  To support a new interpretation of the origin of the dynamic heterogeneity
observed pervasively in fragile liquids as they approach their glass transition
temperatures Tg, we demonstrate that the introduction of ~2 nm structural
inhomogeneities into a homogeneous glassformer leads to a decoupling of
diffusion from viscosity similar to that observed during the cooling of
orthoterphenyl OTP below TA, where Arrhenius behavior is lost. Further, the
decoupling effect grows stronger as temperature decreases (and viscosity
increases). The liquid is cresol and the ~2nm inhomogeneities are
cresol-soluble asymmetric derivatized tetrasiloxy-based (POSS) molecules. The
decoupling is the phenomenon predicted by Onsager in discussing the approach to
a liquid-liquid phase separation with decreasing temperature. In the present
case the observations support the notion of a polyamorphic transition in
fragile liquids that is hidden below the glass transition. A similar decoupling
can be expected as a globular protein is dissolved in dilute aqueous solutions
or in protic ionic liquids.
