Orientational order of motile defects in active nematics

Orientational order of motile defects in active nematics

Experiments and modeling of active nematics reveal a novel defect-ordered phase, in which motile topological defects exhibit system-spanning orientational order.  Such a defect-ordered phase, which has never before been observed in an active system, could enable new material properties such as macroscale flow, self-healing, or spontaneous generation of work.

(A) LC-Polscope images from an system studied in the Dogic lab, in which extensile microtubule bundles are confined to a 2D interface system.  +1/2 defects are identified by red arrows and -1/2 defects by blue crosses. Statistical analysis of tracked defects shows that symmetry is spontaneously broken; the defects align along a randomly chosen axis to form a nematic phase of defects. 

(B) Trajectory from a computational model of extensile rods. Rod orientations are indicated by color, and topological defects are labeled as in (A). The defects align along a spontaneously chosen vector, forming a polar phase of defects.
The videos are from DeCamp, S.J., G.S. Redner, A. Baskaran, M.F. Hagan, and Z. Dogic, Orientational order of motile defects in active nematics. arXiv:1501.06228, 2015