Decoupling Role of Film Thickness and Interfacial Effect on Polymer Thin Film Dynamics

The film thickness and substrate interface are the two most common parameters to tune the dynamics of supported thin films. Here, we investigated the glass transition temperature (T-g) and thermal expansion of thin poly(methyl methacrylate) (PMMA) films with various thicknesses and different interfacial effects. We showed that, although the T-g of the thin films can be modulated equivalently by the two factors, their ability to change the expansivity (beta) is quite different; that is, beta increases notably with a reduction in the thickness, while it is insensitive to perturbations at the interface. We attribute the deviation in modulating beta by the thickness and the interfacial effect to the disparate abilities to change the free volume content in the film by a free surface and substrate interface. This leads to a situation where thin films with dissimilar thicknesses and interfacial properties can have the same T-g but very different beta values, suggesting that T-g alone cannot unequivocally quantify thin film dynamics.

Automated summary

Thin film dynamics can be influenced by both thickness and interfacial effects, affecting parameters such as glass transition temperature (T-g) and expansivity (beta). However, the ability to modulate beta differs significantly between thickness and interface perturbations, leading to variations in thin film properties even when T-g remains constant.