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 glass former 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 ∼2 nm inhomogeneities are cresol-soluble asymmetric derivatized tetrasiloxy-based (polyhedral oligomeric silsesquioxane (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.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Surfaces, Coatings and Films
- Materials Chemistry