30 Search Results

The mass concentrations of ²³²Th and ²³⁸U in several 3D printing filaments and printed polymer parts are reported as measures of their radiopurity. In order to minimize background signals in rare event physics detectors, radiopure polymers are necessary as dielectric and structural materials in their construction. New data are reported for polyvinylidene fluoride (PVDF), polyphenylene sulfide (PPS), and two forms of polyetherimide (PEI, branded ULTEM 1010 and 9085). Data for starting filaments and both simple and complex printed parts are reported. PVDF filaments and simple printed beads, were found to have values of approximately 30 and 50 pg g^-1 formore » ²³²Th and ²³⁸U, respectively, while a more complex spring clip part had slightly elevated ²³²Th levels of 65 pg g^-1, with ²³⁸U remaining at 50 pg g^-1. PPS filament was found to have concentrations of 270 and 710 pg g^-1 for ²³²Th and ²³⁸U, respectively, and were not chosen to be printed as those levels were already higher than other material options. ULTEM 1010 filaments and printed complex spring clip parts were found to have concentrations of around 5 and 7 pg g^-1 for ²³²Th and ²³⁸U, respectively, illustrating no significant contamination from the printing process. ULTEM 9085 filaments were found to have concentrations of around 9 and 5 pg g^-1 for ²³²Th and ²³⁸U, respectively, while the printed complex spring clip part was found to have slightly elevated concentrations of 25 and 7 pg g^-1 for ²³²Th and ²³⁸U, respectively. All these results were obtained using a novel dry ashing method in crucibles constructed of ultralow background electroformed copper or, when applicable, microwave assisted wet ashing digestion. Samples and process blanks were spiked with ²²⁹Th and ²³³U as internal standards prior to dry/wet ashing and determinations were made by inductively coupled plasma mass spectrometry (ICP-MS). In order to maintain high radiopurity levels, pre-cleaning the filaments before printing and post-cleaning the parts is recommended, although the printing process itself has shown to contribute very minute amounts of radiocontaminants.« less

Many river corridor systems frequently experience rapid variations in river stage height, hydraulic head gradients, and residence times. The integrated hydrology and biogeochemistry of such systems is challenging to study, particularly in their associated hyporheic zones. Here we present an automated system to facilitate 4-dimensional study of dynamic hyporheic zones. It is based on combining real-time in-situ and ex-situ measurements from sensor/sampling locations distributed in 3-dimensions. A novel dissolved oxygen (DO) sensor was integrated into the system during a small scale study. We measured several biogeochemical and hydrologic parameters at three subsurface depths in the riverbed of the Columbia Rivermore » in Washington State, USA, a dynamic hydropeaked river corridor system. During the study, episodes of significant DO variations (~+/- 4 mg/l) were observed, with minor variation in other parameters (e.g., <~+/-0.15 mg/l NO ₃ ). DO concentrations were related to hydraulic head gradients, showing both hysteretic and non-hysteretic relationships with abrupt (hours) transitions between the two types of relationships. The observed relationships provide a number of hypotheses related to the integrated hydrology and biogeochemistry of dynamic hyporheic zones. We suggest that preliminary high-frequency monitoring is advantageous in guiding the design of long term monitoring campaigns. The study also demonstrated the importance of measuring multiple parameters in parallel, where the DO sensor provided the key signal for identifying/detecting transient phenomena.« less

This dataset contains time-series data from a vertical profile within the bed and banks of the Columbia river near Richland, WA. Water was sampled through 3 small tubes embedded in the sediment at 50,100, and 200 cm below the sediment-water interface. The goal of this study was to observe the correlations between hydraulic drivers and biogeochemical responses. The results of this study are published in the manuscript “Dissolved oxygen sensor in an automated hyporheic sampling system reveals biogeochemical dynamics”. The file types included in the data package are all time-series spreadsheet data, including hydraulic head gradients, physical parameters (temperature, pressure,more » SpC (specific conductivity)), and biogeochemical parameters (dissolved oxygen, pH, NO3 (nitrate) and ORP (oxidation-reduction potential)).« less

This integrated synthetic and computational effort uses sequence defined polymers such as peptoids, and triazines, capable of mimicking a flexible protein environment to control the positioning of side chains around redox cofactors. This strategy will allow modulation of redox properties through both direct and indirect mechanisms. To this end the aim is defined to test the underlying hypothesis: that principles and critical functionalities governing the binding and tuning of naturally occurring electron carrier co-factors can be identified and used to predictably design and synthesize maquettes based on non-natural polymers resulting in new modular biomimetic scaffolds for Electron Transfer Materials. Thismore » will be achieved through design and synthesis of ligands that can stabilize iron-sulfur clusters and tune the redox potential based on sequence.« less

Pacific Northwest National Laboratory (PNNL), in collaboration with Parker and Hannifin, is developing a compact, inexpensive, and highly sensitive and selective surface acoustic wave sensor coated with fluorophillic sorbent for detecting fluorocarbon leaks from HVAC systems. Having a highly effective sorbent sensitive to fluorocarbon refrigerant vapors provides a means to develop a sensing device for leak detection. Surface acoustic wave (SAW) sensors with a gas sensing film deposited between the delay lines or on the interdigital transducer have been used to detect gas and vapor molecules in harsh environments with high sensitivity. As part of this project, PNNL screened severalmore » sorbent materials that are shown to be selective towards fluorocarbon refrigerant (R32) molecule. The identified sorbent materials were synthesized, characterized, and tested towards R32 using various spectroscopic technique. Next, the sorbent material was coated on a SAW sensor as a thin film using vapor deposition and drop coating methods. The coated thin film was further characterized and tested towards the detection of pure R32 and R32 in ambient air at room temperature to demonstrate the SAW response towards R32 in presence of other competing gases and vapors in air.« less

At PNNL, we have developed a completely new class of synthetic biomimetic sequence-defined polymers based on triazine chemistry, which we call TZPs. PNNL's new polymers offer the opportunity to achieve similar functions to natural macromolecules; specifically we designed and synthesized a diversity of test molecules for antimicrobial activity. Antimicrobial activity against a variety of wild type and drug resistant pathogens was found.

The mass concentrations of 232Th and 238U in several strong, unfilled, high performance polymers are reported as measures of their radiopurity. Highly radiopure polymers are required as dielectric materials in the construction of rare event physics detectors, in order to minimize backgrounds arising from the detector materials themselves. New data are reported for carefully sourced samples of polyetheretherketone (PEEK), polyetherketoneketone (PEKK), a polyamide imide (PAI, branded as Torlon) and polybenzimidazole (PBI). Data for a polyetherimide (PEI, branded as Ultem) are also included from a prior study. Strong high performance polymers PEKK, PBI, PAI and PEI can be found with levelsmore » for 232Th and 238U that are below one mBq/kg. These results were all obtained using a novel dry ashing method in crucibles constructed of ultra low background electroformed copper; these low mass ULB crucibles are completely digested in acid along with the ash. Determinations were made by inductively coupled plasma mass spectrometry (ICP-MS) with liquid nebulizataion sample introduction. Radiopurity is compared graphically relative to measures of mechanical strength for these and several other polymers whose analyses have been reported previously.« less

Triazine-based sequence-defined polymers have recently been developed that are biomimetic and robust (Grate \latin{et al.} Angewandte Chemie 2016). In molecular dynamics (MD) simulations, the triazine polymers were shown to form linear nanorod foldamers through hydrogen bonding and $$\pi$$-$$\pi$$ interactions. The nanorod foldamers have motifs resembling those of DNA, $$\alpha$$-helices, and $$\beta$$-sheets, and have potential to be useful building blocks for new macromolecules and materials. To understand the formation of nanorod foldamers, we investigate how linker structures in the middle of the triazine polymers lead to folding using MD simulations. We found that a variety of linkers can participate in folding,more » but that specific linker structures are more favorable than others, depending on the polymer length. Folding of hexamers into well-defined nanorod foldamers was most favorable with pentanediamine and \emph{ortho}-xylenediamine linkers in the center of the polymers. Foldamers with \emph{ortho}-xylenediamine linkers in the center were investigated for longer polymers, i.e., octamers and decamers, using two different enhanced sampling methods, since regular MD simulations had failed to show any folding for these longer polymers. In particular, the recently developed concurrent adaptive sampling (CAS) algorithm (Ahn \latin{et al.} J. Chem. Phys. 2017) and replica exchange molecular dynamics (REMD) were used. We found that the two enhanced sampling methods did lead to the observation of foldamers, and that REMD revealed new foldamer architectures where \emph{cis}-\emph{trans} isomerizations had occurred. Foldamer formation, diversity, and the strengths and limitations of simulation techniques are discussed. These findings provide new insights into the diversity of foldamer architectures for a new type of biomimetic synthetic polymer.« less

Plastic dielectric materials are required in radiation and rare event physics detectors as structural parts, insulators, seals, light reflectors, and in connectors. In order to observe events of interest rather than counting the radioactivity of the detector itself, these materials must be of high radiopurity. Using a mass spectrometric method, a number of solid plastic materials and parts were analyzed for mass levels of contaminants 232Th and 238U, which were used as an assessment of radiopurity. Sample preparation began with dry ashing the solid subsamples in very low mass containers of ultra low background electroformed copper (ULB EF-Cu) foil thatmore » had been cut and folded into boats serving as crucibles. Final determinations were carried out by inductively coupled plasma mass spectrometry (ICP-MS) with liquid nebulization sample solution introduction. Sample sizes were in the 25 mg to 1.25 g mass, and analyses could be completed in less than two days. Detection limits to pg/g (i.e., parts per trillion) levels are obtained and converted to radioactivity units microBq/kg of material. Determinations on poly(methyl methacrylate) (PMMA) gave values for 238U below 10 microBq/kg, while values for poly(chlorotrifluoroethylene) (PCTFE) rod stock material or acid-leached machined PCTFE parts were at or below 50 microBq/kg in 238U. Results for solid Purad poly(vinylidene fluoride) (PVDF) material are also reported at ca. 5 mBq/kg of 238U, although PVDF Solef 1010 raw material in powder and pellet form has been previously reported as low as 25 microBq/kg, and 200 microBq/kg 238U, respectively. An initial analysis of a polyetherimide(PEI) material, sold as ULTEM, indicated promising radiopurity with a found value of 30 microBq/kg for 238U. A variety of solid dielectric polymer materials were found with radiopurities at less than a milliBq/kg 238U and 232Th.« less

Grate and co-workers at Pacific Northwest National Laboratory recently developed high information content triazine-based sequence-defined polymers that are robust by not having hydrolyzable bonds and can encode structure and functionality by having various side chains. Through molecular dynamics (MD) simulations, the triazine polymers have been shown to form particular sequential stacks, have stable backbone-backbone interactions through hydrogen bonding and π–π interactions, and conserve their cis/trans conformations throughout the simulation. However, we do not know the effects of having different side chains and backbone structures on the entire conformation and whether the cis or trans conformation is more stable for themore » triazine polymers. For this reason, we investigate the role of non-covalent interactions for different side chains and backbone structures on the conformation and assembly of triazine polymers in MD simulations. Since there is a high energy barrier associated with the cis-trans isomerization, we use replica exchange molecular dynamics (REMD) to sample various conformations of triazine hexamers. To obtain rates and intermediate conformations, we use the recently developed concurrent adaptive sampling (CAS) algorithm for dimers of triazine trimers. Here, we found that the hydrogen bonding ability of the backbone structure is critical for the triazine polymers to self-assemble into nanorod-like structures, rather than that of the side chains, which can help researchers design more robust materials.« less