Theory of interface-nucleated changes of dynamical constraints and their spatial transfer in glass-forming films

We formulate a new force-based microscopic theory for how dynamic caging constraints in glass-forming liquids at an interface are modified and spatially transferred into the film interior in the context of the dynamic free energy concept of the Nonlinear Langevin Equation (NLE) approach. The caging constraints vary exponentially with distance from the interface with a correlation length of modest size and weak sensitivity to thermodynamic state. This imparts a roughly exponential spatial variation of all key features of the dynamic free energy, and a double exponential form for the alpha time gradient. Results have been obtained for vapor, rough pinned particle solid, vibrating (softened) particle solid, and smooth hard wall interfaces, with the crucial dynamical differences arising from the first layer where caging constraints can be weaken, softened or hardly changed. Comparison of the predictions for the dynamic localization length and glassy modulus with simulations and experiments for vapor interface films reveals good agreement. Using the new ideas in Elastically Collective NLE theory yields quantitative results for the relaxation time gradient, decoupling phenomena, T_g gradient and other properties of colloidal, molecular and polymeric films.