Advanced research work on radiation cross-linking of polymers in CIAC

Recent research carried out at the Chinese Institute of Applied Chemistry has contributed significantly to the understanding of the radiation chemistry of polymers. High energy radiation has been successfully used to cross-link fluoropolymers and polyimides. Here chain flexibility has been shown to play an important role, and T-type structures were found to exist in the cross-linked fluoropolymers. A modified Charlesby-Pinner equation, based upon the importance of chain flexibility, was developed to account for the sol-radiation dose relationship in systems of this type. An XPS method has been developed to measure the cross-linking yields in aromatic polymers and fluoropolymers, based upon the dose dependence of the aromatic shake-up peaks and the F/C ratios, respectively. Methods for radiation cross-linking degrading polymers in polymer blends have also been developed, as have methods for improving the radiation resistance of polymers through radiation cross-linking.

Influence of interface on radiation effects of crystalline polymer - radiation effects on polyamide-1010 containing BMI

Aimed at saving the radiation dose required to crosslinking the polyamid-1010, BMI/PA1010 systems containing different amounts of difunctional crosslinking agent N,N'-bis-maleimide-4,4'-biphenyl methane (BMI) were prepared and the structure changes at the crystallographic and supermolecular levels before and after irradiation were studied by using WAXD, SAXS, and DSC techniques. It was found that by incorporation of BMI the microcrystal size L-100 is lowered due to the formation of hydrogen bond between the carbonyl oxygen of BMI and the amide hydrogen of PA1010 in the hydrogen bonded plane, and the overall crystallinity W-c is also decreased. The presence of BMI causes the crystal lamella thickness d(c) to decrease and greatly thickens the transition zone d(tr) between the crystalline and amorphous regions. As for the irradiated specimen, the maximum increments in the L-100 and W-c against dose curves decrease with BMI content, and the interception point D-i, at which the L-100 and W-c curves intercept their respective horizontal line of L-100/L-100(0) and W-c/W-c(0)=1, shift to lower dose with an increase in BMI concentration. In addition. the mechanism of the radiation chemical reactions in the three different phases under the action of BMI are discussed with special focus on the interface region. (C) 1999 Published by Elsevier Science Ltd. All rights reserved.

Study on the structure of hemoglobin in organic solvents by in situ STM

In situ STM has been used to study the structure of hemoglobin(Hb) in two kinds of organic media. In hydrophobic organic solvent such as carbon tetrachloride, the structure of Hb is almost the same as in aqueous solution, similar to its native structure. However, when in hydrophilic organic solvent such as dimethylformamide, the two dimers of Hb molecule become separate and unfold to a certain extent.

Thermal, mechanical and ionic conductive behaviour of gamma-radiation induced PEO/PVDF(SIN)-LiClO4 polymer electrolyte system

An effort has been made to modify the mechanical behaviour of our previously reported gel-type gamma-radiation crosslinked polyethylene oxide (PEO)-LiClO4 polymer electrolyte. A highly polar and gamma-radiation crosslinkable crystalline polymer, polyvinylidene fluoride (PVDF), was selected to blend with PEO and then subjected to gamma-irradiation in order to make an simultaneous interpenetrating network (SIN), which was used as a polymer host to impart stiffness to the plasticized system. Experimental results have shown that the presence of PVDF in the system, through gamma-radiation induced SIN formation, could not only give a rather high mechanical modulus of 10(7) Pa at ambient temperature, but also maintain the room temperature ionic conductivity at a high level (greater than 10(-4) S/cm). DSC, DMA and conductivity measurement techniques were used to examine the effects of blending, gamma-irradiation and plasticization on the variations of glass transition and melting endotherm, on the appearance of high elastic plateau and on the temperature dependence of ionic conductivity: In addition, it was found that, in contrast with the unplasticized system, the ionic conductivity mechanism of this gel-type electrolyte seems to conform to the Arrhenius model, suggesting that, as a result of the high degree of plasticization, the polymer chains act mainly as the skeleton of the networks or polymer cages to immobilize the liquid electrolyte solution, whereas the ionic species migrate as if they were in a liquid medium. (C) 1997 Elsevier Science Ltd.

Radiation-induced crystallization of polyamide-1010 containing heterogeneous nuclei

Radiation-induced crystallization of polyamide-1010 (PA1010) or nylon-1010 containing heterogeneous nuclei (neodymium oxide, Nd2O3) is discussed in this paper by Wide Angle X-ray Diffraction (WAXD) and Differential Scanning Calorimetry (DSC). The results show that at low dosage the crystallinities of the irradiated specimens increase, while crystallite size (L(hkl)) decreases, indicating that some new crystallites are produced in the course of irradiation. The new centers were brought about in the fold surface of the lamellae. Copyright (C) 1997 Elsevier Science Ltd

gamma-Radiation damage to nylon 1010 containing neodymium oxide

A comparison of radiation damage to nylon 1010 (denoted nylon-a) and nylon 1010 containing neodymium oxide (Nd2O3) (denoted nylon-b) was made by DSC, WAXD, ESR and the determination of gel fractions. The results show that radiation damage to nylon-b is delayed, and radiation damage to nylon-a is more severe than that to nylon-b, due to the protection of the fold surface of the lamellae. Furthermore, the fact that the damage begins with the fold surface of the lamellae is confirmed. (C) 1996 Elsevier Science Limited

Exploration of post radiation effects on polyamide-1010

Irradiated polyamide-1010 (PA1010) with and without heat treatment after gamma-ray irradiation was compared by wide angle x-ray diffraction (WAXD), differential scanning calorimeter (DSC) and the determination of gel fractions. The results indicate that post radiation effects due to post radiation crosslinking and scissions affect physical properties. Post radiation effects restrain the formation and perfection of the planes (010), and make the crystals imperfect. Post radiation effects change the crystalline structures of polyamide-1010.

Influence of the fold surface of the lamellae on radiation effects - Research on irradiated polyamide-1010 containing heterogeneous nuclei

Irradiated polyamide-1010 (PA1010) and PA1010 containing 0.5% (wt) heterogeneous nuclei were studied by ESR, WAXD, DSC and the determination of gel fractions. The fold surface of the lamellae plays an important role in the effects of radiation on crystalline PA1010. The results show that the direct radiation effects on both samples vary, while after being heated to 220 degrees C, the final radiation effects are identical, regardless of the difference in the amount of the fold surface of the lamellae. The post-radiation effects result predominantly from the fold surface.

Chemiluminescence studies of radiation induced oxidation of various polyethylenes

The chemiluminescence (CL) emission from three kinds of polyethylene, HDPE, LLDPE and LDPE, which had been exposed to 80 kGy dose from Co-60 in both air and nitrogen, has been examined. CL measurement was done under both nitrogen and oxygen atmosphere. The results show that the CL emission from irradiated samples does not result from irradiation itself, but from the oxidation reactions occurring during and after irradiation. Addition of 1 phr of an antioxidant, Irganox 1010, can effectively inhibit the radiation induced oxidation in LLDPE and LDPE. In the case of HDPE, however, it was found that pure HDPE has the best resistance to radiation-induced oxidation of the polymers examined in this work. However, incorporation of Irganox 1010 was found to have not only a stabilizing effect against radiation induced oxidation, but also to promote the oxidation in some cases.

WAXD and SAXS study on gamma-radiation damage to polyamide-1010 crystal structure

In the present work we attempt to settle the controversy on the district wherein the radiation induced reaction preferentially occurs through examining the structural changes of the irradiated polyamide-1010 specimens on both the crystallographic and the supermolecular level by using WAXD and SAXS techniques. Experimental results indicated that the chain crosslinking and scission of the irradiated specimens occur mainly in the amorphous region and on the crystal surface (or interphase), and extend into the inner portion of the crystal with increasing radiation dose.

STM image of tungstosilicic acid molecular layer on highly oriented pyrolytic graphite

Molecular layer of tungstosilicic acid (H4SiW12O40) deposited on freshly-cleaved highly oriented pyrolytic graphite (HOPG) was observed by scanning tunneling microscopy (STM) in air at room temperature. The molecular dimension (11.5 Angstrom) of H4SiW12O40 measured by STM is consistent with known crystallographic parameter. We also imaged the boundary of H4SiW12O40 molecular layer on HOPG showing that molecular layer of H4SiW12O40 was formed. It has been proved that individual tungstosilicic acid species is imaged. The probable reason for the formation of the molecular layer is also discussed.

STM investigation of HOPG superperiodic features caused by electrochemical pretreatment

The surface topography of highly oriented pyrolytic graphite (HOPG) which has been subjected to anodized treatment at a low potential (less positive) has been exhaustively studied using scanning tunneling microscopy (STM). Characterization of graphite surface has revealed that a small percentage of the surface (5%-10%) shows superperiodic features. In this case, the typical topographical features are triangular networks with the observed periodicities in the plane ranging from approximately 26 to 240 nm with peak-to-peak amplitudes out of the plane extending from 7 to 35 Angstrom. We show that this triangular network can be attributed to the injection of electrolyte and solvent in the earliest stages of oxidation of the basal HOPG electrode surface. A simple model is proposed to explain this phenomenon.

THE INFLUENCE OF GAMMA-RADIATION ON POLYAMIDE-1010 AGGREGATE STRUCTURES

The influence of gamma-radiation on polyamide 1010 aggregate structures and crystal damage were examined by using wide angle X-ray diffraction (WAXD) and small angle X-ray scattering (SAXS) techniques. The results revealed that some structural parameters of the aggregated state, the density differences and the degree of crystallinity W-c,W-x, essentially decreased with increasing radiation dose, but the specific surface O-s increased. Crosslinking and scission of irradiated polyamide 1010 samples occurred mainly in amorphous and interphase regions, and crystal damage and amorphization induced by gamma-radiation spread from the interphase and extended into the crystal phase with increasing radiation dose. This result also indicated that the (010) reflection with the hydrogen bond was more susceptible to the action of radiation.

STM OF FOLDED AND UNFOLDED HEMOGLOBIN MOLECULES ELECTROCHEMICALLY DEPOSITED ON HIGHLY ORIENTED PYROLYTIC-GRAPHITE

The structural characterization of folded and unfolded haemoglobin has been performed by scanning tunnelling microscopy (STM) for the first time. STM images show an oval-shaped pattern for the folded structure of this protein, and moreover two dimers consisting of one haemoglobin molecule can be clearly discerned. The dimensions of a folded molecule were determined as 6.4 x 5.4 x 0.7 nm(3), which are in good agreement with the known size obtained from X-ray analysis. We have found that unfolding of haemoglobin molecules on the surface of highly oriented pyrolytic graphite (HOPG) can be achieved by electrochemical deposition. The STM analysis indicates clearly that the tertiary structure of the protein was lost by electrochemical deposition, and most of the haemoglobin molecules were almost fully extended and exhibited a twisted rope-like or a rod-like aggregated structure. Our investigation demonstrates the capability of the electrochemical method in denaturing this redox protein and in preparing stable biological samples for use in STM imaging.

A COMPARATIVE-STUDY ON STM IMAGING AND ELECTROCATALYTIC ACTIVITY OF DIFFERENT SURFACES MODIFIED WITH FLAVIN ADENINE-DINUCLEOTIDE

Flavin adenine dinucleotide (FAD) was modified onto the highly oriented pyrolytic graphite (hopg) and glassy carbon electrode (gee) surfaces with three methods, respectively. Corresponding image analysis for FAD-modified hopg surfaces has been performed by scanning tunnelling microscope (STM) for the first time. The molecular resolution STM image of FAD adsorbed on the freshly-cleaved hopg was obtained, the quantitative size determination suggests that the FAD molecules adsorb side lying on the substrate surface. The anodization treatment of hopg surface yields many pits, which were clearly observed under STM. These pits provide active sites on the hopg surface for modification and the treated hopg can strongly adsorb FAD molecules, the latter exhibiting an irregular cluster structure on such a surface. When FAD was electrochemically deposited on the substrate surface, a chain structure was successfully observed. The adsorbed FAD on anodized glassy carbon electrode (gee) surface can effectively catalyze the reduction of glucose oxidase, hemoglobin and myoglobin, with a large decrease in the overvoltage, whereas the deposited FAD film exhibits excellent electrocatalysis towards dioxygen reduction.