Towards a theory of bubble nucleation in viscous and viscoelastic fluids

《粘性和粘弹性流体中气泡成核理论》项目摘要，俄亥俄州立大学草坂伊萨木。CTS-0626198成核在自然界和制造过程中都扮演着重要的角色。在各种成核现象中，那些发生在凝聚相中的成核现象可能是与许多生物系统和技术应用最相关的。然而，它们仍然是所有案例中最不为人所知的。所谓的经典成核理论在许多工业过程中一直是理论指导的唯一来源，但在定量层面上却严重失败，在许多情况下不足以作为预测工具。为了超越经典理论，这项提议旨在通过关注聚合物二氧化碳混合物中的气泡成核，建立一个具有定量准确性的成核分子理论，能够在工业相关系统中作为指导原则。PI开发的理论框架有望广泛用于研究各种成核现象。聚合物泡沫塑料因其优异的强度重量比、良好的隔热性能和声学性能而被广泛应用。然而，聚合物泡沫很少被用作汽车、航空航天和建筑行业的结构部件，因为与本体聚合物相比，聚合物泡沫的机械强度较低，尺寸和热稳定性较低。通过扭曲泡沫的形态特征，如气泡的大小和密度，可以极大地改善这些性能。然而，经典理论往往无法预测泡沫形态与工艺条件的定性相关性。此外，由于高层大气中的臭氧消耗特性，传统的氯氟烃发泡剂将不得不被环境友好的气体，如超临界二氧化碳所取代。必须迅速重新设计通过多年经验和半经验建模为基于氟氯化碳的技术而优化的操作方法，以便在不久的将来实现这一转换。发展具有定量准确性的分子水平成核理论是克服这一挑战的关键。智力优势：该项目将开发多种理论工具，基于严格的统计力学考虑来研究气泡成核。我们还将检验最近提出的成核自由能垒标度假说的适用性。这种标度方法，如果足够强大，可以将当前的成核分子理论转化为对许多工业相关系统具有定量准确性的预测工具。本项目将首次详细研究这种系统的标度思想的全部潜力。为了实现对成核率的快速和准确的预测，还将开发一种新的唯象描述，通过用几个实验上可测量的关键量来取代昂贵的分子理论计算的输入。广泛的影响：许多将要开发的计算工具将适用于研究各种成核现象。因此，我们开发的模拟代码将以免费下载的开源代码的形式提供，它可以作为向学生教授先进的模拟方法的工具，也可以作为成核领域中对模拟感兴趣但专业知识不是模拟的研究人员的一个方便的起点。该项目还提供了培训研究生和本科生广泛的最先进的理论工具的机会，这些工具可用于对物质的基本分子水平的描述。数据、相关性和理论结果的几个例子将适合用于本科生课程，如混合物热力学、流变学和聚合物加工，以及研究生课程(均由PI教授)，关于分子模拟和界面热力学，这是包括成核在内的各种界面现象的核心重要科目。

Project Abstract Toward a Theory of Bubble Nucleation in Viscous and Viscoelastic FluidsIsamu Kusaka, Ohio State Univ. CTS-0626198Nucleation plays an important role both in nature and in manufacturing processes. Among various nucleation phenomena, those occurring in condensed phases are perhaps the most relevant for many biological systems and technological applications. Yet, they remain to be the least well understood case of all. So-called classical nucleation theory, which has been the only source of theoretical guidance in many industrial processes, fails spectacularly at a quantitative level and is not adequate as a predictive tool in many situations. To go beyond classical theory, this proposal aims to build a molecular theory of nucleation with quantitative accuracy capable of serving as a guiding principle in industrially relevant systems by focusing on bubble nucleation in polymer+CO2 mixtures. The theoretical framework the PI develops is expected to be widely useful in studying various nucleation phenomena. Polymeric foams have been used in many applications because of their excellent strength-to weight ratio, good thermal insulation, and acoustic properties. However, polymer foams are rarely used as structural components in the automotive, aerospace, and construction industries because of poor mechanical strength and low dimensional and thermal stability when compared to bulk polymers. One can greatly improve these properties by contorting the morphological characteristics of the foam such as the size and the density of the gas bubbles. However, classical theory often fails to predict even a qualitative dependence of foam morphology on processing conditions. Further, because of the ozone depleting property in the upper atmosphere, traditional chlorofluorocarbon (CFC) blowing agents will have to be replaced by environmentally benign gases such as supercritical carbon dioxide. The operating methods that have been optimized for CFC based technology through years of experience and semi-empirical modeling must be redesigned quickly in order to make this conversion in the very near future. Development of a molecular level theory of nucleation with quantitative accuracy holds a key to overcoming this challenge.Intellectual merit: This project will develop a multitude of theoretical tools to study bubble nucleation based on rigorous statistical mechanical considerations. We will also examine the applicability of the recently proposed scaling hypothesis for free energy barrier of nucleation. This scaling approach, if sufficiently robust, can transform current molecular theories of nucleation into a predictive tool with quantitative accuracy for many industrially relevant systems.This project will investigate for the first time the full potential of the scaling idea for such systems in detail. A new phenomenological description of nucleation will also be developed in order to achieve a rapid and accurate prediction of nucleation rate by replacing inputs from costly molecular theory calculations by a few experimentally measurable key quantities.Broader impact: Many of the computational tools to be developed will be applicable to study variety of nucleation phenomena. Thus, the simulation code we develop will be made available as a freely downloadable open source code, which can serve as a tool to teach advanced simulation methodology to students and also as a convenient starting point for researchers in the field of nucleation who are interested in simulation, but whose expertise is not in simulation. The project also affords the opportunity to train graduate and undergraduate students on a broad spectrum of the state-of-the-art theoretical tools available for a fundamental molecular level descriptions of matter. Several examples of data, correlations, and theoretical results will be suitable for use in undergraduate courses such as mixture thermodynamics, rheology, and polymer processing, and graduate level courses (both taught by the PI) on molecular simulations and thermodynamics of interfaces, a subject of central importance in various interfacial phenomena including nucleation.