SAXS reveals the magnetic alignment pathway of the goethite columnar liquid crystal phase

The alignment of board-like colloidal goethite particles in the dense rectangular centred columnar liquid crystal phase in an external magnetic field is studied using small angle X-ray scattering (SAXS). Transient SAXS-patterns show broadening of the columnar reflections in specific directions. While the reflections along the field stay at a constant Q-value, the other reflections do not. These results imply a certain pathway of reorientation. It appears that alignment proceeds via collective rotation of domains inducing 'nanoshear' between the layers of particles, which slide over each other. The results support the recently suggested martensitic transition pathway for the simple and centred rectangular columnar phases, which were found to spontaneously transform into each other in another goethite system. The results also provide a fine example of how SAXS can be used to study reorientation behaviour of liquid crystals at the nanoscale.