Accuracy of measuring the nematic order from intensity scatter: a simulation study

Area of Science:

• Soft Matter Physics
• Materials Science
• Liquid Crystals

Background:

• Determining the nematic order parameter (S) and orientational distribution function (ODF) from scattering data relies on approximations.
• The influence of interparticle correlations on these determinations is not fully understood.

Purpose of the Study:

• To assess the validity of approximations used in deriving S and ODF from scattering data.
• To investigate the impact of spatial and orientational correlations on scattering analysis.
• To compare simulated scattering results with exact simulation data.

Main Methods:

• Monte Carlo simulations of hard spherocylinders (aspect ratio 15) across isotropic and nematic phases.
• Direct simulation to obtain exact ODF, S, and scattering intensity I(q).
• Analysis of simulated scattering intensity, including interparticle correlations, to derive ODF and S.

Main Results:

• The nematic order parameter (S) derived from scattering data underestimates the true value by 2-9%.
• S and ODF values are largely independent of scattering vector magnitude (q) within the range 1.2π/D < 2π/D.
• Maier-Saupe distribution best fits ODF without director fluctuations; Gaussian distributions fit best with fluctuations.

Conclusions:

• Interparticle correlations in scattering data affect the accuracy of derived S and ODF.
• The findings support Leadbetter's assumption regarding the independence of I(q,ψ) from q on the equatorial arc.
• Accurate ODF determination requires accounting for nematic director fluctuations.