Conductive coatings on complex fibrous systems are attracting interest for new electronic and other functional systems. Obtaining a quantitative conductivity value for complex surface coatings is often difficult. This work describes a procedure to quantify the effective electrical conductivity of conductive coatings on non‐conductive fibrous networks. By applying a normal force orthogonal to the current and field direction, fiber/fiber contact is improved and consistent conductance values can be measured. Nylon fibers coated with an electroless silver plating shows effective conductivity up to 1950 S cm−1, and quartz fibers coated with tungsten by atomic layer deposition (ALD) show values up to ∼1150 S cm−1. Cotton fibers and paper coated with a range of ZnO film thicknesses by ALD show effective conductivity of up to 24 S cm−1 under applied normal force, and conductivity scaled as expected with film coating thickness. Furthermore, we use the conductive coatings to produce an “all‐fiber” metal–insulator–metal capacitor that functions as a liquid chemical sensor. The ability to reliably analyze the effective conductivity of coatings on complex fiber systems will be important to design and improve performance of similar devices and other electronic textiles structures.
Electrically conductive zinc oxide coatings are applied to polypropylene nonwoven fiber mats by atomic layer deposition (ALD) at 50–155 °C. A low temperature (50 °C) aluminum oxide ALD base layer on the polypropylene limits diffusion of diethyl zinc into the polypropylene, resulting in ZnO layers with properties similar to those on planar silicon. Effective conductivity of 63 S/cm is achieved for ZnO on Al2O3 coated polypropylene fibers, and the fibers remain conductive for months after coating. Without the Al2O3 precoating, the effective conductivity was much smaller, consistent with precursor diffusion into the polymer and sub-surface ZnO nucleation. Mechanical robustness tests showed that conductive samples bent around a 6 mm radius maintained up to 40% of the pre-bending conductivity. Linkages between electrical conductivity and mechanical performance will help inform materials choice for flexible and porous electronics including textile-based sensors and antennas.
Nitrogenase activities and the patterns of in vivo inhibition of nitrogenase by NW were compared in Rhodospiilum rubrum grown under several conditions of nitrogen availability. In cells grown on N2 or glutamate plus N2, nitrogenase activity was relatively low and was totally inhibited by added NH: in 15 to 20 min. In contrast, cells grown on glutamate alone displayed higher nitrogenase activity, and NH: had very little effect. Cells grown on limiting amounts of NH: had lower nitrogenase activity, but NH: produced little inhibitory effect. Uptake of NW could be demonstrated under all of these conditions, and this uptake was blocked by DL-methionine-dl-sulfoximine. The data indicated that cells not recently exposed to NHW had no mechanism for rapidly turning off nitrogenase activity in response to sudden additions of NW. In contrast, cells grown in the presence of N2, which form NW internally, inhibited nitrogenase activity relatively quickly in response to added NW.All species of purple nonsulfur photosynthetic bacteria that have been tested can reduce N2 to ammonia. The nitrogenase systems of these bacteria appear unique because the enzyme activity can be reversibly inhibited by ammonium ions. This effect has been observed only in vivo, and it is probably mediated by products of NW assimilation rather than by NW directly (see reference 13 for review). It also has been shown that cell-free extracts from Rhodospirillum rubrum (6,9), Rhodopseudomonas palustris (16), and Rhodopseudomonas capsulata (14) grown with glutamate or N2 as nitrogen sources have low nitrogenase activities, even though the activities of the intact cells were high at the time of harvest. In all cases, these low in vitro activities could be increased in the presence of Mn2+ and Mg-ATP by the addition of a component isolated from the respective chromatophores. This component, designated activating factor, appears to catalyze the release of a small, covalently bound molecule from the iron protein during the activation process (7). The in vitro activation phenomenon might be related to the regulation by ammonium salts observed in vivo, but no in vitro effect of NW on nitrogenase activity has been demonstrated.
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