Résumé:

We study coalescence of topological defects in nematic liquid crystals confined to spherical shells using both experiments and computer simulations.We observe that the four s = +1 2 defects that are present due to topological constraints imposed by the spherical geometry coalesce by pairs after changing the molecular orientation at the outer surface from tangential to perpendicular; the result is the formation of two single s = +1 defects. It is noteworthy that the speed of the coalescence process is peaked when the defects are at opposite points on the equator of the shell; this maximum results from the thickness inhomogeneity of the shells.