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.

当对高压稳定的聚合物-气体混合体系进行泄压操作时，气体气泡会依次经历成核、生长与碰撞过程，最终形成泡沫典型的多面体泡孔结构。此为常压泄压的常规情形。本研究提出采用非典型泄压策略，即通过设计特定的压力时序来调控发泡过程。具体而言，将压力泄压至中间压力区间时，可抑制气泡生长并避免气泡间的碰撞，由此为研究聚合物发泡乃至聚合物物理领域的相关现象提供了有效手段。本研究以聚丙烯/氮气（PP/N₂）模型体系为研究对象，观测到了气泡生长、紧密气泡间的奥斯特瓦尔德熟化、气泡相互作用引发的形貌演变（从球形向多面体转变，反之亦然）直至聚并的全过程、多种气泡生长模式，以及周期性压力时序作用下的气泡迁移行为。本研究提出的成核聚合物-气体体系压力调控方法，可实现对气泡动力学行为的精准调控，同时为表征聚合物及聚合物-气体体系、验证与探究气泡生长、碰撞及聚并模型提供了强有力的研究工具。