Analysis of the Reversible Character of Radiation-Induced Conductivity in Polymers

The results of numerical simulation of the rise and decay of transient current in a virgin specimen of a model polymer upon continuous irradiation and in the irradiated specimen after its holding for a certain time are presented. The dependence of the annealing effect on the rest time was examined in detail. It was shown that long times are required for significant annealing, which strongly increase with a decrease in the disorder parameter (for example, from 4 × 10³ s at = 0.5 to 10⁷ s at = 0.3). An analysis of irradiation in the intermittent mode showed that this technique does not provide any new information as compared with the classical continuous irradiation (contrary to the opinion existing in the literature) but predictably complicates the interpretation of experimental data; however, it may be successfully used to measure the time-average current.     

Absorption spectra of 2,3-dihydrothionaphthen-3-one and its derivatives

A number of new thioindigoid dyes have been synthesized. They have been subjected to photochemical isomerization. The absorption spectra of the dyes synthesized have been compared with the absorption spectra of analogous dyes not containing bromine. The spectra of the cis forms are less sensitive to the introduction of a bromine atom than those of the trans forms.For Communication XI, see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, Vol. 6, No. 8, pp. 1031–1033, August, 1970.     

An Exceptional Set in the Ergodic Theory of Markov Maps of the Interval

It is known that a Markov map T of the unit interval preservesa measure µ, say, equivalent to Lebesgue measure, andthat almost every point of the interval has a forward orbitunder T that is uniformly distributed with respect to µ.In the opposite direction the main result of this paper statesthat there is a set of points having Hausdorff dimension 1 whoseforward orbits are in a certain sense very far from being sodistributed. 1991 Mathematics Subject Classification: 58F08,28A80.     

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.     

Variation of the composition and properties of lithium manganese oxide spinel in lithiation-delithiation cycles

The behavior of the variable-composition spinel Li_{1 + x} Mn_{2 ? x} O₄ is examined in repeated cycles consisting of lithiation in 0.2 M LiOH and delithiation in 0.3 M HNO₃. For 0 < x < 0.33, delithiation is accompanied by the redox reaction 2Mn³⁺ → Mn⁴⁺ + Mn²⁺ and Li⁺ ? H⁺ ion exchange. The spinel undergoes partial conversion into λ-□MnO₂. Vacancies (□) build up at the 8a sites of the spinel structure. Mn²⁺ ions pass into the solution, and, accordingly, the spinel dissolves. Lithiation is accompanied by the redox reaction 4Mn⁴⁺ → 3Mn³⁺ + Mn⁷⁺ and ion exchange, and the proportion of vacancies □ at the 8a sites of the spinel structure decreases. The spinel undergoes partial dissolution because of Mn²⁺ and MnO _? ⁴ ions passing into the solution. The Li⁺ selectivity of the spinel is the property of the crystallite core. The crystallite surface is capable of sorbing Na⁺ ions.     

The nature of the plateau on the time-of-flight curves in molecularly doped polymers

The transient current curves for a polar molecularly doped polymer were compared for the nearsurface and bulk generation of charge carriers. The horizontal plateau on the first curve was expected to transform into a tilted straight line under the quasiequilibrium transport conditions, but it did not. Instead, for bulk generation, the curve was a hyperbola, on which the slope decreased almost sevenfold during the existence of the plateau. This behavior points to nonequilibrium charge carrier transport. The appearance of a plateau in our case is explained by the effect of the defective surface layer, as indicated in our previous communications.     

The mobility of charge carriers in molecularly doped polymer films with various thicknesses

The dependence of the mobility of charge carriers in molecularly doped polycarbonate on the thickness of the polymer was studied at two dopant DEH concentrations (30 and 50 wt %). The mobility of holes in the more concentrated polymer did decrease as the film thickness increased in close agreement with the predictions of the theory of weakly nonequilibrium transport with a dispersion parameter of 0.75. For films with a lower dopant concentration, such a categorical statement cannot be made, because mobility can either decrease as the film thickness increases or remain almost unchanged depending on the method for data processing. For this reason, it is not recommended to use the dependence of the time of flight on film thickness as a criterion for selecting the mechanism of the transport of charge carriers in molecularly doped polymers.