S. Michael Kilbey

Bio: S. Michael Kilbey is an academic researcher from University of Tennessee. The author has contributed to research in topics: Polymerization & Copolymer. The author has an hindex of 26, co-authored 105 publications receiving 2233 citations. Previous affiliations of S. Michael Kilbey include Pennsylvania State University & Oak Ridge National Laboratory.

Polythiophene-block-polyfluorene and Polythiophene-block-poly(fluorene-co-benzothiadiazole): Insights into the Self-Assembly of All-Conjugated Block Copolymers

Abstract: All-conjugated block copolymers have significant potential for solution-processed optoelectronic applications, in particular those relying on a p/n junction. Herein, we report the synthesis and structure of all-conjugated diblock copolymers poly(3-hexylthiophene)-block-poly(9,9-dioctylfluorene) and poly(3-hexylthiophene)-block-poly(9,9-dioctylfluorene-co-benzothiadiazole) in thin films and in the bulk. The diblock copolymers are prepared using a combination of Grignard metathesis polymerization and Suzuki polycondensation and characterized with NMR spectroscopy, size-exclusion chromatography, multiangle laser light scattering, and UV/vis spectroscopy. Structure in thin films and in the bulk is characterized using differential scanning calorimetry, X-ray diffraction, small-angle X-ray scattering, and atomic force microscopy. Diblock copolymer thin films self-assemble into a crystalline nanostructure with some long-range order after extended solvent annealing, and X-ray scattering measurements show that pow...

Shear Forces between Tethered Polymer Chains as a Function of Compression, Sliding Velocity, and Solvent Quality

Abstract: The shear forces between polystyrene chains end-tethered to opposing surfaces have been measured with the surface forces apparatus (SFA) in both good and near-ϑ solvents. When the shearing velocity was varied, the complex polymer/solvent system responded in a Newtonian-like fashion with the shear force increasing linearly with the shear velocity. The effective viscosity of the end-tethered systems in this Newtonian-like regime was found to be an order of magnitude greater than the viscosity of semidilute solutions of equivalent molecular weight free chains. At larger shear velocities or higher extents of compression, Brownian dynamics simulations suggest the interfacial width will thin, leading to a sublinear increase in the shear force with sliding velocity. Experimental limitations prevented exploration of the higher shear velocities simulated with the Brownian dynamics approach, but increasing confinement eventually did lead to sublinear behavior, in agreement with the simulation prediction.

Materials self-assembly and fabrication in confined spaces

Abstract: Molecular assemblies have been mainly researched in open spaces for a long time. However, recent research has revealed that there are many interesting aspects present regarding self-assemblies in confined spaces. Molecular association within nanospaces such as mesoporous materials provides unusual phenomena based on highly restricted molecular motions. Current research endeavors in materials science and technology are focused on developing either a new class of materials or materials with novel/multiple functionalities which is often achieved via molecular assembly in confined spaces. Template synthesis and guided assemblies are distinguishable examples for molecular assembly in confined spaces. So far, different aspects of molecular confinements are discussed separately. In this review, the focus is specifically to bring some potential developments in various aspects of confined spaces for molecular self-assembly under one roof. We arrange the sections in this review based on the nature of the confinements, accordingly the topological/geometrical confinements, chemical and biological confinements, and confinements within thin films. Following these sections, molecular confinements for practical applications are shortly described in order to show connections of these scientific aspects with possible practical uses. One of the most important facts is that the self-assembly in confined spaces stands at meeting points of top-down and bottom-up fabrications, which would be an ultimate key to push the limits of nanotechnology and nanoscience.

Enhanced Performance Consistency in Nanoparticle/TIPS Pentacene-Based Organic Thin Film Transistors

Abstract: In this study, inorganic silica nanoparticles are used to manipulate the morphology of 6,13-bis(triisopropylsilylethynyl)-pentacene (TIPS pentacene) thin films and the performance of solution-processed organic thin-film transistors (OTFTs). This approach is taken to control crystal anisotropy, which is the origin of poor consistency in TIPS pentacene based OTFT devices. Thin film active layers are produced by drop-casting mixtures of SiO{sub 2} nanoparticles and TIPS pentacene. The resultant drop-cast films yield improved morphological uniformity at {approx}10% SiO{sub 2} loading, which also leads to a 3-fold increase in average mobility and nearly 4 times reduction in the ratio of measured mobility standard deviation ({mu}{sub Stdev}) to average mobility ({mu}{sub Avg}). Grazing-incidence X-ray diffraction, scanning and transmission electron microscopy as well as polarized optical microscopy are used to investigate the nanoparticle-mediated TIPS pentacene crystallization. The experimental results suggest that the SiO{sub 2} nanoparticles mostly aggregate at TIPS pentacene grain boundaries, and 10% nanoparticle concentration effectively reduces the undesirable crystal misorientation without considerably compromising TIPS pentacene crystallinity.

Conjugated Polymer-Mediated Polymorphism of a High Performance, Small-Molecule Organic Semiconductor with Tuned Intermolecular Interactions, Enhanced Long-Range Order, and Charge Transport

Abstract: We use 6,13-bis(triisopropylsilylethynyl)pentacene as a model small molecule organic semiconductor and two conjugated polymer additives to demonstrate conjugated polymer-mediated polymorphism of a small molecule organic semiconductor for the first time. The conjugated polymer additives, used with a slow solution crystallization approach, yield crystal structures that are not accessible by nonconjugated polymer additives and impart excellent long-range order. In both of the small molecule semiconductor/conjugated polymer blends studied here, previously unreported polymorphs of a small molecule semiconductor have been identified which also leads to improved charge transport in the absence of external alignment. These results open up a new exciting avenue to manipulate unit cell structure, long-range order, and charge transport of high performance, solution-processed, small molecule organic semiconductors.

I and i

Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

Fast parallel algorithms for short-range molecular dynamics

Abstract: 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.

Ab initio calculation of vibrational absorption and circular dichroism spectra using density functional force fields

Abstract: : The unpolarized absorption and circular dichroism spectra of the fundamental vibrational transitions of the chiral molecule, 4-methyl-2-oxetanone, are calculated ab initio. Harmonic force fields are obtained using Density Functional Theory (DFT), MP2, and SCF methodologies and a 5S4P2D/3S2P (TZ2P) basis set. DFT calculations use the Local Spin Density Approximation (LSDA), BLYP, and Becke3LYP (B3LYP) density functionals. Mid-IR spectra predicted using LSDA, BLYP, and B3LYP force fields are of significantly different quality, the B3LYP force field yielding spectra in clearly superior, and overall excellent, agreement with experiment. The MP2 force field yields spectra in slightly worse agreement with experiment than the B3LYP force field. The SCF force field yields spectra in poor agreement with experiment.The basis set dependence of B3LYP force fields is also explored: the 6-31G* and TZ2P basis sets give very similar results while the 3-21G basis set yields spectra in substantially worse agreements with experiment. jg