Observation of latent tracks formed by heavy ion irradiation in poly(methyl methacrylate)

The irradiation effect in poly(methyl methacrylate) changed from main‐chain scission to crosslinking, depending on the stopping powers of the Au and Xe ions irradiated with high stopping powers. The latent ion tracks, including an end of the ion range in the polymer, were observed clearly by field emission and atomic force microscopies. Additionally, it was also observed that a crosslinked structure (formed by nuclear stopping) existed across an end of the ion range calculated by a Transport of Ion in Matters code, and it was different from that formed by electronic stopping. The nuclear stopping of the heavy ions can play an important role around the end of the ion range in the polymer. © 2001 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 757–762, 2001     

Finite difference modeling of the gas transport process in glassy polymers

Finite difference modeling has been used to predict the results of gas transport experiments for a concentration-dependent diffusion coefficient. Experiments on the transport of CO₂ in poly(ethylene terephthalate) and poly(ethylene naphthalate) had previously shown a difference between the effective diffusion coefficients for absorption and desorption runs of a double-sided experiment, but this effect had not been seen for single-sided experiments. The finite difference calculations show that such results are to be expected, and the parameters included in the models that attempt to describe the diffusion process in glassy polymers, such as the dual-mode model, and which lead to concentration-dependent diffusion coefficients, can be found by fitting the experimental data for the double-sided experiment using finite difference modeling. The dependence of the effective diffusion coefficient on pressure for the single-sided experiment can be correctly predicted using results from the double-sided experiment for an identical sample. © 1996 John Wiley & Sons, Inc.     

Microstructural evolution of protective La–Cr–O films studied by transmission electron microscopy

Transmission Electron Microscopy (TEM) and Electron Energy Loss Spectroscopy (EELS) were performed to study the microstructural evolution of La–Cr–O thin films deposited by radio frequency (RF)-magnetron sputtering on stainless steel substrates. Chromium L edges and oxygen K edges are analyzed to determine the valence states of the chromium and elucidate the phase evolution of the thin film. The as-deposited amorphous thin film crystallized to LaCrO₄ and finally transformed to the LaCrO₃ stable phase during annealing at 800°C. An intermediate Cr/Mn oxide layer was formed in all annealed samples. The thickness of this oxide layer stabilizes after 700°C, which indicates that the LaCrO₃ thin film plays a role in inhibiting the growth of an oxide layer on the metal surface.     

Recovery as a measure of oriented crystalline structure in poly(ether ester)s based on poly(ethylene oxide) and poly(ethylene terephthalate) used as shape memory polymers

Poly(ether ester)s consisting of poly(ethylene oxide) and poly(ethylene terephthalate) segments, EOET copolymers, could be used as shape memory polymers (SMP). Crystalline structural characters of the copolymers during the memory process were investigated by dynamic mechanical analysis, differential scanning calorimeter, wide-angle X-ray diffraction, polarizing microscopy, and recovery measurements. PEO crystals in stretched EOET copolymer preferentially oriented along fiber axis or stretch direction. During stretching, the structure of the copolymer undertake a transformation from spherulite to fiber, resulting in a crystalline morphology similar to shish-kebab, and recovery properties of stretched EOET samples were dependent on as-described crystalline structural characters that can be influenced by draw ratio. Driving forces for contraction come from the oriented chains, and only oriented or extended chains can be contributive to the recovery of deformation; these extended chains involve both crystalline and amorphous segments. The recovery process in shape memory behavior was noticed to be deorientation of oriented chains due to thermodynamic entropy effect, and was divided into three stages. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 101–112, 1999     

Electron microscopy of high‐pressure crystallized poly(ethylene terephthalate)

The high‐pressure crystallized poly(ethylene terephthalate) samples were investigated with scanning electron microscopy. The striation appearance, which is the most common feature of polymer extended‐chain crystals, was clearly observed. Poly(ethylene terephthalate) extended‐chain crystals with thickness up to 17 m were obtained at high pressure. Fibrous crystals were also formed at high pressure. The fracture behaviors, which affected the exposure of the striations, were also discussed. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1612–1616, 2000     

Structural features of crystallized poly(ethylene terephthalate) polymers

Polyethylene terephthalate (PET) is a widely used polymeric material. In this work, the microstructural features before and after the solid‐state polymerization (SSP) of several DuPont PET products were investigated by low‐voltage scanning electron microscopy (LV‐SEM) and atomic force microscopy (AFM). The microstructural features on the cross section of various PET samples included crystallites, voids, boundaries, defects, and amorphous phases. The SEM images revealed layered and stepped structural features at the micron and 10‐micron scales that are highly crystallized at the near‐edge region of the cross section for both linear and branched PET samples after the SSP process. The AFM images demonstrate that the degree of crystallization for the linear and branched PET samples increases gradually from the central area to the edge on the cross section. The linear crystallized PET has a higher degree of orientation than the branched crystallized PET in the 10‐micron to micron scales, but their crystalline structures have no significant differences in the submicron to nanometer scales. The PET crystallization process occurs when the molecular chains in the amorphous phase are aligned and folded to form straight molecular chains at the nanometer scale, and small crystallites are formed. The crystallites aggregate and align together into a polygon rod‐like‐shaped crystallites at the submicron scale. Finally, large crystallites at the micron size are formed that appear on the edge area of the cross section. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 40: 245–254, 2002     

Rotor-synchronized two-dimensional 13C CP/MAS NMR studies of the orientational order of polymers 2. Melt-extruded poly(ethylene terephthalate) fibers

Determination of the orientational order of morphological components in polyethylene terephthalate (PET) is sought through quantitative application of two-dimensional rotor synchronized magic angle spinning (ROSMAS) ¹³C NMR technique. Previous study in our laboratories had established a procedure for resolution of the carbonyl carbon (CA) and glycol ethylene carbon (GE) resonances into those corresponding to four morphological components.¹ Due to paucity of sidebands in the GE resonances, the focus has been on the CA resonances in this attempt to obtain orientation distributions. A set of PET fibers possessing a broad range of crystalline and orientational order has been used to infer the meaning of NMR-based orientation measurements vis-a-vis other techniques. A surprising finding of this study is the observation that the orientational orders of the broad component in the ¹³C CP/MAS spectrum and the narrow component are very similar in these fibers. ©1995 John Wiley & Sons, Inc.     

Characterization of nanomaterials in food by electron microscopy

Engineered nanomaterials (ENMs) are increasingly being used in the food industry. In order to assess the efficacy and the risks of these materials, it is essential to have access to methods that not only detect the nanomaterials, but also provide information on the characteristics of the materials (e.g., size and shape).This review presents an overview of electron microscopy (EM)-based methods that have been, or have the potential to be, applied to imaging ENMs in foodstuffs. We provide an overview of approaches to sample preparation, including drying, chemical treatment, fixation and cryogenic methods. We then describe standard and non-standard EM-based approaches that are available for imaging prepared samples. Finally, we present a strategy for selecting the most appropriate method for a particular foodstuff.     

Atomic Force Microscopy Characterization and Interpretation of Thin‐Film Poly(butylene adipate) Spherulites with Ring Bands

Atomic force microscopy characterization has been conducted to reveal the morphological difference between single‐ring bands in poly(butylene adipate) (PBA). Furthermore, morphological features of the ring‐less Maltese‐cross spherulites are compared to the ring‐band spherulites. Periodic changes in height seem to be common for either the ring‐band or ring‐less (Maltese‐cross) crystal domains; however, the steepness in height change is greater for the ring‐band crystal, while height change in the ring‐less crystal exhibits a terrace‐like layer pattern. In the ring‐band crystal region, the lamellar stalks, which taper off to pointed needle‐like stalks, monotonously protrude out of the layers of softer materials, with no signs of twisting, bending, or turning. In contrast, all lamellae in the ring‐less (Maltese‐cross) crystal region are uniform platelets arranged like flower petals in a layered pattern.

     

Miscibility of poly(ethylene terephthalate)/poly(ethylene 2,6-naphthalate) blends by transesterification

The effects of transesterification on the miscibility of poly(ethylene terephthalate)/poly(ethylene 2,6-naphthalate) were studied. Blends were obtained by solution precipitation at room temperature to avoid transesterification during blend preparation. The physical blends and transesterified products were analyzed by wide-angle x-ray scattering, differential scanning calorimetry, and nuclear magnetic resonance spectroscopy. It was found that the physical blends are immiscible and when the extent of transesterification reaches 50% of the completely randomized state, independent of blend composition, the blends are not crystallizable and show a single glass transition temperature between those of starting polymers. The interchange reactions were significantly influenced by annealing temperature and time but negligibly by blend composition. © 1996 John Wiley & Sons, Inc.     

Patterning of cells on a PVC film surface functionalized by ion irradiation

Micropatterns of cells on a poly(vinyl chloride) (PVC) film surface were created by using ion irradiation. A PVC film was irradiated with H⁺ ions through a pattern mask in order to create patterns of the hydrophilic/hydrophobic regions on the PVC surface. The effect of ion irradiation on the surface properties of the PVC film was characterized by using Fourier transform‐infrared spectroscopy (FT‐IR), water contact angle measurement, and X‐ray photoelectron spectroscopy (XPS). The results revealed that the chemical environment of the PVC film surface was effectively changed by ion irradiation due to dehydrochlorination and oxidation. The in vitro cell culture on the patterned PVC film surface showed selective adhesion and proliferation of the cells on the ion‐irradiated regions. Well‐defined 50 µm patterns of the cells were obtained on the PVC film surface irradiated to 1 × 10¹⁵ ions/cm². Copyright © 2009 John Wiley & Sons, Ltd.     

Ultraweak spectrally resolved thermoluminescence in polymers

Spectrally resolved thermoluminescence (TL) measurements provide a lot of information concerning trapping and recombination states in various dielectric materials. As long-lived luminescence is typically weak, this technique requires a very sensitive apparatus. This paper describes the measurement system that is used for studying spectrally resolved TL and phosphorescence decay in polymers. Exemplary investigations are presented for poly(N-vinylcarbazole) (PVK) thin films. The obtained spectra clearly indicate the influence of solvents (dioxane, chlorobenzene) and excitation wavelengths on TL in PVK samples.     

Swelling-assisted modification of poly(ethylene terephthalate) by methacrylic acid

When a poly(ethylene terephthalate), PET, film is heated in an aqueous solution of methacrylic acid in the presence of hydrogen peroxide as an initiator, it is found that the weight of the film is increased. The amount of methacrylic acid that may be added onto the film is dependent upon the concentration of the monomer, the initiator, and the temperature at which the reaction occurs. Pretreatment of the film with 1,1,2,2,tetrachloroethane causes swelling and the amount of add-on is increased as the swelling level increases. Methacrylic-acid-modified PET films hydrolyze at room temperature in aqueous sodium hydroxide; the rate of hydrolysis is dependent upon the amount of add-on and the concentration of the base. This procedure leads to a chemically induced blend of polymethacrylic acid and poly(ethylene terephthalate), and grafting of the monomer onto the polymer film does not occur. © 1995 John Wiley & Sons, Inc.     

Mapping of chemically accessible regions in semicrystalline polymers

Important chemical and mechanical properties in semicrystalline polymers are determined by the noncrystalline or nonordered regions. Hence, characterizing these regions is important in developing a morphological model to better define and predict the chemical and mechanical behavior of polymeric materials. With this objective, preferential tagging was accomplished by covalent linking of a heavy element to poly(ethylene terephthalate) (PET). In scanning transmission electron microscopy (STEM), contrast was obtained using a low concentration of thallium (0.4%), the tagging element, thus providing a map of the more accessible regions within the semicrystalline structure. Differential scanning calorimetry (DSC) and wide-angle x-ray scattering (WAXS) were used to characterize the PET film. Elemental analysis using energy dispersive x-ray analysis (EDAX) was used to confirm the presence of the heavy element in the tagged regions. The STEM imaging results were then compared with the characterization results from the DSC and WAXS measurements to gain an understanding of the domains and their size ranges in the semicrystalline microstructure of PET. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 1443–1450, 1998     

Study of the thermal evolution of the cyclic‐oligomer formation in a cyclic‐oligomer‐free PET

A low percentage of cyclic oligomers can be found in poly(ethylene terephthalate) (PET) from its synthesis onward. In this article, a cyclic‐oligomer‐free PET (COFP) obtained by solvent extraction was used to study the thermodynamics of the re‐formation of cyclics from the melt. The cyclic‐oligomer content re‐increased into molten COFP, finally reaching an equilibrium. An analysis of the fraction of the re‐formed cyclic oligomers showed that a majority of cyclic trimer (60–70%) was found at the equilibrium. Before the establishment of the equilibrium, an unusual behavior was observed in the relative proportion of cyclic trimer and tetramer during the first steps of their formation that was probably due to a competition between kinetic and thermodynamic products. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 416–422, 2000     

Studying banded spherulites in HDPE by electron microscopy

HDPE is a semi-crystalline thermoplastic polymer, with remarkable physical properties such as high chemical resistivity, high impact strength, and high modulus. Compared to the other semi-crystalline polymers, HDPE mostly possesses a high crystallinity, due to which, it exhibits a unique combination of mechanical and chemical resistance properties. In the present work, we have characterized the crystalline spherulites of neat and formulated HDPE compositions thoroughly characterized by different electron microscopy techniques such as scanning electron microscopy (SEM) and transmission electron microscopy (TEM). One of the critical steps to obtaining well-resolved SEM images is the sample preparation that typically involves the etching process to elucidate the crystalline spherulites. Though such traditional methodology can effectively be used for neat HDPE, it leads to the creation of undesirable experimental artifacts when used to investigate formulated HDPE compositions. An alternate TEM-based method provides clear images without any artifacts, apart from being a direct and green method and taking relatively a lesser measurement time.     

Interval kinetic gravimetric sorption of acetone in random copolymers of poly(ethylene terephthalate) and poly(ethylene 2,6-naphthalate)

Interval sorption kinetics of acetone in solvent cast films of random poly(ethylene terephthalate)-co-(ethylene 2,6-naphthalate) (PET-co-PEN) are reported at 35°C and at acetone pressures ranging from 0 to 7.3 cm Hg. Polymer composition is varied systematically from 0% to 50% poly(ethylene 2,6-naphthalate). Equilibrium sorption is well described by the dual-mode sorption model. Interval sorption kinetics are described using a two-stage model that incorporates both Fickian diffusion and protracted polymer structural relaxation. The incorporation of low levels of PEN into PET significantly reduces the excess free volume associated with the glassy state and, for these interval acetone sorption experiments in ∼ 5 μm-thick films, decreases the fraction of acetone uptake controlled by penetrant-induced polymer structural relaxation. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2973–2984, 1999     

Microdeformation behavior in nanotemplated epoxy thermosets: A study with in situ tensile deformation technique in transmission electron microscopy

Microdeformation behavior in nanostructured block copolymer‐toughened epoxy resins, or templated epoxy thermosets, was studied using an in situ tensile deformation technique performed directly in a transmission electron microscope. The observed microdeformation modes were found to correlate well with the macroscopic mechanical properties of the materials. In the order of decreasing macroscopic fracture toughness, the microdeformation modes were observed to change from large uniform plastic deformation over an extensive area, to localized plastic deformation bands, to little plastic deformation observed in the most brittle material. A similar trend was also observed when samples of the same material were tested at different temperatures, reflecting changes in the deformation mechanism as a function of temperature. Structural defects were observed in nanotoughening phases when plastic deformation was observed. The implication of the observed microdeformation modes to the macroscopic toughening mechanisms is discussed in the context of the micromorphology of the nanometer sized toughening phases and parameters of the epoxy matrix chemistry such as bromination, molecular weight, and interfacial miscibility. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 393–406, 2009     

非晶聚对苯二甲酸乙二酯的制备与表征

采用引入U-polymer的路线制备了非晶聚对苯二甲酸乙二酯(APET).用DSC和DMA等手段研究了APET的性能.结果表明,经改性后得到的APET无结晶,透明性得到改善,玻璃化转变温度和储能模量都较PET有一定程度提高.