Bubble dynamics manipulation in polymeric foaming

When pressure releasing a high-pressure-stable polymer/gas mixture, gas bubbles nucleate, grow and impinge to define the typical polyhedral cell structure of a foam. This is the case of a trivial pressure release to ambient pressure. We propose here the use of non-trivial pressure release, in fact, of pressure histories designed to manipulate the foaming process. In particular, by releasing the pressure to an intermediate pressure, it is possible to reduce the bubble growth and prevent impingement, thus gaining a tool for studying phenomena involved in polymer foaming and, more generally, in polymer physics. We studied the model PP/N2 system, and observed bubble growth, Ostwald ripening of close bubbles, bubble interaction causing shape change (from spherical to polyhedral and vice versa) up to coalescence, various bubble growth regimes, and bubble travel after periodic pressure histories. The proposed pressure treatment of nucleated polymer/gas systems allows manipulation of bubble dynamics and represents a powerful tool for characterizing polymers and polymer/gas systems and for validating and interrogating growth, impingement, and coalescence models.