The edge fracture occurrence on lyotropic liquid crystals

In the present work, the fracture behavior of the lyotropic liquid crystals during rheological measurements on the cone-and-plate geometry was studied. Three kinds of experiments were performed in order to produce different alignment patterns on the samples under investigation. The results obtained showed that the fracture occurrence depends strongly on the previous history of the sample. If the velocity profile is suddenly changed by a small amount, the system may relax most of the stress jump in a viscous manner instead of an elastic one, which may induce the fracture initiation. The threshold shear rate for the edge fracture to occur depends upon the type and degree of the sample alignment. A compromise between the initiation and the propagation steps was observed. The presence of the orientation defects is necessary for the fracture to initiate but a great number of them will not contribute to decrease the fracture shear rate.