Edmund B. Webb III

Edmund B. Webb III
Lehigh University · Department of Mechanical Engineering and Mechanics

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93
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Publications

Publications (93)
Preprint
Full-text available
A new method based on quasi-independent parallel simulations approach, replica-averaging, has been developed to study the influence of flow on mechanical force-mediated polymer processes such as denaturation and breaking of bonds. This method considerably mitigates the unphysical prediction of force-mediated events inherent in Brownian dynamics (BD...
Article
The globular-stretch transition of a collapsed polymer in low strain rate elongational flow is studied using polymeric protrusion kinetics scaling laws and numerical simulation. Results demonstrate the influence of fluid flow on the occurrence probability of long-length thermally nucleated polymeric protrusions, which regulate collapsed polymer unf...
Article
Full-text available
Aims The study objective was to prospectively assess clinical outcomes for a pilot cohort of tibial shaft fractures treated with a new tibial nailing system that produces controlled axial interfragmentary micromotion. The hypothesis was that axial micromotion enhances fracture healing compared to static interlocking. Methods Patients were treated...
Article
The globular-to-unraveled conformation transition of von Willebrand Factor (vWF), a large polymeric glycoprotein in human blood plasma, is a crucial step in the process of clotting at sites of vascular injury. However, unraveling of vWF multimers in uninjured vasculature can lead to pathology (i.e., thrombus formation or degradation of vWF proteins...
Article
The von Willebrand Factor (vWF) is a large blood glycoprotein that aids in hemostasis. Within each vWF monomer, the A2 domain hosts a cleavage site for enzyme ADAMTS13, which regulates the size of vWF multimers. This cleavage site can only be exposed when an A2 domain unfolds, and the unfolding reaction energy landscape is highly sensitive to the f...
Article
Full-text available
We develop a machine learning tool useful for predicting the instantaneous dynamical state of sub-monomer features within long linear polymer chains, as well as extracting the dominant macromolecular motions associated with sub-monomer behaviors of interest. We employ the tool to better understand and predict sub-monomer A2 domain unfolding dynamic...
Article
We perform single-molecule flow experiments using confocal microscopy and a microfluidic device for shear rates up to 20,000 s-1 and present results for the shear-induced unraveling and elongation of tethered von Willebrand factor (VWF) multimers. Further, we employ companion Brownian dynamics simulations to help explain details of our experimental...
Article
Full-text available
von Willebrand Factor (vWF) is a large multimeric protein that binds to platelets and collagen in blood clotting. vWF A2 domain hosts a proteolytic site for ADAMTS13 (A Disintegrin and Metalloprotease with a ThromboSpondin type 1 motif, member 13) to regulate the size of vWF multimers. This regulation process is highly sensitive to force conditions...
Article
Using Brownian molecular dynamics simulations, we examine the internal dynamics and biomechanical response of von Willebrand factor (vWF) multimers subject to shear flow. The coarse grain multimer description employed here is based on a monomer model in which the A2 domain of vWF is explicitly represented by a nonlinear elastic spring whose mechani...
Preprint
Full-text available
Using Brownian molecular dynamics simulations, we examine the internal dynamics and biomechanical response of von Willebrand Factor (vWF) multimers subject to shear flow. The coarse grain multimer description employed here is based on a monomer model in which the A2 domain of vWF is explicitly represented by a non-linear elastic spring whose mechan...
Article
Von Willebrand factor (VWF) is a large multimeric protein that aids in blood clotting. Near injury sites, hydrodynamic force from increased blood flow elongates VWF, exposing binding sites for platelets and collagen. To investigate VWF binding to collagen that is exposed on injured arterial surfaces, Brownian dynamics simulations are performed with...
Article
Full-text available
Evolution of deformation and stress in growing thin films has been studied in this work using computational simulations that resolve matter at atomic length and time scales. For the surface layers of films laying on the substrate of a dissimilar material, the stress distribution analysis around defects becomes more challenging. Herein, spatial and...
Article
Results are presented from molecular dynamics simulations of Pb(l) nanodroplets containing dispersed Cu nanoparticles (NPs) and spreading on solid surfaces. Three-dimensional simulations are employed throughout, but droplet spreading and pinning are reduced to two-dimensional processes by modeling cylindrical NPs in cylindrical droplets; NPs have r...
Article
Molecular dynamics simulations are used to investigate lithium (Li) transport rates in symmetric tilt graphite grain boundaries (GBs). Experiments have quantified highly varied diffusion rates of Li in graphite and recent computational work exposed similar differences in Li intercalation rates into GBs from a free surface. This work extends finding...
Article
Full-text available
The Kapitza resistance at a segregated, low-angle symmetric tilt grain boundary in β-SiC is investigated using non-equilibrium molecular dynamics simulation. In particular, we assess the role of compositional and thermal disorder on the boundary resistance for various doping scenarios. By examining the local vibrational density of states, we identi...
Article
Full-text available
The impact of grain-boundary segregation on the high-temperature Kapitza resistance of doped β-SiC using non-equilibrium molecular dynamics simulation is investigated. In particular, low-angle, symmetric tilt grain boundaries are examined to assess the roles of dopant concentration and dopant/matrix interaction strength in determining the resistanc...
Article
Lithium-ion diffusion rates in graphitic battery anodes have been shown to vary greatly in experiments, with numerous hypotheses to explain this behavior. Here, we model several grain boundaries using molecular dynamics and quantify intercalation from the free surface. A significant variation in intercalation rates is revealed as dictated by local...
Conference Paper
Facing the pressures of rising fuel costs, intense competition across industries and government regulations on emissions, manufacturing innovation is now largely driven by the search for ultra-efficient structures. One such field of innovation, topology optimization, allows designers to find high-strength, light-weight solutions while minimizing pr...
Article
We employ Monte Carlo simulation in the semi-grand canonical ensemble to obtain the coarse-grained free energy corresponding to an embedded-atom method description of a binary alloy. In particular, the Ginzburg-Landau free energy for a Cu-Ni alloy was determined from a tabulated histogram of the joint probability density of composition, energy, and...
Article
Atomic scale phenomena driving contact line advancement during the wetting of a solid by a liquid are investigated via molecular dynamics simulations of Ag(l) drops spreading on Ni substrates. For the homologous temperature ~5% above melting for Ag, essentially non-reactive wetting is observed with relatively high spreading velocity. Analyzing atom...
Article
Capillary phenomena associated with fluids wetting other condensed matter phases have drawn great scientific interest for hundreds of years; consider the recent bicentennial celebration of Thomas Young's paper on equilibrium contact angles, describing the geometric shape assumed near a three phase contact line in terms of the relevant surface energ...
Article
Film stress and microstructure evolution during the growth of a Ni bicrystal film are investigated by molecular dynamics simulations. The nominal surface orientation of the growing film was (111) and the grain boundaries are Σ79 symmetrical tilt grain boundaries. The growth mode is layer by layer; two-dimensional (2D) islands nucleate on the surfac...
Article
The kinetic Monte Carlo method and its variants are powerful tools for modeling materials at the mesoscale, meaning at length and time scales in between the atomic and continuum. We have completed a 3 year LDRD project with the goal of developing a parallel kinetic Monte Carlo capability and applying it to materials modeling problems of interest to...
Article
Full-text available
Molecular dynamics simulations and selected experiments have been carried out to study the growth of Cu films on (010) bcc Ta and the deposition of Cu <sub>x</sub> Ta <sub>1-x</sub> alloy films on (111) fcc Cu. They indicate that fcc Cu films with a (111) texture are always formed when Cu is deposited on Ta surfaces. These films are polycrystalline...
Article
Molecular dynamics (MD) simulations are presented to investigate the rate of infiltration of liquid Cu through a channel in crystalline Ni. Two temperatures, T = 1750 K and 1500 K, are studied using two types of simulations: non-dissolutive (ND), where Ni atoms are held fixed, and dissolutive (D), where Ni atoms relax according to MD equations of m...
Article
As motivation builds to consider mechanics of nanometer scale objects, it is increasingly advantageous to implement models with finer resolution than standard continuum approaches. For such exercises to prove fruitful, these models must be able to quantify continuum thermomechanical quantities; furthermore, it may be necessary to do so on a sub-sys...
Article
Atomic simulations of the growth of polycrystalline Ni demonstrate that deposited atoms incorporate into the film at boundaries, resulting in compressive stress generation. Incorporated atoms can also leave the boundaries and thus relieve compressive stress. This leads to a complex interplay between growth stress, adatom incorporation, and surface...
Article
Heteroepitaxial growth in the Ge∕Si (001) system is known to lead to the formation of pyramid-like “hut” islands with {105}-oriented facets. Recent calculations of island formation energies in this system have suggested that edge energies lead to an important contribution to the barrier to island formation at small sizes. Here we provide an indepen...
Article
Atomistic simulations will be presented revealing fundamental stress generation mechanisms during later stages of thin film growth when substrate coverage is complete and the film is thickening. Typically, films exhibit texture with grain boundaries intersecting the surface. In situ growth stress experiments reveal compressive stress generation dur...
Article
Controlling the spatial distribution of liquid droplets on surfaces via surface energy patterning can be used to deliver material to specified regions via selective liquid/solid wetting. Although studies of the equilibrium shape of liquid droplets on heterogeneous substrates exist, much less is known about the corresponding wetting kinetics. Here w...
Article
During Volmer-Weber thin film growth, discrete metal islands grow on a substrate. When the separation between their adjacent free surfaces becomes small enough, islands coalesce and trade surface energy for elastic strain energy. While it is understood that traction between island and substrate directly influences coalescence stress, questions rema...
Article
In this study, we perform molecular dynamics simulations of adhesive contact and friction between alkylsilane Si(OH)(3)(CX(2))(10)CX(3) and alkoxylsilane Si(OH)(2)(CX(2))(10)CX(3) (where X = H or F) self-assembled monolayers (SAMs) on an amorphous silica substrate. The alkylsilane SAMs are primarily hydrogen-bonded or physisorbed to the surface. Th...
Article
Full-text available
Tensile stress generation associated with island coalescence is almost universally observed in thin films that grow via the Volmer-Weber mode. The commonly accepted mechanism for the origin of this tensile stress is a process driven by the reduction in surface energy at the expense of the strain energy associated with the deformation of coalescing...
Article
The spreading of liquid nanodroplets of different initial radii R0 is studied using molecular dynamics simulation. Results for two distinct systems, Pb on Cu(111), which is nonwetting, and a coarse-grained polymer model, which wets the surface, are presented for Pb droplets ranging in size from approximately 55,000 to 220,000 atoms and polymer drop...
Article
The polysilicon surfaces used to manufacture microelectromechanical systems are often coated with organic self-assembled monolayers (SAMs) to reduce the adhesion and friction. While a large body of work exists on this topic, there is still not a fundamental understanding of the friction and adhesion between SAM-coated surfaces. This article reviews...
Article
Molecular dynamics simulations are used to study the spreading of binary polymer nanodroplets in a cylindrical geometry. The polymers, described by the bead-spring model, spread on a flat surface with a surface-coupled Langevin thermostat to mimic the effects of a corrugated surface. Each droplet consists of chains of length 10 or 100 monomers with...
Article
Reactive wetting in the eutectic AgCu system is studied with molecular dynamics simulations. As Ag(l) spreads on the Cu surface, Cu dissolves into the liquid. The results for reactive wetting are compared to simulations in which no mixing is permitted, demonstrating that wetting kinetics are enhanced by dissolution reactions. The time dependent rad...
Article
Full-text available
Silicon micromachines in microelectromechanical systems (MEMS) are coated with self-assembled monolayers (SAMs) in order to reduce the wear and stiction that are commonplace during operation. Recently, perfluorinated SAMs have been the focus of attention because they have better processing properties than hydrocarbon SAMs. In this study, we perform...
Article
Atomistic simulations were performed to investigate high temperature wetting phenomena for metals. A sessile drop configuration was modeled for two systems: Ag(l) on Cu and Pb(l) on Cu. The former case is an eutectic binary and the wetting kinetics were greatly enhanced by the presence of aggressive interdiffusion between Ag and Cu. Wetting kinetic...
Article
Volmer-Weber thin film growth involves nucleation of discrete islands that grow, impinge upon one another, and coalesce into a film. Coalescence has been proposed to generate stress in thin films so it is useful to study stress evolution upon coalescence. Results are presented from atomistic simulations of nanometer island coalescence. Molecular dy...
Article
Full-text available
The spreading of liquid nanodroplets of different initial radii $R_{0}$ is studied using molecular dynamics simulation. Results for two distinct systems, Pb on Cu(111), which is non-wetting, and a coarse grained polymer model, which wets the surface, are presented for Pb droplets ranging in size from $\sim55 000$ to $220 000$ atoms and polymer drop...
Article
The adhesion and friction between pairs of ordered and disordered self-assembled monolayers on SiO2 are studied using molecular dynamics. The disorder is introduced by randomly removing chains from a well ordered crystalline substrate and by attaching chains to an amorphous substrate. The adhesion force between monolayers at a given separation incr...
Article
Full-text available
This report is a collection of documents written by the group members of the Engineering Sciences Research Foundation (ESRF), Laboratory Directed Research and Development (LDRD) project titled 'A Robust, Coupled Approach to Atomistic-Continuum Simulation'. Presented in this document is the development of a formulation for performing quasistatic, co...
Article
The spreading of one- and two-component polymer nanodroplets is studied using molecular dynamics simulation in a cylindrical geometry. The droplets consist of polymer chains of length 10, 40, and 100 monomers per chain described by the bead-spring model spreading on a flat surface with a surface-coupled Langevin thermostat. Each droplet contains ap...
Article
The spreading of polymer droplets is studied using molecular dynamics simulations. To study the dynamics of both the precursor foot and the bulk droplet, large hemispherical drops of 200 000 monomers are simulated using a bead-spring model for polymers of chain length 10, 20, and 40 monomers per chain. We compare spreading on flat and atomistic sur...
Article
Wetting in a system where the kinetics of drop spreading are controlled by the rate of formation of a precursor film is modeled for the first time at the atomistic scale. Molecular dynamics simulations of Pb(l) wetting Cu(111) and Cu(100) show that a precursor film of atomic thickness evolves and spreads diffusively. This precursor film spreads sig...
Chapter
One of the key issues of multiscale and mechanical modeling is related to the developing definitions for continuum variables that are calculable within an atomic system. The instantaneous atomic contributions to these averages do not have the same physical interpretation as the corresponding “point-wise” continuum quantities. A classic example is t...
Article
Full-text available
Electronic structure studies are used to probe the interactions and molecular dynamics simulations are used to study the structure of thin poly(dimethylsiloxane) (PDMS) films near hydroxylated SiO2 substrates. Results of the electronic structure calculations show that the PDMS end groups, rather than atoms such as oxygen in the PDMS backbone struct...
Article
The adhesion and friction between pairs of self-assembled monolayers (SAMs) of alkylsilane chains on a silicon dioxide surface are studied using molecular dynamics simulations. We study chains with n=6, 8, 12, and 18 carbons in the backbone for both fully packed and defected monolayers. The defects are introduced by the random removal of chains fro...
Article
Spreading of polymer droplets on corrugated and flat subrates under complete wetting conditions are studied by molecular dynamics simulations using a coarse grained bead-spring model. To minimize finite size effects, large droplets of size ˜ 200,000 monomers are studied, significantly larger than previous studies. Simulations using Langevin and dis...
Article
Wetting of metallic substrates by molten metal droplets are often accompanied by reaction between the liquid and substrate. However for molten Pb on Cu, mutual bulk immiscibility prevents significant reaction from occurring during the spreading, though surface alloying has been observed. To compare wetting for this non-reactive system to prior resu...
Article
A simple procedure is used to formulate a Cu–Pb pair interaction function within the embedded atom (EAM) method framework. Embedding, density and pair functions for pure Cu and pure Pb are taken from previously published EAM studies. Optimization of the Cu–Pb potential was achieved by comparing with experiment the computed heats of mixing for Cu–Pb...
Article
Liquid Ag drops spreading on a Cu(1 0 0) surface are studied with molecular dynamics simulations. Results for reactive wetting by which a Cu/Ag alloy is formed are compared to a frozen substrate for which there is no alloying. The radius of the Ag wetting layer increases initially as t1/2 for both cases but drops spread faster in reactive systems....
Article
Interfaces between liquid hexadecane and low index surfaces of the zeolite silicalite were modeled using molecular dynamics. Pores on the zeolite surface provide access to the interior such that hexadecane molecules diffuse inside. The three surfaces studied differ significantly in the rate of molecular diffusion from the surface into the zeolite b...
Article
We present the results of Molecular Dynamics and Monte Carlo simulations of n-butane and isobutane in silicalite. We begin with a comparison of the bulk adsorption and diffusion properties for two different parameterizations of the interaction potential between the hydrocarbon species, both of which have been shown to reproduce experimental gas−liq...
Article
Molecular dynamics simulations for three embedded atom method (EAM) function sets are used to determine the liquid/vapor surface tension gamma for Al, Ni, Cu, Ag, and Au. The three EAM models differ in both the functional forms employed and the fitting procedure used. All the EAM potentials underestimate gamma but one of the models performs consist...
Article
Using molecular dynamics (MD) simulations, we examine wetting and spreading in metallic systems as described by the embedded atom method (EAM). We first discuss a common shortcoming of EAM potentials for describing metal surfaces and a theoretical correction to this problem. This correction has the ability to bring model predictions for surface pro...
Article
The wetting and spreading of liquid Ag drops on Cu (001) surfaces are studied with molecular dynamics simulations. As the liquid Ag drop spreads on the Cu surface, reactive wetting occurs in that a Ag/Cu alloy is formed. The results for the reactive wetting case are compared to a frozen substrate for which there is no alloying. At the highest tempe...
Article
Self-consistent Polymer Reference Interaction Site Model (PRISM) calculations and molecular dynamics (MD) simulations were performed on the short chain polyolefin liquids: polyethylene, isotactic, syndiotactic, and head-to-head polypropylenes, polyisobutylene, and poly(ethylene propylene). United atom models were used with realistic bond lengths, c...
Article
Full-text available
Molecular dynamics (MD) simulations were performed on dense liquids of polyethylene chains of 24 and 66 united atom CH2 units. A series of models was studied ranging in atomistic detail from coarse-grained, freely-jointed, tangent site chains to realistic, overlapping site models subjected to bond angle restrictions and torsional potentials. These...
Article
Diffusion constants D and activation energies for diffusion Ea were obtained for linear and branched alkanes inside the zeolites TON, EUO, and MFI via molecular dynamics simulations. Molecules with carbon numbers in the range n = 7−30 were studied in the dilute limit. The zeolites used have channels formed by 10-member silicate rings, but the diame...
Article
Molecular dynamics simulations are used to measure the self diffusion constant D of linear decane and n-methylnonanes (n = 2, 3, 4, and 5) at a catalytically relevant temperature in seven 10 member ring zeolites. Two general behaviors are observed in D as the branch position is moved towards the center of the alkane chain. For three of the zeolites...
Article
Full-text available
The crossover to Rouse-type behavior for the self-diffusion constant D, the viscosity η, and the equilibrium structural statistics of n-alkanes (6 ⩽ n ⩽ 66) is studied numerically. For small n the chains are non-Gaussian and the mean squared end-to-end distance 〈R2〉 is greater than 6〈RG2〉, where 〈RG2〉 is the mean squared radius of gyration. As n in...
Article
Molecular dynamics (MD) simulations of united atom models for alkane melts are compared with a recently developed theory for calculating the memory functions of flexible polymers. The theory is based upon an approximate solution of the diffusion equation without hydrodynamic interactions. The polymer dynamics are described by using time correlation...
Article
Previous molecular dynamics simulations have shown that compression of silica glass surfaces occurs upon formation of an interface with a model crystal and that a structural change caused by this process is retained after glass and crystal are separated. The remnant structural modification caused by this stress was an increase in the concentration...
Article
Zeolites, a class of microporous solids, are used as catalysts in the processing of hydrocarbon streams. One specific function they serve is the isomerization of linear alkanes. While many factors influence the catalytic activity of a zeolite system, the transport of linear and branched chains across the interface between the hydrocarbon liquid and...
Article
Molecular dynamics (MD) simulations of alkane melts are compared with a theory for computing the memory functions of flexible polymers that uses an eigenfunction expansion as an approximate solution of the diffusion equation without hydrodynamic interactions (HI). The polymer dynamics are described by time correlation functions expressed as a set o...
Article
The interface between liquid hexadecane and the (010) surface of silicalite was studied by molecular dynamics. The structure of molecules in the interracial region is influenced by the presence of pore mouths on the silicalite surface. For this surface, whose pores are the entrances to straight channels, the concentration profile for partially abso...
Article
Elevated temperature atomistic behavior was investigated using classical molecular dynamics simulations of solid state interfaces. Initially, observations on a Lennard‐Jones (LJ) crystal surface interfaced with an ideal vacuum were made. Assignment of temperatures associated with specific amounts of crystal surface disorder was possible. A temperat...
Article
Room temperature interfacial atomistic behavior between a model Lennard-Jones Pt (111) crystalline surface and a silica glass surface was investigated using classical molecular dynamics simulations. The approach and pulloff of the crystalline surface to two silica glass surfaces was simulated. During approach, both simulated interfaces evolved from...
Article
The simulation of the deposition of model platinum atoms onto a sodium-alumino silicate glass surface was performed using classical molecular dynamics computer simulations. In order to more accurately simulate adatom/adatom atomic interactions, embedded atom method (EAM) potential functions for Pt were used. Results obtained herein are compared to...
Chapter
A primary objective of modern materials modeling is to predict the material response and failure governed by deformation mechanisms, and to assess the mechanical reliability of components. These material deformation mechanisms operate at specific length scales, which vary from nanometers to microns. Multi-scale materials simulations have been the f...