Melting dislocation transition in composite lithium greases with copper(II) carboxylate mesogenic additives

TL;DR

This paper presents a theoretical and experimental study of phase transitions in lithium greases doped with copper(II) carboxylate additives, revealing reversible discotic to isotropic phase changes linked to defect structures.

Contribution

It introduces a model connecting defect structures with electrical properties in composite greases, using BKT transition theory and Monte Carlo simulations.

Findings

Reversible phase transition observed from discotic to isotropic phase.

Electrical conductivity changes correlate with phase and defect evolution.

Monte Carlo simulations elucidate critical defect behaviors in the transition.

Abstract

We propose the theoretical description for the temperature and concentration phase transformations in composite lithium grease doped with the mesogenic additives of the copper(II) carboxylates family, copper(II) valerate and isovalerate, in the concentration range 1, 5, 10, 20 wt. percents. The changes in character of specific electric conductivity of these composites manifested in experiments on dielectric spectroscopy in the measuring electric field of the frequencies 100 Hz - 1 MHz and polarization microscopy, are reliable caused by reversible phase transitions from the discotic phase to isotropic one or at heating from room temperature to 391 K. We study correlations between defect structure and electrical properties of these composites using the model of the BKT transition. This transformation from the discotic to isotropic phase is associated with the evolution of topological defects dislocations induced by the mesogenic additives. The screw, transverse edge and longitudinal dislocations are realized in this case. We apply the numerical Monte Carlo technique to define their critical properties in the BKT transition.