We have synthesized optically active nanostructured composite materials by using an amphiphilic semiconducting polymer, a poly(phenylene ethynylene) (PPE), and a conventional ammonium surfactant as the structure-directing agents. The PPE consists of phenylene units para-substituted with an octyloxy chain and a charged trimethylammoniumethoxy group, resulting in a surfactant-like structure that can assemble into cylindrical micelles. The resulting silica/organic composite material has a hexagonal honeycomb structure with a repeat distance of 45.3 A, as confirmed by low-angle X-ray diffraction and transmission electron microscopy. Scanning electron microscopy indicates that the larger scale particle size is on the order of micrometers. The incorporation of the polymer into the composite was confirmed by elemental analysis, photoluminescence spectroscopy, and fluorescence microscopy. The polymer retains its photophysical properties in the composite, showing luminescence similar to polymers in the solution phase. The polymer displays a high degree of luminescence polarization anisotropy, indicating that the polymer chains are straight and isolated from each other in the composite.

In an effort to favor the formation of straight polymer chains without crystalline grain boundaries, we have synthesized an amphiphilic conjugated polyelectrolyte, poly(fluorene-alt-thiophene) (PFT), which self-assembles in aqueous solutions to form cylindrical micelles. In contrast to many diblock copolymer assemblies, the semiconducting backbone runs parallel, not perpendicular, to the long axis of the cylindrical micelle. Solution-phase micelle formation is observed by X-ray and visible light scattering. The micelles can be cast as thin films, and the cylindrical morphology is preserved in the solid state. The effects of self-assembly are also observed through spectral shifts in optical absorption and photoluminescence. Solutions of higher-molecular-weight PFT micelles form gel networks at sufficiently high aqueous concentrations. Rheological characterization of the PFT gels reveals solid-like behavior and strain hardening below the yield point, properties similar to those found in entangled gels formed from surfactant-based micelles. Finally, electrical measurements on diode test structures indicate that, despite a complete lack of crystallinity in these self-assembled polymers, they effectively conduct electricity.

We have synthesized a conjugated amphiphilic polyelectrolyte, a poly(phenylene ethynylene) (PPE), and the structurally analogous neutral polymer. The solution-phase aggregation of the uncharged PPE can be reversibly controlled by varying the solvent polarity and concentration, while the charged polymer appears to self-assemble at any concentration in compatible solvents. These conclusions are based on a combination of absorption and photoluminescence spectroscopy and dynamic light scattering. Photoinduced absorption spectroscopy was also employed to investigate interchain electronic communication and the photoinduced production of free charge carriers. The uncharged PPE had a relatively high polaron yield, indicating pi-stacking of adjacent PPE chains and efficient exciton splitting, while the charged polymer did not produce polarons, indicating that the polymers are not pi-stacked despite their tendency to form aggregates. This is most likely due to the presence of the cationic trimethylammonium side chains which force neighboring polymer chains too far apart to achieve effective pi-orbital overlap. Polarons were observed in both polymers after chemical doping with iodine. The ability to control aggregation and interchain electronic communication could be a useful tool in designing nanostructured electronic materials.

Various oximes are currently fielded or under investigation in the United States and other countries as a component of autoinjector emergency treatment systems for organophosphate nerve agent chemical weapons. Bis-pyridinium oximes in general have greater efficacy against a broad spectrum of nerve agents, but they have poor stability due to hydrolytic degradation at elevated temperatures. 1,1'-Methylenebis-4-[(hydroxyimino)methyl]pyridinium dimethanesulfonate (MMB4 DMS) is a leading candidate for next-generation nerve agent treatment systems, because it is more stable than other bis-pyridinium oximes, but it still degrades quickly at temperatures often encountered during storage and field use. The primary goal is to increase the stability and shelf life of MMB4 while maintaining the desirable pharmacokinetic (PK) properties of the aqueous formulation. We have developed a formulation to be used in a phase 1 clinical trial consisting of MMB4 micro/nanoparticles suspended in cottonseed oil, a biocompatible vegetable oil. Through various milling techniques, the average particle size can be controlled from approximately 200 to 6000 nm to produce non-Newtonian formulations that are viscous enough to resist rapid particle sedimentation while remaining injectable at a range of concentrations from 5 to 400 mg/mL. The preliminary accelerated stability test shows that MMB4 in these formulations is stable for at least 2 years at temperatures up to 80°C. Preliminary preclinical in vivo studies have demonstrated that all concentrations and particle sizes have desirable PK properties, including high bioavailability and rapid absorption, which is critical to combat potent and fast-acting nerve agents.

This paper describes the dynamic characteristics of a newly-designed force sensor comprised of carbon nanoparticles embedded in a polyphenylene sulfide matrix and operating on the principle of contact resistance change with pressure. Sensor performance was investigated for frequencies ranging from 1 to 1,000 Hz using two testing setups: a load frame for low frequency characterization and a piezo-electric stack for describing higher-frequency behavior. Bode magnitude and phase response plots were developed and it was determined that the sensor under study can be modeled as a first order system up to 600 Hz. The −3 dB bandwidth was found to be 90 Hz and the sensor’s time constant was determined to be 0.0018 seconds. A dynamic model of the sensor is constructed and compared against performance data. The sensor was found to have non-linear spring properties, allowing for two damping coefficients, one for each spring constant range, to be calculated. The damping coefficient was calculated to be 619 lb-s/in for loadings under 600 lbs and 1928 lb-s/in for loadings greater than 600 lbs. The sensor’s time response was also found to be more similar in shape to the input loading waveform when it was compared to piezoelectric load transducers.