Molecular weight decrease in the early pyrolysis of crystalline and amorphous cellulose

Samples of ordinary “ash-free” cellulose papers and similar samples decrystallized by swelling in liquid ammonia were pyrolyzed in vacuo to a weight loss ranging from <0.1% to nearly 20%. The samples were then nitrated and their molecular weight distributions determined by gel permeation chromatography. When weight loss reached 1%, both the ordinary and the ammonia-swelled celluloses showed a large drop in average degree of polymerization (D.P.). However, the ordinary cellulose showed this sharp drop long before there was any measurable weight loss; the ammonia-swelled cellulose changed D.P. only gradually in the early stages. Further, x-ray diffraction measurements showed that by the time the D.P. of the ammonia-swelled cellulose had dropped appreciably, the material had developed a significant crystalline pattern. These results support the suggestion that initial rupture of the cellulose molecule occurs at strain points at the crystalline–amorphous boundaries.     

The synthesis of14C- and3H-labeled glycerol ethers

The racemic¹⁴C-and³H-labeled alpha and beta derivatives of octadecyl glycerol ether (batyl alcohol) and of hexadecyl glycerol ether (chimyl alcohol) of high specific activity were synthesized by treating the appropriate alkyl halides with a large excess of the potassium salts of isopropylidene or benzylidene glycerol. By use of the trifluoroacetic anhydride esterification procedure, the labeled diesters of alpha and beta octadecyl and hexadecyl glycerol ethers were prepared. The labeled monoesters of beta octadecyl and of beta hexadecyl glycerol ethers were isolated from the reaction mixtures by silicic acid column chromatography. Work done in partial fulfillment for PhD Degree, Department of Biochemistry, University of North Carolina.     

Poly(vinyl chloride) thermal stability. I. Evaluation by melt rheology

Capillary rheometry is used to characterize the thermal stability of poly(vinyl chloride). By isothermally extruding the polymer melt at constant shear rate, apparent viscosity–time relationships are obtained having three distinct regions: (1) obtainment of equilibrium viscosity, (2) constant viscosity, and (3) rapidly changing viscosity. During regions 2 and 3 the polymer extrudate gradually changes in color from water clear to black. These characteristic regions are related to the temperature of extrusion by Arrhenius plots. An activation energy of 40 kcal./g.-mole was calculated for the decomposition of PVC. Infrared spectroscopy, thermal gravimetric analysis, and intrinsic viscosity experiments are used to corroborate the results of the melt flow data.     

Preparation of hydroxy acids by sulfation of oleic and linoleic acids

Summary Monohydroxystearic acids were prepared by sulfation and subsequent hydrolysis of oleic acid, and the effect of reaction conditions on yield was studied. Monohydroxystearic acids were obtained from commercial oleic acid in 72% yield and from pure oleic acid in 86% yield. Conditions for the best yields apparently gave increased amounts of isomeric hydroxy acids. Hydroxy acids prepared by the sulfation and subsequent hydrolysis of linoleic acid were converted to methyl esters, and purified by fractional distillation and low temperature crystallization. Experimental evidence indicates that sulfuric acid reacts with one double bond of linoleic acid to form isomeric monohydroxyoleic acids and with both double bonds to form dihydroxystearic acids. The by-products formed by the sulfation of linoleic acid include both ester-type polymers and additional polymeric material which cannot be converted to monomers by alkaline saponification. When commercial oleic acid is sulfated and subsequently hydrolyzed, the monohydroxystearic acid thus obtained presumably contains monohydroxyoleic acids and dihydroxystearic acids resulting from the linoleic acid present in the starting material. The formation of an unsaponifiable polymer during the sulfation of linoleic acid accounts in part for the lower yield of hydroxy acids obtained from commercial oleic acid, as compared with that of purified oleic acid. One of the laboratories of the Bureau of Agricultural and Industrial Ohemistry, Agricultural Research Administration, U. S. Department of Agriculture.     

Measuring the optical properties of astrophysical dust analogues: instrumentation and methods

Dust is found throughout the universe and plays an important role for a wide range of astrophysical phenomena. In recent years, new IR facilities have provided powerful new data for understanding these phenomena. However, interpretation of these data is often complicated by a lack of complementary information about the optical properties of astronomically relevant materials. The Optical Properties of Astronomical Silicates with Infrared Techniques (OPASI-T) program at NASA's Goddard Space Flight Center is designed to provide new high-quality laboratory data from which we can derive the optical properties of astrophysical dust analogues. This program makes use of multiple instruments, including new equipment designed and built specifically for this purpose. The suite of instruments allows us to derive optical properties over a wide wavelength range, from the near-IR through the millimeter, also providing the capability for exploring how these properties depend upon the temperature of the sample. In this paper, we discuss the overall structure of the research program, describe the new instruments that have been developed to meet the science goals, and demonstrate the efficacy of these tools.     

Optically- and thermally-responsive programmable materials based on carbon nanotube-hydrogel polymer composites

A simple approach is described to fabricate reversible, thermally- and optically responsive actuators utilizing composites of poly(N-isopropylacrylamide) (pNIPAM) loaded with single-walled carbon nanotubes. With nanotube loading at concentrations of 0.75 mg/mL, we demonstrate up to 5 times enhancement to the thermal response time of the nanotube-pNIPAM hydrogel actuators caused by the enhanced mass transport of water molecules. Additionally, we demonstrate the ability to obtain ultrafast near-infrared optical response in nanotube-pNIPAM hydrogels under laser excitation enabled by the strong absorption properties of nanotubes. The work opens the framework to design complex and programmable self-folding materials, such as cubes and flowers, with advanced built-in features, including tunable response time as determined by the nanotube loading.     

Design and characterization of a theta-pinch imploding thin film plasma source for atomic emission spectrochemical analysis

A new atomization device for direct atomic spectrochemical analysis has been developed that uses the theta-pinch configuration to generate a pulsed, high-energy-density plasma at atmospheric pressure. Energy from a 20-kV, 6.05-μF capacitive electrical discharge was inductively coupled to a sacrificial aluminum thin film to produce a cylindrical plasma. Current waveform analysis indicates an average power dissipation of 0.5 MW in the plasma. Electromagnetic modeling studies were used to identify theta-pinch designs possessing characteristics favorable to both plasma initiation and plasma heating. The discharge was most robust when the induced current and rate of magnetic field change were maximized. Minimizing the ratio of the coil's width to its radius was also critical. Counter to intuition, a larger diameter was found to be more successful. Spectroscopic studies indicate that the discharge forms a heterogeneous plasma with a dense, cylindrical plasma sheet confined by the walls of the discharge tube surrounding a less energetic plasma in the center. Al(II) emission in the outer plasma cylinder was temporally aligned with the induced current whereas in the center it aligns with the magnetic field. Ionization of support gas species (Ar, He, and air) was not observed, although the identity of the gas had a significant influence on the plasma reproducibility. The optimized design utilized a 5.5-turn, 19-mm-diameter theta coil with argon as the support gas. Sb(I) emission from an antimony oxide solid powder sample deposited on the thin film was observed primarily in the outer part of the plasma. Analyte emission shows contributions from magnetic compression early in the discharge and from the induced current late in the discharge. The discharge produced analytically useful signals from solid antimony oxide samples. Using spatially and temporally resolved detection, the line-to-background ratio for Sb(I) was found to be greater than 4 for emission integrated from 55 to 120 μs.     

Imaging the hidden modes of ultrathin plasmonic strip antennas by cathodoluminescence

We perform spectrally resolved cathodoluminescence (CL) imaging nanoscopy using a 30 keV electron beam to identify the resonant modes of an ultrathin (20 nm), laterally tapered plasmonic Ag nanostrip antenna. We resolve with deep-subwavelength resolution four antenna resonances (resonance orders m = 2-5) that are ascribed to surface plasmon polariton standing waves that are confined on the strip. We map the local density of states on the strip surface and show that it has contributions from symmetric and antisymmetric surface plasmon polariton modes, each with a very different mode index. This work illustrates the power of CL experiments that can visualize hidden modes that for symmetry reasons have been elusive in optical light scattering experiments.