Simulation of scattering and phase behavior around the isotropic–nematic transition of discotic particles

Rui P. S. Fartaria, Nadeem Javid, Jan Sefcik, Martin B. Sweatman

Research output: Contribution to journalArticle

4 Citations (Scopus)

Abstract

The detailed study of the isotropic-nematic phase transition in a system of discotic particles of aspect ratios L/D <= 0.1 presented here is relevant to a broad range of colloidal suspensions of chemically modified clay particles. Using Monte Carlo simulation techniques the equation of state, radial distribution functions, structure factors and normalized scattering intensities are calculated for each phase. The results are interpreted and related to previously reported free energy calculations [Fartaria and Sweatman, Chem. Phys. Lett. 478 (2009) 150], suggesting a nearly continuous isotropic-nematic transition for lower aspect ratios. Given this behavior we examined the structural information for each phase to determine how experimental scattering data might be used to distinguish the two phases. The radial distribution functions in each phase depend strongly on aspect ratio, and for larger aspect ratios a dramatic increase in the local ordering of discotic particles (represented here as cut-spheres) is observed just before the phase transition. However, this nearest-neighbor ordering seen in g(r) around r/D = 0.1 would hardly be discernible in experimental scattering data subject to usual statistical errors. The structure factors and scattering intensities were calculated for L/D = 0.1, 0.04 and 0.01 for the isotropic and nematic phases at and away from the isotropic-nematic transition. While the isotropic-nematic phase transition can be detected from the height and shape of the first scattering peak around 7QD for larger aspect ratios, this feature becomes much less discriminatory with decreasing aspect ratio. Instead, scattering intensities at low scattering vector amplitudes (Q -> 0) can be used for detection of the phase transition at low aspect ratios. These results provide useful insight to guide interpretation of X-ray and light scattering measurements for colloidal dispersions of thin platelets undergoing isotropic-nematic transitions. (C) 2012 Elsevier Inc. All rights reserved.

LanguageEnglish
Pages94-104
Number of pages11
JournalJournal of Colloid and Interface Science
Volume377
Issue number1
DOIs
Publication statusPublished - 1 Jul 2012

Fingerprint

Phase behavior
Aspect ratio
Phase transitions
Scattering
Platelets
X ray scattering
Dispersions
Light scattering

Keywords

  • cut-sphere
  • algorithm
  • isotropic
  • nematic
  • phase transition
  • light scattering
  • clay
  • Monte Carlo
  • nanocomposite
  • dispersion

Cite this

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abstract = "The detailed study of the isotropic-nematic phase transition in a system of discotic particles of aspect ratios L/D <= 0.1 presented here is relevant to a broad range of colloidal suspensions of chemically modified clay particles. Using Monte Carlo simulation techniques the equation of state, radial distribution functions, structure factors and normalized scattering intensities are calculated for each phase. The results are interpreted and related to previously reported free energy calculations [Fartaria and Sweatman, Chem. Phys. Lett. 478 (2009) 150], suggesting a nearly continuous isotropic-nematic transition for lower aspect ratios. Given this behavior we examined the structural information for each phase to determine how experimental scattering data might be used to distinguish the two phases. The radial distribution functions in each phase depend strongly on aspect ratio, and for larger aspect ratios a dramatic increase in the local ordering of discotic particles (represented here as cut-spheres) is observed just before the phase transition. However, this nearest-neighbor ordering seen in g(r) around r/D = 0.1 would hardly be discernible in experimental scattering data subject to usual statistical errors. The structure factors and scattering intensities were calculated for L/D = 0.1, 0.04 and 0.01 for the isotropic and nematic phases at and away from the isotropic-nematic transition. While the isotropic-nematic phase transition can be detected from the height and shape of the first scattering peak around 7QD for larger aspect ratios, this feature becomes much less discriminatory with decreasing aspect ratio. Instead, scattering intensities at low scattering vector amplitudes (Q -> 0) can be used for detection of the phase transition at low aspect ratios. These results provide useful insight to guide interpretation of X-ray and light scattering measurements for colloidal dispersions of thin platelets undergoing isotropic-nematic transitions. (C) 2012 Elsevier Inc. All rights reserved.",
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Simulation of scattering and phase behavior around the isotropic–nematic transition of discotic particles. / Fartaria, Rui P. S.; Javid, Nadeem; Sefcik, Jan; Sweatman, Martin B.

In: Journal of Colloid and Interface Science, Vol. 377, No. 1, 01.07.2012, p. 94-104.

Research output: Contribution to journalArticle

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