Nematic-isotropic transition with quenched disorder

Area of Science:

• Soft Matter Physics
• Materials Science
• Polymer Physics

Background:

• Landau-De Gennes mean field theory predicts a first-order phase transition for quadrupolar ordering in 3D nematic elastomers.
• Experimental observations show nematic elastomers do not exhibit this predicted discontinuous transition.
• Network crosslinks in elastomers are suspected sources of quenched orientational disorder.

Purpose of the Study:

• To investigate the effect of quenched orientational disorder on the phase transition behavior of nematic elastomers.
• To reconcile the discrepancy between theoretical predictions and experimental observations of nematic elastomer phase transitions.
• To understand how random anisotropy influences the Landau-De Gennes theory predictions.

Main Methods:

• Theoretical analysis using a modified Landau-De Gennes framework.
• Inclusion of weak random anisotropy to model quenched orientational disorder.
• Renormalization of the Landau-De Gennes free energy expression.

Main Results:

• Addition of weak random anisotropy introduces an energy term proportional to 1/Q^4 to the Landau-De Gennes expression.
• This renormalization significantly reduces the first-order discontinuity in the order parameter (Q).
• At higher disorder strengths, the phase transition becomes continuous, deviating from the predicted first-order behavior.

Conclusions:

• Quenched orientational disorder, arising from network crosslinks, is responsible for the continuous phase transitions observed in nematic elastomers.
• The modified Landau-De Gennes theory accurately describes the transition from first-order to continuous behavior with increasing disorder.
• The findings provide a theoretical basis for understanding the unique phase transition dynamics in disordered soft materials.