Entropic partitioning and entropy-enthalpy compensation (EEC) effect in relaxation of nanopatterned polymer blend and nanocomposite films

Surface textured polymer nanocomposite films are utilized in many device applications, therefore understanding the relaxation behavior of  such films is important. By imprinting methods, we are able to create nanopatterns of different polymer mixtures and polymer nanocomposite (PNC) films with entropy driven differential segregation of components into patterned regions characterized by a partition coefficient, K and associated free energy of mixing gain or loss. We study slumping of imprinted polymer grafted nanoparticle (PGNP) systems, high molecular weight, block copolymer systems under direct immersion annealing (DIA) in solvent mixture, and cyclic polymer systems compared to linear ones. These differential partitioning results are also extended to polymeric blend systems of disparate molecular weight.  By extending an in-situ wrinkle relaxation method, we observe that the thermal stability of wrinkled PNC films, both above and below the glass transition temperature (Tg) is proportional to film’s NP (polymer grafted and bare) concentration, with a slope that changes sign at a compensation temperature (Tcomp), determined to be in the vicinity of the film’s Tg. This provides unambiguous confirmation of entropy-enthalpy compensation (EEC) as a general feature of PNC films, implying that the stability of PNC films changes from being enhanced to becoming diminished by simply passing through this characteristic temperature, a phenomenon having evident practical ramifications. We suggest EEC will also arise in films where residual stresses are associated with the film fabrication process, relevant to nanotech device applications.