辐射接枝法制备离子交换膜的研究现状

聚合物离子交换膜有多种制备方法，其中高分子材料辐射引发接枝功能性单体是一种文献中屡见报道且简单可行的方法．通过在不同聚合物基体上接枝各种类型的单体，可以改变接枝膜的电化学性能、物理化学等性能．丈中详细介绍了不同的高分子基材辐射接枝各类单体制备聚合物离子交换膜的研究现状．     

Water aerosols spraying for SO2 and NOx removal from gases under E-beam irradiation

The gas-phase transport process of an admixture to the surface of spraying aerosol droplets has been experimentally investigated with reference to E-beam gas cleaning processes. The rate of SO₂ uptake by alkali aerosol droplets with average radius 30 μm has been measured in gas-aerosol jet using light absorption technique. It has been shown that the rate of gas-phase transport is described by the molecular flux of the admixture. Gas-liquid reactions are considered to explain the observed improvement of radiation-induced NO removal in the presence of spraying alkali aerosol.     

Dose effects in radiation-induced conductivity of polypyromellitimide

Dose effects in radiation-induced conductivity of polypyromellitimide were numerically simulated in terms of the Rose-Fowler-Vaisberg model with allowance for bipolar carrier transport and the generation of radiation traps during irradiation. The reasons for the lack of a noticeable dose effect in this polymer upon pulse irradiation in light of its presence in the case of continuous irradiation are discussed.     

Numerical simulation of annealing of dose effects in radiation-induced conductivity of polymers

Numerical simulation of dose effects in radiation-induced conductivity in polymers and of roomtemperature annealing of these effects was performed in the formalism of the generalized Rose-Fowler-Vaisberg model, which allows for bipolar electron transport of charge carriers and for generation of radiationinduced traps. It was shown that neither the distinct dose effect nor its long annealing time can be explained unless the radiation-chemical aspect of irradiation is taken into account. It was found that satisfactory fit of theoretical prediction to published data for a number of polymers (PS, PET, LDPE, polyvinylcarbazole) can be achieved in the case of the reasonable choice of the parameter for the injection of radiation-induced traps (free radicals), although certain difficulties are met. This coincidence is attainable if the other parameters of the model are fixed and their values have been determined in independent experiments.     

Effect of dose on radiation-induced conductivity in polymers

Numerical simulation of radiation-induced conductivity in polymers upon long-term irradiation on the basis of the generalized Rose-Fowler-Vaisberg model, which allows for both dipolar carrier transport and generation of radiation traps during irradiation, was performed. The unusual properties of radiation-induced conductivity, such as the appearance of a maximum on current transients, the absence of a steady state, and a substantial difference between these curves for the first and subsequent irradiation, are rationalized in terms of the formation of free radicals, the major feature of radiolysis in the chemical aspect. This interpretation does not require the involvement of degradation or crosslinking processes, unlike other interpretations that appear in the literature. With the use of low-density polyethylene as an example, it was shown that radiation-induced conductivity both upon pulse and continuous irradiation can satisfactorily be described with the unified set of parameters of the generalized Rose-Fowler-Vaisberg model.     

Hole transport and bimolecular recombination of charge carriers in polycarbonate molecularly doped with aromatic hydrazone

General questions about hole transport and bimolecular recombination of charge carriers in molecularly doped polycarbonate with a low dopant concentration (10 wt %) are considered. The experiment is performed via a radiation-induced time-of-flight technique with bulk generation of charge carriers. Transient-current curves are calculated numerically via a multiple-trapping model. There is good agreement between the calculated and experimental results on the transient-current waveform. Nonequilibrium hole transport is observed in the studied molecularly doped polymer, and the bimolecular recombination is close to the Langevin recombination as described by the multiple-trapping model.     

Effect of preliminary electron-beam irradiation on hole transport in molecularly doped polycarbonate

The effect of preliminary electron-beam irradiation on hole transport in a molecularly doped polymer was studied with the use of the time-of-flight technique in the radiation-induced mode. Specimens that exhibit a plateau on their time-of-flight curves were selected for the study, since they suggest the occurrence of quasi-equilibrium transport in the system according to the conventional point of view. In the extremely small signal mode, current transients in the case of bulk irradiation have a form corresponding to dispersive, rather than Gaussian, transport, although hole movement is observed in the presence of charged sites (trapped electrons). On passing to the moderately large signal mode (preirradiation to a dose of up to 5 Gy), the current transients undergo noticeable changes, which might be mistakenly interpreted as evidence for the influence of charged sites on hole transport in accordance with the predictions of the dipolar glass theory. In actuality, these changes are due to the effect of a space charge field and the hole mobility remains almost unchanged in this case. The appearance of the plateau on the current transients is an artifact of the procedure, and the hole transport is dispersive.     

The effect of temperature on carrier transport in molecularly doped polycarbonate

Hole transport in low-polarity polystyrene (PS) doped with 10 wt % tritolylamine was studied. The radiation-induced mode of the time-of-flight technique (TOF) with the carrier generation zone of a variable thickness was used. A theoretical treatment of the data in terms of the Gaussian disorder model has shown the mobility value to be fundamentally inconsistent with the flat shape of the plateau, a contradiction that cannot be resolved within the framework of this model. It has been shown that hole transport is actually dispersive, rather than quasi-equilibrium. The contribution of radiation conductivity of the polymer matrix to the TOF signal was evaluated.     

Universal technique for studying electron transport in polymers

A universal technique was developed for studying electron transport in polymers, which consists in the combination of the time-of-flight technique in the surface and bulk carrier generation modes with measurement of transient radiation-induced conductivity. Central to the technique in question is the time-of-flight method with homogeneous irradiation. The procedure was implemented on the basis of an ELA-50 electron beam device with variable electron energy (3–50 keV). The practicability of the universal technique was demonstrated using the model polymers polyvinylcarbazole and molecularly doped polycarbonate as examples.     

Electron transport of holes in molecularly doped polycarbonate and its radiation-induced conductivity

The salient features of charge transport in a typical molecularly doped polymer (polycarbonate + 30 wt % DEH hydrazone) were studied by time-of-flight and nonsteady-state radiation-induced conductivity measurements. It was shows that the mobility of holes (major carriers) is due to dispersive transport in the temperature range 296–353 K covering the glass transition temperature at an observation time of up to a few seconds. The appearance of a plateau on the current transient, presumably manifesting the establishing of quasiequilibrium (Gaussian) transport, is the artifact of the time-of-flight technique when the charge carrier generation takes place at the sample surface. All of the obtained results can be satisfactorily rationalized in terms of the Rose-Fowler-Weisberg model with a uniform set of parameters of the model. Such an approach is compatible with the basic concepts of the radiation chemistry of condensed phase (the Onsager theory and the Langevin recombination mechanism), structural features of a disordered medium (transport zone, structural traps), and rotational diffusion of small molecules or their molecular groups in vitrified polymers.     

Radiation-Induced Conductivity of Plasticized Flexible-Chain Polymers

The radiation-induced conductivity of cured and transformer-oil extended polybutadiene and polyisoprene rubbers was studied. It was shown that the extender ratio and degree of cure of a polymer system have a much greater effect on the radiation conductivity than the addition of donor–acceptor dopants trapping mobile charge carriers. It was concluded that the molecular mobility is the major factor determining the electron transport properties of the systems of interest.     

On the Involvement of Geminate Pairs in Radiation-Induced Conductivity of Polystyrene

Basic parameters of the generalized Rose–Fowler–Weisberg theory were experimentally determined for polystyrene. The obtained data were used to comprehensively analyze the evolution of geminate pairs in this polymer. It was shown that the generation of the prompt component of radiation-induced conductivity occurs by the trapping mechanism with two charge carrier states involved, the quasi-free and trapped. This generation under equilibrium transport conditions (diffusivity and mobility of carriers are constant) reportedly ensured by the geminate recombination itself was not observed in a real experiment. With allowance for dispersive transport of holes (the major carriers), the lifetime of geminate pairs were found to be as long as a few hundred of milliseconds at 300 K. The published data on the formation and decay kinetics in doped polystyrene upon its pulse radiolysis or photolysis were thoroughly analyzed. It was shown that, at ultrashort times before localization of generated carriers, the contribution of electrons to the observed conductivity prevails, although the basic contribution is made by holes in later times.     

Theoretical analysis of the Rose-Fowler-Vaisberg model: Dipolar conductivity

Results of numerical calculations on the kinetics of radiation-induced conductivity (current transients) in a case polymer in terms of the Rose-Fowler-Vaisberg model assuming dipolar carrier transport (irradiation times of 10⁴–10⁶ s) are reported. Unlike the case of unipolar transport, the pattern of current transients noticeably changes at times after passing a maximum in current. A steady-state value is still attained; however, its increase relative to the case of unipolar conductivity is disproportionately high with respect to a relatively small value of the parameter χ, which characterizes the relative contribution of minority carriers to the current. Allowance for the formation of radiation traps during irradiation somewhat mitigates this effect; however, the discrepancy between the conclusions of the theory for the two types of conduction strongly increases for the estimates of polymer recovery time after preliminary irradiation.     

Radiation-induced grafting polymerization by the ionic mechanism

A technique of radiation-induced grafting under conditions of extreme drying of monomers has been developed. Under such conditions, radiation-induced grafting polymerization of isobutylene, -methylstyrene, vinyl-n-butyl ether, styrene, acrylonitrile, and 4-vinylpyridine by the ionic mechanism at room temperature has been performed. The grafted copolymers of polyethylene, Teflon and polyvinyl chloride with monomers polymerized only ionically (isobutylene, -methylstyrene, vinyl-n-butyl ether) have been obtained for the first time. The kinetics of the radiation-induced grafting of vinyl-n-butyl ether on to polyethylene have been studied; the ionic mechanism has been confirmed. It has been found that the rates of the radiation-induced ionic grafting of styrene, acrylonitrile, and 4-vinylpyridine are much greater than those for radical grafting. The highest grafting rates are observed for 4-vinylpyridine. The mechanism of radiation-induced ionic grafting polymerization has been discussed; generalized kinetic equations have been derived to account for the contributions from radical and ionic processes.     

HALS和抗氧剂对PE辐射致色的影响

聚乙烯;稳定剂;HALS和抗氧剂对PE辐射致色的影响     

Temporary changes in electrical properties of polymer dielectrics due to ionizing radiation

Measurements of conductivity, permittivity, and dissipation factor on polystyrene, low-density polyethylene, poly(ethylene terephthalate), and polytetrafluoroethylene under irradiation with x-rays at exposure rates from 0.004 to 400 r/sec. are presented. The radiation-induced anomalous conductivity as well as the induced dielectric loss are interpreted by Maxwell-Wagner polarization due to radiation imbalance in surface layers of the specimen. The nature of radiation-induced steady-state conductivity is also discussed.     

Swelling and water transport in temperature-sensitive hydrogels based on 2-methoxyethylacrylate

A series of thermoresponsive hydrogels based on copolymers of 2-methoxyethylacrylate with acrylamide or N,N-dimethylacrylamide were prepared by radiation-induced polymerization in dimethylformamide solution in the presence of a crosslinking agent. The swelling behaviour of the hydrogels was studied by immersing the polymer samples in water at 5°C, 10°C and 37°C. The data were found to satisfactorily fit Fick's law with a constant diffusion coefficient. The results indicate that the swelling ratio increases with increasing the content of the hydrophilic monomers in the hydrogels and at the same time the equilibrium swelling time decreases. The effect of temperature on water transport mechanism was observed.     

Theoretical analysis of the Rose-Fowler-Vaisberg model

Results of numerical calculations based on the Rose-Fowler-Vaisberg model of radiation-induced conductivity in a case polymer upon long (10⁴ s) irradiation at doses of 5 × 10⁵–10⁷ Gy are reported. Two irradiation modes were considered: (1) preliminary irradiation and irradiation repeated at variable times after the end of the first irradiation and (2) probing the virgin and irradiated polymer with a standard pulse of ionizing radiation. It was shown that the properties of radiation-induced conductivity, such as its overshoot kinetics, a considerable difference between current transients for the initial and the repeated irradiation, extremely long annealing times of dose effects, and the absence of a steady state, are naturally explained in terms of this model (with allowance for the generation of radiation-induced traps as regards the last property). The Rose-Fowler-Vaisberg theory should be considered at present a well-approved semiempirical model of radiation-induced conductivity in polymers.     

A Monte Carlo simulation of radiation-induced conductivity of disordered solids

The Monte Carlo method was used to perform a theoretical study of the kinetics of radiation-induced conductivity under pulsed irradiation of a disordered solid with traps having different energy distributions. The kinetics of radiation-induced conductivity in a weak electric field was satisfactorily described by the Rose-Fowler-Vaisberg model. In a strong field, radiation-induced conductivity became a nonlinear field strength function because of distortions of the energy spectrum of trap centers.