Solution‐crystallization and related phenomena in 9,9‐dialkyl‐fluorene polymers. II. Influence of side‐chain structure

Solution‐crystallization is studied for two polyfluorene polymers possessing different side‐chain structures. Thermal analysis and temperature‐dependent optical spectroscopy are used to clarify the nature of the crystallization process, while X‐ray diffraction and scanning electron microscopy reveal important differences in the resulting microstructures. It is shown that the planar‐zigzag chain conformation termed the β‐phase, which is observed for certain linear‐side‐chain polyfluorenes, is necessary for the formation of so‐called polymer‐solvent compounds for these polymers. Introduction of alternating fluorene repeat units with branched side‐chains prevents formation of the β‐phase conformation and results in non‐solvated, i.e. melt‐crystallization‐type, polymer crystals. Unlike non‐solvated polymer crystals, for which the chain conformation is stabilized by its incorporation into a crystalline lattice, the β‐phase conformation is stabilized by complexation with solvent molecules and, therefore, its formation does not require specific inter‐chain interactions. The presented results clarify the fundamental differences between the β‐phase and other conformational/crystalline forms of polyfluorenes. © 2015 The Authors. Journal of Polymer Science Part B: Polymer Physics published by Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 1492–1506     

Nuclear‐Spin‐Induced Cotton–Mouton Effect in a Strong External Magnetic Field

Novel, high‐sensitivity and high‐resolution spectroscopic methods can provide site‐specific nuclear information by exploiting nuclear magneto‐optic properties. We present a first‐principles electronic structure formulation of the recently proposed nuclear‐spin‐induced Cotton–Mouton effect in a strong external magnetic field (NSCM‐B). In NSCM‐B, ellipticity is induced in a linearly polarized light beam, which can be attributed to both the dependence of the symmetric dynamic polarizability on the external magnetic field and the nuclear magnetic moment, as well as the temperature‐dependent partial alignment of the molecules due to the magnetic fields. Quantum‐chemical calculations of NSCM‐B were conducted for a series of molecular liquids. The overall order of magnitude of the induced ellipticities is predicted to be 10^?11–10^?6 rad T^?1 M ^?1 cm^?1 for fully spin‐polarized nuclei. In particular, liquid‐state heavy‐atom systems should be promising for experiments in the Voigt setup.     

PELDOR Spectroscopy Distance Fingerprinting of the Octameric Outer‐Membrane Protein Wza from Escherichia coli.

Distance fingerprinting : Pulsed electron–electron double resonance spectroscopy (PELDOR) is applied to the octameric membrane protein complex Wza of E. coli. The data yielded a detailed distance fingerprint of its periplasmic region that compares favorably to the crystal structure. These results provide the foundation to study conformation changes from interaction with partner proteins.

     

Spectroscopic study of suspensions of single-wall carbon nanotubes in polyaniline solutions in <Emphasis Type="Italic">N</Emphasis>-methylpyrrolidone in UV—Vis—NIR regions

Stable suspensions of carbon nanoparticles in polyaniline solutions in N-methylpyrrolidone were compared with the suspensions in aqueous solutions of cetyltrimethylammonium bromide using spectrophotometry in UV— Vis—NIR regions. Polyaniline in low concentrations in N-methylpyrrolidone was found to be a more efficient surfactant than cetyltrimethylammonium bromide in water. Analysis of the optical spectra of suspensions of carbon soots in solutions of the polymer made it possible to reveal a noticeable change in the spectra of the starting polyaniline and nanotubes, indicating the chemical interaction of polyaniline with the carbon nanotubes.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2584–2588, December, 2004.