title: Mode coupling behavior in glass-forming liquid crystalline isopentylcyanobiphenyl.
abstract: Linear and nonlinear dielectric measurements of liquid crystalline chiral isopentylcyanobiphenyl (5*CB) and n -pentylcyanobiphenyl (5CB), combined with viscosity eta (T) data, are presented. The 5*CB compound glassifies on cooling in the cholesteric phase whereas 5CB crystallizes in the nematic phase. In both compounds the temperature evolution of dielectric relaxation times, the dc conductivity, and the viscosity are well described by the "critical-like" description from mode coupling theory (MCT). However, for 5*CB a unique coincidence of the MCT "critical" temperature and extrapolated temperature of the hypothetical continuous isotropic-cholesteric (T*) phase transition was found. The temperature dependence of the strong electric-field-induced changes of the dielectric permittivity exhibits a strong anomaly in the direction of negative values on approaching T* , not observed up to now. The anomaly is described by the susceptibility-related critical exponent gamma=1 . The divergence of the "nonlinear" dielectric relaxation follows a power dependence described by the exponent y=1 . This paper recalls the recent discussions on the glassy dynamics of a "hard-ellipsoid" liquid and the possible relationship between the glass transition, critical phenomena, and isotropic-nematic transition.
authors.affiliation: Institute of Physics, Silesian University, ul. Uniwersytecka 4, 40-007 Katowice, Poland.
authors.forename: Aleksandra
authors.initials: A
authors.lastname: Drozd-Rzoska
authors.forename: Sylwester J
authors.initials: SJ
authors.lastname: Rzoska
authors.forename: Marian
authors.initials: M
authors.lastname: Paluch
authors.forename: Sebastian
authors.initials: S
authors.lastname: Pawlus
authors.forename: Jerzy
authors.initials: J
authors.lastname: Zioło
authors.forename: Patrick G
authors.initials: PG
authors.lastname: Santangelo
authors.forename: C Michael
authors.initials: CM
authors.lastname: Roland
authors.forename: Krzysztof
authors.initials: K
authors.lastname: Czupryński
authors.forename: Roman
authors.initials: R
authors.lastname: Dabrowski