Molecular Motions and Ordering of the Interfacial, Droplet and Binder Regions of Polymer-Dispersed Liquid-Crystal Displays: A Paramagnetic-Resonance Spin-Probe Study

The molecular dynamics and ordering of polymer‐dispersed liquid‐crystal displays are studied using the technique of paramagnetic resonance of spin probes. A complex spectrum is observed in which components are identified from probes dissolved in the droplet, binder, and interfacial regions of the display. In particular, the liquid‐crystal curing, phase separation, and structure of displays with both thermoplastic and epoxy binders are investigated. Observations are also performed as the liquid‐crystal droplet size is varied. Among the more interesting results is the demonstrated ability to observe the interfacial region. It appears to be quite fluid and has little or no average order. It is also observed that the compatibility between the binder and liquid crystal, seen from some of the formulations studied, correlates with the reported electro‐optical properties. These include the magnitude and hysteresis of switching voltages and the magnitudes of switching times.</p

Magnetic Properties of Spin-crossover Systems in Iron(III) Thioseleno- and Diselenocarbamates

The temperature-dependent magnetic moments between 8 and 310 K have been measured for a series of iron(III) tris-thioselenocarbamates, Fe(SSeCNR2)3, where NR2 is N(CH2C6H5)2, N(CH2)4, N(CH2)5, N(CH2)4O or N(C6H11)2. Whereas the dibenzyl, piperidyl and morpholyl derivatives clearly show spin-crossover behavior at room temperature reaching the low-spin state near liquid nitrogen temperature, the dicyclohexyl derivative is in the pure low-spin state at all temperatures measured. The pyrrolidyl complex, mainly high spin at higher temperatures, exhibits substantial spin-crossover behavior even at 8 K. The EPR powder spectra of the iron(III) tris-thioselenocarbamates, diluted (1:99%) with the corresponding cobalt(III) or indium(III) tris-thioselenocarbamate have been recorded between 120 K and room temperature. These spectra can be used as fingerprints to study qualitatively the influences of temperature and matrix effects on the electronic configuration of spin-crossover systems. In most cases they exhibit a relatively narrow signal at g ≈ 2 and two broad signals with g ≈ 4 and g ≈ 2 which have been attributed to the S=1/2 and S=5/2 state, respectively. Spectra for the corresponding tris- diselenocarbamates are also included and correlated. © 1990