Grid-Sphere Electrodes for Contact with Ionospheric Plasma

Grid-sphere electrodes have been proposed for use on the positively biased end of electrodynamic space tethers. A grid-sphere electrode is fabricated by embedding a wire mesh in a thin film from which a spherical balloon is formed. The grid-sphere electrode would be deployed from compact stowage by inflating the balloon in space. The thin-film material used to inflate the balloon is formulated to vaporize when exposed to the space environment. This would leave the bare metallic spherical grid electrode attached to the tether, which would present a small cross-sectional area (essentially, the geometric wire shadow area only) to incident neutral atoms and molecules. Most of the neutral particles, which produce dynamic drag when they impact a surface, would pass unimpeded through the open grid spaces. However, partly as a result of buildup of a space charge inside the grid-sphere, and partially, the result of magnetic field effects, the electrode would act almost like a solid surface with respect to the flux of electrons. The net result would be that grid-sphere electrodes would introduce minimal aerodynamic drag, yet have effective electrical-contact surface areas large enough to collect multiampere currents from the ionospheric plasma that are needed for operation of electrodynamic tethers. The vaporizable-balloon concept could also be applied to the deployment of large radio antennas in outer space

Solid expellant plasma generator

An improved solid expellant plasma generator has been developed. The plasma generator includes a support housing, an electrode rod located in the central portion of the housing, and a mass of solid expellant material that surrounds the electrode rod within the support housing. The electrode rod and the solid expellant material are made of separate materials that are selected so that the electrode and the solid expellant material decompose at the same rate when the plasma generator is ignited. This maintains a point of discharge of the plasma at the interface between the electrode and the solid expellant material

Synthesis, Complex Formation, and Dilute-Solution Associative Behavior of Linear Poly(methacrylic acid)-Graft-Poly(2-ethyl-2-oxazoline)

Poly(methacrylic acid) (PMA) and poly(2-ethyl-2-oxazoline) (PEOZO) are a polyacid/polybase pair capable of forming reversible, pH-responsive, hydrogen-bonding complexes stabilized by hydrophobic effects in aqueous media. Linear PMA was modified with long-chain (number-average molecular weight: 10,000) PEOZO via statistical coupling reactions in organic media to prepare a series of PXIA-graft-PEOZO copolymers. Potentiometric titrations revealed that the presence of tethered PEOZO markedly increases the pK(a) values for PMA-g-PEOZO copolymers as compared with simple PMA/PEOZO mixtures at degrees of ionization, alpha, between 0.0 and 0.1. The dilute-solution PMA-PEOZO intramolecular association has been probed by monitoring the PEOZO NMR spin-spin (T-2) relaxation as a function of pH. Covalently attached PEOZO side chains participate in complexation at higher values of a than untethered PEOZO. Surprisingly, most PEOZO side chains did not take part in hydrogen bonding at low a, and the highest level of PEOZO incorporation induced a decrease in the number of PMA/PEOZO hydrogen bonds. The polymer self-diffusion as a function of a was measured with dynamic light scattering. At low pH, the copolymers had no charge and they were in a collapsed form. At high pH, the expected conformational expansion of the PMU units was enhanced at moderate levels of PEOZO incorporation. However, the highest PEOZO incorporation induced the onset of intramolecular associations between PEOZO units along the copolymer chains. Low shear rheometry and light scattering measurements were used in conjunction with the T-2 NMR measurements to propose a model consistent with the aforementioned behavior. (C) 2004 Wiley Periodicals, Inc

Enhanced Coil Expansion and Intrapolymer Complex Formation of Linear Poly(methacrylic acid) Containing Poly(ethylene glycol) Grafts

Poly(methacrylic acid) (PMA) and poly(ethylene glycol) (PEG) represent a polyacid/polybase pair capable of forming reversible, pH-responsive, hydrophobic complexes stabilized by hydrogen bonding in aqueous media. Linear PMA was modified with methoxy-terminated, long-chain (5000 M-w) poly(ethylene glycol) (MPEG) via random coupling in dimethyl sulfoxide using dicyclohexylearbodiimide as a coupling agent. The degree of ionization, alpha, was deteremined utilizing potentiometric titration. The presence of tethered MPEG markedly increased the pK(a) values over those of the PMA homopolymer or PMA/MPEG mixtures at alpha \u3c 0.35. The dilute solution PMA-PEG intramolecular association was probed by monitoring the PEG nuclear magnetic resonance (NMR) spin-spin (T-2) relaxation as a function of pH. Two populations of MPEG exist at appropriate ionizations: those participating in hydrogen bonding with the PMA backbone and those not participating in hydrogen bonding. Polymer self-diffusion at varying degrees of ionization was measured using pulsed gradient spin echo (PGSE) NMR and dynamic light scattering. Acidic conditions produced coil collapse, apparently arising from the formation of intramolecular hydrogen-bonded complexes along the polymer backbone. Under basic conditions, coil expansion was observed due to conformational changes (polyelectrolyte effect), and the added volume of the tethered MPEG as well as the reduction of intramolecular complexation as the number of carboxylate anions increased

The Synthesis of Hydrophobically Modified Water-Soluble Polyzwitterionic Copolymers and Responsiveness to Surfactants in Aqueous Solution

A novel zwitterionic surfactant monomer containing a carboxybetaine moiety and a 10 carbon aliphatic tail was synthesized and copolymerized with acrylamide to yield a water-soluble, hydrophobically modified zwitterionic polymer [Poly(acrylamide-co-(3-(N,N-dimethyl-N-3\u27-(N\u27-acryloyl)aza-tridecyl) ammonio butanoate))]. The response of aqueous polymer solutions to the addition of various classes of surfactant was investigated and compared to that of an analogous novel polymer containing the sulfobetaine zwitterion [Poly(acrylamide-co-(N,N-dimethyl-N-3\u27-(N\u27-acryloyl) aza-tridecyl) ammonio propane sulfonate))]. It was found that the addition of sodium dodecyl sulfate (SDS) produced a pronounced maximum in viscosity, while dodecyltrimethylammoniumbromide (DTAB), N-dodecyl-N,N-dimethylammonio-1-propanesulfonate (SB3-12), and Triton X-100 either had no effect, or produced a decrease in viscosity. The effect of pH on polymer-SDS interaction was also studied. Lowering pH increased the SDS-polymer interaction and significantly shifted viscosity enhancement to a higher SDS concentration