A new thermal instability in a lyotropic uniaxial nematic liquid crystal is described. A roll structure with the axes perpendicular to the initial orientation of the director appears when the vertical thermal gradient starts to decrease. The wavelength of the roll structure is about 10 times smaller than the sample thickness. The relaxation of the roll structure to the initial planar geometry is studied. A mechanism is suggested based on the change in the size of the micelles as a function of the temperature.

• Received 14 March 1990

DOI:https://doi.org/10.1103/PhysRevLett.65.2800