Dawn D. Dominguez

Low-melting Phthalonitrile Oligomers: Preparation, Polymerization and Polymer Properties:

A series of low-melting phthalonitrile oligomers were prepared in which variable-length multiple aromatic ether linkages interconnect the terminal phthalonitrile units. These materials were designed to address the need for a processable resin system with good high-temperature properties. The melt-processable oligomers are obtained using a modified-Ullman ether reaction between a bisphenol and a dihalobenzene to form a hydroxyl-terminated oligomeric intermediate that is endcapped by reaction with 4-nitrophthalonitrile. Viscosity measurements show that the phthalonitrile oligomers are polymerized at a moderate temperature (200°C) using the typical aromatic diamine curing additives, bis[4-(4-aminophenoxy)phenyl]sulfone and 1,3-bis(3-aminophenoxy)benzene. The oligomeric phthalonitrile/diamine mixtures exhibit a low complex melt viscosity (0.01-0.1 Pa s) at 200°C. Differential scanning calorimetric analysis is used to follow the polymerization as the oligomeric phthalonitrile/diamine mixtures are heated to elevated temperatures. Thermal and dynamic mechanical properties of thermally-cured oligomeric phthalonitrile polymers are systematically evaluated and compared with those of two other high temperature thermosetting phthalonitrile polymers, 4,4~-bis(3,4-dicyanophenoxy)biphenyl and 1,3- bis(3,4-dicyanophenoxy)benzene. After thermal treatment at 425°C for 8 h, the oligomeric phthalonitrile polymers exhibit char yields of 70% when heated to 1000°C in flowing nitrogen and decomposition temperatures in excess of 500°C when heated in either flowing nitrogen or air. Rheometric measurements indicate that the fully cured oligomeric phthalonitrile polymers do not soften or exhibit a glass transition temperature upon heating to 450°C. Overall, studies on the phthalonitrile oligomers and the corresponding polymers reveal an attractive combination of processability, thermal and thermo-oxidative stability and good dynamic mechanical properties for these materials

The “NRL-SAWRHINO”: a nose for toxic gases

Abstract At the Naval Research Laboratory (NRL), surface acoustic wave (SAW) chemical sensor systems have been in development since 1981. The primary focus has been the detection and identification of chemical agents and other toxic gases or vapors. In the recently developed “NRL-SAWRHINO” system (Rhino, Gr. Nose), a self-contained unit has been developed capable of autonomous field operation. An automated dual gas sampling system is included, for immediate and periodic detection capability. The latter, utilizes a trap-and-purge miniature gas chromatographic column, which serves to collect, concentrate, and separate vapor or gas mixtures prior to SAW analysis. The SAWRHINO includes all the necessary electronic and microprocessor control, SAW sensor temperature control, onboard neural net pattern recognition capability, and visual/audible alarm features for field deployment. The SAWRHINO has been trained to detect and identify a range of nerve and blister agents, and related simulants, and to discriminate against a wide range of interferent vapors and gases.

Evaluation of SAW chemical sensors for air filter lifetime and performance monitoring

Abstract A miniature surface acoustic wave (SAW) chemical sensor has been utilized to monitor the progression and breakthrough of the nerve agent simulant dimethylmethylphosphonate (DMMP) through a porous carbon filter-bed. The SAW sensor was successfully operated in carbon filter-beds under high air flow rates and a variety of humidity conditions with no active temperature control applied to the filter bed or SAW sensor. The SAW sensor successfully monitored the progression of DMMP through the filter-bed, from low to high vapor concentrations. The inclusion of the SAW sensor in the middle or at the end of the filter-bed did not degrade the performance of the filter-bed.

Development of an oligomeric cyanate ester resin with enhanced processability

The synthesis, polymerization, thermal and mechanical properties of a novel cyanate ester resin have been examined. The resin is a liquid at ambient temperature, exhibits high thermal stability, and displays good mechanical properties up to about 150 °C.

Performance of an embedded SAW sensor for filter bed monitor and the development of a wireless monitoring prototype system

Methods of measuring the residual adsorption capacity of porous carbon gas filters are virtually non-existent. The main objective of our work is to evaluate the performance of gas sensors that can be operated successfully when embedded in the carbon of a gas filter. This paper describes how polymer-coated SAW sensors have been utilized to monitor the progression of dimethyl methylphosphonate through a filter test bed filled with carbon adsorbent. Performance of the sensor and the breakthrough characteristics of the filter test bed are described. We also describe the design of a miniature, wireless, remotely-powered SAW sensor system.

Photonic micro-gas-chromatography detection of chemical threat agents

A significant remaining challenge in chemical detection is the ability to rapidly detect with high fidelity a full suite of CWAs and TICs in a single point-detection system. Gas chromatography (GC) is a proven laboratory technique that can achieve the stated detection goal, but not at the required speed and not in a wearable (or even portable) form factor. Efforts in miniaturizing GCs yielded small devices, but they remain slow as they retain the end-of-column detection paradigm which results in long elution times of CWAs and TICs. We describe a novel concept of in-column detection by probing the sorbent coating (stationary phase) of a micro-GC column through optical evanescent field interactions in the long-wave infrared (“chemical fingerprint”) spectral region (U.S. Patent US9599567B2). Detection closer to the injection port ensures a rapid response for slow-eluting analytes. Although this results in poor separation (i.e. poor ability to identify chemicals), this is more than compensated by having full IR absorbance spectra at each location. This orthogonal spectral signature (along with GC retention times) is used in a powerful algorithm to quickly identify components in a complex mixture under conditions of incomplete separation. We present results with an ATR-based system that uses a focused tunable quantum cascade laser beam directed by galvo mirrors at points along a molded micro-GC column whose bottom wall is the sorbent coated ATR prism. Efforts are under way to further miniaturize this device by employing novel long-wave-IR photonic waveguides for a truly portable integrated photonic chromatographic detector of CBRNE threats.