Entropy-Enthalpy Compensation (EEC) Behavior in Relaxation of Nanoparticle-Brush Filled Imprinted Polymer Films

Entropy-enthalpy compensation (EEC) effect signifies a linear correlation between the activation parameters of a relaxation process and is routinely observed in the dynamics of many condensed materials such as molecular additives and glass-forming materials. Herein we present relaxation behaviour of nanoparticle-brush filled imprinted polymer films showing similar compensation effect leading to slower decay kinetics above the compensation temperature (T_comp) compared to the neat polymer film. The compensation of the activation enthalpy with the entropy of activation led to the observed increase in the relaxation time constant with concentration above T_comp. Kinetics of structural decay in imprinted thin films of polymethyl methacrylate (PMMA) matrix with different nanoparticle-brush systems (PMMA-grafted TiO₂ and PMMA-grafted SiO₂) were investigated and EEC was robustly observed for both the systems. This is the first experimental study of structural decay (“slumping”) of a patterned nanocomposite film and the relaxation behaviour witnessed here is similar to relaxation dynamics of ultrathin wrinkled polymer films. Our results suggest a common origin of EEC behaviour in patterned thin films and provides a simple nanoparticle additive strategy to tune the structural stability.