Nematic Glasses Research Articles

Dielectric relaxations in a supercooled liquid and glassy smectic phase

The real and imaginary parts of the complex dielectric permittivity of the supercooled smectic G phase of N-(4′-n-pentyloxybenzylidene)-4-n-butylaniline have been measured from 50 Hz to 200 kHz and 77 to 260 K. The glass transition temperature of the smectic phase is 181 K. Two relaxation regions were observed; one above and the second below Tg, designated as α and β relaxations, respectively. The half-width of the spectrum for both relaxations increases on cooling. The rate of α relaxation follows the Vogel–Fulcher–Tamman equation, but that of β relaxation an Arrhenius equation with an activation energy of 14 kJ mol−1. The increase in static dielectric permittivity on cooling is consistent with Curie law and indicates no change in the orientational correlation with temperature. The dielectric relaxation in the smectic phase is similar to that observed in amorphous polymers, rigid molecular glasses, nematic and cholesteric glasses, and the glasslike state of orientationally disordered crystals. This suggests that the molecular mechanism of relaxations in the glassy state is less dependent upon the presence of internal degrees of freedom of molecules or the degree of order in their arrangement than is generally considered.

EPR Studies on Copper and Cobalt Triazene-1-Oxide Complexes in a Frozen Nematic Medium

Abstract EPR spectra of copper and cobalt complexes of certain triazene-1-oxide ligands have been measured in frozen nematic liquid crystal glasses in order to identify the principal directions of the magnetic interaction tensors. It is pointed out that the nature of solute alignment is primarily determined by its molecular shape and any chemical interaction between the metal complex and the functional groups of the solvent molecules. Once these factors are properly understood, oriented glass spectra can be used to identify the principal axes of the g and A tensors even for systems which deviate considerably from gross molecular planarity. The spin Hamiltonian parameters are discussed on the basis of the ligand field model. It is pointed out that all the cobalt complexes reported here have the unpaired electron in the dyz orbital.

Electron paramagnetic resonance spectra of copper (II) and oxovanadium (IV) complexes oriented in nematic glasses from liquid crystal solvent

Electron paramagnetic resonance spectra of copper (II) and oxovanadium (IV) complexes oriented in nematic glasses from liquid crystal solvent

Electron paramagnetic resonance spectra of metal complexes oriented in nematic glasses

Electron paramagnetic resonance spectra of metal complexes oriented in nematic glasses