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Results for “Molecular Weight”

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.

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At least 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
NASA NTRS1995

The glycan keratan sulfate in inner ear crystals

The otoconial matrix (OM) of chicks (Gallus domesticus) inner ear was analyzed. Histochemically the OM was reacted with phosphotungstic acid (PTA) and immunohistochemically with the monoclonal antibody antikeratan sulfate (antiKS). The OM was digested with the enzyme endo-beta-galactosidase (E beta Galase) or separated by 1D and 2D gel electrophoresis. PTA which reacts with glycoproteins precipitated the OM, suggesting that the OM contains glycoproteins. A central core in each crystal had no PTA staining, suggesting that the core lacked glycoproteins. Anti KS antibody stained the OM with increased density in older embryos as determined by color thresholding. E beta Galase, which cleaves the lactosamine repeating units in KS, decreased the immunostain by 30% in the OM and by 20% in the cartilage. The OM from the utricle, saccule and macula lagena contained similar molecular weight bands. Five dense bands in the OM were less dense in tissue and blood controls, suggesting that such bands are enriched in the OM. Isoelectric focusing of the OM showed a negatively charged high molecular weight smear not present in blood and faint in tissue controls. The high affinity of the OM for the cationic PTA stain, the strong immunohistochemical reaction of the OM with anti KS antibody and high molecular weight negative smear in 2D gels taken together suggest that: a) the OM contains large amounts of glycoproteins and glycans, one of which is keratan sulfate, because its immuno stain with antiKS antibody was decreased by the enzyme E beta Galase, b) the utricle, saccule and macula lagena may have similar composition, and c) the concentration of KS may increase gradually until complete mineralization of the OM is reached.

Non-NASA Center↗
NASA NTRS1997

Multiple forms of ADP-glucose pyrophosphorylase from tomato fruit

ADP-glucose pyrophosphorylase (AGP) was purified from tomato (Lycopersicon esculentum Mill.) fruit to apparent homogeneity. By sodium dodecyl sulfate-polyacrylamide gel electrophoresis the enzyme migrated as two close bands with molecular weights of 50,000 and 51,000. Two-dimensional polyacrylamide gel electrophoresis analysis of the purified enzyme, however, revealed at least five major protein spots that could be distinguished by their slight differences in net charge and molecular weight. Whereas all of the spots were recognized by the antiserum raised against tomato fruit AGP holoenzyme, only three of them reacted strongly with antiserum raised against the potato tuber AGP large subunit, and the other two spots (with lower molecular weights) reacted specifically with antisera raised against spinach leaf AGP holoenzyme and the potato tuber AGP small subunit. The results suggest the existence of at least three isoforms of the AGP large subunit and two isoforms of the small subunit in tomato fruit in vivo. The native molecular mass of the enzyme determined by gel filtration was 220 +/- 10 kD, indicating a tetrameric structure for AGP from tomato fruit. The purified enzyme is very sensitive to 3-phosphoglycerate/inorganic phosphate regulation.

NASA Discipline Life Support Systems↗
NASA NTRS1996

The stability of compressible mixing layers in binary gases

We present the results of a study of the inviscid two-dimensional spatial stability of a parallel compressible mixing layer in a binary gas. The parameters of this study are the Mach number of the fast stream, the ratio of the velocity of the slow stream to that of the fast stream, the ratio of the temperatures, the composition of the gas in the slow stream and in the fast stream, and the frequency of the disturbance wave. The ratio of the molecular weight of the slow stream to that of the fast stream is found to be an important quantity and is used as an independent variable in presenting the stability characteristics of the flow. It is shown that differing molecular weights have a significant effect on the neutral-mode phase speeds, the phase speeds of the unstable modes, the maximum growth rates and the unstable frequency range of the disturbances. The molecular weight ratio is a reasonable predictor of the stability trends. We have further demonstrated that the normalized growth rate as a function of the convective Mach number is relatively insensitive (Approx. 25%) to changes in the composition of the mixing layer. Thus, the normalized growth rate is a key element when considering the stability of compressible mixing layers, since once the basic stability characteristics for a particular combination of gases is known at zero Mach number, the decrease in growth rates due to compressibility effects at the larger convective Mach numbers is somewhat predictable.

Kozusko, F.↗
NASA NTRS1977

Production of simple molecules on the surface of Mercury

Lunar sample studies have shown that solar-wind irradiation of the lunar surface has produced a variety of low-molecular-weight compounds. Analysis of the lunar soils has revealed the presence of H2, CH4, H2O, N2, CO, CO2, He, Ne and other components which are extralunar. Irradiation experiments on lunar materials and analogs have shown that solar-wind and solar-flare irradiation of the lunar surface produces selected low-molecular-weight components. Solar-wind irradiation of Mercury's surface should also produce a wide variety of low-molecular-weight species because of the increased solar flux, which results from Mercury being nearer the sun than the moon. The thermal regime of Mercury's surface would result in thermal evaporation of low-temperature components followed by 'cold-trapping' on the night-time side of the planet. Such desorption-adsorption processes assist chemical weathering of Mercury's regolith.

Gibson, E. K., Jr.↗
NASA NTRS1987

Cure study of soluble aromatic polyimide films

Several soluble aromatic poly(amic acid) films were staged at intervals to 325 C and characterized by IR spectroscopy and various solution property techniques. A series of films in which the polymer had been endcapped in an effort to control chain extension was also examined. Much of the behavior observed is consistent with an interpretation that a reduction in molecular weight occurred during cure before the ultimate molecular weight was achieved as a polyimide.

Young, Philip R.↗
NASA NTRS1997

Adhesive Properties of Cured Phenylethynyl Containing Imides

Considerable attention has been directed towards acetylene terminated oligomers over the last 20 years' and recent work has focused on phenylethynyl terminated imide (PETI) oligomers. These reactive oligomers possess several features which make them attractive candidates for use as composite matrices and adhesives. The phenylethynyl group can be readily incorporated into many different functionalized oligomers. The reactive oligomers possess relatively low melt viscosities and thermally cure without the evolution of volatile by-products. Once cured, they typically display high glass transition temperatures (Tgs), excellent solvent resistance and high mechanical properties. new modified phenylethynyl-terminated imide (LaRC MPEI) oligomers were synthesized at various molecular weights utilizing a small amount of trifunctional amine. As long as the amount of triamine is relatively small, this approach produces a mixture of linear, star-shaped and branched polymer chains that has lower melt and solution viscosity than an equivalent molecular weight linear phenylethynyl terminated imide oligomers. The work reported herein involves the synthesis and characterization of a copolymer using this approach and the preparation of blends utilizing a phenylethynyl containing reactive plasticizer of lower molecular weight called LaRC LV-121. The chemistry and properties of this new MPEI as well as some blends of MPEI with LV-121, are presented and compared to the linear version, LARC-PETI-5.

Jensen, Brian J.↗
NASA NTRS1996

Investigation of Polymer Liquid Crystals

The positron annihilation lifetime spectroscopy (PALS) using a low energy flux generator may provide a reasonably accurate technique for measuring molecular weights of linear polymers and characterization of thin polyimide films in terms of their dielectric constants and hydrophobity etc. Among the tested samples are glassy poly arylene Ether Ketone films, epoxy and other polyimide films. One of the proposed techniques relates the free volume cell size (V(sub f)) with sample molecular weight (M) in a manner remarkably similar to that obtained by Mark Houwink (M-H) between the inherent viscosity (eta) and molecular wieght of polymer solution. The PALS has also demonstrated that free-volume cell size in thermoset is a versatile, useful parameter that relates directly to the polymer segmental molecular weight, the cross-link density, and the coefficient of thermal expansion. Thus, a determination of free volume cell size provides a viable basis for complete microstructural characterization of thermoset polyimides and also gives direct information about the cross-link density and coefficient of expansion of the test samples. Seven areas of the research conducted are reported here.

Han, Kwang S.↗
NASA NTRS1994

Preparation and characterization of poly (arylene ether isoxazole)s by fluoride ion-mediated aromatic nucleophilic displacement reactions

As part of a continuing effort to prepare novel thermally stable high-performance polymers, poly(arylene ether isoxazole)s have been prepared by fluoride ion-catalyzed aromatic nucleophilic substitution reactions with bis(trimethylsiloxyphenyl) isoxazoles and activated bisarylhalides in diphenyl sulfone. Initial investigation involving the preparation of these materials with isoxazole bisphenols and activated bisarylhalides in the presence of potassium carbonate indicated that, under reaction conditions necessary to prepare high-molecular-weight materials, the isoxazole monomer was converted to an enamino ketone. This side reaction was avoided by using fluoride as a base. However, trimethylsilyl ether derivatives of the isoxazole bisphenols were required in these polymerizations for the preparation of high-molecular-weight materials. Moderate to high inherent viscosity eta(sub inh): 0.43-0.87 dl/g) materials with good thermal stability (air: 409-477 C, helium: 435-512 C) can be prepared by the silyl ether method. Glass transition temperatures ranged from 182 to 225 C for polymers with phenyl pendants and from 170 to 214 C for those without. Molecular weight control by 2% endcapping and the incorporation of a phenyl pendant at the 4 position of the isoxazole is necessary to yield polymers soluble in polar aprotic solvents at room temperature. There is evidence, however, indicating the existence of crosslinks between the polymer chains when the silyl ether approach is utilized.

Herbert, C. G.↗
NASA NTRS1988

Synthesis, curing and physical behavior of maleimide terminated poly(arylene ethers)

This paper describes the synthesis of maleimide terminated poly(ether ketones) using the solution imidization process described by Summers et al. (1987). Amorphous poly(arylene ether ketones), as well as poly(arylene ether sulfones, of controlled end group functionalities and molecular weights were synthesized by nucleophilic step polymerization of bisphehol-A phenolates with activated halides, such as 4,4'-difluorobenzophenone, and 'monofunctional' end cappers such as m-aminophenol. The thermal properties of the system included glass transition temperature (Tg) values of 160-170 C, with modulus above Tg proportional to cross-link density, which in turn was reciprocally related to oligomer molecular weight. The measurements of the fracture toughness values showed the materials to be very ductile, with the toughness increasing with oligomer molecular weight.

Lyle, G. D.↗
NASA NTRS2009

Effects of Temperature on Polymer/Carbon Chemical Sensors

Experiments were conducted on the effects of temperature, polymer molecular weight, and carbon loading on the electrical resistances of polymer/carbon-black composite films. The experiment were performed in a continuing effort to develop such films as part of the JPL Electronic Nose (ENose), that would be used to detect, identify, and quantify parts-per-million (ppm) concentration levels of airborne chemicals in the space shuttle/space station environments. The polymers used in this study were three formulations of poly(ethylene oxide) [PEO] that had molecular weights of 20 kilodaltons, 600 kilodaltons, and 1 megadalton, respectively. The results of one set of experiments showed a correlation between the polymer molecular weight and the percolation threshold. In a second set of experiments, differences among the temperature dependences of resistance were observed for different carbon loadings; these differences could be explained by a change in the conduction mechanism. In a third set of experiments, the responses of six different polymer/carbon composite sensors to three analytes (water vapor, methanol, methane) were measured as a function of temperature (28 to 36 C). For a given concentration of each analyte, the response of each sensor decreased with increasing temperature, in a manner different from those of the other sensors.

Manfireda, Allison↗
NASA NTRS2017

Graphene Oxide Reduces the Hydrolytic Degradation in Polyamide-11

Graphene oxide (GO) was incorporated into polyamide-11 (PA11) via in-situ polymerization. The GO-PA11 nano-composite had elevated resistance to hydrolytic degradation. At a loading of 1 mg/g, GO to PA11, the accelerated aging equilibrium molecular weight of GO-PA11 was higher (33 and 34 kg/mol at 100 and 120 °C, respectively) compared to neat PA11 (23 and 24 kg/mol at 100 and 120 °C, respectively). Neat PA11 had hydrolysis rate constants (kH) of 2.8 and 12 ( × 10(exp -2) day(exp -1)) when aged at 100 and 120 °C, respectively, and re-polymerization rate constants (kP) of 5.0 and 23 ( × 10(exp -5) day(exp -1)), respectively. The higher equilibrium molecular weight for GO-PA11 loaded at 1 mg/g was the result of a decreased kH, 1.8 and 4.5 ( × 10(exp -2) day(exp -1)), and an increased kP, 10 and 17 ( × 10(exp -5) day(exp -1)) compared with neat PA11 at 100 and 120 °C, respectively. The decreased rate of degradation and resulting 40% increased equilibrium molecular weight of GO-PA11 was attributed to the highly asymmetric planar GO nano-sheets that inhibited the molecular mobility of water and the polymer chain. The crystallinity of the polymer matrix was similarly affected by a reduction in chain mobility during annealing due to the GO nanoparticles' chemistry and highly asymmetric nano-planar sheet structure.

Samuel J A Hocker↗
NASA NTRS1976

Noise produced by fluid inhomogeneities

In an actual engine system, one mechanism for production of hot spots is the burning of various fluid elements at various different mixture ratios. Variable mixture ratio means variable temperature, and this is the effect that has been studied insofar as a noise source is concerned. However, variable mixture ratio also implies variable molecular weight and heat capacity. The paper investigates whether either of these last two variations may be responsible for a significant noise source. The analysis is made within the context of one-dimensional unsteady flow as in the work of Candel (1972). A mixture of thermally perfect gases is assumed as the working fluid, and the fluid composition consists of species 1 and a small and variable mole fraction of species 2 which has different molecular weight and specific heats as compared with species 1. In the absence of changes in the ratio of specific heat (gamma), the entropy variations due to temperature and molecular weight variations are equivalent as a sound source. The portion of sound called 'gamma prime' noise is discussed.

Strahle, W. C.↗
NASA NTRS2020

Interpreting Exo-Planetary Atmospheres with the Next Generation Space-Based Telescope

We will soon have the technological capability to measure the atmospheric composition of temperate Earth-sized planets orbiting nearby stars. Interpreting these atmospheric signals poses a new challenge to planetary science. In contrast to jovian-like atmospheres, whose bulk compositions consist of hydrogen and helium, terrestrial planet atmospheres are likely comprised of high mean molecular weight secondary atmospheres, which have gone through a high degree of evolution. In order to understand the processes which affect a planetary atmosphere, I use early Mars as a case study. I leverage a combination of one-dimensional climate, photochemical and energy balance models in order to create one self-consistent model that closely matches currently available climate data. However, unlike in-situ observations from our own solar system, remote sensing techniques need to be developed and understood in order to accurately characterize exo-atmospheres. I describe the models used to create synthetic transit transmission observations, which includes models of transit spectroscopy and instrumental noise. Using these, I lay the framework for an information content-based approach to optimize our observations and maximize the retrievable information from exo-atmospheres. First I test the method on observing strategies of the well-studied, low-mean-molecular weight atmospheres of warm-Neptunes and hot Jupiters. Upon verifying the methodology, I finally address optimal observing strategies for temperate, high-mean-molecular weight atmospheres (Earths/super-Earths).

Batalha, Natasha↗
NASA NTRS2000

Cold Spots in the Martian Polar Regions: Evidence of Carbon Dioxide Depletion?

Regions of very low, rapidly varying brightness temperatures have been observed near the martian winter poles by several spacecraft. One possibility is that the CO2 condensation temperature is lowered by depletion of CO2 in the air at the surface. We estimate the rate at which this low-molecular-weight air would disperse into the high-molecular-weight air above and show that it is generally faster than the rate of supply. This dispersal could be prevented if there is a strong temperature inversion (warm air above colder air) near the surface. Without an inversion, the entire atmospheric column could become depleted. However, depleted columns take a long time to form, and they are inconsistent with the rapid fluctuations in the cold spot locations and temperatures. Because low-altitude temperature inversions cannot be ruled out by existing observations, CO2 depletion is still a viable explanation for the martian cold spots.

Weiss, Benjamin P.↗
NASA NTRS1992

Availability of the B beta(15-21) epitope on cross-linked human fibrin and its plasmic degradation products

The binding of radiolabeled monoclonal antifibrin antibody 59D8 (specific for fibrin but not fibrinogen) to a series of degraded fibrin clots showed that the availability of the B beta(15-21) epitope (against which 59D8 had been raised) was inversely proportional to the extent of clot lysis. Examination of digest supernatants revealed that the B beta(15-21) epitope was released from clots as a high molecular weight degradation product in the presence of calcium ions but that the generation of low molecular weight peptides occurred in the absence of calcium ions. To address the question of epitope accessibility, we compared levels of fibrin clot binding among four radioactively labeled antibodies: antifibrin monoclonal antibody 59D8, two antifibrinogen monoclonal antibodies that cross-reacted with fibrin, and an affinity-purified polyclonal antifibrinogen antibody. We expected that the antifibrinogen antibodies would show enhanced binding to clots in comparison with the antifibrin antibody. However, the epitope accessibility experiments showed that all four antibody preparations bound fibrin clots at comparable levels. Taken together, these studies demonstrated that one fibrin-specific epitope, B beta(15-21), remains available on clots as they undergo degradation by plasmin and, importantly, that the epitope is not solubilized at a rate faster than the rate at which the clot is itself solubilized. The availability of the B beta(15-21) epitope during the course of plasminolysis assures the potential utility of antifibrin antibodies such as 59D8 for detecting thrombi and targeting plasminogen activators.

NASA Discipline Regulatory Physiology↗
NASA NTRS1985

Polyimide analysis using diffuse reflectance-FTIR

The thermal imidization of a number of polyimide precursors in the form of powders, films, and prepregs was examined by an in situ diffuse reflectance-FTIR technique where infrared spectra were determined while the material was being heated. An analysis of these spectra revealed that, with the exception of one water soluble adhesive, each precursor developed an anhydride band around 1850 cm/cu during imidization. This band diminished in intensity during final stages of cure. Efforts were made to quantify the amount of anhydride in several samples. Evidence obtained could be interpreted to mean that poly(amic acid) resins undergo an initial reduction in molecular weight during imidization before recombining to achieve their ultimate molecular weights as polyimides. Several reports in the literature are cited to support this interpretation. This report serves both to document anhydride formation during imidization and to increase our fundamental understanding of how polyimides cure.

Young, P. R.↗
NASA NTRS1992

Polyimide processing additives

A process for preparing polyimides having enhanced melt flow properties is described. The process consists of heating a mixture of a high molecular weight poly-(amic acid) or polyimide with a low molecular weight amic acid or imide additive in the range of 0.05 to 15 percent by weight of additive. The polyimide powders so obtained show improved processability, as evidenced by lower melt viscosity by capillary rheometry. Likewise, films prepared from mixtures of polymers with additives show improved processability with earlier onset of stretching by TMA.

Fletcher, James C.↗
NASA NTRS1993

Polyimide processing additives

A process for preparing polyimides having enhanced melt flow properties is described. The process consists of heating a mixture of a high molecular weight poly-(amic acid) or polyimide with a low molecular weight amic acid or imide additive in the range of 0.05 to 15 percent by weight of the additive. The polyimide powders so obtained show improved processability, as evidenced by lower melt viscosity by capillary rheometry. Likewise, films prepared from mixtures of polymers with additives show improved processability with earlier onset of stretching by TMA.

Pratt, J. Richard↗