Nematic order of model goethite nanorods in a magnetic field

TL;DR

This study models the nematic ordering of goethite nanorods under magnetic fields, revealing complex phase behaviors including reentrant transitions and stability of biaxial nematic phases, using density functional theory.

Contribution

It introduces a theoretical framework combining magnetic effects and particle interactions to predict intricate phase behaviors of nanorods in magnetic fields.

Findings

Reentrant phase transitions observed.

Biaxial nematic order can be stabilized.

Magnetic field influences nematic-smectic transition.

Abstract

We explore the nematic order of model goethite nanorods in an external magnetic field within Onsager-Parsons density functional theory. The goethite rods are represented by monodisperse, charged spherocylinders with a permanent magnetic moment along the rod main axis, forcing the particles to align parallel to the magnetic field at low field strength. The intrinsic diamagnetic susceptibility anisometry of the rods is negative which leads to a preferred perpendicular orientation at higher field strength. It is shown that these counteracting effects may give rise to intricate phase behavior, including a pronounced stability of biaxial nematic order and the presence of reentrant phase transitions and demixing phenomena. The effect of the applied field on the nematic-to-smectic transition will also be addressed.