Duane L. Simonson

Towards Enhanced Detection of Chemical Agents: Design and Development of a Microfabricated Preconcentrator

Cascade Avalanche Sorbent Plate ARray (CASPAR), a micromachined hotplate coated with sorbent polymer, has been demonstrated earlier as a selective preconcentrator for chemical agents and explosives. Up to two orders of magnitude increase in sensitivity has been established by incorporating CASPAR as a front end-modification to commercial detectors. Experimental evidence obtained via thermal imaging and fluorescent particle flow tagging suggests that an 8.5 mm times 8.5 mm current hotplate design is sub-optimal due to non-uniformities in the heating and vapor/particle collection profiles. In this study, we discuss the CASPAR design optimization with the aim to enhance the collection efficiency of hazardous chemical vapor while maintaining thermal stability and precise control before injection of a focused pulse of analyte into a detector.

Improving Mechanical Properties of Thermoset Biocomposites by Fiber Coating or Organic Oil Addition

Two different thermoset biocomposite systems are experimented in this study with the hope to improve their mechanical properties. Fiberglass and hemp, in form of fabrics, are used to reinforce the thermoset polymer matrix, which includes a traditional epoxy resin and a linseed oil-based bioresin (UVL). The fiber/polymer matrix interface is modified using two different approaches: adding a plant-based oil (pine or linseed) to the polymer matrix or coating the fibers with 3-(aminopropyl)triethoxysilane (APTES) prior to integrating them into the polymer matrix. Epoxy resin is cured using an amine-based initiator, whereas UVL resin is cured under ultraviolet light. Results show that hemp fibers with APTES prime coat used in either epoxy or UVL matrix exhibit some potential improvements in the composite’s mechanical properties including tensile strength, modulus of elasticity, and ductility. It is also found that adding oil to the epoxy matrix reinforced with fiberglass mostly improves the material’s modulus of elasticity while maintaining its tensile strength and ductility. However, adding oil to the epoxy matrix reinforced with hemp doubles the material’s ductility while slightly reducing its tensile strength and modulus of elasticity.

Laser embedding electronics on 3D printed objects

Additive manufacturing techniques such as 3D printing are able to generate reproductions of a part in free space without the use of molds; however, the objects produced lack electrical functionality from an applications perspective. At the same time, techniques such as inkjet and laser direct-write (LDW) can be used to print electronic components and connections onto already existing objects, but are not capable of generating a full object on their own. The approach missing to date is the combination of 3D printing processes with direct-write of electronic circuits. Among the numerous direct write techniques available, LDW offers unique advantages and capabilities given its compatibility with a wide range of materials, surface chemistries and surface morphologies. The Naval Research Laboratory (NRL) has developed various LDW processes ranging from the non-phase transformative direct printing of complex suspensions or inks to lase-and-place for embedding entire semiconductor devices. These processes have been demonstrated in digital manufacturing of a wide variety of microelectronic elements ranging from circuit components such as electrical interconnects and passives to antennas, sensors, actuators and power sources. At NRL we are investigating the combination of LDW with 3D printing to demonstrate the digital fabrication of functional parts, such as 3D circuits. Merging these techniques will make possible the development of a new generation of structures capable of detecting, processing, communicating and interacting with their surroundings in ways never imagined before. This paper shows the latest results achieved at NRL in this area, describing the various approaches developed for generating 3D printed electronics with LDW.

Functionalized Sorbent Membranes for Use with Ion Mobility Spectrometry

Ion mobility spectrometry (IMS) is a technique commonly used for trace detection of hazardous chemicals. The inlet of an IMS typically utilizes a membrane made of generic polymers such as polydimethylsiloxane or polyvinylidene fluoride. These membranes are designed to allow analytes through but protect the detector from dust and keep a controlled relative humidity and pressure. IMS signals can be enhanced using sorbent polymer membranes to concentrate vapors of interest. Specifically, in this work a strong hydrogen bond acid (HBA) sorbent polymer (HCSFA2) was synthesized to reversibly bind with hydrogen bond basic (HBB) analytes. HCSFA2 has suitable thermal stabilities but offers low viscosities above 50degC. To mitigate this problem HCSFA2 was combined with fillers to maintain the membranes physical structure. The HCSFA2 composites were characterized using various techniques including thermogravimetric analysis, optical microscopy, inverse gas chromatography, FTIR, and differential scanning calorimetry. Additionally, data from a membrane interfaced with an ion mobility spectrometer (IMS) is described.

Deposition of functionalized nanoparticles in multilayer thin-film structures by resonant infrared laser ablation

We report the successful fabrication of layers of functionalized nanoparticles using a novel infrared, laser-based deposition technique. A frozen suspension of nanoparticles was ablated with a laser tuned to a vibrational mode of the solvent, resulting in the disruption of the matrix and ejection of the nanoparticles. The solvent was pumped away and the nanoparticles collected by a receiving substrate in a conformal process. Photoluminescence measurements of nanoparticles containing two common dyes showed no significant change to the emission properties of either dye, suggesting that no damage occurred during the laser ablation process. The process is generally applicable to particles of various sizes, shapes, and chemistries provided that an appropriate solvent is chosen. Deposition through shadow masks turned out to be straightforward using this technique, suggesting its potential utility in preparing designer sensor structures using functionalized nanoparticles.

Neutron/gamma pulse shape discrimination (PSD) in plastic scintillators with digital PSD electronics

Pulse shape discrimination (PSD) is a common method to distinguish between pulses produced by gamma rays and neutrons in scintillator detectors. This technique takes advantage of the property of many scintillators that excitations by recoil protons and electrons produce pulses with different characteristic shapes. Unfortunately, many scintillating materials with good PSD properties have other, undesirable properties such as flammability, toxicity, low availability, high cost, and/or limited size. In contrast, plastic scintillator detectors are relatively low-cost, and easily handled and mass-produced. Recent studies have demonstrated efficient PSD in plastic scintillators using a high concentration of fluorescent dyes. To further investigate the PSD properties of such systems, mixed plastic scintillator samples were produced and tested. The addition of up to 30 wt. % diphenyloxazole (DPO) and other chromophores in polyvinyltoluene (PVT) results in efficient detection with commercial detectors. These plastic scintillators are produced in large diameters up to 4 inches by melt blending directly in a container suitable for in-line detector use. This allows recycling and reuse of materials while varying the compositions. This strategy also avoids additional sample handling and polishing steps required when using removable molds. In this presentation, results will be presented for different mixed-plastic compositions and compared with known scintillating materials

Sorbent Coatings and Processing Techniques for Trace Analysis of Hazardous Materials in Micro/Nano Sensors

The trend towards developing portable instruments for detecting diverse hazardous substances on-site has required the integration of increasingly dense arrays of micro-or nanometer sized sensors. This system complexity evolved as a direct result of the demanding technical specifications to be met by these detectors such as less than six second analysis times, low false alarms and parts per trillion level detections. Sorbent polymers used in conjunction with the proper transducer can enhance sensitivity as well as selectivity to a class of analytes. This paper describes our efforts in designing sorbent polymers with hydrogen bond (hb) acidic groups for trace analysis of hazardous hb bases including chemical agents, toxic industrial chemicals and explosives. Further, we summarize our efforts at developing suitable coating techniques for fragile, micron-sized sensor arrays to improve analytical performance.

Carbosilane polymers with hydrogen bond acidic functionalization for chemical preconcentrator applications

Vapor collection systems, including solid phase microextraction (SPME), require the ability to selectively collect and concentrate a sample from a large volume of air. In the case of SPME, polymers are needed to adhere to the fiber for greater reproducibility and longer lasting fibers. The polymerization of carbosilanes was investigated and produced polymers with molecular weights over 500,000. This polymer class was then functionalized with hexafluoro-2-propanol (HFIP) end groups that will selectively sorb hydrogen bond basic vapors. The results of vapor testing with these polymers utilizing a variety of platforms such as preconcentrators, Surface Acoustic Wave (SAW) sensors, and microcantilevers will be discussed.

Chemoselective Polymers, Nanoparticles, and Nanotubes in Chemical Sensor and Preconcentrator Applications

The functionalization of polymers and nano-materials with 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) groups provides materials suitable for a variety of preconcentrator and sensor applications. These are especially useful in high vapor pressure, hydrogen-bond basic vapor collection. These specific interactions lead to high efficiency collection of basic analytes such as DMMP (organophosphonates), DNT, and TNT (nitroaromatics). The lower vapor pressure analytes such as RDX have a larger dependence on surface interactions without specific (hydrogen bond) interactions. The use of carbosilane polymers with HFIP pendant groups offers dramatic improvements over fluoropolyol (FPOL) and siloxane polymers in sensor and precon applications. The sorbent capacity and thermal stability are both dramatically improved. In this work we will demonstrate the use of Carbon Nanotube (CNT) composites with HFIP polymers as sorbent coatings and evaluate their use as SPME coatings.