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Copolymers and blends of polyhedral oligomeric silsesquioxane (POSS) and polyimides have been shown to resist atomic-oxygen (AO) attack, making them promising candidates as space-durable materials in the harsh oxidizing environment of low Earth orbit (LEO). CORIN® is a commercially available and colorless POSS–polyimide which has the desirable but uncommon property among polyimides that it may be dissolved in a solvent and applied at room temperature, thus making it possible to have a widely applicable clear coating for protection from AO in LEO. The physical properties of CORIN® have been largely characterized, but its AO resistance has received limited study. We have thus used a hyperthermal AO beam to expose CORIN® and other POSS-containing polyimides, 7.3 wt% and 9.1 wt% Si7O9 trisilanolphenyl POSS blended with poly(pyromellitic dianhydride-co-4,4′-oxydianiline), to characterize their resistance to AO attack. CORIN® was found to have a particularly low erosion yield that is ≲1% that of the ubiquitous satellite material, Kapton, which agrees favorably with a result from an experiment on the International Space Station. The other POSS-containing polymers exhibited somewhat higher erosion yields of 1.4 and 2.2% that of Kapton, respectively. Surface characterization of CORIN® showed that it remained relatively smooth during AO exposure and implied that a passivating silicon oxide was formed. The comparison of the AO effects on CORIN® and the other POSS–polyimides suggests that the net effect of AO on such POSS–polyimides depends on the density of Si atoms as well as the reactivity of the organic component of the polymer. This work adds to our confidence in the use of POSS-containing polymers in LEO and, especially, in very LEO, where the necessity of protecting satellite materials and components from AO attack is critical.

Methylphenidate is a psychostimulant used to treat attention deficit hyperactivity disorder. Neurogenesis occurs throughout adulthood within the dentate gyrus of the hippocampus and can be altered by psychoactive medications; however, the impact of methylphenidate on neurogenesis is not fully understood. We investigated the effects of chronic low (1 mg/kg) and high (10 mg/kg) intraperitoneal doses of methylphenidate on neurogenesis in mouse hippocampus following 28 days and 56 days of treatment. Interestingly, methylphenidate, at both doses, increased neurogenesis. However, if methylphenidate treatment was not continued, the newly generated cells did not survive after 28 days. If treatment was continued, the newly generated neurons survived only in the mice receiving low-dose methylphenidate. To investigate the mechanism for this effect, we examined levels of proteins linked to cell proliferation in the hippocampus, including brain-derived neurotrophic factor (BDNF), glial cell line-derived neurotrophic factor (GDNF), vascular endothelial growth factor (VEGF), tropomyosin receptor kinase B (TrkB), and beta-catenin. BDNF or GDNF levels were not significantly different between groups. However, hippocampal VEGF, TrkB, and beta-catenin were significantly increased in mice receiving low-dose methylphenidate for 28 days compared to controls. Interestingly, high-dose methylphenidate significantly decreased beta-catenin after 28 days and decreased VEGF, beta-catenin, and TrkB after 56 days compared to controls. Thus, low-dose methylphenidate appears to increase cell proliferation and cell survival in the hippocampus, and these effects may be mediated by increase in VEGF, TrkB, and beta-catenin. While high dose methylphenidate may initially increase neuronal proliferation, newly generated neurons are unable to survive long-term, possibly due to decrease in VEGF, TrkB and beta-catenin.

The reaction of living anions of polystyrene (PS) or poly(methyl methacrylate) (PMMA) with epibromohydrin for the synthesis of well-defined epoxy end-functionalized polymers is reported. Polyanions were reacted with an excess of epibromohydrin in tetrahydrofuran (THF) at -78°C. The functionalities of the resulting polymers were analyzed by matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS), NMR, and size exclusion chromatography (SEC). The epoxy end groups were reacted with 1,1-diphenyl- hexyllithium, and MALDI-TOF MS and NMR before and after this chemical modification were used to determine the presence of the epoxy end groups. The presence of the epoxy end group was confirmed by anionically polymerizing ethylene oxide from these epoxy end group. The formation of a block copolymer due to the epoxy end groups was proved by SEC analysis. The combined MALDI-TOF MS, 1 H NMR, and SEC results indicate that epoxy end-capped PS was obtained in quantitative yield. The method was extended to the synthesis of epoxy end-capped PMMA. With this polymer the extent of end-functionalization was high but not quantitative, with non-dimeric byproducts detected by MALDI-TOF MS.

This paper describes recent advancements of the Lightweight Integrated Solar Array and Transceiver (LISA-T) currently being developed at NASA's Marshall Space Flight Center. The LISA-T array comprises a launch stowed, orbit deployed structure on which thin-film photovoltaic (PV) and antenna devices are embedded. The system provides significant electrical power generation at low weights, high stowage efficiency, and without the need for solar tracking. Leveraging high-volume terrestrial-market PVs also gives the potential for lower array costs. LISA-T is addressing the power starvation epidemic currently seen by many small-scale satellites while also enabling the application of deployable antenna arrays. Herein, an overview of the system and its applications are presented alongside sub-system development progress and environmental testing plans.

Well-defined linear and branched polystyrenes with complex architectures (regular combs and centipedes) were characterized via on-line size exclusion chromatography (SEC), in the good solvent tetrahydrofuran and the theta solvent trans-decalin, in order to measure their radii of gyration (R g ), hydrodynamic radii (R H ), and intrinsic viscosities. Various measures of the sizes of these macromolecules were plotted as a function of the retention volume (V R ) in order to examine the validity of different universal calibration strategies for SEC. Hydrodynamic-based calibration curves were found to be universal, whereas a plot of log R g versus V R did not yield universal curves in either solvent. These findings are consistent with previously published data for linear and branched polymers in thermodynamically good solvents. In addition, good solvent data were used to derive values of the epsilon parameter relating radius of gyration-based and intrinsic viscosity-based chain shrinkage factors. Value...

The molecular weight dependence of the radii of gyration R{sub g} in a {var_theta} solvent (trans-decalin) of one regular branched comb and three regular centipede polystyrenes was studied using a gel permeation chromatography system equipped with a two-angle light scattering detector and a refractive index detector. R{sub g} in trans-decalin for each sample of particular molecular weight was about 25% smaller than that in a good solvent (tetrahydrofuran, THF). On the other hand, they are 20--40% larger than the theoretical values from the Gaussian chain model. This difference can be explained with the wormlike comb model developed by Nakamura et al. (Macromolecules 2000, 33, 8323-8328). Persistence lengths thus obtained for each sample were about half of that determined in THF solution. However, they are significantly larger than that for linear polystyrene. These results suggest that a main chain stiffening effect exists in comb polystyrenes even in a {var_theta} solvent.

Poly(acrylic acid-co-itaconic acid) copolymers containing pendent methacrylates were synthesized and used to formulate redox-initiated in situ cured glass-ionomer cements (GICs) by mixing with reactive glass fillers (Fuji II LC). Various formulations for the redox initiator were studied, and flexural strength (FS) was used as a screening tool for optimization. Effects of molecular weight (MW), grafting ratio, comonomer, polymer content in the liquid composition, powder/liquid (P/L) ratio, and aging on FS were investigated. The results show that the in situ cured GICs demonstrated higher FS (89.6–123.2 MPa), as compared to commercial Fuji II LC GIC (57.1 MPa). The optimal concentrations for redox initiators were found to be 0.15% (by weight) for K2S2O8 and 0.2% for ascorbic acid (or 0.6% for microencapsulated ascorbic acid), respectively. Effects of MW, grafting ratio, P/L ratio and polymer content in the liquid formulation were significant. During aging, the cement showed an increase in strength over 24 h and then no change for time periods up to six months. SEM analysis supports the strength data associated with the formulations. The exotherm and setting time suggest that novel redox-initiated resin-modified GICs hold promise as biocompatible and workable cement for orthopedic applications.

Polymeric phosphonate esters are an interesting class of organophosphorus polymers because both the polymer backbone and phosphorus substituents can be modified. These polymers have been prepared by ring-opening polymerizations of cyclic phosphites, stoichiometric polycondensations of dimethyl phosphonate with diols in conjunction with diazomethane treatment and by transesterification of polyphosphonate oligomers. Our initial attempts to prepare high molecular weight polymeric phosphonate esters by the transesterification methods were unsuccessful. Results indicate that the reactions of dimethyl phosphonate with diols to form polyphosphonate oligomers with only methyl phosphonate end groups are plagued by a serious side reaction that forms phosphonic acid end groups. These end groups do not participate in the transesterification reaction and limit the molecular weights of the polymers that can be obtained. The phosphonic acid end groups can be converted into reactive methyl phosphonate end groups by treatment with diazomethane, however diazomethane is explosive and the polymerization is slow. An alternative route for the production of high molecular weight polymers is the transesterification of the 1,12-bis(methyl phosphonato)dodecane, formed by the reaction of excess dimethyl phosphonate and 1,12-dodecanediol, with a Na 2 CO 3 promoter. This allows polymers with molecular weights of up to 4.5×10 4 to be prepared, and no phosphonic acid end groups are observed in these polymers. Thermal analyses of the poly(1,12-dodecamethylene phosphonate) have shown that this polymer has reasonable thermal stability (onset of thermal decomposition at 273 °C). This polymer also undergoes a cold crystallization process at 15 °C similar to that which has been observed in some polyesters, polyamides and elastomers.

The desire to field space-based telescopes with apertures in excess of 10 meter diameter is forcing the development of extreme lightweighted large optomechanical structures. Sparse apertures, shell optics, and membrane optics are a few of the approaches that have been investigated and demonstrated. Membrane optics in particular have been investigated for many years. The MOIRE approach in which the membrane is used as a transmissive diffractive optical element (DOE) offers a significant relaxation in the control requirements on the membrane surface figure, supports extreme lightweighting of the primary collecting optic, and provides a path for rapid low cost production of the primary optical elements. Successful development of a powered meter-scale transmissive membrane DOE was reported in 2012. This paper presents initial imaging results from integrating meter-scale transmissive DOEs into the primary element of a 5- meter diameter telescope architecture. The brassboard telescope successfully demonstrates the ability to collect polychromatic high resolution imagery over a representative object using the transmissive DOE technology. The telescope includes multiple segments of a 5-meter diameter telescope primary with an overall length of 27 meters. The object scene used for the demonstration represents a 1.5 km square complex ground scene. Imaging is accomplished in a standard laboratory environment using a 40 nm spectral bandwidth centered on 650 nm. Theoretical imaging quality for the tested configuration is NIIRS 2.8, with the demonstration achieving NIIRS 2.3 under laboratory seeing conditions. Design characteristics, hardware implementation, laboratory environmental impacts on imagery, image quality metrics, and ongoing developments will be presented.

Methylphenidate (MPH) is a psychostimulant that blocks reuptake of dopamine and norepinephrine via their transporters. Currently, MPH is used for the treatment of narcolepsy and is the most common ...

The Membrane Optical Imager (for) Real-time Exploitation (MOIRE) programs’ primary optics are constructed using a membrane material. Using a membrane enables the goal of the MOIRE program to launch large, greater than 10m aperture, optics while simultaneously reducing the weight of the optic. Achieving the desired performance of the membrane as an optical material is highly dependent upon the ability to control that membrane through the design and fabrication process via an understanding of the material properties of the membrane. This paper will cover the material property characterization, testing performed and lessons learned about the unique attributes of membranes, both as a material and as an optic.

Polymeric phosphonate esters have a variety of potential applications. These polymers can be prepared by the polycondensations of dimethyl phosphonate with certain diols. However, this method does not consistently yield high molecular weight polymers. NMR spectroscopy and size exclusion chromatography studies demonstrate that low molecular weights result from methyl group transfer from a methyl phosphonate end group to an alcohol. The inactive phosphonic acid end groups formed by this reaction can be converted into reactive methyl phosphonate end groups by treatment with diazomethane. This allows the preparation of polymers with number average molecular weights greater than 104 Da.

The desire to field space-based telescopes with apertures in excess of 10 meter diameter is forcing the development of extreme lightweighted large optics. Sparse apertures, shell optics, and membrane optics are a few of the approaches that have been investigated and demonstrated. Membrane optics in particular have been investigated for many years. The majority of the effort in membrane telescopes has been devoted to using reflective membrane optics with a fair level of success being realized for small laboratory level systems; however, extending this approach to large aperture systems has been problematic. An alternative approach in which the membrane is used as a diffractive transmission element has been previously proposed, offering a significant relaxation in the control requirements on the membrane surface figure. The general imaging principle has been demonstrated in 50-cm-scale laboratory systems using thin glass and replicated membranes at long f-number (f/50). In addition, a 5-meter diameter f/50 transmissive diffractive optic has been demonstrated, using 50-cm scale segments arrayed in a foldable origami pattern. In this paper we discuss Membrane Optical Imager Real-time Exploitation (MOIRE) Phase 1 developments that culminated in the development and demonstration of an 80 cm diameter, off-axis, F/6.5 phase diffractive transmissive membrane optic. This is a precursor for an optic envisioned as one segment of a 10 meter diameter telescope. This paper presents the demonstrated imaging wavefront performance and collection efficiency of an 80 cm membrane optic that would be used in an F/6.5 primary, discusses the anticipated areal density in relation to existing space telescopes, and identifies how such a component would be used in previously described optical system architectures.

Deformable mirrors using polyvinylidene fluoride (PVDF) membranes in a bimorph configuration have been previously investigated. Kratos Defense and Security Solutions, in partnership with Advanced Optical Systems, Inc. and NeXolve, Inc., have been evaluating the utility of unimorph PVDF films for fabrication of deformable mirrors. Actuation using a unimorph film is achieved by creating a gradient in the piezoelectric response of the film through a proprietary process. This eliminates the requirement to bond multiple films and improves the optical quality of the films. To assist in the development and design of the films, a multiphysics design tool has been developed by tightly integrating several commercial software packages. This tool has then been used to model the performance of the films and extract significant material parameters. This paper reports on the initial modeling results and characterization of this novel material.

The ability to fabricate 4-level diffractive structures with 1 µm critical dimensions has been demonstrated for the creation of fast (∼f/3.1 at 633 nm) Fresnel zone lenses (FZLs) with >60% diffraction efficiency into the −1 focusing order and nearly complete suppression of 0 and +1 orders. This is done using tooling capable of producing optics with 800 mm apertures. A 4-level grating fabricated in glass at 300 mm aperture is shown to have