Annihilation of Point Defects in Smectic-C Liquid Crystal Films

An experimental study of the pair annihilation of c-director defects with topological strength +1 and -1 in a freely suspended Sm-C film is described. Many pairs of +1 and -1 point defects are produced mechanically on the film by transient generation of compressive in-plane stress, and their subsequent behavior is studied using polarized video microscopy. The defects show local positional fluctuations and are attracted by long-range elastic forces. Immediately following their generation several hundred defects are observed, which attract and annihilate until only a few are left. The subsequent dynamics of isolated pairs of defects are then studied. It is found that r(t)\textbullet v(r(t)), the product of defect separation and the mean velocity of attraction v(r)=dr/dt, decreases as r-$>$0. The behavior of r(t)\textbullet v(r(t)) is not understood theoretically. This work is supported by a NSF and by NSF MRSEC Grant DMR0213918. \newline [1] D. Svensek and S. Zumer, Phys.Rev.Lett. \textbf{90}, 155501 (2003). \newline [2] G\'eza T\'oth, Colin Denniston, and J. M. Yeomans, Phys.Rev.Lett. \textbf{88}, 105504 (2002). \newline [3] Patrick Oswald and Jordi Ign\'es-Mullol, Phys.Rev.Lett. \textbf{95}, 027801 (2005).