Orientational order of a spin probe dissolved in nematic liquid crystals. An electron resonance investigation

1976 ◽  
Vol 72 ◽  
pp. 996 ◽  
Author(s):  
Geoffrey R. Luckhurst ◽  
Richard N. Yeates
Keyword(s):  
Liquid Crystals ◽  
Spin Probe ◽  
Nematic Liquid Crystals ◽  
Orientational Order ◽  
Electron Resonance ◽  
Resonance Investigation

Line broadening in the electron resonance spectra of spin probes dissolved in anisotropic media: the effect of nuclear spin quantization

1977 ◽  
Vol 353 (1672) ◽  
pp. 87-102 ◽  
Keyword(s):  
Liquid Crystal ◽  
Liquid Crystals ◽  
Nuclear Spin ◽  
Dynamic Properties ◽  
Orientational Order ◽  
Anisotropic Media ◽  
Approximate Theory ◽  
Spin Probes ◽  
Line Broadening ◽  
Electron Resonance

The line broadening in the electron resonance spectra of monoradicals dissolved in anisotropic media, such as liquid crystals, provides a valuable probe of both the orientational order and the molecular dynamics. However, the fast-motion relaxation theory employed to extract this information from the linewidths assumes that the nuclear spin is quantized along the direction of the magnetic field. This approximation is only correct when the symmetry axis of a uniaxial liquid crystal is either parallel or perpendicular to the field. We have therefore removed this assumption and have developed a general theory of line broadening valid for all orientations of the liquid crystal. The theory is then used to evaluate the angular dependence of the linewidths and this is compared with the dependence predicted by the approximate theory, for two classes of nitroxide spin probes. These comparisons reveal that for steroidal spin probes the error, introduced by assuming the nuclear spin to be quantized along the field, is confined to the dynamic properties derived from the linewidths. In contrast, significant errors appear in both the dynamic and static properties obtained from an analysis of the linewidth variations for fatty acid spin probes based on the approximate theory. It would seem that the exact theory must be employed to obtain precise information from linewidth investigations of liquid crystals, except when the orientational order is extremely small.

Molecular Ordering in Nematic MBCA and EPAPU

1990 ◽  
Vol 45 (1) ◽  
pp. 29-32
Author(s):  
S. Sreehari Sastry ◽  
V. Venkata Rao ◽  
P. Narayana Murty ◽  
G. Satyanandam ◽  
T. F. Sundar Raj
Keyword(s):  
Phase Transition ◽  
Liquid Crystals ◽  
Order Parameter ◽  
Nematic Phase ◽  
Spin Probe ◽  
Nematic Liquid Crystals ◽  
Experimental Techniques ◽  
First Order ◽  
Molecular Ordering

AbstractBy EPR, two nematic liquid crystals (MBCA and EPAPU) were investigated using a steroidal nitroxide spin probe. In both liquid crystals the isotropic-nematic phase transition is of first order. The observed variation of the order parameter with temperature is compared with predictions from the Maier-Saupe and Humphries-James-Luckhurst models and with results obtained by several other experimental techniques.

Short range orientational order in nematic liquid crystals

Pramana ◽  
1977 ◽  
Vol 8 (1) ◽  
pp. 22-35 ◽  
Author(s):  
N V Madhusudana ◽  
K L Savithramma ◽  
S Chandrasekhar
Keyword(s):  
Liquid Crystals ◽  
Short Range ◽  
Nematic Liquid Crystals ◽  
Orientational Order

Orientational order of near D3h solutes in nematic liquid crystals

2009 ◽  
Vol 130 (15) ◽  
pp. 154506 ◽  
Author(s):  
Zorana Danilović ◽  
E. Elliott Burnell
Keyword(s):  
Liquid Crystals ◽  
Nematic Liquid Crystals ◽  
Orientational Order

EPR and ENDOR Investigations of a Cholestane Spin Probe in Liquid Crystals

1987 ◽  
Vol 42 (11) ◽  
pp. 1296-1304 ◽  
Author(s):  
B. Kirste
Keyword(s):  
Liquid Crystals ◽  
Dynamic Behavior ◽  
Spin Probe ◽  
Liquid Crystalline ◽  
Orientational Order ◽  
Spin Probes ◽  
Smectic Phases ◽  
Crystalline Solution

A detailed ENDOR study of anisotropic proton hyperfine shifts in the nitroxide spin probe 3-doxylcholestane (CSL) in liquid-crystalline solution is described. The data are interpreted by means of theoretically calculated proton hyperfine tensors (McConnell-Strathdee-Derbyshire treatment), providing an independent check of the ordering matrix. The orientational order and the dynamic behavior of the nematic and smectic phases of the liquid crystals (40,6), (50,6), and 8CB are investigated by EPR using CSL and phenalenyl as spin probes.

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