Methanol, ethanol, and isopropanol do not radially swell or produce supercontrac tion (SC) of spider major ampullate silk fibers. Their aqueous solutions do so at rates associated with water concentrations, but produce no levels of SC ratios other than those expected of water Itself. Saturated aqueous solutions of NaSCN and LiBr produce swelling and lowered birefringences of axially restrained fibers. On unre strained fibers NaSCN produces further SC. After SC, the wetted fibers can be stretched to their original lengths, and on drying they are in a stable state from which further SC and re-stretching cycles can be repeated. On both unrestrained major and minor ampullate fibers, LiBr causes irreversible gellation. X-ray diffraction measure ments show that the crystallite unit cell rotates due to macro distortion during SC, but is otherwise unchanged. The suggestion is that water ruptures hydrogen bonds between amino and carboxy groups, in the anti-parallel rippled sheet model of silk, to produce radial swelling and allow SC. The internal axial retractive force present in the wetted fibers, which is the driving force for SC, provides axial tension in the restrained condition and in turn prevents access to LiBr, which in the unrestrained condition brings about gellation.
Plasma polymerizations (under 13.5‐MHz radiofrequency inductively coupled glow discharge) of some organic compounds are investigated by their properties (elemental analysis, surface energy, and infrared spectra) and their relations to the concentrations of free radicals in the polymers as detected by electron spin resonance (ESR) spectroscopy. Monomers that have been investigated are hexamethyldisiloxane, tetrafluoroethylene, acetylene, acetylene/N2, acetylene/H2O, acetylene/N2/H2O, allene, allene/N2, allene/H2O, allene/N2/H2O, ethylene, ethylene/N2, ethylene oxide, propylamine, allylamine, propionitrile, and acrylonitrile. Plasma‐polymerized polymers generally contain oxygen, even if the starting monomers do not contain oxygen. This oxygen incorporation is related to the free‐radical concentration in the polymer. Molecular nitrogen copolymerizes with other organic monomers such as acetylene, allene, and ethylene, and their properties are very similar to those of plasma‐polymerized polymers from nitrogen‐containing compounds such as amines and nitriles. The addition of water to the monomer mixture reduces in a dramatic manner the concentration of free radicals in the polymer and consequently the oxygen‐incorporation after the polymer is exposed to air. The concentrations of free radicals (by ESR) are directly correlated to the change of the properties of plasma‐polymerized polymers with time of exposure to the atmosphere. These changes are primarily the introduction of carbonyl (and possibly hydroxyl) groups. The addition of water to the plasma introduces these groups during the polymerization.
SynopsisThe small-angle x-ray scattering (SAXS) patterns of a number of linear polyethylene (PE) and polyoxymethylene (POM) samples have been measured and compared to the intensity functions of one-dimensional paracrystalline lattices. It was found that the ratio of the angular positions of the second and first scattering maxima (8&) is generally less than or equal to 2.0, implying that the paracrystalline lattice statistics are symmetric or moderately skewed to larger periods. The Braggspacing ("long period") of such samples is within 3y0 of the identity period of the macrolattice. With quenched POM the ratio 81/81 is substantially larger than 2.0, which indicates either extremely asymmetric lattice statistics or coexisting structures within the material. From consideration of the reduced widths of the first scattering maxima, it was found that some broadening is present in addition to that from the paracrystallinity. This excess broadening could result from a finite lattice length of ~1 0 0 0 b. The need for careful experimental technique for obtaining the actual position of the scattering maximum is emphasized. In addition, it is demonstrated that the scattering curve and the correlation function of the system yield essentially the same apparent structural periods.
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