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Journal of Physical Chemistry B, Vol.108, No.43, 16601-16605, 2004
Type a versus type B glass formers: NMR relaxation in bulk and confining geometry
We report H-2 NMR spin-lattice relaxation times T, and spectra of two fragile molecular glass forming liquids, deuterated o-terphenyl-d(14) (OTP) and toluene-d(5), confined in a nanoporous SBA-15 type matrix with a pore diameter of 7.1-nm size. We compare these results with bulk data of several glass formers. The temperature dependence of T-1 allows us to differentiate type A (without secondary beta process) from type B glass formers (with process). We find that the a process of both OTP (type A) and toluene (type B) in confinement is governed by a broad heterogeneous distribution of correlation times, not seen in the bulk. Additionally, there is evidence that the beta process in toluene changes under confinement conditions, where it exhibits a distribution of spin-lattice relaxation times that is substantially broadened toward faster times. In contrast, the excess wing for OTP is not altered in confinement.