The dielectric behavior of polybutadiene copolymers with different
compositions of 1,2 and
1,4 units is analyzed to study the influence of the microstructure on
the relaxation spectrum, especially
the β relaxation. The experimental data were obtained between
10-2 and 106 Hz and temperatures
above
and below T
g. Above
T
g, the relaxation spectra are described by the
superposition of two processes, the
main α relaxation at low frequencies and a β relaxation at high
frequencies. The α relaxation has the
typical Vogel−Fulcher−Tammann behavior and exhibits a quasi-linear
shift of time scale upon change
of the vinyl content. The high-frequency process shows Arrhenius
behavior only in the case of the
homopolymers. For the other samples with a mixture of
microstructures, spectral broadening occurs
and deviation from the Arrhenius behavior is observed. In these
samples, the relaxation can be modeled
by the simple assumption that the high-frequency process consists of a
superposition of two separate
processes, each with the properties of the β relaxation of one of the
homopolymers. This suggests that
secondary relaxations can relax quite independently from the segmental
relaxation and are therefore
restricted to a very local environment influenced by intramolecular
interaction.
Die Verbindungen Sr2[Ga2S5], Ba2[In2S5] und Ba2[In2Se5] wurden aus stöchiometrischen Gemischen der Elemente bei Temperaturen zwischen 1150°C und 1250°C dargestellt. Sie kristallisieren zueinander isotyp (Raumgruppe Pbca, Z = 8) mit den Gitterkonstanten Sr2Ga2S5 a = 1252,3(6) pm, b = 1203,4(6) pm, c = 1118,0(5) pm; Ba2In2S5 a = 1316,7(6) pm, b = 1272,3(6) pm, c = 1178,4(5) pm; Ba2In2Se5 a = 1365,7(6) pm, b = 1318,2(6) pm, c = 1222,5(5) pm. In der Anionenteilstruktur sind GaS4(InS4/InSe4)‐Tetraeder über drei gemeinsame Ecken zu unendlich ausgedehnten Netzen verknüpft, in denen Ringe aus vier und acht Tetraedern vorliegen. Die Kationen befinden sich zwischen den Schichten und erreichen die Koordinationszahl sieben.
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