Glass Transition Dynamics and Crystallization Kinetics in the Smectic Liquid Crystal 4-n-Butyloxybenzylidene-4'-n'-octylaniline (BBOA).
The molecular dynamics of 4-n-butyloxybenzylidene-4'-n'-octylaniline (BBOA, abbreviated also as 4O.8) was studied by broadband dielectric spectroscopy (BDS) for samples that were exposed to various thermal treatments. Phase transitions between liquid crystalline phases (N, SmA, SmBhex, and SmBCr) were evidenced by abrupt changes in the temperature dependence of the dielectric permittivity spectra and dielectric relaxation times. A particularly complex dynamic behavior was revealed for the highly ordered SmBCrphase that showed clear evidence for cooperative dynamics of a glass-forming liquid as manifested by a Vogel-Fulcher-Tammann (VFT)-type temperature dependence of its structural relaxation time τ(T). At low temperatures, dependence τ(T) again changes from VFT to Arrhenius behavior, a phenomenon commonly observed for supercooled liquids confined to nanometer length scales and occasionally discussed as strong-fragile transition on heating. In this context, our observation supports the idea of partial orientation disorder in a quenched SmBCrphase, where the length scale of cooperative motions is restricted to the nanometer size of glassy domains causing the deviation from "bulk" VFT-type behavior. Finally, the isothermal crystallization kinetics of the metastable SmBCrphase was studied in detail. On the basis of structural information about the SmBhexand SmBCrphases, determined by X-ray diffraction, the subtle relation between molecular order and relaxation behavior is discussed.
The Henryk Niewodniczanski Institute of Nuclear Physics, Polish Academy of Sciences , Radzikowskiego 152, 31-342 Kraków, Poland.
Małgorzata
M
Jasiurkowska-Delaporte
Department of Physics and Astronomy, Soft Matter and Biophysics Section, KU Leuven , Celestijnenlaan 200D, B-3001 Leuven, Belgium.|Laboratory of Polymer and Soft Matter Dynamics, Faculté des Sciences, Université Libre de Bruxelles (ULB) , Boulevard du Triomphe, Bruxelles 1050, Belgium.
Simone
S
Napolitano
Department of Physics and Astronomy, Soft Matter and Biophysics Section, KU Leuven , Celestijnenlaan 200D, B-3001 Leuven, Belgium.
Jan
J
Leys
The Henryk Niewodniczanski Institute of Nuclear Physics, Polish Academy of Sciences , Radzikowskiego 152, 31-342 Kraków, Poland.
Ewa
E
Juszyńska-Gałązka
Department of Physics and Astronomy, Soft Matter and Biophysics Section, KU Leuven , Celestijnenlaan 200D, B-3001 Leuven, Belgium.
Micheal
M
Wübbenhorst
The Henryk Niewodniczanski Institute of Nuclear Physics, Polish Academy of Sciences , Radzikowskiego 152, 31-342 Kraków, Poland.
Maria
M
Massalska-Arodź