Bryan C. Hathorn

Photonic polymers: a new class of photonic wire structure from intersecting polymer-blend microspheres

We report a new kind of photonic wire structure made from the sequential attachment of polymer-blend microparticles. Using a linear quadrupole to manipulate the particles in space, we are able to take advantage of a modified surface structure in the blend particle to actively assemble particles in programmable two- or three-dimensional architectures. Strong resonance features in fluorescence are observed near the intersection of linked spheres that cannot be interpreted with a two-dimensional (equatorial plane) model. Three-dimensional ray optics calculations show long-lived periodic trajectories that propagate in great circles linked at an angle with respect to the plane containing the sphere centers.

On the Distribution of Fragment Sizes in the Fragmentation of Polymer Chains

The fragmentation pattern of a single-step cleavage of a polymer is calculated using a simple model based on Transition State Theroy to describe the distribution of fragment sizes. Subsequent molecular fragmentations can be simulated by repeated application of the model. The results for the fragmentation pattern are compared to those observed for molecular dynamics calculations perfomed at high temperatures.

Molecular alignment in a shock wave

Molecular dynamics simulations of dense nitrogen show that nonspherical molecules have a weak tendency to align their molecular axis such that it lies parallel to the plane of a shock wave front. As a consequence, there is also an even weaker tendency for the molecular rotation axis to align perpendicular to the shock front. The underlying mechanism is discussed and it is argued that this phenomenon can only be observed for dense fluids and only when considering realistic molecular interactions. A single relevant nondimensional parameter is proposed.

Manipulation with molecules

Abstract Photonic molecules are mesoscopic hierarchical structures, constructed from ‘monomer’ units with typical dimensions of 1–5 μm, which function as coupled optical resonators. These structures are so named because they confine electromagnetic fields in modes that are closely analogous to bonding and antibonding electronic molecular orbitals in real molecules. Recent experimental advances have shown that photonic molecules can be fabricated in a variety of ways with different functionality. We review here recent work in this newly developing interdisciplinary field that blends chemistry, materials science, and optical physics. Finally, we speculate on possible applications and future research directions. For many years now, researchers in materials and photonics have been keenly interested in the design and fabrication of structures that confine and manipulate electromagnetic fields on length scales comparable to optical wavelengths. The ultimate goal is an all-optical information processing and computation platform using photons in ways analogous to electrons in silicon devices on similar length scales. Specific focus areas such as wafer-scale integration, parallel processing, and frequency management (e.g. add-drop filters), on micron or sub-micron length scales are active areas of photonics research. While a great deal of progress has been made in the burgeoning field of microphotonics , we are still a long way off from realizing important goals such as the optical transistor and all-optical integrated circuits 1 .

Computational simulation of polymer particle structures: vibrational normal modes using the time averaged normal coordinate analysis method

The structures composed of individual polymer nanoparticles are simulated using a molecular dynamics technique. Structures composed of model polyethylene particles consisting of between 3000 and 24,000 monomer units are paired into dimers in a molecular dynamics simulation. The vibrational motion of the polymer particle structures corresponding to the stretching vibration between particles is studied using the time averaged normal coordinate analysis method. The data are fit to an empirical formula based on the expected scaling of the force constants with the surface contact area, yielding a formula which could be extrapolated to large particle structures which can be experimentally generated.

Molecular dynamics simulation of polymer nanoparticle collisions: orbital angular momentum effects

Abstract The collisional dynamics of polymer nanoparticles is investigated using molecular dynamics, with a particular focus on angular momentum effects. Unlike zero impact parameter collisions discussed elsewhere, which are greatly weighted toward sticking collisions, the outcome of collisions with non-zero angular momentum show much greater variability, showing both reactive (where polymer chains are exchanged between particles) and purely scattering trajectories. In the case of inelastic scattering trajectories, the profile for translation to vibration energy transfer is calculated.

Comparison of transition state theory rate constants for internal conformational motion with those obtained from molecular dynamics simulations

The results of molecular dynamics (MD) simulations are compared to transition state theory estimations for formation of conformational defects in a polymer crystal. The rates of conformational defect formation and destruction are obtained in terms of a distribution over possible conformational states. The rate constant obtained by this method, when normalized by the number of possible defect sites, is independent of the size of the system, in apparent contrast with the results of MD simulations. The difference is interpreted in terms of the effective temperature of the MD calculation.

Higher moments of the velocity distribution function across a shock wave

Large‐scale molecular dynamics simulations of a Ms =4 .3 shock in dense argon ( = 532 kg/m 3 , T = 300 K) and a Ms =3 .6 shock in dense nitrogen ( = 371 kg/m 3 , T = 300 K) have been performed. Results for moments (up to order 10) of the velocity distribution function are shown. The excess even moments of the shock‐normal velocity component (i.e., in the direction of shock propagation) are positive for most parts of the shock wave, but become negative towards the cold side of the shock before reverting back to zero. The even excess moments of the shock‐parallel velocities and the odd moments of the shock‐normal velocity do not change signs within the shock. The magnitude of the excess moments increases with the order of the moment, i.e., the higher moments correspond less and less to those of a Maxwell‐Boltzmann distribution function.