Liquid-crystalline textures in binary and ternary block copolymer–solvent systems

A number of characteristic liquid-crystalline textures can be obtained in binary and ternary systems (i.e., including one or two solvents) based on polystyrene-poly(ethylene oxide) (PS-PEO) and polystyrene-polyisoprene block copolymers. These textures include oily streaks, myelinic figures, and vesicles, all characteristic of a lamellar structure; fan-shaped textures of cylindrical structure; and isotropic domains indicative of a cubic structure. Experimental conditions used to systematically produce the mesomorphic textures are described, and the rather critical solubility conditions which the solvents must meet are indicated. The rules and described procedures should be quite general and applicable to other copolymers as well. Finally, highly unusual examples of “pseudomorphosis” typical of liquid-crystalline textures occurring in bulk upon melting and crystallization of the PEO sequences in PEO-PS copolymers are also reported.     

Gamow-Teller resonance in β+ decay of 147mDy and spin-isospin current renormalization

The total absorption spectrum of γ-rays following β⁺ decay of ^147mDy has been investigated. The decay energy Q_ε = 7.18 (10) MeV and an improved value of half-life $\text{T}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{= 55.7 (7)}\text{s}$ are determined. The intensity of the transitions from the isomeric state is 31 (3)%, the internal conversion being included. More than 40% of decays populate ¹⁴⁷Tb levels with the excitation energy E_ex ? 4.4 MeV. The β⁺ strength function S_β⁺ exhibits a pronounced narrow maximum at E_ex = 4.84 MeV and some structure at higher energy. The total probability of ^147mDy β⁺ decay corresponds to the value $\text{log}\text{?t = 3.67 (8)}$.The calculation of S_β carried out in the random-phase approximation gives the correct resonance energy. The coefficient of the spin-isospin current renormalization found from the comparison of the calculated β-decay probability with the experimental one is |;G_A/g_v|; = 0.7±0.1.     

Uncatalyzed reactions in the classical Belousov-Zhabotinsky system. 2. The malonic acid-bromate reaction in acidic media

The title reaction was studied with various techniques in 1 M sulfuric acid, a usual medium for the oscillatory Belousov-Zhabotinsky (BZ) reaction. It was found to be a more complex process than the bromomalonic acid (BrMA)-BrO3- reaction studied previously in the first part of this work. Malonic acid (MA) can react with acidic bromate by two parallel mechanisms. The main aim of the present research was to determine the mechanisms, the rate laws, and the rate constants for these parallel channels. In one reaction channel the first molecular products are glyoxalic acid (GOA) and CO2 while in the other channel mesoxalic acid (MOA) is the first molecular intermediate, that is, no CO2 is formed in this step. To prove these two independent routes specific colorimetric techniques were developed to determine GOA and MOA selectively. The rate of the GOA channel was determined by following the rate of the carbon dioxide evolution characteristic for this reaction route. In this step, regarding it as an overall process, one MA is oxidized to GOA and CO2 and one BrO3- is reduced to HOBr, which forms BrMA with another MA. The initial rate of the GOA channel is a bilinear function of the initial MA and BrO3- concentrations with a second-order rate constant k(GOA)= 2.4 x 10(-7) M(-1) s(-1). The rate of the other channel was calculated from the rate of the BrO3- consumption measured in separate experiments, assuming that the measured depletion is a sum of two separate terms reflecting the consumptions due to the two independent channels. In the MOA channel one MA is oxidized to MOA and one BrO3- is consumed while another MA is brominated as in the GOA channel. It was found that the initial rate of the MOA channel is also a bilinear function of the MA and BrO3- concentrations with a second-order rate constant k(MOA)= 2.46 x 10(-6) M(-1) s(-1). Separate chemical mechanisms are suggested for both channels. In all of the various bromate-substrate reactions of these mechanisms oxygen atom transfer from the bromate to the substrate occurs generating bromous acid intermediate. This can be of high importance in BZ systems as bromous acid is the autocatalytic intermediate there. GOA and MOA also can be oxidized by acidic bromate but a study of these reactions will be published later.     

Quantitative analysis of electron diffraction data from epitaxially grown crystals

Epitaxial growth produces oriented crystal projections where a long unit cell axis is parallel to the major crystal face rather than perpendicular to it and thus provides a favorable condition for electron diffraction data collection which minimizes perturbations due to elastic crystal bending. Even though the crystals are not so perfect as those produced by solution growth, the intensity data from them have been useful for the quantitative crystal structure analysis of several molecular organic compounds and linear polymers as discussed in this review.     

Fluoreszenzmikroskopische Untersuchungen an verholzten Zellwänden

Zusammenfassung Da die verholzte Zellwand ein sehr komplexes Gebilde darstellt, wurde untersucht, ob ihre blaue Primärfluoreszenz als spezifische Nachweisreaktion für Verholzung überhaupt gelten kann.Dies ist nicht der Fall, da die Blaufluoreszenz durch erschöpfende Extraktion mit heißem Wasser (Jayme- und Phloroglucin-Salzsäure-Reaktion positiv), ebenso aber auch durch schwache Oxydationsmittel (Jayme-Reaktion positiv, Phloroglucin-Salzsäure-Reaktion negativ) zum Verschwinden gebracht werden kann, obwohl dadurch der Ligningehalt der Membran nur wenig verändert wird.Es ist sehr wahrscheinlich, daß die Blaufluoreszenz durch die vorhandenen wasserlöslichen Lignine bedingt ist.

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Summary Since the lignified cellwall represents a very complex structure, a study was made to determine whether its blue fluorescence can serve at all as a specific test reaction for lignification. This is not the case, since the blue fluorescence can be made to disappear by exhaustive extraction with hot water (Jayme and phloroglucinol-hydrochloric acid reaction positive) and also by treatment with a weak oxidizing agent (Jayme reaction positive, phloroglucinol-hydrochloric acid reaction negative), even though the lignin content of the membrane is changed but little. It is very probable that the blue fluorescence is conditioned by the water-soluble lignins present.

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Résumé Du fait que la paroi lignifiée de la cellule représente un dessin très complexe, on a recherché si la fluorescence primaire bleue pouvait convenir comme réaction qualitative spécifique pour le tissu ligneux en général. Ce n'est pas le cas; du fait que la fluorescence bleue, par épuisement à l'eau chaude (Réaction deJayme positive ainsi que la réaction au phloroglucinolacide chlorhydrique) et que par un oxydant faible (Réaction deJayme positive, réaction phloroglucinol-acide chlorhydrique négative), elle peut être amenée à disparaître, il s'ensuit que la teneur en lignine de la membrane n'est que très peu altérée. Il est très probable que la fluorescence bleue est déterminée par les lignines préexistantes, solubles dans l'eau.

     

I(+1) transfer from diiodomalonic acid to malonic acid and a complete inhibition of the CO and CO2 evolution in the Briggs-Rauscher reaction by resorcinol

A recent report on an intense CO 2 and CO evolution in the Briggs-Rauscher (BR) reaction revealed that iodination of malonic acid (MA) is not the only important organic reaction in the classical BR oscillator. To disclose the source of the gas evolution, iodomalonic (IMA) and diiodomalonic (I2MA) acids were prepared by iodinating MA with nascent iodine in a semibatch reactor. The nascent iodine was generated by an iodide inflow into the reactor, which contained a mixture of MA and acidic iodate. Some CO2 and a minor CO production was observed during these iodinations. It was found that in an aqueous acidic medium the produced I2MA is not stable but decomposes slowly to diiodoacetic acid and CO2. The first-order rate constant of the I 2MA decarboxylation at 20 degrees C was found to be k1 = 9 x 10(-5) s(-1), which is rather close to the rate constant of the analogous decarboxylation of dibromomalonic acid under similar conditions (7 x 10(-5)s(-1)). From the rate of the CO2 evolution, the I2MA concentration can be calculated in a MA-IMA-I2MA mixture as only I2MA decarboxylates spontaneously but MA and IMA are stable. Following CO2 evolution rates, it was proven that I2MA can react with MA in the reversible reaction I2MA + MA <--> 2 IMA. The equilibrium constant of this reaction was calculated as K = 380 together with the rate constants of the forward k 2 = 6.2 x 10 (-2) M (-1)s(-1) and backward k-2 = 1.6 x 10(-4) M(-1)s(-1) reactions. The probable mechanism of the reaction is I(+1) transfer from I2MA to MA. The presence of I(+1) in a I2MA solution is demonstrated by its reduction with ascorbic acid. To estimate the fraction of CO2 coming from the decarboxylation of I2MA in an oscillatory BR reaction, the oscillations were inhibited by resorcinol. Unexpectedly, all CO2 and CO evolution was interrupted for more than one hour after injecting a small amount of resorcinol (10(-5) M initial concentration in the reactor). Finally, some implications of the newly found I(+1) transfer reactions and the surprisingly effective inhibition by resorcinol regarding the mechanism of the oscillatory BR reaction are discussed. The latter is explained by the ability of resorcinol to scavenge free radicals including iodine atoms without producing iodide ions.     

Comparative time-resolved study of solid-state and liquid ablation of polyethylene-glycol 1000: temperature, viscosity and surface tension dependence

Comparative study of solid and liquid phase ablation on the same sample by time-resolved investigations is presented in this paper. Polyethylene-glycol (PEG) 1000 having relatively low melting point (35 °C) was used in our experiments. By varying the sample temperature in the 20–80 °C range we could study the ablation mechanism in both solid and liquid (below and above the melting point) state of matter. An ArF excimer laser (λ=193 nm, FWHM=20 ns) was used for ablation at 1.95 J/cm² fluence. Ablation processes were observed by transmission fast photographic arrangement. It was demonstrated that plasma development and expansion (primer ablation, in 0–50 ns time range), formation and propagation parameters of shock wave and contact front did not depend on sample temperature and state of matter. The secondary material ejection (between 1–100 μs) showed a strong temperature dependence. Material ejection in the case of solid target occurred in the form of dense material cloud, and in the form of splashing for liquid (molten) sample. The ejection velocity of splashed jets depended on the sample temperature, significantly. This can be due to the change of molten PEG 1000 viscosity. Received: 1 November 1999 / Accepted: 17 April 2000 / Published online: 5 July 2000