The comprehension of mechanisms that drive the dynamics of hydrophilic polymer chains at the interface between two surfaces is relevant for fundamental research and, at the same time, can bring useful applicative implications in industrial field. In particular, understanding all the involved processes at molecular level is useful to clarify and optimize the welding mechanism between hydrophilic polymers, identifying the key parameters which control an efficient sealing in a short time. In this framework, Polyvinil-alcohol (PVA) is selected as hydrophilic polymer and welding between polymer layers is carried out using the water as diffusivity enhancer. As water is a good solvent for PVA, water acts as an adhesive, triggering different processes at the interface. In our approach, we focused on the molecular comprehension of polymer-solvent interactions and their diffusion mechanisms, as well as the role of crystallization at interface. We observed that the welding process of PVA films is likely to involve not only the dynamics of the chains, and polymer dissolution by effect of water, but also the crystallization taking place at the interface including melting/recrystallization phenomena, nucleation and/or grown rate of the crystals, location of nuclei, etc.. By the individuation of the parameters affecting the final welding, this work lays the basis for implementing a more efficient welding process, tuning the sealing strength, and opens the way for the design of different films suitable for specific commercial needs
