Length Scale of Dynamic Heterogeneities at the Glass Transition Determined by Multidimensional Nuclear Magnetic Resonance

We directly measure the equilibrium length scale of dynamic heterogeneities close to the glass transition by means of a new multidimensional NMR experiment. The spatial information is gained from a proton spin diffusion experiment combined with two 2D ${}^{13}\mathrm{C}$ exchange sequences via appropriate back and forth transfer of magnetization between ${}^{13}\mathrm{C}$ and ${}^1\mathrm{H}$ spins. For poly(vinyl acetate) at 10 K above the glass transition we detected a length scale of $3\pm 1\mathrm{nm}$.