Continued Development of Compact Multi-Gas Monitor for Life Support Systems Control in Space

Miniature optical gas sensors based on luminescent materials have shown great potential as alternatives to NIR-based gas sensor systems for the Portable Life Support System (PLSS). The unique capability of luminescent sensors for carbon dioxide and oxygen monitoring under wet conditions has been reported, as has the fast recovery of humidity sensors after long periods of being wet. Lower volume and power requirements are also potential advantages over both traditional and advanced non-dispersive infrared (NDIR) gas sensors, which have so far shown longer life than luminescent sensors. In this paper we present the most recent results in the development and analytical validation of a compact multi-gas sensor unit based on luminescent sensors for the PLSS. Results of extensive testing are presented, including studies conducted in Intelligent Optical Systems laboratories, a United Technologies Corporation Aerospace Systems (UTC) laboratory, and a Johnson Space Center laboratory. The potential of this sensor technology for gas monitoring in PLSSs and other life support systems, and the advantages and limitations found through detailed sensor validation are discussed

Electrochemical and Photovoltaic Properties of Electropolymerized Poly(thienyl-silole)s

Electrochemical and photoelectrochemical properties were studied of a series of donor−acceptor materials based on polythiophene modified with silole moieties. The materials were prepared by electrochemical anodic polymerization of 2,5-bis([2,2′-bithiophen]-5-yl)-1,1-dimethyl-3,4-diphenylsilole and 2,5-bis([2,2′-terthiophen]-5-yl)-1,1-dimethyl-3,4-diphenylsilole, as well as copolymerization of these monomers with 2,2′-bithiophene. Photocurrent measurements showed that introduction of silole resulted in a considerable enhancement of the photovoltaic properties of silole-containing materials and especially the fill factor. However, as demonstrated by Mott−Schottky measurements, electropolymerized silole-containing materials showed a substantial degree of disorder and high density of states in the midgap, which negatively affected their photovoltaic properties. Atomic force microscopy (AFM) and phase imaging revealed the presence of phase segregation and heterogeneity of the silole-containing materials. Interestingly, introduction of siloles suppressed the cathodic (n-type) doping typical for polythiophenes. This work demonstrates that siloles show great promise as electron-acceptor groups for all-organic solar cells; however, further work is required to optimize the properties and performance of poly(thienylsilole)-based materials

Conjugated Polymer Nanostructures and Supercapacitors

Controlling the nanostructure of conjugated polymers is essential for their application to functional materials. In Part 1 of this work, I present two novel methods for controlling conjugated polymer nanostructure using electrochemical polymerization in hard templates. First, we report the synthesis and characterization of a series of nanostructures and propose a mechanism whereby morphology changes as a function of building block. We show how side-chain hydrophobicity can be used to prepare nanostructures with a geometry that is different from the shape of the template. Hydrophobic side-chains result in collapsed, nonlinear, and nonrigid shapes, while hydrophilic side-chains lead to linear nanostructures. Second, I present a study of the morphology of polythiophene nanostructures synthesized in different solvent/electrolyte systems. We find that the wall thickness of such nanostructures is greatly influenced by the choice of solvent/electrolyte, which affects the rate of polymerization. Solvent/electrolyte systems that increase the rate of thiophene polymerization yield solid nanowires, whereas systems that decrease the rate of polymerization yield thin-wall nanotubes. A solvent/electrolyte system that leads to an intermediate polymerization rate yields thick wall nanotubes. The results in Part 1 open new opportunities for preparing nanostructures with greater complexity, functionality, and distinct optical properties. Conjugated polymers that can store both a positive and negative charge can function as both the positive and negative charge storage material in a supercapacitor device, however few have been explored for this application. In part 2, I describe the synthesis of several monomers and their electrodeposited polymer electrodes. First, using different donor-acceptor molecular structures we examine the effect of electron acceptor concentration and show that device stability is improved significantly by increasing the acceptor concentration. Supercapacitors with specific energy and power of 11 Wh/kg (at 0.5 A/g) and 20 kW/kg (at 50 A/g with an energy of 3.6 Wh/kg) are reported. Further, we provide computational insight into the important chemical requirements for achieving even better performing supercapacitors. Working from these experimental and computational results, we selected thieno[3,4-b]pyrazines as a class of molecule to explore. Thieno[3,4-b]pyrazines form narrow band gap homopolymers, storing both positive and negative charge. Initial investigations into four poly(thieno[3,4-b]pyrazine)s as charge storage electrodes is presented.Ph.D.2017-06-08 00:00:0

Gold Nanotubes as Sensitive, Solution-Suspendable Refractive Index Reporters

Gold Nanotubes as Sensitive, Solution-Suspendable Refractive Index Reporter

Heterocycle-Induced Phase Separation in Conjugated Polymers

Grignard metathesis polymerization was used to synthesize a series of poly­(3-hexylselenophene)-<i>block</i>-poly­(3-hexylthiophene) copolymers with two different molecular weights and varying selenophene content. These polymers were characterized by optical absorption spectroscopy (film and solution), differential scanning calorimetry, powder X-ray diffraction, variable temperature absorption spectroscopy, and atomic force microscopy (on self-assembled polymer nanofibers). The selenophene to thiophene ratio has a large influence on optical properties, and absorption is tunable across the range of both homochromophores. We observe phase separation in the solid state in both pristine and annealed samples. When allowed to slowly assemble in solution, high molecular weight copolymers have a very sharp transition from the molecularly dissolved to the aggregated state. Most interestingly, increasing polyselenophene content induces the polymer to assemble more readily (at a higher temperature) but also appears to hinder the degree of ordered assembly when the thiophene block is not sufficiently long. This study furthers the understanding of the differences between these structurally similar conjugated polymer building blocks and provides insight into the factors that control heterocycle-induced phase separation

Donor–Acceptor Polymers for Electrochemical Supercapacitors: Synthesis, Testing, and Theory

Donor–acceptor polymers can store both a positive and negative charge allowing them to function as both the positive and negative charge storage material in a supercapacitor device, however few have been explored for this application. Here, we describe the synthesis of several donor–acceptor polymers and their electrodeposited polymer electrodes. We use differing molecular structures to examine the effect of electron acceptor concentration and show that device stability can be improved significantly by increasing the acceptor concentration. Further, we provide computational insight into the important chemical requirements for achieving even higher performance supercapacitors based on donor–acceptor conjugated polymers. Supercapacitor devices with specific energy and specific power as high as 11 Wh kg^–1 (at 0.5 A g^–1) and 20 kW kg^–1 (at 50 A g^–1 with an energy of 3.6 Wh kg^–1) are reported, which are some of the highest values achieved to date