Behavior of the smectic A phase of colloidal goethite in a magnetic field

Abstract

The behavior of the smectic A phase of colloidal goethite in a magnetic field has been studied using small-angle X-ray scattering. It was found that in systems with a high polydispersity the smectic phase aligns parallel to a small field and it transforms into a columnar phase in high fields. In these systems a columnar phase is already present at higher concentrations without field. It apparently becomes more stable in a large magnetic field, when the particles orient perpendicular to the field. In systems with a low polydispersity the smectic phase aligns along a small magnetic field as well, but in high fields it reorients perpendicular to the field. The results suggest that the reorientation process follows a rather complex pathway. The particle orientation and the orientation of the layers seem to be able to decouple leading to smectic C-type deviations. No columnar phase is found in the low polydispersity systems without field nor does it form in a magnetic field.