Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a fixed subset of atoms; the second assigns each a fixed subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently—those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 100,000,000 atoms on several parallel supercomputers--the nCUBE 2, Intel iPSC/860 and Paragon, and Cray T3D. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and a 1840-node Intel Paragon performs up to 165 faster than a single Cray C9O processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.

Fast parallel algorithms for short-range molecular dynamics

The influence of nanoparticle size on the mechanical properties of polymer nanocomposites and the associated interphase region: A multiscale approach

Recent research on the interfacial characteristics of carbon nanotube-polymer nanocomposites is reviewed. The state of knowledge in the characteristics of the interface between the carbon nanotubes and the polymer matrix is presented. Emphasis is placed on the progress of the relationships between interfacial characteristics and nanocomposite properties. Research methodologies used in studying the characteristics of the interface are described. Challenges and opportunities associated with the characterization of the interface are discussed. Critical issues in the research on the interactions at the interface are reviewed, and the advantages and disadvantages of covalent and non-covalent functionalization of carbon nanotubes are delineated. Furthermore, how the properties of the nanocomposites depend on the characteristics of the interface is discussed. The latest developments of the techniques for interface characterization are reviewed, and the strengths and limitations of these techniques are discussed. Potential topics of oncoming focus are finally highlighted.

Interfacial characteristics of carbon nanotube-polymer composites: A review

A common strategy to enhance the fibre-to-matrix adhesion of carbon fibres is to increase the surface polarity using extensive and harsh oxidation techniques. In this work, we use a novel and scalable strategy to significantly increase the hydrophobicity of carbon fibres without any sacrifice in the fibres' physical properties and demonstrate simultaneous increases to the fibre-to-matrix adhesion (59–216%). These findings contradict the commonly accepted paradigm of high fibre polarity correlating to increased interfacial adhesion. We demonstrate the ability to covalently modify the surface of carbon fibres through electrochemical reduction of nitroaryldiazonium salts to generate perfluorinated alkyl radicals. Surface modification was confirmed by XPS, ATRIR, and TEM. The surfaces produced are highly hydrophobic, though this may be mitigated through the reduction of nitro groups to amines, or increased through the accumulative effects of perfluoroalkyl chains and nitro groups (WCA ranges from 99.9 ± 0.4° up to 135.5 ± 0.2°, versus pristine fibre 98.4 ± 0.6°). Hydrophobic fibres functionalized only with perfluoroalkyl groups were stable to both acidic (pH 1) and basic (pH 12) environments. All surface chemistries demonstrated comparable or improved interfacial shear strength and these results correlated well with calculated values of interfacial shear stress, determined via molecular dynamics simulations.

/pdf/simultaneously-increasing-the-hydrophobicity-and-interfacial-cw5sq2qqfp.pdf

Simultaneously increasing the hydrophobicity and interfacial adhesion of carbon fibres: a simple pathway to install passive functionality into composites

Colored and color-changing materials are central to perception and interaction in nature and have been exploited in an array of modern technologies such as sensors, visual displays, and smart mater...

/pdf/fiber-with-butterfly-wings-creating-colored-carbon-fibers-2f10lno0ii.pdf

Fiber with Butterfly Wings: Creating Colored Carbon Fibers with Increased Strength, Adhesion, and Reversible Malleability.

The interface strength and debonding for composite structures: Review and recent developments

A theoretical analysis of interface debonding for coated sphere with functionally graded interphase

Hooke's law is a principle of physics that states that the force needed to extend a spring by some distance is proportional to that distance. The law is always valid for an initial portion of the elastic range for nearly all helical macrosprings. Here we report the sharp nonlinear force-displacement relation of tightly wound helical carbon nanotubes at even small displacement via a molecular mechanics model. We demonstrate that the van der Waals (vdW) interaction between the intertube walls dominates the nonlinear relation based on our analytical expressions. This study provides physical insights into the origin of huge nonlinearity of the helical nanosprings.

Does Hooke's law work in helical nanosprings?

The vibration of tightly helical nanosprings affected by van der Waals (vdW) interactions is investigated based on continuum modelling. Explicit solutions are derived to clarify the influence of initial pitch, stiffness and the number of nanosprings on the period, frequency and amplitude of the vibration. Unlike classic linear/nonlinear springs, the waveform of the vibration is always asymmetric for tightly helical nanosprings due to the asymmetry of vdW attraction and repulsion. The at most three equilibrium positions for the nanosprings strongly depend on the deformation due to competition between the vdW interactions and the elastic energy of the nanosprings. This study provides physical insights into the origin of the novel dynamic properties of such nanosprings.

https://royalsocietypublishing.org/doi/pdf/10.1098/rspa.2016.0242

Sudong Ben

Papers

The interface strength and debonding for composite structures: Review and recent developments

A theoretical analysis of interface debonding for coated sphere with functionally graded interphase

Does Hooke's law work in helical nanosprings?

The vibration of nanosprings affected by van der Waals interactions.