  The spreading of a circular liquid drop on a solid substrate can be described
by the time evolution of its base radius R(t). In complete wetting the
quasistationary regime (far away from initial and final transients) typically
obeys the so-called Tanner law, with R t^alpha_T, alpha_T=1/10. Late-time
spreading may differ significantly from the Tanner law: in some cases the drop
does not thin down to a molecular film and instead reaches an equilibrium
pancake-like shape; in other situations, as revealed by recent experiments with
spontaneously spreading nematic crystals, the growth of the base radius
accelerates after the Tanner stage. Here we demonstrate that these two
seemingly conflicting trends can be reconciled within a suitably revisited
energy balance approach, by taking into account the line tension contribution
to the driving force of spreading: a positive line tension is responsible for
the formation of pancake-like structures, whereas a negative line tension tends
to lengthen the contact line and induces an accelerated spreading (a transition
to a faster power law for R(t) than in the Tanner stage).
