Water Clustering in Polyvinyl Butyral (PVB): Evidenced by Diffusion and Sorption Experiments.

Polyvinyl butyral (PVB) is a transparent amorphous polymer often used to protect fragile surfaces such as glass or photovoltaic panels. The polymer is then packaged in the form of adhesive sheets and bonded to the surfaces. The transport and retention of water in PVB are crucial properties to understand as they modulate the polymer's adhesion properties. In this work, we propose a detailed experimental study of water diffusion and sorption in PVB over a wide range of temperatures and humidity levels in the surrounding atmosphere. Using spectroscopic and gravimetric measurements, our study elucidates how the diffusion coefficient varies with temperature or vapor concentration and provides the activation energy for this process. In addition, dynamic vapor sorption experiments reveal (i) a strong dependence of sorption on hydroxyl group (-OH) concentration and (ii) that the solubility of vapor in PVB decreases with temperature. This enables us to trace the heat of the solution of water in PVB. A comparison of the thermodynamic data obtained with those for water in volume and with the engaged species induced clustering model supports the microscopic view of water organization in PVB in the form of clusters induced by hydrogen bonding.