  Aging to the equilibrium liquid state of organic glasses is studied. The
glasses were prepared by cooling the liquid to temperatures just below the
glass transition. Aging following a temperature jump was studied by measuring
the dielectric loss at a fixed frequency using a microregulator in which
temperature is controlled by means of a Peltier element. Compared to
conventional equipment the new device adds almost two orders of magnitude to
the span of observable aging times. Data for the following five glass-forming
liquids are presented: Dibutyl phthalate, diethyl phthalate, 2,3-epoxy
propyl-phenyl-ether, 5-polyphenyl-ether, and triphenyl phosphite. The aging
data were analyzed using the Tool-Narayanaswamy formalism. The following
features are found for all five liquids: 1) Each liquid has an "internal
clock", a fact that is established by showing that the aging of the structure
is controlled by the same material time that controls the dielectric
properties. 2) There are no so-called expansion gaps between the long-time
limits of the relaxation rates following up and down jumps to the same
temperature. 3) At long times the structural relaxation is not stretched, but a
simple exponential decay. 4) For small temperature steps the rate of the
long-time exponential structural relaxation is identical to that of the
long-time decay of the dipole autocorrelation function.
