SEARCH · Engineering Papers
Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
Turbulent pipe-flow frictional pressure drop of very dilute aqueous solutions of polyethylene oxides measured and correlated with polymer molecular weight and concentration
The transition to turbulence in a plane Poiseuille flow of dilute polymer solutions is studied by direct numerical simulations of a finitely extensible nonlinear elastic fluid with the Peterlin closure. The range of Reynolds number ($Re$)$2000 \le Re \le 5000$is studied but with the same level of elasticity in viscoelastic flows. The evolution of a finite-amplitude perturbation and its effects on the transition dynamics are investigated. A viscoelastic flow begins transition at an earlier time than its Newtonian counterparts, but the transition time appears to be insensitive to polymer concentration in the dilute and semi-dilute regimes studied. Increasing polymer concentration, however, decreases the maximum attainable energy growth during the transition process. The critical or minimum perturbation amplitude required to trigger transition is computed. Interestingly, both Newtonian and viscoelastic flows follow almost the same power-law scaling of$Re^\gamma$with the critical exponent$\gamma \approx -1.25$, which is in close agreement with previous studies. However, a shift downward is observed for viscoelastic flow, suggesting that smaller perturbation amplitudes are required for the transition. A mechanism of the early transition is investigated by the evolution of wall-normal and spanwise velocity fluctuations and flow structure. The early growth of these fluctuations and the formation of quasi-streamwise vortices around low-speed streaks are promoted by polymers, hence causing an early transition. These vortical structures are found to support the critical exponent$\gamma \approx -1.25$. Once the transition process is completed, polymers play a role in dampening the wall-normal and spanwise velocity fluctuations and vortices to attain a drag-reduced state in viscoelastic turbulent flows.
Abstract Polyzwitterions (PZs) are considered as model synthetic analogs of intrinsically disordered proteins. Based on this analogy, PZs in dilute aqueous solutions are expected to attain either globular (i.e. molten, compact) or random coil conformations. Addition of salt is expected to open these conformations. To the best of our knowledge, these hypotheses about conformations of PZs have never been verified. In this study, we test these hypotheses by studying effects of added salt [potassium bromide (KBr)] on gyration and hydrodynamic radii of poly(sulfobetaine methacrylate) in dilute aqueous solutions using dynamic light scattering and small-angle X-ray scattering, respectively. Effects of zwitteration are revealed by direct comparisons of the PZs with the polymers of the same backbone but containing (1) no explicit charges on side groups such as poly(2-dimethylaminoethyl methacrylate)s and (2) explicit cationic side groups with tertiary amino bromide pendants. Zeta-potential measurements, transmission electron microscopy, and ab initio molecular dynamics simulations reveal that the PZs acquire net positive charge in near salt-free conditions due to protonation but retain coiled conformations. Added KBr leads to nonmonotonic changes exhibiting an increase followed by a decrease in radius of gyration (and hydrodynamic radius), which are called antipolyelectrolyte and polyelectrolyte effects, respectively. Charge regulation and screening of charge–charge interactions are discussed in relation to the antipolyelectrolyte and polyelectrolyte effects, respectively, which highlight the importance of salt in affecting net charge and conformations of PZs.
Evaporative injector system for capillary column gas chromatography for solutes in dilute solution
In the present work two diacetylene derivatives of pyrrole which are predicted by semiempirical AM1 calculations to have very different properties, are synthesized; the polymerizability of these diacetylenes in the solid state is determined, and the results are compared to the computer predictions. Diacetylene 1 is novel in that the monomer is a liquid at room temperature; this may allow for the possibility of polymerization in the liquid state as well as the solid state. Thin poly(diacetylene) films are obtained from compound 1 by growing films of the monomer using vapor deposition and polymerizing with UV light; these films are then characterized. Interestingly, while the poly(diacetylene) from 1 does not possess good nonlinear optical properties, the monomer exhibits very good third-order effects (phase conjugation) in solution. Dilute acetone solutions of the monomer 1 give intensity-dependent refractive indices on the order of 10 exp -6 esu; these are 10 exp 6 times better than for CS2.
Room temperature behavior of oriented tungsten single crystals with rhenium in dilute solid solution
Electrolysis of CO 2 at gas-diffusion electrodes (GDEs) has typically been limited by the supply of gas to the electrocatalyst, overshadowing the importance of the supply of water. However, at high current densities that approach 1 A cm –2 , where the electrolyte becomes highly concentrated in the catalyst layer of a GDE, the activity of water and solutes deviate from their bulk dilute solution values, potentially slowing reaction rates and changing reaction equilibrium potentials. In addition, as flow plates for the gas stream are introduced to enable larger electrodes and high single pass conversion of CO 2 to product, variations in the gas composition will become important. By drawing upon literature for the oxygen reduction reaction (ORR), here we explain how to account for these effects in future modeling and experimental work, with particular attention to accurate use of the Nernst equation for electrode potentials and the Arrhenius equation for reaction rates. Specifically, using measurements of KOH solvent and solute activity reported in literature, and assuming the second protonation of CO 2 by water as the rate-determining step, we show the Nernst equation dilute-solution approximation of the CO 2 to CO equilibrium potential to be accurate below 5 M KOH, but it has a 74 mV error when increasing the concentration up to 10 M KOH. Finally, a simple one-dimensional model of a serpentine flow-field on a GDE demonstrated that a reactor with constant pressure of 1 bar and 1 A cm –2 at the inlet had only ~0.3 A cm –2 at the outlet for a conversion in CO 2 partial pressure from 0.90 to 0.48 bar, showing the significant practical implications of this work.
This dataset includes Python scripts for analyzing the neutron and X-ray scattering and neutron spin-echo data presented in the paper “Signatures of Thermoreversible Associations in X-ray and Neutron Scattering from Dilute Polyzwitterion Solutions” by Li et al. (https://doi.org/10.1021/acs.macromol.5c02554).
The fundamental principles that govern antiferroelectric (AFE)–ferroelectric (FE) transitions are not well understood for many solid solutions of perovskite compounds. For example, crystal chemical considerations based on the average Goldschmidt tolerance factor or ionic polarizability do not precisely predict the boundary between the AFE and FE phases in dilute solid solutions of alkali niobates, such as K x Na 1– x NbO 3 ( x ≤ 0.02). Here, based on detailed structural analysis from neutron total scattering experiments, we provide insights about how the relative local distortions around the A- and B-sites of the ABO 3 perovskite structure affect the AFE/FE order of the average crystallographic phases in K x Na 1– x NbO 3 . Specifically, we show that a higher (lower) ratio of B-site-centered distortions over A-site-centered distortions drives transition toward a long-range FE (AFE) phase, which is based on a competition between the long-range polarizing field of the Nb–O dipoles and the disordering effect of local distortions around the A-site. Our study provides a predictive tool for designing complex solid-solution perovskites with tunable (anti)ferroelectric polarization properties, which can be of interest for various energy-related applications such as high-density energy storage and solid-state cooling.
One of the current challenges in polymer physics and engineering is to understand the behavior of circular macromolecules. Though such molecules have been made by dilute solution ring closure methods in the past, such procedures have been limited to relatively small, unentangled rings as well as to small sample quantities. Initial studies were also hampered by issues surrounding purity of the rings, though this problem has been somewhat overcome by the use of liquid chromatography at critical conditions (LCCC) methods that separate rings and linear chains. Furthermore, in spite of the continued progress a full understanding of ring dynamics remains elusive. The present work has addressed multiple aspects of the behavior of ring molecules by using a novel synthetic route: reversible radical recombination redox polymerization (R3P) to produce poly(3,6-dioxa-1,8-octanedithiol) (PolyDODT) molecules. The synthesis conditions were chosen to produce linear (LDODT), cyclic (RDODT) and linear-cyclic mixtures (LRDODT) in order to investigate dilute solution and rheological responses of the materials. Importantly, the R3P synthesis makes larger quantities and higher molecular weights than do the dilute solution ring closure methods and also has the potential to be scaled to industrial quantities, thus becoming commercializable. We emphasize two important outcomes of the work. The first is that the rheological investigation shows that very large molecular weight the PolyDODT rings permitted the investigation of ring dynamics from glassy towards terminal flow for molecular sizes corresponding to approximately 300 entanglements of the linear counterpart. At the same time, these very large sized rings could be diluted in a solvent in order to reduce the molecular entanglement density to less than unity. The results demonstrate that ring viscosity follows a Rouse-like linear dependence on molecular weight or entanglement number to approximately 15 entanglements. This range of "Rouse-like" response is greater than what was achieved in all prior works where synthesis conditions have limited the molecular sizes achievable. After the entanglement number $Z_w$ increases beyond approximately 15, we find that the viscosity-molecular weight scaling undergoes a rapid change from the Rouse-like $η\sim{Z}^1_w$ to a very strong power-law scaling that is approximately $η\sim{Z}^{5.8}_w$. This aspect of the work strongly suggests that prior investigations on highly pure rings have invariably been performed on unentangled systems simply because ring molecules have very high entanglement thresholds. The results are further supported by plateau modulus measurements that show that in the "Rouse-like" viscosity regime, for the RDODT samples there is a corresponding lack of a rubbery entanglement plateau and once entanglement coupling is seen, the rubbery plateau also appears in the dynamic modulus data. Furthermore, upon appropriate scaling, we show that the unentangled polyDODT rings (i.e., the diluted high molecular weight rings) show virtually identical dynamics (upon appropriate scaling to account for the chain dilutions) to the dynamics of similarly unentangled LCCC fractionated polystyrene rings.
There has been significant interest in the engineering of polymer topology to control rheology and mechanical stability in dilute solutions for applications involving extreme shear rate flows. However, methods to experimentally probe properties at relevant shear rates (≈ 10 4 –10 6 s –1 ) have remained ex situ, obscuring access to measures of polymer deformation and rheology that would otherwise provide mechanistic insight into the topology-dependent properties that control their behavior in extreme shear flows. In this study, we used novel in situ small angle neutron scattering measurements in a capillary rheometer (capillary rheo-SANS) to simultaneously measure solution viscosities and polymer deformations in high shear on a series of chemically homologous topology-defined polymers including linear, randomly branched, and star-shaped molecules. We demonstrate that differences in the onset of chain stretching and shear thinning of these polymers in dilute solution are controlled primarily by differences in their molecular relaxation time. These differences correlate with differences in chain scission inferred from ex situ measurements at more extreme shear rates. Together, the results demonstrate a direct coupling between chain deformation and scission, and suggest that the dominant effect of branching as a means to impart resilience against mechanical degradation is through differences in relaxation dynamics due to branching. We anticipate that these results will provide key insights to engineer topology-controlled polymers for rheological modification, mechanical stability, and controlled mechano-chemistry.
The adhesion of fiber reinforcement such as high modulus graphite to a matrix resin such as polycarbonate is greatly enhanced by applying a very thin layer, suitably from 50 Angstroms to below 1000 Angstroms, to the surface of the fiber such as by immersing the fiber in a dilute solution of the matrix resin in a volatile solvent followed by draining to remove excess solution and air drying to remove the solvent. The thin layer wets the fiber surface. The very dilute solution of matrix resin is able to impregnate multifilament fibers and the solution evenly flows onto the surface of the fibers. A thin uniform layer is formed on the surface of the fiber after removal of the solvent. The matrix resin coated fiber is completely wetted by the matrix resin during formation of the composite. Increased adhesion of the resin to the fibers is observed at fracture. At least 65 percent of the surface of the graphite fiber is covered with polycarbonate resin at fracture whereas uncoated fibers have very little matrix resin adhering to their surfaces at fracture and epoxy sized graphite fibers exhibit only slightly higher coverage with matrix resin at fracture. Flexural modulus of the composite containing matrix resin coated fibers is increased by 50 percent and flexural strength by 37 percent as compared to composites made with unsized fibers.
Explore the source record for details and available documents.
We have successfully made synthetic polymer rings that are larger than previously reported having entanglement numbers as high as Z w ≈300 if the rings entangled as do linear chains. The synthesis was carried out using reversible radical recombination polymerization (R3P) of dithiols which produces a polymer with a very small persistence length. The reported results show surprising dilute solution behaviors due to the fact that polymeric rings expand more than their linear counterparts for polymer chains having a large number of persistence lengths, as developed in this study. The results strongly argue for a systematic investigation of the dilute solution properties of rings having different persistence lengths in different quality solvents, where the theta-condition should lead to results that are independent of the persistence length. For the rheological investigations related to chain entanglements, the polyDODT rings could be diluted so that the rheological data covered from less than one entanglement spacing relative to the linear counterpart to a value of Z w =300. Importantly, because we were able to dilute extremely high entanglement number polyDODT rings to a similar entanglement number as those reported for polystyrene rings that were highly purified using LCCC, we demonstrated that the dynamics of the polyDODT rings virtually overlaps with the dynamics of the polystyrene rings which is very strong evidence that these high molecular weight polyDODT rings are of high purity. Our results demonstrate that the onset of entanglement in rings, as evidenced by the appearance of a rubbery plateau G N 0 and by the onset of a strong power-law dependence of the viscosity on molecular weight (η~M w 5.8 ) or entanglement number (η~Z w 5.8 ), occurs at much higher molecular weights or polymer concentrations than is the case for linear chains. These results should serve as a benchmark for future investigations of the behavior of entangled, circular macromolecules.
We have successfully made synthetic polymer rings that are larger than previously reported having entanglement numbers as high as $Z_w$≈300 if the rings entangled as do linear chains. The synthesis was carried out using reversible radical recombination polymerization (R3P) of dithiols which produces a polymer with a very small persistence length. The reported results show surprising dilute solution behaviors due to the fact that polymeric rings expand more than their linear counterparts for polymer chains having a large number of persistence lengths, as developed in this study. The results strongly argue for a systematic investigation of the dilute solution properties of rings having different persistence lengths in different quality solvents, where the theta-condition should lead to results that are independent of the persistence length. For the rheological investigations related to chain entanglements, the polyDODT rings could be diluted so that the rheological data covered from less than one entanglement spacing relative to the linear counterpart to a value of $Z_w$=300. Importantly, because we were able to dilute extremely high entanglement number polyDODT rings to a similar entanglement number as those reported for polystyrene rings that were highly purified using LCCC, we demonstrated that the dynamics of the polyDODT rings virtually overlaps with the dynamics of the polystyrene rings which is very strong evidence that these high molecular weight polyDODT rings are of high purity. Our results demonstrate that the onset of entanglement in rings, as evidenced by the appearance of a rubbery plateau $G_N^0$ and by the onset of a strong power-law dependence of the viscosity on molecular weight (η~$M_w^{5.8}$) or entanglement number (η~$Z_w^{5.8}$), occurs at much higher molecular weights or polymer concentrations than is the case for linear chains. These results should serve as a benchmark for future investigations of the behavior of entangled, circular macromolecules.
The integrity of the final printed components is mostly dictated by the adhesion between the particles and phases that form upon solidification, which is a major problem in printing metallic parts using available In-Space Manufacturing (ISM) technologies based on the Fused Deposition Modeling (FDM) methodology. Understanding the melting/solidification process helps increase particle adherence and allows to produce components with greater mechanical integrity. We developed a phase-field model of solidification for binary alloys. The phase-field approach is unique in capturing the microstructure with computationally tractable costs. The developed phase-field model of solidification of binary alloys satisfies the stability conditions at all temperatures. The suggested model is tuned for Ni-Cu alloy feedstocks. We derived the Ginzburg-Landau equations governing the phase transformation kinetics and solved them analytically for the dilute solution. We calculated the concentration profile as a function of interface velocity for a one-dimensional steady-state diffuse interface neglecting elasticity and obtained the partition coefficient, k, as a function of interface velocity. Numerical simulations for the diluted solution are used to study the interface velocity as a function of undercooling for the classic sharp interface model, partitionless solidification, and thin interface.
Explosives are often used in industry, geology, mining, and other applications, but it is not always clear what remains after a detonation or the fate and transport of any residual material. The goal of this study was to determine to what extent intact molecules of high explosive (HE) compounds are detectable and quantifiable from post-detonation dust and particulates in a field experiment with varied topography. We focused on HMX (1,3,5,7-Tetranitro-1,3,5,7-tetrazocane), which is less studied in field detonation literature, as the primary explosive material and RDX (1,3,5-Trinitroperhydro-1,3,5-triazine) as the secondary material. The experiment was conducted at Site 300, Lawrence Livermore National Laboratory’s Experimental Test Site, in California, USA. Two 20.4 kg and one 40.8 kg above ground explosions (primarily comprised of LX-14, an HMX-based polymer-bonded high explosive) were detonated on an open-air firing area on separate days. The complex terrain of the firing area (e.g., buildings, berm, low-height obstacles) was advantageous to study HE deposition in relation to plume dynamics. Three types of samples were collected up to 100 m away from each shot: surface swipes of aluminum plates, surface swipes of fixed objects, and filters from air samples. We used atmospheric flow tube-mass spectrometry (AFT-MS) to quantify picogram levels of molecular residue of HE material in the post-detonation dust. An aliquot of sample extract in methanol (e.g., 1 µL of 0.5 mL) was placed onto a resistive material and then thermally desorbed into the AFT-MS. We successfully detected and quantified both HMX and RDX in many of the samples. Based on mass (pg) detected and solution dilution, we back-calculated the mass collected on the swipe or filter (ng per sample). The aerial distribution of molecular residue was consistent with the path of the plume, which was strongly determined by wind speed and direction at the time of each shot. The quantity of material detected appeared to correlate more with distance from the shot and the wind conditions than with shot size. This study demonstrates that the picogram detection levels of AFT-MS are well-suited for quantification of analytes (e.g., HMX and RDX) in environmental samples.
The formation of alteration phases on uranium ore concentrates and used nuclear fuels under oxidizing conditions is key to understanding the potential mobility of radionuclides in the environment and designing optimal storage conditions of materials. However, the time-dependent distribution of alteration phases on α– and β–U 3 O 8 under oxidizing conditions has yet to be explored. Here, in this study, crystalline powders of α– and β–U 3 O 8 were submerged in aqueous solutions of hydrogen peroxide (1.6 × 10 −1 to 5.4 × 10 −5 M) with aliquots of solution and solid removed for analysis at 1, 8, 15, 22, 29, 36, 46, 58, 71, and 83 days. Within one day there is significant alteration of U 3 O 8 to the uranyl peroxide metastudtite, [(UO 2 )(O 2 )(H 2 O) 2 ], that is replaced by studtite, [(UO 2 )(O 2 )(H 2 O) 2 ]·2H 2 O, within a week regardless of the polymorph of U 3 O 8 or the initial concentration of H 2 O 2 in solution, as determined by partial least squares regression (PLSR) of Raman spectra collected from the solids. A dissolution/reprecipitation mechanism is proposed for both the alteration of U 3 O 8 to metastudtite and the subsequent alteration of both U 3 O 8 and metastudtite to studtite. The two polymorphs of U 3 O 8 exhibit similar rates and extents of alteration over time. The rehydration of metastudtite to studtite has not been previously reported and highlights the need for future work to determine the mechanism by which metastudtite is converted to studtite and what other conditions facilitate this rehydration.