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

abstract

We propose the theory for the temperature and concentration phase transformations in composite lithium grease doped with the mesogenic additives, copper(II) carboxylates valerate and isovalerate, in the range 1, 5, 10, 20 wt. %. The changes in specific electric conductivity manifested in dielectric spectroscopy in the measuring electric field of 100 Hz – 1 MHz and polarization microscopy are reliable caused by reversible transitions from the discotic to isotropic phase or at heating from room temperature to 391 K. To define critical properties of the transitions, we applied Monte Carlo simulations using the Berezinsky-Kosterlitz-Thouless model describing screw, transverse edge and longitudinal dislocations.

Keywords:

• Cu(II) carboxylates
• dislocations
• discotic phase
• lattice Monte Carlo
• lithium grease
• the BKT model

Acknowledgments

The authors are thankful to Prof. O. B. Akopova and Dr. V.V. Terentyev for delivery the lithium greases for dielectric spectroscopy experiments and to Prof. V.V. Belyaev for useful discussions. The measurements on polarization microscopy and dielectric spectroscopy were made using the equipment of the Collaborative Access Center "Сenter for Polymer Research" of ISPM RAS”, and the authors are very grateful to V.P. Chekusova for test operation.