E. Bryan Coughlin

Carborane-Containing Poly(fluorene): Response to Solvent Vapors and Amines

Hybrid conjugated polymers containing carborane directly bonded in the aromatic backbone repeat structure have interesting electronic bonding structures and are potentially useful new materials in organic electronics. Conjugated polymers based on o-carborane are particularly interesting for applications in sensing and detection because of the cages unique bonding scheme and its bent geometry. Poly(fluorene) containing o-carborane displays multiple emission pathways that can be modulated through interactions with small molecules. In this paper, we report that films of poly(fluorene) with o-carborane in the backbone function as vapochromatic photoluminescent sensors toward volatile organic molecules.

Interactions between Antimicrobial Polynorbornenes and Phospholipid Vesicles Monitored by Light Scattering and Microcalorimetry

Antimicrobial polynorbornenes composed of facially amphiphilic monomers have been previously reported to accurately emulate the antimicrobial activity of natural host-defense peptides (HDPs). The lethal mechanism of most HDPs involves binding to the membrane surface of bacteria leading to compromised phospholipid bilayers. In this paper, the interactions between biomimetic vesicle membranes and these cationic antimicrobial polynorbornenes are reported. Vesicle dye-leakage experiments were consistent with previous biological assays and corroborated a mode of action involving membrane disruption. Dynamic light scattering (DLS) showed that these antimicrobial polymers cause extensive aggregation of vesicles without complete bilayer disintegration as observed with surfactants that efficiently solubilize the membrane. Fluorescence microscopy on vesicles and bacterial cells also showed polymer-induced aggregation of both synthetic vesicles and bacterial cells. Isothermal titration calorimetry (ITC) afforded free energy of binding values (Delta G) and polymer to lipid binding ratios, plus revealed that the interaction is entropically favorable (Delta S>0, Delta H>0). It was observed that the strength of vesicle binding was similar between the active polymers while the binding stoichiometries were dramatically different.

Physicochemical properties of 1,2,3-triazolium ionic liquids

Ionic liquids composed of four different 1,2,3-triazolium cations with tosylate or triflate counter anions have been synthesized and characterized. Physicochemical properties of these ionic liquids including ion cluster behavior, thermal properties, electrochemical stability and ionic conductivity were determined and compared to corresponding imidazolium based ionic liquids. The impact of structure variations, in terms of substituents on the ring of the 1,2,3-triazolium cation and identity of the anion (i.e. tosylate versus triflate) is discussed. Stability of the 1,2,3-triazolium salts towards hydroxide ion at 80 °C was studied. Key features of 1,2,3-triazolium salts are their high electrochemical stability and ionic conductivity, comparable to imidazolium ionic liquids, but better chemical stability under alkaline conditions.

Directed Self‐Assembly of Poly(2‐vinylpyridine)‐b‐polystyrene‐b‐poly(2‐vinylpyridine) Triblock Copolymer with Sub‐15 nm Spacing Line Patterns Using a Nanoimprinted Photoresist Template

Low molecular weight P2VP-b-PS-b-P2VP triblock copolymer (poly(2-vinlypyridine)-block-polystyrene-block-poly(2-vinylpyridine)] is doped with copper chloride and microphase separated into lamellar line patterns with ultrahigh area density. Salt-doped P2VP-b-PS-b-P2VP triblock copolymer is self-assembled on the top of the nanoimprinted photoresist template, and metallic nanowires with long-range ordering are prepared with platinum-salt infiltration and plasma etching.

Peptide-Directed PdAu Nanoscale Surface Segregation: Toward Controlled Bimetallic Architecture for Catalytic Materials

Bimetallic nanoparticles are of immense scientific and technological interest given the synergistic properties observed when two different metallic species are mixed at the nanoscale. This is particularly prevalent in catalysis, where bimetallic nanoparticles often exhibit improved catalytic activity and durability over their monometallic counterparts. Yet despite intense research efforts, little is understood regarding how to optimize bimetallic surface composition and structure synthetically using rational design principles. Recently, it has been demonstrated that peptide-enabled routes for nanoparticle synthesis result in materials with sequence-dependent catalytic properties, providing an opportunity for rational design through sequence manipulation. In this study, bimetallic PdAu nanoparticles are synthesized with a small set of peptides containing known Pd and Au binding motifs. The resulting nanoparticles were extensively characterized using high-resolution scanning transmission electron microscopy, X-ray absorption spectroscopy, and high-energy X-ray diffraction coupled to atomic pair distribution function analysis. Structural information obtained from synchrotron radiation methods was then used to generate model nanoparticle configurations using reverse Monte Carlo simulations, which illustrate sequence dependence in both surface structure and surface composition. Replica exchange with solute tempering molecular dynamics simulations were also used to predict the modes of peptide binding on monometallic surfaces, indicating that different sequences bind to the metal interfaces via different mechanisms. As a testbed reaction, electrocatalytic methanol oxidation experiments were performed, wherein differences in catalytic activity are clearly observed in materials with identical bimetallic composition. Taken together, this study indicates that peptides could be used to arrive at bimetallic surfaces with enhanced catalytic properties, which could be leveraged for rational bimetallic nanoparticle design using peptide-enabled approaches.

One-pot synthesis of hybrid TiO2–polyaniline nanoparticles by self-catalyzed hydroamination and oxidative polymerization from TiO2–methacrylic acid nanoparticles

A simple self-catalyzed hydroamination method for creating hybrid TiO(2)-polyaniline core-shell nanoparticles (NP) has been shown. Hybrid NPs with a range of possible sizes are afforded in high yield under mild reaction conditions and simultaneously show improved charge transport and electrochromic behavior compared to either polyaniline alone or physically blended with TiO(2).

Line Patterns from Cylinder‐Forming Photocleavable Block Copolymers

A robust route for the preparation of nanoscopic line patterns from polystyrene-block-poly(ethylene oxide) featuring a photocleavable o-nitrobenzyl ester junction is demonstrated. After mild UV (λ = 365 nm) exposure and selective removal of the PEO microdomains, the polymer trench patterns are used as scaffold to fabricate highly ordered arrays of silica or Au line patterns.

Synthesis and Characterization of the Polyhydroxyamide/Polymethoxyamide Family of Polymers

The poly(hydroxy-amide) [PHA] family of polymers possess not only high temperature stability, but also form a more thermally stable polymer (polybenzoxazole) [PBO] during thermal decomposition. The synthesis occurs in solution at low temperature, preventing premature ring cyclization to PBO. The molecular structure was confirmed from 1H-, 13C-NMR, and elemental analysis. One drawback for the highly aromatic PHA is the lack of a softening temperature before the onset of ring closure to PBO. Thus, poly(methoxy-amide) [PMeOA] and random copolymers of PHA and PMeOA have been synthesized and characterized. From microcalorimetry, the peak heat release capacity values for the copolymers is typically higher than that of the pure PHA (while still much lower than most other polymers); however, differential scanning calorimetry (DSC) analysis has shown glass transition temperatures to as low as 151°C for the copolymers. Thermo-gravimetric analysis (TGA) displays a three-step degradation associated with two ring closures to PBO from PHA and PMeOA (with the release of small low-fuel molecules) and the thermal degradation of PBO. The magnitude of the weight loss associated with each step is dependant on the percent of PHA, PMeOA, and aliphatic content in the copolymer. TGA and DSC analysis of PMeOA films under isothermal conditions show degradation and demethylation (cyclization) occurring simultaneously above 300°C and FT-IR displays benzoxazole ring forming under the same condition. Fibers have been spun from the molten state of PMeOA using a Micro-compounder. Fibers spun at 320°C, with average diameter of 180 μm, show an ultimate tensile strength, elongation at break, and Youngs modulus of 60 MPa, 2.2% and 3.6 GPa, respectively. Films were also made by spin-coating or solvent casting to observe the effect of cyclization on tensile properties. These films had an ultimate tensile strength and Youngs modulus of 120 MPa and 3 GPa, respectively.

Duplex strand formation using alternating copolymers

The regular arrangement of complementary diaminopyridine-thymine (DAP-THY) on alternating copolymers permits cooperative binding events and the effective formation of well-controlled micrometre-scale aggregates.

Preparation and characterization of Pt/Pt:CeO2-x nanorod catalysts for short chain alcohol electrooxidation in alkaline media

Multi-functional anode catalysts composed of platinum (Pt) nanoparticles electrodeposited on 2 wt% Pt decorated ceria (Pt:CeO2−x) nanorod supports were shown to enhance the alkaline electrocatalytic oxidation of methanol, ethanol and n-butanol over electrodeposited Pt nanoparticles alone or ones supported with pure ceria nanorods. The Pt:CeO2−x nanorod support was demonstrated to increase the current density of the investigated alkaline electrooxidation of methanol, ethanol and n-butanol by more than 30% over the other two catalysts.