advanced-self-healing-asphalt-reinforced-graphene-structures-an

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 ...

City University of Hong Kong

Accurate measurement of interfacial properties is critical any time two materials are bonded--in composites, tooth crowns, or when biomaterials are attached to the human body. Yet, in spite of this importance, reliable methods to measure interfacial properties between dissimilar materials remain elusive. Here we present an experimental approach to quantify the interfacial fracture energy Γi that also provides unique mechanistic insight into the interfacial debonding mechanism at the nanoscale. This approach involves deposition of an additional chromium layer (superlayer) onto a bonded system, where interface debonding is initiated by the residual tensile stress in the superlayer, and where the interface can be separated in a controlled manner and captured in situ. Contrary to earlier methods, our approach allows the entire bonded system to remain in an elastic range during the debonding process, such that Γi can be measured accurately. We validate the method by showing that moisture has a degrading effect on the bonding between epoxy and silica, a technologically important interface. Combining in situ through scanning electron microscope images with molecular simulation, we find that the interfacial debonding mechanism is hierarchical in nature, which is initiated by the detachment of polymer chains, and that the three-dimensional covalent network of the epoxy-based polymer may directly influence water accumulation, leading to the reduction of Γi under presence of moisture. The results may enable us to design more durable concrete composites that could be used to innovate transportation systems, create more durable buildings and bridges, and build resilient infrastructure.

A robust nanoscale experimental quantification of fracture energy in a bilayer material system.

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. 

Thermal insulating concrete wall panel design for sustainable built environment.

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. 

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

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. 

Nano- and mesoscale modeling of cement matrix.

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. 

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

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.

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

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.

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

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.

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

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.

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

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.

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

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.

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

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.

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

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.

Aerosolization and Fluid Spillage During Phacoemulsification in Human Subjects.

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.

Deterioration Mechanisms and Advanced Inspection Technologies of Aluminum Windows.

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.

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

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

Denvid Lau

Department of Architecture and Civil Engineering

City University of Hong Kong

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

Denvid Lau

.css-o250i3{font-size:18px;font-family:Open Sans,sans-serif;line-height:21.6px;}Department of Architecture and Civil Engineering

City University of Hong Kong

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

Department of Architecture and Civil Engineering