Preparation and characterization of a polyimide nanofoam through grafting of labile poly(propylene glycol) oligomer

Preparation of a polyimide nanofoam (PI‐F) for microelectronic applications was carried out using a polyimide precursor synthesized from poly[(amic acid)‐co‐(amic ester)] and grafted with a labile poly(propylene glycol) (PPG) oligomer. Polyimide precursor was synthesized by partial esterification of poly(amic acid) (PAA) derived from pyromellitic dianhydride (PMDA) and 4,4′‐oxydianiline (ODA). The precursor was then grafted with bromide‐terminated poly(propylene glycol) in the presence of K₂CO₃ in hexamethylphosphoramide and N‐methylpyrrolidone, imidized at 200°C in nitrogen and the product was subsequently decomposed in air at 300°C to eliminate the labile PPG oligomer to produce PMDA/ODA polyimide nanofoam. Nuclear magnetic resonance spectroscopy (¹H‐NMR) and Fourier transform infrared spectroscopy (FT‐IR) techniques were used to characterize the formation of polyimide precursor and extent of grafting of PPG with polyimide. The results of thermogravimetric analysis (TGA) showed three step decomposition of nanofoam with the removal of PPG at 350°C and decomposition of polyimide at around 600°C. The polyimide nanofoams were also characterized by small angle X‐ray scattering (SAXS), field‐emission scanning electron microscopy (FE‐SEM) and transmission electron microscopy (TEM). The morphology showed nanophase‐separated structures with uniformly distributed and non‐interconnected pores of 20–40 nm in size. Dynamic mechanical analysis (DMA) indicated higher storage modulus for the foamed structure compared to the pure PI with reduction in loss tangent for the former system. Copyright © 2004 John Wiley & Sons, Ltd.     

Nitridation of V5Al8 films with NH3 by Rapid Thermal Processing (RTP)

V₅Al₈ films (thickness about 100 nm) were deposited on sapphire substrates by RF‐sputtering and nitridated with NH₃ at 600‐1250 °C (1 min) in a RTP system. The as deposited and nitridated films were investigated by ESCA (electron spectroscopy for chemical analysis), XRD (X‐ray diffraction), XRR (X‐ray reflectometry), AFM (atomic force microscopy) and SEM (scanning electron microscopy). Formation of an aluminum nitride layer at the surface and precipitation of V(Al) in the bulk was found. In the temperature regime from 600 °C to 900 °C a considerable amount of oxygen is incorporated in the aluminum nitride layer. The roughness of the surface increased with increasing temperature and at 1250 °C a partially detaching of the AlN layer could be observed.     

Preferential orientation of crystallites spatially confined in lamellar microdomains of polyethylene‐block‐[atactic poly(propylene)]

Synchrotron small angle X‐ray scattering (SAXS), wide angle X‐ray scattering (WAXS), and transmission electron microscopy were carried out for an oriented polyethylene‐block‐[atactic poly(propylene)] with a molecular weight of 1.13×10⁵ and a volume fraction of polyethylene of 0.5. Isothermal crystallization at 93°C did not destroy the pre‐formed microdomain, however, with a higher crystallization temperature, the microdomain was more heavily deformed and more crystalline lamella grew. In WAXS profiles, preferential orientation of (020) reflection peak was observed, indicating that the crystalline lamella grew in parallel with the micro domain interface.     

Morphology and structure of nylon‐2,14 single crystals from dilute solution

A perfect single crystal of nylon‐2,14 was prepared from 0.02% (w/v) 1,4‐butanediol solution by a “self‐seeding” technique and isothermal crystallization at 120 and 145 °C. The morphology and structure features were examined by transmission electron microscopy with both image and diffraction modes, atomic force microscopy, and wide‐angle X‐ray diffraction (WAXD). The nylon‐2,14 single crystal grown from 1,4‐butanediol at 145 °C inhabited a lathlike shape with a lamellar thickness of about 9 nm. Electron diffraction and WAXD data indicated that nylon‐2,14 crystallized in a triclinic system with lattice dimensions a = 0.49 nm, b = 0.51 nm, c = 2.23 nm, α = 60.4°, β = 77°, and γ = 59°. The crystal structure is different from that of nylon‐6,6 but similar to that of other members of nylon‐2Y. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1913–1918, 2002     

Synthesis,characterization and application of 3‐methyl‐1‐sulfonic acid imidazolium tetrachloroferrate as nanostructured catalyst for the tandem reaction of β‐naphthol with aromatic aldehydes and amide derivatives

3‐methyl‐1‐sulfonic acid imidazolium tetrachloroferrate {[Msim]FeCl₄} was prepared and fully characterized by fourier transform infrared spectroscopy (FT‐IR), X‐ray diffraction (XRD), thermal gravimetric analysis (TGA), differential thermal gravimetric (DTG), field emission scanning electron microscopy (FESEM), energy dispersive X‐ray analysis (EDX) and vibrating sample magnetometer (VSM) and used, as an efficient catalyst, for the tandem reaction of β‐naphthol with aromatic aldehydes and benzamide at 110 °C under solvent‐free conditions to give 1‐amidoalkyl‐2‐naphthols in high yields and very short reaction times.     

Fibrils separated from polyacrylonitrile fiber by ultrasonic etching in dimethylsulphoxide solution

A novel method for the separation of polyacrylonitrile (PAN) fibrils from fibers by ultrasonic etching in a 90 wt % aqueous dimethylsulphoxide (DMSO) solution at 75 °C ± 2 °C for 6 h with a frequency of 40 kHz is demonstrated. These fibrils with a diameter of about 450 nm were systematically investigated by field emission scanning electron microscopy (FESEM), high resolution transmission electron microscopy (HRTEM), and wide‐angle X‐ray diffraction (WAXD). It was found that the fibrils consisted of microfibrils with about 200 nm diameter, including periodic lamellae with thickness of 30–45 nm perpendicular to the fiber axis. The PAN fiber crystallinity and crystal size slightly decreased under the ultrasonic etching. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 617–619, 2010     

溶剂热微乳法合成CdS微米球

CdS microspheres were prepared by a hydrothermal microemulsion method in cyclohexane/Triton X-100/pentanol/water at 180℃. The as-prepared samples were characterized by X-ray diffraction analysis, transmission electron microscopy, electron diffraction, energy diffraction X-ray analysis and photoluminescence spectra. It was found that CdS microspheres with diameter of 1.5-2.5μm were aggregated by nanocrystals. The formation mechanism was proposed.     

Structure development in multistage stretching of PTFE films

The structure of expanded poly(tetrafluoroethylene) (ePTFE) films that were produced by uniaxial or biaxial stretching of a calendared sheet were studied by wide angle X‐ray diffraction (WAXD), small angle X‐ray scattering, differential scanning calorimetry (DSC), and scanning electron microscopy. The molecular orientation of the stretched films was analyzed by WAXD flat films and pole figures. Biaxial orientation factors were computed to interpret the level of orientation quantitatively. DSC scans showed that oriented samples exhibited two melting peaks, one at the commonly observed temperature in the range 340–345 °C and one around 380 °C. The possible causes of this high‐temperature melting peak and its relation to previously described processes is discussed. The microporous nature of the ePTFE films is also briefly discussed. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2010     

Deposition of copper‐doped iron sulfide (CuxFe1−xS) thin films using aerosol‐assisted chemical vapor deposition technique

Copper‐doped iron sulfide (Cu_xFe_1?xS, x = 0.010–0.180) thin films were deposited using a single‐source precursor, Cu(LH)₂Cl₂ (LH = monoacetylferrocene thiosemicarbazone), by aerosol‐assisted chemical vapor deposition technique. The Cu‐doped FeS thin films were deposited at different substrate temperatures, i.e. 250, 300, 350, 400 and 450 °C. The deposited thin films were characterized by X‐ray diffraction (XRD) patterns, Raman spectra, scanning electron microscopy, energy dispersive X‐ray analysis (EDX) and atomic force microscopy. XRD studies of Cu‐doped FeS thin films at all the temperatures revealed formation of single‐phase FeS structure. With increasing substrate temperature from 250 to 450 °C, there was change in morphology from wafer‐like to cylindrical plate‐like. EDX analysis showed that the doping percentage of copper increased as the substrate temperature increased from 250 to 450 °C. Raman data supports the doping of copper in FeS films. Copyright © 2010 John Wiley & Sons, Ltd.     

Effects of melt‐processing conditions on the quality of poly(ethylene terephthalate) montmorillonite clay nanocomposites

Organically modified montmorillonite was synthesized with a novel 1,2‐dimethyl‐3‐N‐alkyl imidazolium salt or a typical quaternary ammonium salt as a control. Poly(ethylene terephthalate) montmorillonite clay nanocomposites were compounded via melt‐blending in a corotating mini twin‐screw extruder operating at 285 °C. The nanocomposites were characterized with thermal analysis, X‐ray diffraction, and transmission electron microscopy to determine the extent of intercalation and/or exfoliation present in the system. Nanocomposites produced with N,N‐dimethyl‐N,N‐dioctadecylammonium treated montmorillonite (DMDODA‐MMT), which has a decomposition temperature of 250 °C, were black, brittle, and tarlike resulting from DMDODA degradation under the processing conditions. Nanocomposites compounded with 1,2‐dimethyl‐3‐N‐hexadecyl imidazolium treated MMT, which has a decomposition temperature of 350 °C, showed high levels of dispersion and delamination. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2661–2666, 2002     

The double melting behavior of a liquid crystalline polyimide derived from PMDA and 1,3‐bis[4‐(4′‐aminophenoxyl) cumyl] benzene

The double melting behavior of a thermotropic liquid crystalline polyimide was studied by means of differential scanning calorimetry (DSC), polarized light microscopy (PLM), transmission electron microscopy (TEM), wide‐angle X‐ray diffraction (WAXD), and small‐angle X‐ray scattering (SAXS). This liquid crystalline polyimide exhibited a normal melting peak around 278 °C and transformed into a smectic A phase. The smectic A phase changed to nematic phase upon heating to 298 °C, then became isotropic melt around 345 °C. The samples annealed or isothermally crystallized at lower temperature showed double melting endotherms during heating scan. The annealing‐induced melting endotherm was highly dependent on annealing conditions, whereas the normal melting endotherm was almost not influenced by annealing when the annealing temperature was low. Various possibilities for the lower melting endotherm are discussed. The equilibrium melting points of both melting peaks were extrapolated to be 283.2 °C. Combined analytical results showed that the double melting peaks were from the melting of the two types of crystallites generated from two crystallization processes: a slow and a fast one. Fast crystallization may start from the well‐aligned liquid crystal domains, whereas the slow one may be from the fringed or amorphous regions. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 3018–3031, 2000     

Rational Design of Ag/TiO2 Nanosystems by a Combined RF‐Sputtering/Sol‐Gel Approach

The present work is devoted to the preparation of Ag/TiO₂ nanosystems by an original synthetic strategy, based on the radio‐frequency (RF) sputtering of silver particles on titania‐based xerogels prepared by the sol–gel (SG) route. This approach takes advantage of the synergy between the microporous xerogel structure and the infiltration power characterizing RF‐sputtering, whose combination enables the obtainment of a tailored dispersion of Ag‐containing particles into the titania matrix. In addition, the system′s chemico‐physical features can be tuned further through proper ex situ thermal treatments in air at 400 and 600 °C. The synthesized composites are extensively characterized by the joint use of complementary techniques, that is, X‐ray photoelectron and X‐ray excited Auger electron spectroscopies (XPS, XE‐AES), secondary ion mass spectrometry (SIMS), glancing incidence X‐ray diffraction (GIXRD), field emission scanning electron microscopy (FE–SEM), transmission electron microscopy (TEM), electron diffraction (ED), high‐angle annular dark field scanning TEM (HAADF–STEM), energy‐filtered TEM (EF–TEM) and optical absorption spectroscopy. Finally, the photocatalytic performances of selected samples in the decomposition of the azo‐dye Plasmocorinth B are preliminarily investigated. The obtained results highlight the possibility of tailoring the system characteristics over a broad range, directly influencing their eventual functional properties.     

Synthesis,characterization and application of nano‐CoAl2O4 as an efficient catalyst in the preparation of hexahydroquinolines

In this work, nano‐CoAl₂O₄ was prepared and characterized by FT‐IR, energy dispersive X‐ray analysis (EDX), X‐ray diffraction patterns (XRD), scanning electron microscopy (SEM), vibrating sample magnetometer (VSM) and transmission electron microscopy (TEM). Nano‐CoAl₂O₄ was applied for the synthesis of hexahydroquinoline derivatives by the condensation reaction between ethyl acetoacetate, dimedone and various aldehydes. These reactions were carried out at 80 °C under solvent‐free conditions.     

Synthesis and Characterization of Core‐Shell Selenium/Carbon Colloids and Hollow Carbon Capsules

A novel Se/C nanocomposite with core‐shell structures has been prepared through a facile one‐pot microwave‐induced hydrothermal process. The new material consists of a trigonal‐Se (t‐Se) core and an amorphous‐C (a‐C) shell. The Se/C composite can be converted to hollow carbon capsules by thermal treatment. These products were characterized by transmission electron microscopy (TEM), powder X‐ray diffraction (XRD), scanning electron microscopy (SEM), selected area electron diffraction (SAED), energy‐dispersive X‐ray (EDX) spectroscopy, and X‐ray photoelectron spectroscopy (XPS).     

Photo and Thermal Cured Silicon‐Containing Diethynylbenzene Fibers via Melt Electrospinning with Enhanced Thermal Stability

An inorganic–organic hybrid material, poly(dimethylsilylene ethynylenephenyleneethynylene) (PMSEPE), was synthesized in a mild condition and its microfiber was successfully produced by melt electrospinning. The electrospinning parameters, which affected the morphology and diameter of fibers, were well investigated. To maintain the fiber structure at thermal cured temperature (above melting point), the PMSEPE fibers were enhanced via thiol‐yne photo polymerization. Followed by the thermal curing reaction, the heat‐resistance and mechanical properties of fibers were enhanced. The mechanism of two‐step curing was explored and confirmed by means of Fourier transform infrared, differential scanning calorimetry, and X‐ray photoelectron spectroscopy (XPS). Thermaogravimetric analysis and scanning electron microscopy results show that after carbonization at 800 °C, the two‐step cured fibers had only a small weight loss (20%) and the fibers can still maintain the original morphology. Moreover, the two‐step cured fiber exhibited a high tensile strength (55.4 MPa) and a small elongation at break (0.02%). All the results indicate that the fibers could be applied as fiber‐reinforced materials. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 2815–2823     

Effects of Halogen Bonding in Chemical Activity of Lead(II) Electron Pair: Sonochemical Synthesis,Structural Studies,and Thermal Analysis of Novel Lead(II) Nano Coordination Polymer

The nanoflower lead(II) coordination compound {[Pb(phen)(μ‐CH₃COO)][PF₆]}_n ( 1 ) (phen = 1,10‐phenanthroline) was synthesized by a sonochemical method. The nanostructure was characterized by using scanning electron microscopy (SEM), X‐ray powder diffraction, elemental analysis, and thermal analysis. The single‐crystal X‐ray structure shows that the overall structure of 1 is a 1D coordination polymer. Complex 1 has a bridging acetate pathway. Three halogen bonds observed in the structure and the strong halogen bonding of F–Pb causes chemical activity of the lead electron pair. This is further extended into a 3D supramolecular structure by weak π–π intermolecular interactions. The coordination number of the lead(II) ions is six, resulting in PbN₂O₄. PbO nanoparticles were obtained by the thermolysis of 1 at 180 °C with oleic acid as a surfactant. The morphology and size of the prepared PbO nanoparticles were further observed using scanning electron (SEM) and transmission electron microscopy (TEM), and were analyzed by X‐ray photoelectron spectroscopy (XPS).     

Preparation of amphiphilic networks by Diels-Alder reactions between oligo(butyl methacrylate) with furan end-groups and a poly(ethylene oxide-co-acetylenedicarboxylate)

A butyl methacrylate oligomer with furan end-groups was synthesized by ozonolysing a poly(butyl methacrylate-co-butadiene) latex. The end-groups of this oligomer were amidated with aminomethylfuran to give a coagulated mass of derivatized oligomers. This furan functional oligomer was then mixed with poly(ethylene oxide-co-acetylenedicarboxylate) and heated at 60°C or 125°C. The material cured at 125°C was found to contain a higher gel fraction (55 wt.-%) than that cured at 60°C (30 wt.-%).     

Origin of double melting behavior of poly(p‐phenylene succinate)

The origin of double melting behavior of poly(p‐phenylene succinate) (PPSc) was investigated by differential scanning calorimetry (DSC) and wide‐angle X‐ray diffraction. As‐polymerized PPSc showed two melting peaks: the low melting (LM) and high melting (HM) peaks at 286 and 311 °C, respectively. When PPSc was annealed at 270 °C, the LM peak constantly shifted toward higher temperatures and grew in its area with annealing time, and eventually merged into the HM peak located at 308 °C. X‐ray diffractograms of PPSc annealed at 270 °C became sharper with increasing the annealing time while the peak positions did not change. The X‐ray diffractograms obtained from the LM and the HM peak exhibited the same diffraction peaks. It was concluded from these results that the double melting behavior of PPSc is due to the distribution of crystals having the same crystal form but differing in size and perfection. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1868–1871, 2000     

Wet‐Chemical Synthesis of Nanoscale Iron Boride,XAFS Analysis and Crystallisation to α‐FeB

The reaction of lithium tetrahydridoborate and iron bromide in high boiling ether as reaction medium produces an ultrafine, pyrophoric and magnetic precipitate. X‐ray and electron diffraction proved the product to be amorphous. According to X‐ray absorption fine structure spectroscopy (XAFS) the precipitate has FeB structure up to nearly two coordination spheres around an iron absorber atom. Transmission electron microscopy (TEM) confirms the ultrafine powder to be nanoscale. Subsequent annealing at 450 °C causes the atoms to arrange in a more distinct FeB structure, and further thermal treatment to 1050 °C extends the local structure to the α‐modification of FeB. Between 1050 °C and 1500 °C α‐FeB is transformed into β‐FeB.     

Flame retardant properties and mechanism of an efficient intumescent flame retardant PLA composites

The charring agent (CNCA‐DA) containing triazine and benzene rings was combined with ammonium polyphosphate (APP) to form intumescent flame retardant (IFR), and it was occupied to modify polylactide (PLA). The flame retardant properties and mechanism of flame retardant PLA composites were investigated by the limited oxygen index (LOI), vertical burning test (UL‐94), thermogravimetric analysis, microscale combustion calorimetry, scanning electron microscopy, laser Raman spectroscopy analysis and X‐ray photoelectron spectroscopy. The analysis from LOI and UL‐94 presented that the IFR was very effective in flame retardancy of PLA. When the weight ratio of APP to CNCA‐DA was 3:1, and the IFR loading was 30%, the IFR showed the best effect, and the LOI value reached 45.6%. It was found that when 20 wt% IFR was loaded, the flame retardancy of PLA/IFR still passed UL‐94 V‐0 rating, and its LOI value reached 32.8%. The microscale combustion calorimetry results showed that PLA/IFR had lower heat release rate, total heat release, and heat release capacity than other composites, and there was an obvious synergistic effect between APP and CNCA‐DA for PLA. IFR containing APP/CNCA‐DA had good thermal stability and char‐forming ability with the char residue 29.3% at 800°C under N₂ atmosphere. Scanning electron microscopy observation further indicated that IFR could promote forming continuous and compact intumescent char layer. The laser Raman spectroscopy analysis and X‐ray photoelectron spectroscopy analysis results indicated that an appropriate graphitization degree of the residue char was formed, and more O and N were remained to form more cross‐linking structure. Copyright © 2016 John Wiley & Sons, Ltd.