Scanning Brillouin microscopy visualizes the temporal evolution of a heterogeneous hypersonic pro. le during chemical reactions and transport processes around a planar phase boundary between an epoxy resin and hardener. The hypersonic investigations are interpreted in terms of structural formation and annihilation in the layered sample and are compared to results obtained for a well mixed bulk sample of the same composition of reactants. Chaotic transport channels are made responsible for the creation of local glassy heterogeneities not observable in the bulk material on a macroscopic level. (C) 2009 Elsevier B.V. All rights reserved.