Articles you may be interested inHydrogen bond dynamics and water structure in glucose-water solutions by depolarized Rayleigh scattering and low-frequency Raman spectroscopy Depolarized Raman spectra below 250 cm -I in water and heavy water were measured and analyzed from 373 K to the supercooled region. The spectral feature of the central component below 20 cm -I is stressed in the present work. The spectra below 250 cm -I in water and heavy water are interpreted as a superposition of one Debye-type relaxation mode and two damped harmonic oscillators. The damped harmonic oscillators (broadbands around 60 cm -1 and 190 cm -I) are interpreted as the restricted translational modes. Analyzing the temperature dependence of the relaxation mode, the reciprocal relaxation time 1"-1 in heavy water changes linearly with 7-1 0:: (T -240 K) in the whole temperature range. On the other hand, the temperature dependence of the reciprocal relaxation time in water above 303 K deviates from a straight line which holds below 298 K as 7-1 0:: (T -225 K).

No abstract

The chain end radical of polyethylene molecules anchored on a fresh polymer surface was produced by block copolymerization of ethylene monomer which was initiated by mechanoradicals formed by mechanical fracture of a solid polymer and located on the fresh surface. The molecular motion of the radical of polyethylene molecule anchored on a fresh surface of polyethylene (PE) is induced by a spin exchange of ß protons between two equilibrium states at dihedral angles of 15°and 45°, and having spin exchange rates of 7.1 X 107s-1 at 77 K and 4.0 X 108 s-1 at 104 K. This results in weak adsorption of the radical on the PE surface. The mobility of the radical is mildly inhibited by intermolecular forces holding the radical to the PE surface. On the other hand, the molecular motion of the radical anchored on the fresh surface of polytetrafluoroethylene (PTFE) allows free rotation around the C"-Cg bond axis even at 77 K. The high mobility of the radical in this latter case is attributed to weak intermolecular forces between the radical and PTFE molecules and causes the radical to protrude from the PTFE surface. It is suggested that the polymer chain has relatively high mobility, even at temperatures as low as 77 K, if the chain is isolated from other molecules.

Chain end peroxy radicals of polyethylene (PE) molecules tethered on a fresh surface of poly(tetrafluoroethylene) (PTFE) were produced in the following way. Ethylene monomer was block copolymerized by initiation of mechanoradicals formed by mechanical fracture of the PTFE powder. The propagating radical in the block copolymerization, −CH2CH2 •, located on the fresh surface of PTFE was converted into peroxy radicals, −CH2CH2OO•, after introduction of oxygen molecules. Temperature−dependent ESR spectra of the peroxy radicals were successfully observed. The remarkable change with anisotropic g-values of the radicals was analyzed by computer simulation, and it was found that the PE peroxy radicals on the PTFE surface have extremely high mobility in comparison with the PE radicals on the PE surface and the PTFE radicals on the PTFE surface. This is a reflection of the properties of the protruding PE chains on the PTFE surface; i.e., interaction between PE chains from the PTFE surface must be much weaker than those on the surface of the homopolymer, because of the extremely low segmental concentration of the PE molecules on the PTFE surface.