functioning of aluminum windows. In this regard, inspecting the performance of aluminum windows is a necessary task to keep buildings healthy. This review illustrates the deterioration mechanisms of aluminum windows under various environmental conditions with an intention to provide comprehensive information for developing damage protection and inspection technologies. The illustrations reveal that moisture and chloride ions have the most detrimental effect on deteriorating aluminum windows in the long run, while mechanical loads can damage aluminum windows in a sudden manner. In addition, multiple advanced inspection techniques potential to benefit assessing aluminum window health state are discussed in order to help tackle the efficiency problem of traditional visual inspection. The comparison among those techniques demonstrates that infrared thermography can help acquire a preliminary defect profile of inspected windows, whereas ultrasonic phased arrays technology demonstrates a high level of competency in analyzing comprehensive defect information. This review also discusses the challenges in the scarcity of nanoscale corrosion information for insightful understandings of aluminum window corrosion and reliable window inspection tools for lifespan prediction. In this regard, molecular dynamics simulation and artificial intelligence technology are recommended as promising tools for better revealing the deterioration mechanisms and advancing inspection techniques, respectively, for future directions. It is envisioned that this paper will help upgrade the aluminum window inspection scheme and contribute to driving the construction of intelligent and safe cities.

Adhesion Strengthening Mechanism of Carbon Nanotube-Embedded Epoxy Composites: A Fracture-Based Approach.

Interfacial bonding integrity between different materials is critical to maintain the functionality of the entire physical system in any scale, ranging from building structures down to semiconductor transistors. For example, micro-patterned polymers embedded with conductive nanoparticles [e.g., carbon nanotubes (CNTs)] bonded with integrated circuits have been applied as many emerging chemical/biological microelectronic sensors. Nonetheless, it is challenging to measure and ensure the interfacial bonding integrity between materials for consistent and sustainable operations. Herein, we apply multiple interface characterization methods based on micro-engineering and microscopy as an integrative approach to reveal the mechanism of interfacial reinforcement by adding CNTs in a matrix material. An epoxy/CNT micro-beam is fabricated onto a silicon substrate, sandwiching a gold layer as an interfacial precrack. Superlayers of chromium are then repeatedly deposited onto the microstructure, inducing stepwise increasing stress over the materials and the corresponding micro-beam bending after detachment from the bonded interface. Accordingly, we can quantify key interfacial fracture parameters such as crack length, steady-state energy release rate, and fracture toughness. By further examining the formation and distribution of the micro-/nanostructures along the debonded interface using bright-field microscopy, 3D fluorescence imaging, and scanning electron microscopy, we can identify the underlying dominant interfacial strengthening and fracture toughening mechanisms. We further compare experimental results and theoretical predictions to quantify the interfacial bonding properties between epoxy/CNT and silicon and unveil the underlying reinforcement mechanisms. The results provide insights to develop polymer/nanoparticle composites with reinforced interfacial bonding integrity for more sustainable and reliable applications including microelectronics, surface coatings, and adhesive materials.

Aerosolization and Fluid Spillage During Phacoemulsification in Human Subjects.

BACKGROUND: Concerns had been raised for the potential hazard of SARS-CoV-2 transmissions via aerosols and fluid droplets during cataract surgeries amid the COVID-19 pandemic. This study aims to evaluate the rate of visible aerosol generation and fluid spillage from surgical wounds during phacoemulsification in human subjects. METHODS: This is a prospective consecutive interventional case series. High-resolution video captures of 30 consecutive uncomplicated phacoemulsification surgeries, performed by 3 board-certified specialists in ophthalmology, were assessed by 2 independent and masked investigators for intraoperative aerosolization and fluid spillage. Water-contact indicator tape was mounted on the base of the operating microscope, around the objective lens, to detect any fluid contact. RESULTS: No visible intraoperative aerosolization was detected in any of the cases, irrespective of different surgical practices among the surgeons with regard to wound size and position, lens fragmentation technique, power settings and means of ocular lubrication, or the different densities of cataract encountered. Large droplets spillage was noted from the paracentesis wounds in 70% of the cases. For all cases where fluid spill was detected on video, there was no fluid contact detected on the water-contact indicator tape. CONCLUSION: Visible aerosolization was not detected during phacoemulsification in our case series. Although the rate of fluid spillage was high, the lack of detectable contact with the indicator tape suggested that these large droplets posed no significant infectious risks to members of the surgical team.

Nondestructive quantification of single-cell nuclear and cytoplasmic mechanical properties based on large whole-cell deformation.

The mechanical properties of cell nuclei have been recognized to reflect and modulate important cell behaviors such as migration and cancer cell malignant tendency. However, these nuclear properties are difficult to characterize accurately using conventional measurement methods, which are often based on probing or deforming local sites over a nuclear region. The corresponding results are sensitive to the measurement position, and they are not decoupled from the cytoplasmic properties. Microfluidics is widely recognized as a promising technique for bioassay and phenotyping. In this report, we develop a simple and nondestructive approach for the single-cell quantification of nuclear elasticity based on microfluidics by considering different deformation levels of a live cell captured along a confining microchannel. We apply two inlet pressure levels to drive the flow of human nasopharyngeal epithelial cells (NP460) and human nasopharyngeal cancerous cells (NPC43) into the microchannels. A model considering the essential intracellular components (cytoplasm and nucleus) for describing the mechanics of a cell deforming along the confining microchannel is used to back-calculate the cytoplasmic and nuclear properties. On the other hand, we also apply a widely used chemical nucleus extraction technique to examine its possible effects (e.g., reduced nuclear modulus and reduced lamin A/C expression). To determine if the decoupled nuclear properties are representative of cancer-related attributes, we classify the NP460 and NPC43 cells using the decoupled physical properties as classification factors, resulting in an accuracy of 79.1% and a cell-type specificity exceeding 74%. It should be mentioned that the cells can be recollected at the device outlet after the nondestructive measurement. Hence, the reported cell elasticity measurement can be combined with downstream genetic and biochemical assays for general cell research and cancer diagnostic applications.

Regenerated and rotation-induced cellulose-wrapped oriented CNT fibers for wearable multifunctional sensors.

Recently, wearable multifunctional fibers have attracted widespread attention due to their applications in wearable smart textiles. However, stable application, large-scale production and more functions are still the greatest challenges for functional fiber devices. In this study, wearable multi-functional coaxial fibers with oriented carbon nanotubes (CNTs) were achieved for the first time coaxial wet-spinning with rotating coagulation bath. Specifically, the cellulose solution can be regenerated in the coagulation bath and the CNTs dispersion will be oriented under the rotating force. The synergy between hydrogen bonding and van der Waals interaction enhance the mechanical strength of coaxial fibers. Especially, CNTs can prevent the rotation of the cellulose chain and the bending of the glycosidic twist angle at the atomic scale as indicated by molecular dynamics (MD) simulations. When the fibers are strained, the cellulose sheath will drive the movement of CNTs, causing changes involving the effective contact area and number of conductive paths. Therefore, the high electrical resistance response change enables the as-obtained coaxial fibers to exhibit a great potential in wearable strain sensors. Furthermore, coaxial fibers can be made into electric heaters based on the Joule heating principle. The heating temperature reaches more than 160 °C within 6 s at 10 V, which is of a great value for large area flexible heaters. Besides, the coaxial fibers can further be used as temperature-sensitive devices to accurately perceive the external temperature. Therefore, the scalable synthesis of multifunctional coaxial fibers is significantly expected to provide a platform for the large-scale production of multifunctional wearable intelligent textiles.

Antibody-coated microstructures for selective isolation of immune cells in blood.

Cell isolation from blood is an important process for diagnosing immune diseases. There are still demands for a user-friendly approach to achieve high cell extraction efficiency and purity of a target immune cell subtype for more promising diagnosis and monitoring. For selective immune cell isolation, we developed a microstructured device, which consists of antibody-coated micropillars and micro-sieve arrays, for isolating a target immune cell subtype from bovine blood samples. The focusing micropillars can guide immune cells flowing to the subsequent micro-sieves based on deterministic lateral shifts of the cells. The arrangement of these microstructures is characterized and configured for the maximal cell capture rate. Surface modification with a selected antibody offers selective cell capture in the micro-sieves based on the antigen-antibody reaction. We prepare a cell mixture of human CD14-expressing leukemia cells (THP-1) and epithelial cells (MDA-MB-231) in diluted blood to characterize the cell isolation operation, with a selective cell isolation yield of >80%, cell purity of ∼100% and cell viability of >93%. Together, this microstructured device strategy can achieve high-yield selective isolation of immune cells from blood samples and support downstream genetic and biochemical cell analyses, contributing to the medical diagnosis of a broad range of immune diseases.

Atomic arrangement in CuZr-based metallic glass composites under tensile deformation.

Lacking macroscopic plasticity severely limits structure applications of bulk metallic glasses (BMGs). In general, particle-reinforced BMGs have an enhanced ductility but show reduced strength, whereas body-centered-cubic CuZr phase (B2 phase)-reinforced bulk MGs display improved ductility and strength. The underlying reason for the improvement in B2 phase-reinforced BMGs is still ambiguous. Herein, the atomic arrangement in Cu48Zr48Al4 BMGs with and without the B2 phase under tensile deformation is studied using molecular dynamics simulation. Different from pure MG where shear transformation zones (STZs) are activated along the same direction to form the domain shear band, STZs in the B2 phase-reinforced MG are activated along different directions disturbing the formation of a domain shear band. More plastic deformation and increased stress are allowed because of the phase transformations of B2 phases. The revealed deformation mechanism of B2 phase-reinforced MGs enables us to design heterogeneous structures with excellent strength and toughness.

Experimental Investigation on Interfacial Defect Criticality of FRP-Confined Concrete Columns.

Defects between fiber reinforced polymer (FRP) and repaired concrete components may easily come out due to misoperation during manufacturing, environmental deterioration, or impact from external load during service life. The defects may cause a degraded structure performance and even the unexpected structural failure. Different non-destructive techniques (NDTs) and sensors have been developed to assess the defects in FRP bonded system. The information of linking up the detected defects by NDTs and repair schemes is needed by assessing the criticality of detected defects. In this study, FRP confined concrete columns with interfacial defects were experimentally tested to determine the interfacial defect criticality on structural performance. It is found that interfacial defect can reduce the FRP confinement effectiveness, and ultimate strength and its corresponding strain of column deteriorate significantly if the interfacial defect area is larger than 50% of total confinement area. Meanwhile, proposed analytical model considering the defect ratio is validated for the prediction of stress⁻strain behavior of FRP confined columns. The evaluation of defect criticality could be made by comparing predicted stress⁻strain behavior with the original design to determine corresponding maintenance strategies.

Elasticity-Modulated Microbeads for Classification of Floating Normal and Cancer Cells Using Confining Microchannels.

Engineered microbeads have a wide range of applications in cancer research including identification, characterization, and sorting of cancer cells. In particular, the microbead-based cancer identification techniques are mainly based on the known genetic or biochemical biomarkers; and detection specificity is yet to be improved. On the other hand, it has been discovered that biomechanical properties of cancer cells such as cell-body elasticity can be considered as cancer biomarkers. Here, we report a straightforward microfluidic classification scheme for floating/dissociated normal and cancer epithelial cells using a confining microchannel device together with calcium-alginate hydrogel microbeads. The hydrogel microbeads are generated based on the microfluidic emulsion process, with characterization on the process parameters (e.g., liquid driving pressure and cross-linking duration) in order to specify the resultant bead diameter and elasticity. These engineered microbeads are first mixed with a cell mixture of dissociated human nasopharyngeal epithelial cells (NP460) and nasopharyngeal carcinoma cells (NPC43). The cell elasticity can then be reflected from the locations of captured cells in the device. Experiments further demonstrate that the cell classification has a success rate of >95%. Furthermore, we performed the microbead-based cell classification on a whole blood sample containing floating human breast epithelial cells (MCF-10A) and breast cancer epithelial cells (MDA-MB-231) with a success rate of >75%, revealing its directly applicability to identification of circulating tumor cells in human blood. Together, this research demonstrates a new application of engineered hydrogel microbeads for classification of cells based on their mechanical properties.

Moisture effect on interfacial integrity of epoxy-bonded system: a hierarchical approach.

The epoxy-bonded system has been widely used in various applications across different scale lengths. Prior investigations have indicated that the moisture-affected interfacial debonding is the major failure mode of such a system, but the fundamental mechanism remains unknown, such as the basis for the invasion of water molecules in the cross-linked epoxy and the epoxy-bonded interface. This prevents us from predicting the long-term performance of the epoxy-related applications under the effect of the moisture. Here, we use full atomistic models to investigate the response of the epoxy-bonded system towards the adhesion test, and provide a detailed analysis of the interfacial integrity under the moisture effect and the associated debonding mechanism. Molecular dynamics simulations show that water molecules affect the hierarchical structure of the epoxy-bonded system at the nanoscale by disrupting the film-substrate interaction and the molecular interaction within the epoxy, which leads to the detachment of the epoxy thin film, and the final interfacial debonding. The simulation results show good agreement with the experimental results of the epoxy-bonded system. Through identifying the relationship between the epoxy structure and the debonding mechanism at multiple scales, it is shown that the hierarchical structure of the epoxy-bonded system is crucial for the interfacial integrity. In particular, the available space of the epoxy-bonded system, which consists of various sizes ranging from the atomistic scale to the macroscale and is close to the interface facilitates the moisture accumulation, leading to a distinct interfacial debonding when compared to the dry scenario.

Flexibility of backbone fibrils in α-chitin crystals with different degree of acetylation.

Acetyl groups are backbone outreaches that enhance inter-fibril connection in chitin and chitosan fibril bundle. Removal of acetyl groups affects flexibility of chitosan fibril bundle, thereby affecting mechanical strength of chitosan-based products. Understandings of relationship between degree of acetylation and flexibility of chitin fibril bundle conduce to optimization of synthetic chitin materials. Here, the relationship is examined by performing molecular dynamics simulations. Coiling of chitin and chitosan fibril bundle with different degree of acetylation is observed and flexibility of fibrils is measured. Number and alignment of acetyl groups are found to be important factors determining the flexibility of chitin and chitosan fibril bundle. Structural instability can be caused by incompatible alignment of acetyl groups. Our findings on synthetic chitin-based materials indicate that adding a small amount of acetyl groups to chitosan can significantly enhance the integrity of fibril bundle.

Mesoscopic packing of disk-like building blocks in calcium silicate hydrate.

At 100-nanometer length scale, the mesoscopic structure of calcium silicate hydrate (C-S-H) plays a critical role in determining the macroscopic material properties, such as porosity. In order to explore the mesoscopic structure of C-S-H, we employ two effective techniques, nanoindentation test and molecular dynamics simulation. Grid nanoindentation tests find different porosity of C-S-H in cement paste specimens prepared at varied water-to-cement (w/c) ratios. The w/c-ratio-induced porosity difference can be ascribed to the aspect ratio (diameter-to-thickness ratio) of disk-like C-S-H building blocks. The molecular dynamics simulation, with a mesoscopic C-S-H model, reveals 3 typical packing patterns and relates the packing density to the aspect ratio. Illustrated with disk-like C-S-H building blocks, this study provides a description of C-S-H structures in complement to spherical-particle C-S-H models at the sub-micron scale.

Effect of Acetyl Group on Mechanical Properties of Chitin/Chitosan Nanocrystal: A Molecular Dynamics Study.

Chitin fiber is the load-bearing component in natural chitin-based materials. In these materials, chitin is always partially deacetylated to different levels, leading to diverse material properties. In order to understand how the acetyl group enhances the fracture resistance capability of chitin fiber, we constructed atomistic models of chitin with varied acetylation degree and analyzed the hydrogen bonding pattern, fracture, and stress-strain behavior of these models. We notice that the acetyl group can contribute to the formation of hydrogen bonds that can stabilize the crystalline structure. In addition, it is found that the specimen with a higher acetylation degree presents a greater resistance against fracture. This study describes the role of the functional group, acetyl groups, in crystalline chitin. Such information could provide preliminary understanding of nanomaterials when similar functional groups are encountered.

Nano- and mesoscale modeling of cement matrix.

Atomistic simulations of cementitious material can enrich our understanding of its structural and mechanical properties, whereas current computational capacities restrict the investigation length scale within 10 nm. In this context, coarse-grained simulations can translate the information from nanoscale to mesoscale, thus bridging the multi-scale investigations. Here, we develop a coarse-grained model of cement matrix using the concept of disk-like building block. The objective is to introduce a new method to construct a coarse-grained model of cement, which could contribute to the scale-bridging issue from nanoscale to mesoscale. PAC codes: 07.05.Tp, 62.25.-g, 82.70.Dd.

Development of a coarse-grained α-chitin model on the basis of MARTINI forcefield.

At nanoscale, atomistic simulation is widely used for investigating crystalline chitin fibers, the structural component for many biological materials. However, the longitudinal dimension of naturally occurring chitin fibers exceeds hundreds of nanometer, beyond the investigation range of all-atom simulation due to the limitation of computational power. Under this context, coarse-grained simulation is a useful alternative that facilitates the investigation of a large system. We develop a coarse-grained model for describing the structural and mechanical properties of α-chitin. The developed coarse-grained model can reasonably predict these properties. Moreover, this model is consistent with existing coarse-grained force fields for proteins. The present model of α-chitin possesses good potential and applicability in the investigation of natural chitin-based materials at the length scale of several hundred nanometers.

Thermal insulating concrete wall panel design for sustainable built environment.

Air-conditioning system plays a significant role in providing users a thermally comfortable indoor environment, which is a necessity in modern buildings. In order to save the vast energy consumed by air-conditioning system, the building envelopes in envelope-load dominated buildings should be well designed such that the unwanted heat gain and loss with environment can be minimized. In this paper, a new design of concrete wall panel that enhances thermal insulation of buildings by adding a gypsum layer inside concrete is presented. Experiments have been conducted for monitoring the temperature variation in both proposed sandwich wall panel and conventional concrete wall panel under a heat radiation source. For further understanding the thermal effect of such sandwich wall panel design from building scale, two three-story building models adopting different wall panel designs are constructed for evaluating the temperature distribution of entire buildings using finite element method. Both the experimental and simulation results have shown that the gypsum layer improves the thermal insulation performance by retarding the heat transfer across the building envelopes.