Length scale of dynamic heterogeneity in supercooled glycerol near Tg

This letter presents the first direct measurement of the length scale of dynamic heterogeneity in a low molecular weight glass former without the perturbing effect of probe molecules or confinement. Using a multidimensional ${}^{13}\mathrm{C}$ solid-state exchange NMR experiment, 1 nm heterogeneities were found in glycerol for temperatures ranging from 199 K to 207 K ${\mathrm{(T}}_g\text{=189}$ K). This small size and weak temperature dependence allow some distinctions to be made among different models of the glass transition. It is shown that the dynamics are not influenced by a low concentration (0.1 wt. %) relaxation agent ${\mathrm{Cu(NO}}_{\mathrm{3}}{\mathrm{)}}_{\mathrm{2}}.$