Studies on Polybenzoxazine/Capron PK4/octakis(dimethylsiloxypropylglycidylether) Silsesquioxane Nanocomposites for Radiation Resistant Applications

Polymeric materials can erode when exposed to the radiation environment that includes atomic oxygen (AO), ultraviolet (UV) ionizing radiation, and ultrahigh vacuum (UHV). Many studies have been devoted to develop polymeric materials that can withstand decades of exposure on radiation. In this connection an attempt has been made to develop polyhedral oligomeric silsesquioxane (POSS) reinforced capron PK₄ (CPL) modified polybenzoxazine nanocomposites in the present work and to assess their ability to resist radiation for a prolonged period. Varying weight percentages of (0, 1, 3, and 5 wt%) POSS were reinforced in to 1:1 (w/w) PBZ/CPL copolymerization through chemical ring opening polymerization. The POSS reinforced PBZ/CPL nanocomposites have been studied their tensile strength and morphological behavior before and after exposure of UV irradiation. Data resulted from the studies indicated that the neat PBZ-CPL has significantly eroded after UV exposure, whereas POSS reinforced PBZ/CPL composites have eroded only an insignificant extent and the value of tensile properties are reduced to a small extent. The POSS reinforced nanocomposites during exposure under UV radiation undergo changes on the surface and lead to the formation of silica (Si-O-Si) passivation layer. The formation of silica layer protects (act as inert layer) from further erosion of the composites and was ascertained from SEM images. Data obtained from thermal and dielectric studies indicate that thermal stability and dielectric behavior of composites were appreciably improved when compared with those of neat PBZ/CPL matrix.     

Antiadhesion elastomer seal coatings for UV and atomic oxygen protection

Radiation blocking sunscreen coatings have been developed for the protection of elastomer seals used in low‐Earth‐orbit (LEO). The coatings protect the seals from ultraviolet (UV) radiation and atomic oxygen (AO) damage. The coatings were developed for use on NASA docking seals. Docking seal damage from the UV and AO present in LEO can constrain mission time‐line, flight mode options, and increases risk. A low level of adhesion is also required for docking seals so undocking push‐off forces can be low. The coatings presented also mitigate this unwanted adhesion. Greases with low collected volatile condensable materials (CVCM) and low total mass loss (TML) were mixed with slippery and/or UV blocking powders to create the protective coatings. Coatings were applied at rates up to 2 mg/cm². Coated seals were exposed to AO and UV in the NUV (near‐UV) and UV‐C wavelength ranges (300 to 400 nm and 254 nm, respectively). Ground based ashers were used to simulate the AO of space. The Sun's UV energy was mimicked assuming a nose forward flight mode, resulting in an exposure rate of 2.5 MJ/m² day. Exposures between 0 and 147 MJ/m² (UV‐C) and 245 MJ/m² (NUV) were accomplished. The protective coatings were durable, providing protection from UV after a simulated docking and undocking cycle. The level of protection begins to decline at coverage rates less than 0.9 mg/cm². The leakage of seals coated with Braycote + 20%Z‐cote ZnO sunscreen increased by a factor of 40 after moderate AO exposure; indicating that this coating might not be suitable due to AO intolerance. Seals coated with DC‐7–16.4%Z‐cote ZnO sunscreen were not significantly affected by combined doses of 2 × 10²¹ atoms/cm² AO with 73 MJ/m² UV‐C. Unprotected seals were significantly damaged at UV‐C exposures of 0.3 MJ/m² and DC‐7–16.4%Z‐cote coated seals were undamaged at all exposures up to the limits tested thus far which were 147 MJ/m² UV‐C and 245 MJ/m² NUV. The coatings decreased adhesion sufficiently for docking seals at temperatures equal to or greater than ?8°C thus offer a simple and inexpensive way to mitigate adhesion. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41662.     

A near edge X-ray absorption fine structure study of oxidized single crystal and polycrystalline diamond surfaces

The influence of oxidizing environments on single crystal diamond and polycrystalline chemical vapor deposited CVD diamond films was studied using the near edge X-ray absorption fine structure (NEXAFS) pre-edge region in both bulk and surface sensitive modes. The NEXAFS of (100) oriented single crystal diamond was measured following (i) exposure to a microwave (MW) hydrogen plasma, (ii) annealing to 1000 °C, (iii) exposure of the as annealed surface to H₂O, and (iv) exposure of the as annealed surface to O₂. From these measurements particular surface bonding configurations have been assigned to features in the pre-edge structure. The NEXAFS of microcrystalline CVD diamond films was studied following different oxidative treatments using (i) a thermal atomic oxygen (AO) environment, (ii) a hyperthermal (5 eV) AO source, and (iii) an RF oxygen plasma exposure. The nature of the surface layer was found to be different for differently oxidized surfaces. These treatments were carried out as part of a study of CVD diamond durability in the low Earth orbit space environment.     

Effects of atomic oxygen and ultraviolet in low earth orbit on low surface energy polymer film

Effects of atomic oxygen (AO) and ultraviolet (UV) on a polymer film with surface energy of 8.0 mJ m⁻² derived from poly(1H,1H‐perfluorooctyl methylacrylate) were investigated by contact angle measurements, X‐ray photoelectron spectroscopy, and atomic force microscope. The film was exposed to AO with a flux of 6.73 × 10¹⁵ atoms cm⁻² s⁻¹ and UV with intensity of 15.8 mW cm⁻² at wavelength of 200–450 nm, respectively. It is found that AO and UV irradiation resulted in the reduction of film thickness, change of wettability, and increase of surface energy, and AO exhibited more serious effects than UV on the fluorinated polymer film. Reduced rate of thickness of the film was almost proportional to the AO exposure time. After exposed to AO and UV irradiation, the surface energy of the film increased to 17.3 mJ m⁻² and 11.0 mJ m⁻², respectively. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Tribological properties of the polyacrylate/PTFE coating modified by POSS in the space environment

The irradiation conditions in the low earth orbit (LEO) severely inhibit the development of polymeric materials for solid lubrication coatings used on the external surfaces of spacecraft. To solve the problem, octavinyl polyhedral oligomeric silsesquioxanes (OvPOSS) were covalently grafted onto poly(methyl/butyl methacrylate) composites (PMB). The results showed that the appropriate incorporation of OvPOSS (10 wt %) significantly reduced the friction coefficient and improved the wear resistance of the OvPOSS/PMB composite coatings. Furthermore, the impact of OvPOSS on the tribological properties of PMB/polytetrafluoroethylene (PTFE) lubrication coatings in the space environment was investigated. In particular, the degradations, mass losses, surface morphologies, and chemical compositions of POSS/PMB/PTEF composite coatings were characterized under ultraviolet (UV), electric irradiation (EI), and atomic oxygen (AO). The results indicated that OvPOSS provides numerous Si O Si bonds in the polymer matrix that improve the resistance to UV and EI. Besides, a passivating SiO₂ layer was formed to prevent further erosion and degradation of the underlying PMB and PTFE components during AO irradiation. Particularly, the wear resistance of OvPOSS/PMB/PTFE coatings under AO irradiation increased significantly compared with the pristine PMB/PTFE coating. Overall, our results indicate that POSS-containing composites are a good prospective material for space application in the LEO. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48730.     

Superior energy storage performance of all-inorganic flexible antiferroelectric-insulator multilayer thin films

In this work, we develop an all-inorganic flexible capacitor films that by growing antiferroelectric Pb_0.94(Li_0.5Al_0.5)_0.06ZrO₃ (PLAZO) and insulating Al₂O₃ (AO) layer by layer on the flexible mica substrates. The results show that the low-annealing temperature below 600°C endows the PLAZO films to have low polarization loss and high breakdown strength, conversely, the high-annealing temperature above 650°C gives rise to large maximum polarization at the expense of breakdown strength. The insulating AO layers are introduced to reconcile the polarization and breakdown strength, achieving a remarkable improvement in the energy storage density of 41.78 J/cm³ with an efficiency of 91.2% in the AO/PLAZO/AO/PLAZO/AO (APAPA) multilayer films, which can be attributed to the significant improvement in breakdown strength and suppression of polarization loss by introducing AO insulator layer. Moreover, the energy storage performance of the APAPA flexible thin film capacitors possesses excellent frequency stability as well as bending cyclic endurance.     

UV degradation of clay‐reinforced polypropylene nanocomposites

The aim of this work is to experimentally characterize the UV‐degradation process at both the surface and at different layers across the thickness of injection‐molded polypropylene (PP) matrix containing different amounts of nanosized montmorillonite (MMT) clay particles. These nanocomposite materials have been exposed to UV irradiations (λ = 320 nm) at different preset temperatures (25, 45, and 65°C) in the presence of oxygen and during different exposure times. The extent of such process at these layers was determined using both the FTIR spectroscopy and the wide‐angle X‐ray diffraction analyses. The micromechanical properties across the thickness have been characterized using the nanoindentation technique. The obtained results have indicated that the UV‐degradation process for the nanocomposite materials is much more intense than the one observed for the neat PP. Moreover, it has been noted that such degradation process is not uniform across the thickness of the exposed materials. Results obtained from the X‐ray analysis have shown an increase of the crystallinity of the polymer molecules at only the external surface of the exposed materials. This was confirmed using the nanoindentation test as an increase of the Young's modulus at this layer was noted. POLYM. ENG. SCI., 56:469–478, 2016. © 2016 Society of Plastics Engineers     

Damage behavior of atomic oxygen on zirconium carbide coating modified carbon/carbon composite

Zirconium carbide (ZrC) components were induced as coating modification on carbon/carbon (C/C). These ZrC–C/C specimens were investigated after atomic oxygen (AO) exposure for different assessment times, low earth orbit (LEO) ground-based environmental simulator was employed. The results indicate that ZrO₂ is the major production generated by the AO chemical reaction with the ZrC coating. Upon further exposure to AO, the production of ZrO₂ would drop off, then exfoliate easily, due to the mechanical impacting effect. Then the exposed graphite matrix and carbon fiber get corroded. Amorphous diamond-like carbon (DLC) is detected by X-ray photoelectron spectroscopy during AO exposure. Bending strength performance increased by 25% under AO exposure at first 10 h, then dropped by 52.1% from 10 h to 30 h of AO exposure. The AO damage mechanisms of ZrC–C/C composites are revealed.     

Ultraviolet photodetectors based on ZnO nanorods-seed layer effect and metal oxide modifying layer effect

Pt/ZnO nanorod (NR) and Pt/modified ZnO NR Schottky barrier ultraviolet (UV) photodetectors (PDs) were prepared with different seed layers and metal oxide modifying layer materials. In this paper, we discussed the effect of metal oxide modifying layer on the performance of UV PDs pre- and post-deposition annealing at 300°C, respectively. For Schottky barrier UV PDs with different seed layers, the MgZnO seed layer-PDs without metal oxide coating showed bigger responsivity and larger detectivity (D _λ*) than those of PDs with ZnO seed layer, and the reason was illustrated through energy band theory and the electron transport mechanism. Also the ratio of D ₂₅₄* to D ₅₄₆* was calculated above 8 × 10² for all PDs, which demonstrated that our PDs showed high selectivity for detecting UV light with less influence of light with long wavelength.     

Digital light processing of SiC ceramic from allylhydridopolycarbosilane with limited acrylate monomers

Digital light processing of ceramic precursor was used to prepare SiC rich ceramic parts in this study. In order to achieve appropriate light curing rate, the ceramic precursor allylhydropolycarbosilane (LHBPCS) was mixed with acrylate monomers tripropylene glycol diacrylate and trimethylolpropane triacrylate. The content of acrylate monomers was optimized to increase the ceramic yield and reduce the shrinkage during pyrolysis. According to the results of thermogravimetric analysis and photolithography experiment, 15 wt% acrylate monomers was appropriate. 330 mJ/cm² UV irradiation dose was selected for every layer with a thickness of 25 μm, and green bodies with different shapes were successfully printed. During pyrolysis, these printed parts changed from transparent yellow to black accompanying uniform shrinkage. At 1000 °C, the shrinkage was 24.0–26.0%, and crack-free SiC rich ceramic parts with density of 2.11 g/cm³ and chemical formula of SiC_1.31O_0.26 were obtained.     

Atomic oxygen erosion resistance of titania–polyimide hybrid films derived from titanium tetrabutoxide and polyamic acid

A series of polyimide/titania (PI/TiO₂) hybrid films have been successfully synthesized based on titanium tetrabutoxide (Ti(OEt)₄), 3,3′,4,4′‐bezonphenone tetracarboxylic dianhydride (BTDA), 4,4′‐oxydianiline (ODA), and 1,3‐bis(aminopropyl) tetramethyldisiloxane (APrTMOS) by a sol–gel process. The atomic oxygen (AO) exposure tests were carried out using a ground‐based AO effects simulation facility. The chemical structure of PI/TiO₂ films was characterized by Fourier transform‐infrared (FT‐IR) spectroscope before and after AO exposure. The glass transition temperature (T_g) and mechanical properties were examined by dynamic mechanical analysis (DMA) and universal mechanical testing machine, respectively. The tensile strength and elongation of the hybrid film decreased with the increase of TiO₂ content, whereas the T_g increased with the increase of TiO₂ content. The effects of TiO₂ content on the morphology and structure evolvement of PI/TiO₂ hybrid films were also investigated using field emission scanning electron microscopy (FE‐SEM) and X‐ray photoelectron spectroscope (XPS), respectively. The results indicated that a TiO₂‐rich layer resulting from the Ti(OEt)₄ formed on the PI film after AO exposure, which decreased the mass loss rate and obviously improved the AO resistance of PI films. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Hydrogenated nitrile butadiene rubber and hindered phenol composite. II. Characterization of hydrogen bonding

This article reports on the relationship between the variation of hydrogen bonding and macroscopic properties of composites composed of hydrogenated nitrile butadiene rubber (HNBR) and 3,9‐bis {1,1‐dimethyl‐2 [β‐(3‐tert‐butyl‐4‐hydroxy‐5‐methylphenyl) propionyloxy] ethyl}‐2,4,8,10‐tetraoxaspiro [5,5]‐undecane (AO‐80). Hydrogen bonding of the composites was studied by Fourier‐transform infrared (FT‐IR) and ultraviolet (UV) spectroscopies. FT‐IR spectra at room temperature revealed that the stretching vibration peak of O? H and C?O of AO‐80 red shifted with increasing AO‐80 content, whereas that of C≡N of HNBR blue shifted only when the AO‐80 content exceeded 10 parts per 100 resin (phr). At elevated temperatures, the shift was the opposite for C?O and C≡N bands resulting from hydrogen bonding dissociation. In the UV spectra, the E₂ band of benzene ring of AO‐80 exhibited two peaks differing in shape. POLYM. ENG. SCI., 2011. © 2010 Society of Plastics Engineers     

Effects of compaction and UV exposure on performance of acrylate/glass‐fiber composites cured layer by layer

With an aim to reducing manufacturing costs, in general and specifically to provide a solution to the thick laminate curing depth issue for composite materials, UV curing technology was combined with a fiber placement process to fabricate acrylate/glass‐fiber composites. A novel layer‐by‐layer UV in situ curing method was employed in this article and interlaminar shear strength (ILSS) tests and SEM were used to evaluate the effect of processing parameters, including compaction force and UV exposure dose, on ILSS. The SEM images from short‐beam strength test samples and the results of ILSS showed that the fibers' distribution was uniform in the cured matrix resin resulting from the compaction forces and that beneficially influenced the ILSS of the composite greatly. However, the matrix resin produced large shrinkage stresses when it reached a high degree of conversion (DC) in one‐step, which resulted in poor interlaminar adhesion. In addition, the fast curing speed of UV on the composite resulted in poor wetting between fiber and resin, and accordingly resulted in lower ILSS. To overcome these problems and obtain high ILSS value composites, an optimized compaction force and UV exposure dose were determined experimentally. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Modification of cotton,rayon, and silk with urethane acrylate under ultraviolet radiation

Ten different formulations were developed with Ebcryl 264, a urethane acrylate in combination with other monofunctional monomers in the presence of some additives and coadditives. Thin films prepared from these formulations under ultraviolet (UV) radiation were characterized. Natural fibers such as cotton, rayon, and silk were treated with the formulations and cured under UV radiation. Their physical and mechanical properties were studied. It was found that the tensile strength (TS) of cotton, rayon, and silk was significantly increased as a result of this treatment under UV radiation (TS_cotton = 150%, TS_rayon = 30%, and TS_silk = 40%). Elongation of cotton and silk increased to 380 and 50%, respectively. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 63: 1703–1711, 1997     

Synthesis and photoconductivity study of phthalocyanine polymers. III. PVK-CuPC(NO2)2

Cu-dinitro-diamine phthalocyanine was synthesized, the corresponding diazonium salt was reacted with vinylcarbazole (VK), and a novel polyvinylcarbazole (PVK) -bonded CuPc(NO₂)₂ ( I ) was synthesized. The chemical structure of polymer ( I ) is identified by elemental analysis and IR and UV / VIS spectroscopy. Polymer ( I ) contains about 21 mol % CuPc(NO₂)₂ rings that are covalently bonded to PVK. Polymer ( I ) shows good pho-toconductivity, which is much better than that of the corresponding phthalocyanine monomers. The influence of the interface layer and the charge-transportation material on the photoconductivity of polymer ( I ) is also discussed. © 1993 John Wiley & Sons, Inc.     

Shape memory polymers based on uniform aliphatic urethane networks

Aliphatic urethane polymers have been synthesized and characterized, using monomers with high molecular symmetry, to form amorphous networks with very uniform supermolecular structures, which can be used as photo‐thermally actuable shape memory polymers (SMPs). The monomers used include hexamethylene diisocyanate (HDI), trimethylhexamethylenediamine (TMHDI), N,N,N′,N′‐tetrakis(hydroxypropyl)ethylenediamine (HPED), triethanolamine (TEA), and 1,3‐butanediol (BD). The new polymers were characterized by solvent extraction, NMR, XPS, UV/VIS, DSC, DMTA, and tensile testing. The resulting polymers were found to be single phase amorphous networks with very high gel fraction, excellent optical clarity, and extremely sharp single glass transitions in the range of 34–153°C. Thermomechanical testing of these materials confirms their excellent shape memory behavior, high recovery force, and low mechanical hysteresis (especially on multiple cycles), effectively behaving as ideal elastomers above T_g. We believe these materials represent a new and potentially important class of SMPs, and should be especially useful in applications such as biomedical microdevices. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Hydrophilization of silicone–urea copolymer surfaces by UV/ozone: Influence of PDMS molecular weight on surface oxidation and hydrophobic recovery

Hydrophilization of polydimethylsiloxane–urea copolymer (PSU) surfaces and the extent of hydrophobic recovery were investigated as a function of; (i) UV/ozone (UV/O) exposure time, (ii) the aging period after UV/O exposure, (iii) sample preparation method, and (iv) polydimethylsiloxane (PDMS) soft segment molecular weight of the copolymer (1500, 3000 and 11,000 g/mol). All copolymers had a constant urea hard segment content of 15% by weight. Samples were prepared by three different methods, which were; solution casting, spin-coating and electrospinning. XPS spectra clearly showed transformation of PDMS into SiO₂ and sub-oxides, which increased gradually with increasing UV/O exposure time. XPS and ATR-FTIR measurements also revealed that the copolymer based on PDMS-11000 displayed the highest amount of SiO₂ formation and overall surface modification. Static water contact angle values of the spincoated silicone–urea copolymer films decreased significantly from 110° to 43° after 3 h of UV/O exposure. Interestingly, the hydrophobicity of the electrospun fibers was retained under similar UV/O exposure conditions, most probably due to the preserved surface roughness. Hydrophobic recovery was evaluated after 2 months of storage at ambient conditions. The slowest recovery was observed for spin-coated copolymer film based on PDMS-11000, due to higher amount of surface oxidation and formation of a thicker SiO₂ barrier layer.     

Synthesis and cationic photopolymerization of fluorine‐containing vinyl ether monomers for the hydrophobic films

Fluorine‐containing vinyl ether monomer is a combination of UV‐curing technology and low surface energy materials. In this article, a type of fluorine‐containing vinyl ether monomer was synthesized by the reaction of fluorinated alcohols, hexafluorobenzene, 2‐vinyloxy ethanol, and sodium hydride. These monomers exhibit low viscosity and good fluidity. The effect of the fluorine content of the monomers on their UV‐curing behavior was monitored by photo‐differential scanning calorimetry. The photo‐polymerization process was efficient because the double‐bond conversed sufficiently (>85%) and the curing rate was fast (<20 s). In addition, the surface energy of homopolymer and copolymer films was researched. The surface free energy was very low and could even reach 0.92 mJ m^?2. The low surface energy was due to high fluorine content and the diffusion of uncured monomers, which was on the basis of X‐ray photoelectron spectroscopy data and observed conversions. The structure of homopolymers and copolymers was one of the most important influences on the surface free energy and the thermal properties. The copolymers exhibited better thermal stability than the homopolymers. All of these results demonstrated that these monomers are suitable for a wide range of practical applications such as UV coatings, UV inks, and photoresists. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41019.     

Synthesis and characterization of imine‐coupled polyphenols containing carbazole units

Imine coupled phenolic monomers containing carbazole unit were synthesized in four steps. The monomers were polymerized via oxidative polycondensation by air as oxidant in an aqueous alkaline medium at 50°C. The structures of compounds were confirmed by ultraviolet–visible (UV–vis), Fourier transform infrared, and ¹H‐ and ¹³C‐NMR techniques. The conductivity measurements of these polymers were made by the four‐point probe technique and iodine was used as doping agent. The highest occupied molecular orbital, the lowest unoccupied molecular orbital, and electrochemical and optical band gap values were calculated by the results of the UV–vis and the cyclic voltammetry measurement, respectively. The number‐average molecular weight, weight‐average molecular weight, and polydispersity index values were determined by the size exclusion chromatography technique. Also, thermal behavior of these polymers was determined by thermogravimetric/differential thermal analysis measurements in a N₂ atmosphere between 20 and 1000°C. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Synthesis of magnetic nanocomposite microparticles for binding of chlorinated organics in contaminated water sources

In this work, the development of novel magnetic nanocomposite microparticles (MNMs) via free radical polymerization for their application in the remediation of contaminated water is presented. Acrylated plant-based polyphenols, curcumin multiacrylate (CMA) and quercetin multiacrylate (QMA), were incorporated as functional monomers to create high affinity binding sites for the capture of polychlorinated biphenyls (PCBs), as a model pollutant. The MNMs were characterized by Fourier transform infrared spectroscopy, thermogravimetric analysis, scanning electron microscopy, dynamic light scattering, and UV–visible spectroscopy. The affinity of these novel materials for PCB 126 was evaluated and fitted to the nonlinear Langmuir model to determine binding affinities (K_D). The results suggest the presence of the polyphenolic moieties enhances the binding affinity for PCB 126, with K_D values comparable to that of antibodies. This demonstrates that these nanocomposite materials have promising potential as environmental remediation adsorbents for harmful contaminants.