2, Roskilde University, Roskilde, , Denmark
3, Chalmers, Götheborg, , Sweden
It is well known that for a large number of glass forming liquids the static structure factor, S(Q), shows no or only subtle changes when passing from the liquid into the glass. In contrast the dynamic structure factor S(q,ω) of simple or more complex glass forming liquids evidences in the GHz - THz frequency range and close to the glass transition clear and common signatures which have been addressed by several theories over the last decades. In spite of large experimental and theoretical activity in this field the glass transition is still not fully understood. Quasielastic neutron scattering plays a vital role for the experimental investigation of dynamic properties of disordered materials, glasses and undercooled liquids. We will give a brief overview over typical experimental findings near the glass transition and over recent instrumental progress on neutron spectrometers before presenting some examples. We then focus on our recent investigations on simple organic, hydrogen bonded and ionic liquids for which we have probed the dynamics near the glass transition by simultaneous dielectric and neutron spectroscopy. For these simultaneous experiments we have controlled both temperature and pressure which did allow us to map lines in the (P,T)-diagram along which the dynamics is unchanged and therefore is isochronous over a wide time range.