Passive Solar Distillation of Acid Rock Drainage

Arkansas Razorback Distillers (A.R.D.) has developed a passive solar distillation system for treating acid rock drainage (ARD) from legacy (i.e., abandoned) mines. The solar still addresses the need to reduce both the metal sulfate contaminants as well as the acidity of acid rock drainage. During the design phase, A.R.D. addressed the need for the system to be low cost, simple, and effective for general use as well as a specified location. To demonstrate the applicability of the solar still, A.R.D. used the Freeport McMoRan Inc. Copper Queen legacy mine in Bisbee, Arizona, as a base case scenario. The mine was visited to gain insight about the problem and its solution. Research was conducted to evaluate treatment technologies including, solar stills, bioreactors, solar ponds and reverse osmosis to determine the best way to clean contaminated water. The key factors in choosing the appropriate technology included long-term cost, durability, required maintenance, simplicity, and efficiency. A.R.D’s design is close to that of a traditional solar still with the exception that water vapor is not reclaimed. Evaporating pure water to the atmosphere is the most passive and cost-effective solution. Five gallons per minute of ARD water is being evaporated, and the vapor is not condensed because no beneficial or economical use was determined. In the full-scale design, sunlight enters through a six-millimeter thick double pane polycarbonate roof, heating the water and vaporizing it. The water vapor/air mixture is forced from the still via a thermosiphon. The purpose of the thermosiphon is to maintain a low relative humidity within the still to increase the driving force for greater evaporation rates. In the bench-scale design, the thermosiphon effect is demonstrated by using exhaust fans. Rather than removing the salt brine continuously throughout the process, A.R.D. has decided to allow the salts to precipitate and collect at the bottom of the solar stills. The salts can be removed in a batch process every twenty years with little effect to the efficiency of the solar still. The removal of salts after a long period simplifies the operation of the still as well as reduces operating costs. The solar still will be positioned near mining stockpiles where the acid rock drainage originates. Rather than building one large solar still, A.R.D.’s design uses multiple smaller solar stills in parallel to achieve the same results. Each solar still is 102 feet long, 22 feet wide and 10.5 feet high. The full-scale solar distillation unit was designed to handle the task mandated five gallons per minute of contaminated water. Each solar still is estimated to cost $40,000, which includes the cost of materials and construction. Twenty-seven stills are required to achieve five gallons per minute of evaporation and the total capital cost for twenty years for the system is$1,100,000. This corresponds to $18 per square foot, which is 28$25 per square foot. The design parameters of the still were determined by testing a bench-scale apparatus and developing a mathematical model. At this point, A.R.D. has shown that the bench-scale can achieve close to the desired flow rate, and there are plans to improve the still to achieve ten mL/min. The maximum experimental flow rate obtained thus far is an average seven mL/min over twelve hours of sunlight. Experiments are planned to demonstrate the required ten mL/min. This report provides a detailed explanation of the location, technology, process summary, economic analysis, experimental results, regulations, safety considerations, and scalability for a solar distillation system in Bisbee, Arizona

Topology and Ground State Control In Open-Shell Donor-Acceptor Conjugated Polymers

Donor-acceptor (DA) conjugated polymers (CPs) with narrow bandgaps and open-shell (diradical) character represent an emerging class of materials whose rich behavior emanates from their collective electronic properties and diminished electron pairing. However, the structural and electronic heterogeneities that define these materials complicate bandgap control at low energies and connections linking topology, exchange interactions, and (opto)electronic functionality remain nascent. To address these challenges, we demonstrate structurally rigid and strongly π-conjugated copolymers comprised of a solubilizing thiadiazoloquinoxaline acceptor and cyclopenta[2,1-b:3,4-b′]dithiophene or dithieno[3,2-b:2′,3′-d]thiophene donors. Atom-specific substitution modulates local aromatic character within the donor resulting in dramatic differences in structural, physicochemical, electronic, and magnetic properties of the polymers. These long-range π-mediated interactions facilitate control between low-spin aromatic and high-spin quinoidal forms. This work provides a strategy to understand the evolution of the electronic structure within DA CPs, control the ground state spin multiplicity, tune spin-spin interactions, and articulate the emergence of their novel properties

Backbone-Driven Host-Dopant Miscibility Modulates Molecular Doping In NDI Conjugated Polymers

Molecular doping is the key to enabling organic electronic devices, however, the design strategies to maximize doping efficiency demands further clarity and comprehension. Previous reports focus on the effect of the side chains, but the role of the backbone is still not well understood. In this study, we synthesize a series of NDI-based copolymers with bithiophene, vinylene, and acetylenic moieties (P1G, P2G, and P3G, respectively), all containing branched triethylene glycol side chains. Using computational and experimental methods, we explore the impact of the conjugated backbone using three key parameters for doping in organic semiconductors: energy levels, microstructure, and miscibility. Our experimental results show that P1G undergoes the most efficient n-type doping owed primarily to its higher dipole moment, and better host–dopant miscibility with N-DMBI. In contrast, P2G and P3G possess more planar backbones than P1G, but the lack of long-range order, and poor host–dopant miscibility limit their doping efficiency. Our data suggest that backbone planarity alone is not enough to maximize the electrical conductivity (σ) of n-type doped organic semiconductors, and that backbone polarity also plays an important role in enhancing σ via host–dopant miscibility. Finally, the thermoelectric properties of doped P1G exhibit a power factor of 0.077 μW m−1 K−2, and ultra-low in-plane thermal conductivity of 0.13 W m−1K−1 at 5 mol% of N-DMBI, which is among the lowest thermal conductivity values reported for n-type doped conjugated polymers

Backbone-driven host-dopant miscibility modulates molecular doping in NDI conjugated polymers

Molecular doping is the key to enabling organic electronic devices, however, the design strategies to maximize doping efficiency demands further clarity and comprehension. Previous reports focus on the effect of the side chains, but the role of the backbone is still not well understood. In this study, we synthesize a series of NDI-based copolymers with bithiophene, vinylene, and acetylenic moieties (P1G, P2G, and P3G, respectively), all containing branched triethylene glycol side chains. Using computational and experimental methods, we explore the impact of the conjugated backbone using three key parameters for doping in organic semiconductors: energy levels, microstructure, and miscibility. Our experimental results show that P1G undergoes the most efficient n-type doping owed primarily to its higher dipole moment, and better host–dopant miscibility with N-DMBI. In contrast, P2G and P3G possess more planar backbones than P1G, but the lack of long-range order, and poor host–dopant miscibility limit their doping efficiency. Our data suggest that backbone planarity alone is not enough to maximize the electrical conductivity (σ) of n-type doped organic semiconductors, and that backbone polarity also plays an important role in enhancing σ via host–dopant miscibility. Finally, the thermoelectric properties of doped P1G exhibit a power factor of 0.077 μW m(−1) K(−2), and ultra-low in-plane thermal conductivity of 0.13 W m(−1)K(−1) at 5 mol% of N-DMBI, which is among the lowest thermal conductivity values reported for n-type doped conjugated polymers

Tacky Elastomers to Enable Tear-Resistant and Autonomous Self-Healing Semiconductor Composites

Mechanical failure of π-conjugated polymer thin films is unavoidable under cyclic loading conditions, due to intrinsic defects and poor resistance to crack propagation. Here, the first tear-resistant and room-temperature self-healable semiconducting composite is presented, consisting of conjugated polymers and butyl rubber elastomers. This new composite displays both a record-low elastic modulus

Tacky Elastomers to Enable Tear-Resistant and Autonomous Self-Healing Semiconductor Composites

Mechanical failure of π-conjugated polymer thin films is unavoidable under cyclic loading conditions, due to intrinsic defects and poor resistance to crack propagation. Here, the first tear-resistant and room-temperature self-healable semiconducting composite is presented, consisting of conjugated polymers and butyl rubber elastomers. This new composite displays both a record-low elastic modulus

THERMOMECHANICS OF SEMICONDUCTING POLYMERS AND THEIR MORPHOLOGICAL PHENOMENA

In contrast to conventional silicon-based electronics, semiconducting polymers show great promise for emerging applications in soft, flexible, and ductile electronic technologies. This is due to their polymeric nature, tailorable structure, and sub-100 nm device thickness. Despite this mechanical novelty, there remains a poor understanding of their structure-property-processing relationships, which has hindered growth within the field. This dissertation elucidates these relationships through investigation of their thermomechanics, and morphological phenomena. This was accomplished through the following projects: 1) To demonstrate the impact of backbone rigidity on semiconducting polymer thermomechanics, we varied the backbone rigidity of an NDI-based polymer by inserting flexible methylene units of varying lengths along the backbone of the monomer unit. Incorporation of the spacer resulted in a vast reduction of the glass transition temperature (Tg) and profound improvements in ductility. 2)We developed a free-standing tensile technique that enabled the characterization of polystyrene and poly(3-hexylthiophene) films down to 19 nm and 80 nm, respectively. Confinement was demonstrated to impact yield stress and strain at failure of polystyrene films, while modulus was relatively unaffected, despite literature suggestion of a sub-room temperature Tg. We then compared water-supported and free-standing films to elucidate their interfacial influence on the observed mechanical performance. 3) Amide and urea moieties were incorporated into a DPP-based polymer to demonstrate the role of hydrogen bonding strength on thermomechanical performance. Amide and urea were discovered to minimize and promote crystallinity, respectively, which led to a 400% increase in strain at failure for the amide-containing polymer. This finding demonstrated that hydrogen bonding may dictate mechanical performance through control of the crystalline morphology, rather than energy dissipation. 4) Due to the semicrystalline nature of semiconducting polymers, it has been postulated that they may possess a rigid amorphous fraction (RAF) which may dictate their optoelectronic performance. To illuminate the existence and impact of the RAF on semiconducting polymer performance we established a spectroscopic ellipsometry method to fully characterize their temperature-dependent thickness, optical profile, and degree of anisotropy. All semicrystalline semiconducting polymers were observed to possess a RAF which strongly dictated their optoelectronic performance

Water-Assisted Mechanical Testing of Polymeric Thin-Films

Thin films with a nanometer-scale thickness are of great interest to both scientific and industrial communities due to their numerous applications and unique behaviors different from the bulk. However, the understanding of thin-film mechanics is still greatly hampered due to their intrinsic fragility and the lack of commercially available experimental instruments. In this review, we first discuss the progression of thin-film mechanical testing methods based on the supporting substrate: film-on-solid substrate method, film-on-water tensile tests, and water-assisted free-standing tensile tests. By comparing past studies on a model polymer, polystyrene, the effect of different substrates and confinement effect on the thin-film mechanics is evaluated. These techniques have generated fruitful scientific knowledge in the field of organic semiconductors for the understanding of structure–mechanical property relationships. We end this review by providing our perspective for their bright prospects in much broader applications and materials of interest

Glass Transition Phenomenon for Conjugated Polymers

Conjugated polymers are emerging as promising building blocks for a broad range of modern applications including skin‐like electronics, wearable optoelectronics, and sensory technologies. In the past three decades, the optical and electronic properties of conjugated polymers have been extensively studied, while their thermomechanical properties, especially the glass transition phenomenon which fundamentally represents the polymer chain dynamics, have received much less attention. Currently, there is a lack of design rules that underpin the glass transition temperature of these semirigid conjugated polymers, putting a constraint on the rational polymer design for flexible stretchable devices and stable polymer glass that is needed for the devices’ long‐term morphology stability. In this review article, the glass transition phenomenon for polymers, glass transition theories, and characterization techniques are first discussed. Then previous studies on the glass transition phenomenon of conjugated polymers are reviewed and a few empirical design rules are proposed to fine‐tune the glass transition temperature for conjugated polymers. The review paper is finished with perspectives on future directions on studying the glass transition phenomena of conjugated polymers. The goal of this perspective is to draw attention to challenges and opportunities of controlling, predicting, and designing polymeric semiconductors, specifically to accommodate their end use

Roll-to-Roll Scalable Production of Ordered Microdomains Through Nonvolatile Additive Solvent

A new method, “nonvolatile solvent vapor annealing” (NVASA), has been developed to anneal block copolymers during film deposition by controlling the solvent drying process. Precise amounts of high boiling point additive added to the polymer solution briefly remain in the polymer film after casting, leaving the film in a swollen state, increasing its chain mobility, and ultimately improving domain order. We demonstrated the effectiveness of NVASA on several block copolymer systems and used in situ grazing incidence small-angle X-ray scattering (GISAXS) to validate the ordering process during the self-assembly. The simplicity and reproducibility of the method is attractive for implementation in large-scale manufacturing processes such as roll-to-roll printing as swell ratio is easily controlled by the amount of additive used and separate annealing steps are not needed. This work potentially introduces a new way to quickly and cost effectively anneal block copolymers