Aleksandra Drozd-Rzoska

ANOMALOUS DECOUPLING OF THE DC CONDUCTIVITY AND THE STRUCTURAL RELAXATION TIME IN THE ISOTROPIC PHASE OF A ROD-LIKE LIQUID CRYSTALLINE COMPOUND

Recently, the isotropic phase of rod-like liquid crystalline compounds is advised as an experimental model system for studying complex glassy dynamics. One of unique phenomena occuring close to the glass temperature, for the time scale 10−7±1 s T I−N is shown. The link between this behavior and the FDSE is suggested, namely: S = ϕ′/ϕ. Finally the call for further pressure studies is formulated.

Pretransitional Behavior and Dynamics in Liquid Crystal–Based Nanocolloids

The impact of nanoparticles on phase transitions in liquid crystal (LC)—nanoparticle nanocollids is still little known. This contribution results for dodecylcyanobiphenyl (12CB), pentylcyanobiphenyl (5CB), and hexyl isothiocyanatobiphenyl (6BT) as the LC host with the addition of BaTiO3 barium titanate barium titanate nanoparticles. The latter has a strong impact on the value of dielectric constant, relaxation time, and the discontinuity of the isotropic–mesophase transitions. The first-ever high-pressure studies in such systems are also presented.

Critical Behavior of the Dielectric Modulus in Nitrobenzene-Dodecane Mixture

The dielectric properties of a homogenous critical mixture of nitrobenzene-decane were studied in the range 1 Hz< f1 Mz. The temperature dependences of the “static” dielectric permittivity ε’ (1 MHz) and the electric conductivity σ(1 Hz) exhibit pretransitional anomalies which may be associated with the same critical exponent ø = 1−α ≈ 0.88, where α is the critical exponent of the specific heat. The same data were analyzed using the dielectric modulus representation. They show loss curves for the imaginary part of the modulus M ̋( f ). It was found that the temperature evolutions of the peak frequency τ = 1/2π fp and the peak maximum of M ̋ =M ̋( fp) also exhibit critical anomalies. Their forms resemble anomalies obtained for the imaginary part of the dielectric permittivity ε̋( f ), carried out for 40 MHz < f <1 GHz, in an ethanol-dodecane critical mixture [S. J. Rzoska, K. Orzechowski, and A. Drozd-Rzoska, Phys. Rev. E 65, 042501 (2002)]. - PACS: 64.70.Ja, 77.20.+y , 64.60.Fr

The Link Between the Pressure Evolution of the Glass Temperature in Colloidal and Molecular Glass Formers

Recently, Voigtmann [Phys. Rev. Lett. 101, 095701 (2008)] suggested the existence of the universal “generic steep“ behavior for the glass pressure vs. temperature dependence in molecular glass formers. We indicate that such behavior disappear when the absolute stability limit in the negative pressures domain is taken as the reference. It is a parasitic artifact of omitting the stability limit in the negative pressures domain for the log-log scale plot. Results presented suggest a totally common pattern for the evolution of the glass temperature in colloidal fluids and molecular liquids. However, for molecular liquids both positive and negatives pressures domains have to be taken into account. Consequently the pattern for colloidal glass formers introduced by Sciortino “One Liquid, Two Glasses“ [Nature Materials 1, 1-3 (2002)] may appear to be valid also for molecular glass formers.

Consistency of the Vogel — Fulcher — Tammann (VFT) Equations For The Temperature-, Pressure-, Volume-and Density- Related Evolutions of Dynamic Properties in Supercooled and Superpressed Glass Forming Liquids/Systems

A consistent set of temperature- (T), pressure- (P), volume- (V) and density- (ρ) related VFT-type equations for portraying the evolution of the structural relaxation time or viscosity is presented, namely:

Complex dielectric relaxation in supercooling and superpressing liquid-crystalline chiral isopentylcyanobiphenyl.

\begin{array}{rcl} \tau \left(P \right) & = & \tau _0 \,\exp \left[ {{{D_P \left({P - P_{SL} } \right)}/{\left({P_0 - P} \right)}}} \right] \\ \tau \left(T \right) & = & \tau _0 \,\exp \left[ {{{D_T \left({T_{SL} - T} \right)\left({{{T_0 }/{T_{SL} }}} \right)}/{\left({T - T_0 } \right)}}} \right],\\ \tau \left(\rho \right) & = & \tau _0 \,\exp \left[ {{{D_\rho \left({\rho - \rho _{SL} } \right)}/{\left({\rho _0 - \rho } \right)}}} \right]\\ \end{array}

Metastable Systems under Pressure

andτ (V) = τ 0 exp[D T (V SL — V)(V 0 V SL )/(V — V 0)], where T 0,P 0,V 0 and ρ0 are VFT estimates of the ideal glass loci and T SL , P SL , V SL and ρ SL are estimates of the location of the absolute stability limit, partially hidden in the negative pressures domain (P<0). For these equations prefactors are well defined via ρ 0 = ρ (T SL ,P SL , V SL ,ρ SL ), ie. they are linked to the absolute stability limit loci (gas-liquid spinodal). Noteworthy is their smooth transformation into VFT-type equations, used so far, on approaching the glass transition, and into Arrhenius-type equations remote from the glass transition, on approaching the absolute stability limit. The latter may suggest the re-examination of experimental data suggesting the VFT-to-Arrhenius crossover far away from the glass transition. Novel VFT counterparts also lead to the consistent set of fragility strength coefficients (D T ,D P ,D V ,D ρ) and fragilities associated with the slope (steepness index) at appropriate “Angell plot” counterparts.