We review the structure and mechanical properties of topological defects in nematic elastomers and membranes. Nematic elastomers crosslinked in the isotropic phase (isotropic-genesis polydomains) exhibit anomalously soft mechanical response, which is explained by anisotropic orientational correlation in the polydomain state. In contrast, nematic-genesis polydomains show large mechanical stress due to memory of initial defect distributions. Orientation-curvature coupling in nematic membranes causes a correlation pattern similar to that of isotropic-genesis polydomains, which results in low-energy defected states and anomalously slow ordering kinetics. The notion of relative orientational correlation function is introduced to characterize the multi-defect states in these and other materials.
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