Towards a theory of bubble nucleation in viscous and viscoelastic fluids

项目摘要：粘性和粘弹性流体中气泡成核理论的研究/ isamu Kusaka，俄亥俄州立大学。成核在自然界和制造过程中都起着重要的作用。在各种成核现象中，发生在凝聚相中的成核现象可能与许多生物系统和技术应用最相关。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，在定量水平上明显失败，并且在许多情况下不足以作为预测工具。为了超越经典理论，本提案旨在通过关注聚合物+CO2混合物中的气泡成核，建立具有定量精度的成核分子理论，能够作为工业相关系统的指导原则。PI开发的理论框架有望广泛应用于研究各种成核现象。聚合物泡沫由于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，聚合物泡沫很少用作汽车、航空航天和建筑行业的结构部件，因为与体聚合物相比，其机械强度差，尺寸和热稳定性低。人们可以通过改变泡沫的形态特征，如气泡的大小和密度，来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对加工条件的定性依赖。此外，由于上层大气中的臭氧消耗特性，传统的氯氟烃（CFC）发泡剂将不得不被超临界二氧化碳等对环境无害的气体所取代。通过多年的经验和半经验建模，为基于CFC的技术优化的操作方法必须迅速重新设计，以便在不久的将来实现这种转换。发展具有定量精度的分子水平成核理论是克服这一挑战的关键。智力优势：该项目将开发大量的理论工具来研究气泡成核基于严格的统计力学考虑。我们还将研究最近提出的成核自由能垒的标度假设的适用性。这种缩放方法，如果足够强大，可以将当前的分子成核理论转化为许多工业相关系统的定量精确预测工具。该项目将首次详细研究此类系统的缩放思想的全部潜力。还将发展成核的一种新的现象学描述，以便通过用几个实验可测量的关键量取代昂贵的分子理论计算的输入，实现对成核率的快速和准确的预测。更广泛的影响：许多待开发的计算工具将适用于研究各种成核现象。因此，我们开发的仿真代码将作为可免费下载的开源代码提供，可以作为向学生教授高级仿真方法的工具，也可以作为对仿真感兴趣但不擅长仿真的成核领域研究人员的方便起点。该项目还提供了培训研究生和本科生的机会，使他们能够广泛使用最先进的理论工具来描述物质的基本分子水平。一些数据、相关性和理论结果的例子将适用于本科课程，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的课程，这是包括成核在内的各种界面现象的核心重要主题。

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.