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Isotropic-nematic transition in liquid-crystalline elastomers.

Jonathan V Selinger1, Hong G Jeon, B R Ratna

  • 1Center for Bio/Molecular Science and Engineering, Naval Research Laboratory, Code 6900, 4555 Overlook Avenue, SW, Washington, DC 20375, USA.

Physical Review Letters
|December 18, 2002
PubMed
Summary

Liquid-crystalline elastomers exhibit a smooth, not discontinuous, transition between nematic and isotropic phases. This smooth variation in strain is explained by quenched disorder, applied stress, and internal stress effects.

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Area of Science:

  • Materials Science
  • Polymer Physics
  • Soft Matter Physics

Background:

  • Liquid-crystalline elastomers (LCEs) display unique phase transitions.
  • The isotropic-nematic transition in LCEs is typically expected to be first-order, showing a discontinuity.

Purpose of the Study:

  • Investigate the observed smooth variation of the nematic order parameter and strain across the isotropic-nematic transition in LCEs.
  • Explain the underlying mechanisms causing this deviation from expected first-order behavior.

Main Methods:

  • Experimental measurement of strain as a function of temperature under various applied stress conditions.
  • Analysis of LCEs cross-linked in both nematic and isotropic phases.
  • Theoretical modeling using a modified Landau theory framework.

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Main Results:

  • The study confirmed a smooth, rather than discontinuous, variation in strain across the isotropic-nematic transition.
  • Analysis revealed that quenched disorder within the elastomer is a key factor.
  • Applied and internal stresses were also identified as significant contributors to the smooth transition.

Conclusions:

  • Quenched disorder, in conjunction with applied and internal stresses, reconciles the experimental observations with Landau theory.
  • The findings clarify the physics governing phase transitions in disordered soft materials like LCEs.