Cell adhesion plays a crucial role in many biological processes of cells, e.g., immune responses,... more Cell adhesion plays a crucial role in many biological processes of cells, e.g., immune responses, tissue morphogenesis, and stem cell differentiation. An essential problem in the molecular mechanism of cell adhesion is to characterize the binding affinity of membrane-anchored receptors and ligands under different physiological conditions. In this paper, a theoretical model is presented to study the binding affinity between a large number of anchored receptors and ligands under both tensile and compressive stresses, and corroborated by demonstrating excellent agreement with Monte Carlo simulations. It is shown that the binding affinity becomes lower as the magnitude of the applied stress increases, and drops to zero at a critical tensile or compressive stress. Interestingly, the critical compressive stress is found to be substantially smaller than the critical tensile stress for relatively long and flexible receptor-ligand complexes. This counterintuitive finding is explained by usin...
Journal of the Mechanics and Physics of Solids, 2015
ABSTRACT Surface wrinkling in thin films on compliant substrates is of considerable interest for ... more ABSTRACT Surface wrinkling in thin films on compliant substrates is of considerable interest for applications involving surface patterning, smart adhesion, liquid/cell shaping, particle assembly, design of flexible electronic devices, as well as mechanical characterization of thin film systems. When the in-plane size of the system is infinite, the critical wrinkling strain is known to be governed by the moduli ratio between the film and substrate. Here we show a surprising result that the lateral dimension of the film can play a critical role in the occurrence of surface wrinkling. The basic phenomenon was established through selective UV/Ozone (UVO) exposure of a strain-free PDMS slab via composite copper grids with different meshes, followed by treatment using mixed ethanol/glycerol solvents with different volume fractions of ethanol. To understand the physics behind the experimental observations, finite element (FE) simulations were performed to establish an analytical expression for the distribution of shear tractions at the film–substrate interface. Subsequent theoretical analysis leads to closed-form predictions for the critical growth/ swelling strain for the onset of wrinkling. Our analysis reveals that the occurrence of surface wrinkling and post-wrinkling pattern evolution can be controlled by tuning the lateral size of the thin film for a given moduli ratio. These results may find broad applications in preventing surface wrinkling, creating desired surface patterns, evaluating the interfacial shear strength of a film/substrate system and designing flexible electronic devices.
Modulation of the physical and mechanical properties of nanowires is a challenging issue for thei... more Modulation of the physical and mechanical properties of nanowires is a challenging issue for their technological applications. In this paper, we investigate the effects of surface modification on the mechanical properties of gold nanowires by performing molecular dynamics simulations. It is found that by modifying a small density of silver atoms to the surface of a gold nanowire, the residual surface stress state can be altered, rendering a great improvement of its plastic yield strength. This finding is in good agreement with experimental measurements. The underlying physical mechanisms are analyzed by a core-shell nanowire model. The results are helpful for the design and optimization of advanced nanomaterial with superior mechanical properties.
The propagation of Love waves in the structure consisting of a nanosized piezoelectric film and a... more The propagation of Love waves in the structure consisting of a nanosized piezoelectric film and a semi-infinite elastic substrate is investigated in the present paper with the consideration of surface effects. In our analysis, surface effects are taken into account in terms of the surface elasticity theory and the electrically-shorted conditions are adopted on the free surface of the piezoelectric film and the interface between the film and the substrate. This work focuses on the new features in the dispersion relations of different modes due to surface effects. It is found that with the existence of surface effects, the frequency dispersion of Love waves shows the distinct dependence on the thickness and the surface constants when the film thickness reduces to nanometers. In general, phase velocities of all dispersion modes increase with the decrease of the film thickness and the increase of the surface constants. However, surface effects play different functions in the frequency dispersions of different modes, especially for the first mode dispersion. Moreover, different forms of Love waves are observed in the first mode dispersion, depending on the presence of the surface effects on the surface and the interface.
In the present paper, the constitutive relation and failure behaviorsof carbon nanotube-reinforce... more In the present paper, the constitutive relation and failure behaviorsof carbon nanotube-reinforced composites are studied using methods of micromechanics and nanomechanics. First, we examined the factors that influence the overall mechanical property of carbon nanotube composites, including the weak bonding between carbon nanotubes and matrix, the curviness and agglomeration of carbon nanotubes. Second, we established a hybrid continuum/micromechanics/atomistic method to investigate the defect nucleation in a carbon nanotube embedded in a polymer matrix.
ABSTRACT Atomic-scale surface steps play an important role in the mechanical behaviors of nanopar... more ABSTRACT Atomic-scale surface steps play an important role in the mechanical behaviors of nanoparticles. Both molecular dynamics and finite element simulations are performed to investigate the elastic compression of copper nanoparticles. When surface steps are taken into account, the finite element calculation predicts the same compressive load-depth relation as the atomistic simulation. It is revealed that the compression of crystalline nanoparticles on facets should be characterized by a flat punch indenting an elastic half space, instead of the widely adopted Hertzian model with smooth spherical surface. As the particle size increases from nanometers to microns, the influence of atomic-scale surface steps becomes insignificant and the compressive load-depth relation transmits from the flat punch model to the Hertzian model. This study bridges the contact of an individual particle from nanoscale to microscale, and is helpful for using the indentation technique to measure the mechanical properties of particles.
In this paper, a numerical method is presented for calculating the effective elastic moduli and t... more In this paper, a numerical method is presented for calculating the effective elastic moduli and the tensile strength as well as for simulating the failure process of brittle materials associated with microcracking damage. By introducing two criteria for microcrack growth and coalescence in terms of Griffith's energy release rate, the above numerical method is used here to simulate the coalescence process of microcracks that results in a fatal crack and the final rupture of a specimen.
Self-assembled nanostructures of lipids and nanoparticles hold great promise for applications in ... more Self-assembled nanostructures of lipids and nanoparticles hold great promise for applications in such fields as nanomedicine. This paper uses the self-consistent field theory to investigate the self-assembly behavior of lipid molecules and nanoparticles with different shapes in an aqueous solution. It is found that the lipid molecules can form monolayered and bilayered nanostructures around the nanoparticles with different shapes (e.g., triangular, square, hexagonal and octangular). With decreasing the size of nanoparticles or increasing the number of polygon edges, the shape of lipid layers will approach an approximately spherical shape. These findings may help to predict and design novel drug delivery nanocarriers.
This article appeared in a journal published by Elsevier. The attached copy is furnished to the a... more This article appeared in a journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution and sharing with colleagues.
This article appeared in a journal published by Elsevier. The attached copy is furnished to the a... more This article appeared in a journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution and sharing with colleagues.
Cell adhesion plays a crucial role in many biological processes of cells, e.g., immune responses,... more Cell adhesion plays a crucial role in many biological processes of cells, e.g., immune responses, tissue morphogenesis, and stem cell differentiation. An essential problem in the molecular mechanism of cell adhesion is to characterize the binding affinity of membrane-anchored receptors and ligands under different physiological conditions. In this paper, a theoretical model is presented to study the binding affinity between a large number of anchored receptors and ligands under both tensile and compressive stresses, and corroborated by demonstrating excellent agreement with Monte Carlo simulations. It is shown that the binding affinity becomes lower as the magnitude of the applied stress increases, and drops to zero at a critical tensile or compressive stress. Interestingly, the critical compressive stress is found to be substantially smaller than the critical tensile stress for relatively long and flexible receptor-ligand complexes. This counterintuitive finding is explained by usin...
Journal of the Mechanics and Physics of Solids, 2015
ABSTRACT Surface wrinkling in thin films on compliant substrates is of considerable interest for ... more ABSTRACT Surface wrinkling in thin films on compliant substrates is of considerable interest for applications involving surface patterning, smart adhesion, liquid/cell shaping, particle assembly, design of flexible electronic devices, as well as mechanical characterization of thin film systems. When the in-plane size of the system is infinite, the critical wrinkling strain is known to be governed by the moduli ratio between the film and substrate. Here we show a surprising result that the lateral dimension of the film can play a critical role in the occurrence of surface wrinkling. The basic phenomenon was established through selective UV/Ozone (UVO) exposure of a strain-free PDMS slab via composite copper grids with different meshes, followed by treatment using mixed ethanol/glycerol solvents with different volume fractions of ethanol. To understand the physics behind the experimental observations, finite element (FE) simulations were performed to establish an analytical expression for the distribution of shear tractions at the film–substrate interface. Subsequent theoretical analysis leads to closed-form predictions for the critical growth/ swelling strain for the onset of wrinkling. Our analysis reveals that the occurrence of surface wrinkling and post-wrinkling pattern evolution can be controlled by tuning the lateral size of the thin film for a given moduli ratio. These results may find broad applications in preventing surface wrinkling, creating desired surface patterns, evaluating the interfacial shear strength of a film/substrate system and designing flexible electronic devices.
Modulation of the physical and mechanical properties of nanowires is a challenging issue for thei... more Modulation of the physical and mechanical properties of nanowires is a challenging issue for their technological applications. In this paper, we investigate the effects of surface modification on the mechanical properties of gold nanowires by performing molecular dynamics simulations. It is found that by modifying a small density of silver atoms to the surface of a gold nanowire, the residual surface stress state can be altered, rendering a great improvement of its plastic yield strength. This finding is in good agreement with experimental measurements. The underlying physical mechanisms are analyzed by a core-shell nanowire model. The results are helpful for the design and optimization of advanced nanomaterial with superior mechanical properties.
The propagation of Love waves in the structure consisting of a nanosized piezoelectric film and a... more The propagation of Love waves in the structure consisting of a nanosized piezoelectric film and a semi-infinite elastic substrate is investigated in the present paper with the consideration of surface effects. In our analysis, surface effects are taken into account in terms of the surface elasticity theory and the electrically-shorted conditions are adopted on the free surface of the piezoelectric film and the interface between the film and the substrate. This work focuses on the new features in the dispersion relations of different modes due to surface effects. It is found that with the existence of surface effects, the frequency dispersion of Love waves shows the distinct dependence on the thickness and the surface constants when the film thickness reduces to nanometers. In general, phase velocities of all dispersion modes increase with the decrease of the film thickness and the increase of the surface constants. However, surface effects play different functions in the frequency dispersions of different modes, especially for the first mode dispersion. Moreover, different forms of Love waves are observed in the first mode dispersion, depending on the presence of the surface effects on the surface and the interface.
In the present paper, the constitutive relation and failure behaviorsof carbon nanotube-reinforce... more In the present paper, the constitutive relation and failure behaviorsof carbon nanotube-reinforced composites are studied using methods of micromechanics and nanomechanics. First, we examined the factors that influence the overall mechanical property of carbon nanotube composites, including the weak bonding between carbon nanotubes and matrix, the curviness and agglomeration of carbon nanotubes. Second, we established a hybrid continuum/micromechanics/atomistic method to investigate the defect nucleation in a carbon nanotube embedded in a polymer matrix.
ABSTRACT Atomic-scale surface steps play an important role in the mechanical behaviors of nanopar... more ABSTRACT Atomic-scale surface steps play an important role in the mechanical behaviors of nanoparticles. Both molecular dynamics and finite element simulations are performed to investigate the elastic compression of copper nanoparticles. When surface steps are taken into account, the finite element calculation predicts the same compressive load-depth relation as the atomistic simulation. It is revealed that the compression of crystalline nanoparticles on facets should be characterized by a flat punch indenting an elastic half space, instead of the widely adopted Hertzian model with smooth spherical surface. As the particle size increases from nanometers to microns, the influence of atomic-scale surface steps becomes insignificant and the compressive load-depth relation transmits from the flat punch model to the Hertzian model. This study bridges the contact of an individual particle from nanoscale to microscale, and is helpful for using the indentation technique to measure the mechanical properties of particles.
In this paper, a numerical method is presented for calculating the effective elastic moduli and t... more In this paper, a numerical method is presented for calculating the effective elastic moduli and the tensile strength as well as for simulating the failure process of brittle materials associated with microcracking damage. By introducing two criteria for microcrack growth and coalescence in terms of Griffith's energy release rate, the above numerical method is used here to simulate the coalescence process of microcracks that results in a fatal crack and the final rupture of a specimen.
Self-assembled nanostructures of lipids and nanoparticles hold great promise for applications in ... more Self-assembled nanostructures of lipids and nanoparticles hold great promise for applications in such fields as nanomedicine. This paper uses the self-consistent field theory to investigate the self-assembly behavior of lipid molecules and nanoparticles with different shapes in an aqueous solution. It is found that the lipid molecules can form monolayered and bilayered nanostructures around the nanoparticles with different shapes (e.g., triangular, square, hexagonal and octangular). With decreasing the size of nanoparticles or increasing the number of polygon edges, the shape of lipid layers will approach an approximately spherical shape. These findings may help to predict and design novel drug delivery nanocarriers.
This article appeared in a journal published by Elsevier. The attached copy is furnished to the a... more This article appeared in a journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution and sharing with colleagues.
This article appeared in a journal published by Elsevier. The attached copy is furnished to the a... more This article appeared in a journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution and sharing with colleagues.
Uploads
Papers by Xi-Qiao Feng