Elastic continuum theory cutoffs and order in nematics and solids

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Abstract
Thermal disorder in liquid crystal molecular orientation and thermal displacement of atoms in monatomic crystals can be described with analogous elastic continuum theories having short wavelength cutoffs. Half the short wavelength cutoff that gives the observed displacement is remarkably close to 1.8 times the cube root of the atomic volume in monatomic crystals. Half the short wavelength cutoff that gives the observed order parameter in PAA is also about 1.8 times the cube root of the molecular volume. Some data give a number about twice as large for MBBA. This large cutoff may be due to a large error in measured order parameter, or it may suggest that MBBA molecules tend to form groups in the nematic phase.