Neutron scattering studies of the model glass former ortho-terphenyl

The van der Waals liquid ortho-terphenyl has long been used as a model syst em in the study of the glass transition. Motivated by mode-coupling theory, extensive experiments have been undertaken to monitor the onset of structu ral relaxation on microscopic time- and lengthscales. Using in particular q uasielastic neutron scattering, the decay of density and tagged-particle co rrelations has been measured as a function of temperature, pressure and wav enumber. A consistent picture is developed, in which the mode-coupling sing ularity appears as a change of transport mechanism in the moderately viscou s liquid, at temperatures far above the conventional (caloric) glass transi tion.