Modifying the thermosensitivity of copolymers of sodium styrene sulfonate and<Emphasis Type="Italic"> N</Emphasis>-isopropylacrylamide with dodecyltrimethylammonium chloride

The interactions between copolymers of sodium styrene sulfonate (SSS) and N-isopropylacrylamide (NIPAM), anionic polyelectrolytes, and dodecyltrimethylammonium chloride (DTAC), a cationic surfactant, were studied in aqueous solutions of various ionic strengths. The copolymers were found to be thermoresponsive, showing a lower critical solution temperature (LCST). The influence of the polymer composition, the surfactant concentration, and the ionic strength on the LCST was studied. The surfactant was found to interact strongly with the polymer, forming mixed polymer-surfactant micelles. The critical aggregation concentration (cac) of the polymer-surfactant system was found from fluorescence spectroscopy using pyrene as a fluorescent probe. A strong dependence of the anionic polyelectrolyte-cationic surfactant interactions on the structure of the ionic comonomer was observed.     

Almost constant sequences and well-distribution in compact groups

We study the properties of sequences (c _n ) in a compact groupG such that (x _n ) being (weakly) well-distributed implies (c _n x _n ) being (weakly) well-distributed and give a complete characterisation in terms of almost constant sequences as well as a generalisation to non-compact locally compact groups.     

An investigation of the complete post-buckling behavior of axisymmetric spherical shells

Summary The post-buckling behavior of an elastic spherical shell is studied for large axisymmetric deformations. The complete post-buckling path is given for the experimentally confirmed single dimple solution in a load-deformation diagram, making use of the methods of local bifurcation theory, singular perturbation analysis and numerical analysis. From the specific form of the post-buckling path with its predominating unstable part follows the strong imperfection sensitivity of the shell structure.

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Zusammenfassung Es wird das Nachbeulverhalten einer elastischen Kugelschale für große achsensymmetrische Deformationen untersucht. Der gesamte Nachbeulpfad wird für die experimentell bestätigte single dimple Lösung, die eine starke lokale Eindellung darstellt, angegeben, wobei Methoden der lokalen Verzweigungstheorie, der singulären Störungsrechnung und der numerischen Analysis verwendet wurden. Aus der besonderen Form des Nachbeulpfades mit seinem überwiegend instabilen Teil ist die starke Imperfektionsempfindlichkeit dieser Konstruktion deutlich erkennbar.

     

Solutions of the spatially homogeneous Boltzmann equation with time-dependent Lorentz force term

We obtain a certain transformation relating the solutions of the space-uniform Boltzmann equation with the Lorentz force term to those of the Boltzmann equation without external force. This enables us, in the case of angular cut-off intermolecular potentials, to prove the global existence, uniqueness and positivity of strict solutions for the former equation by means of known results on the latter one.     

Template synthesiS: Geometrical and electronic structures of the Fe nitrosyl complex formed by bis(S-methylisothiosemicarbazone)-2,4-pentandione

Sodium acetylacetonate reacts with S-metliylisothiosemicarbazidium nitrate and Fe(NO₃)₃ · 9H₂O in ethanol to make [Fe(HL)NO]NO₃, in which H₃L is bis(S-methyl-isothiosemicarbazone)-2,4-puntandione. The [Fe(HL)NO]⁺ cation has a square pyramidal structure with the HL^2- arranged around the central ion in the basal plane and the nitrogen atom of the NO group in the apical position, with the iron atom diverging from the plane of the base of the pyramid by 0.477 Å. The FeN0 moiety has a linear structure (FeNO = l72.7°). XRD, IR, and Mössbauer spectroscopy have been combined with calculations on the electronic structure to demonstrate that the Fe-NO bond is covalent.Chemical Institute, Academy of Sciences of Moldavian SSR. Applied Physics Institute, Academy of Sciences of the Moldavian SSR. Kishinev. Institute of Crystallography, Academy of Sciences of the USSR. Kurnakov Institute for General and Inorganic Chemistry, Academy of Sciences of the USSR, Moscow. Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 27, No, 3, pp. 376–381, May–June, 1991. Original article submitted February 18, 1991.     

Oxygen quenching of tris(2,2′-bipyridine) ruthenium(II) complexes in thin organic films

A study is presented of the quenching, by oxygen, of the luminescence of tris(2,2′-bipyridine) ruthenium(II) complexes immobilized in thin, transparent, polymer-based films. The film media consist of a water-insoluble linear polymer plasticized with a trialkylphosphate ester, in which the complex ruthenium cations are solubilized by ion pairing with organophilic anions such as tetraphenylborate.

Luminescence lifetimes were studied in relation oxygen concentration in a gas stream contiguous with the film medium, film thickness and concentration of the metal complex within the film medium. It is shown that the microheterogeneous environment of the luminescent complex, which has recently been implicated in the non-linear quenching responses of polymer-immobilized, transition metal complex oxygen sensors, may arise simply as a consequence of the limited solubility of the complex in the film medium. When solubility is limited, the partial precipitation of the complex results in a colloidal of luminescent particles which exhibit non- uniform susceptibilities to quenching by oxygen. Good solubility, and therefore linear quenching characteristics, are promoted by methyl substitution of the bipyridyl ligand and by use of a plasticizer (tributylphosphate) with marked cation solvating powers.     

An approximate description of the double capture process in He2+ + He collisions with static correlation

It is shown that the process of resonant double electron capture in high energy He²⁺+He collisions can be approximately described by a sum over products of one-electron CDW amplitudes. The summation coefficients are determined by stationary ground-state calculations with CI wavefunctions. Total and differential cross sections are calculated and compared with experimental values.     

Electronic detection of the enzymatic degradation of starch

[reaction: see text] The enzymatic degradation of starch can be monitored electronically using single-walled carbon nanotubes (SWNTs) as semiconducting probes in field-effect transistors (FETs). Incubation of these devices in aqueous buffer solutions of amyloglucosidase (AMG) results in the removal of the starch from both the silicon surfaces and the side walls of the SWNTs in the FETs, as evidenced by direct imaging and electronic measurements.     

Diffusion of reagents in macrobeads

A simple and effective method of measuring diffusion rates of various acylating reagents in macro beads (in this work diameters greater than 570 microm) of amino-functionalized resins is presented. The extent of diffusion at various points of time was determined by treating beads with a staining reagent ("chloranil", 2,3,5,6-tetrachloro-1,4-benzoquinone) that colored the regions of the beads that had not yet been permeated by reagent (the central part of the beads). The volume of unstained resin (permeated part) was compared with the volume of the stained part, and diffusion rate constants were calculated. Factors influencing diffusion such as reagent concentration, solvent, temperature, resin type, and mechanical effects were investigated. The results showed that diffusion was promoted by increased temperature, good swelling of the resin, small reagents, and high concentrations but not by sonication or mechanical agitation.