CAREER: Morphological Control in Polymer Blends Using Polymeric Surfactants

摘要：非混相聚合物的共混是获得具有特殊性能材料的有效和高效的策略。通常，只有当共混物具有特定的形态时，才能实现所需的性能，例如，扩散屏障材料要求低扩散率成分以片状或血小板的形式存在。因此，控制形态的能力对于设计新的聚合物材料至关重要。这一提议的假设是，不混溶聚合物共混物的形态可以通过添加聚合物表面活性剂来控制。具体来说，我们建议利用界面流动和表面活性剂浓度之间的耦合来操纵形貌。研究建议：两相共混得到的结构是共混产生的水动应力和界面张力产生的界面应力相互作用的结果。后者使得在共混物中难以获得小尺度的各向异性形貌。添加表面活性剂的一个众所周知的作用是通过降低不混相之间的平衡界面张力来降低这些界面应力。不太明显的是，流动和界面上表面活性剂浓度之间的耦合导致界面张力偏离其平衡值，以及沿界面的界面张力梯度。本研究的重点是量化这些非平衡表面活性剂效应，并利用它们来控制结构演化。该方法的关键要素是有助于突出界面现象的简单材料和流场，以及由界面偶联反应产生的表面活性剂。后者确保大部分表面活性剂留在界面上，很少溶解在体中。一个关键的创新是荧光标记表面活性剂的使用，它允许在混合物中定位表面活性剂，并通过共聚焦激光扫描显微镜测量局部界面张力。通过表面活性剂可以实现不寻常的形态，如分散板，分散带，或双相连续性的机制，将阐明。将探讨确定表面活性剂负载界面粘弹性的流变学方法。教育计划：教育计划解决了将本科化学工程课程转向化学产品设计的需要。中心教育目标是在整个课程中介绍产品设计思想，而不仅仅是作为附加的产品设计课程。可以纳入现有化学工程课程的短模块将被设计为促进整个课程对化学产品设计的介绍。这些将在新开发的化工产品设计顶点课程达到高潮。在模块和课程中，所有的案例研究都将被选择，以强调核心化学工程学科，如传输现象和热力学。智力优势：聚合物表面活性剂（通常称为“相容剂”）通常用于促进不相容聚合物的混合。这一建议是基于同样的表面活性剂也可以用来操纵形态的想法。在过去的研究中，该领域的主要科学进展是结构的各向异性，以及流动与界面表面活性剂之间的耦合，将首次被量化。这项研究将为多相流的流体力学提供基本的见解，并将为使用表面活性剂控制非混相聚合物共混物的结构提供指导。更广泛的影响：虽然该研究将在聚合物系统上进行，但其结果适用于所有含有表面活性剂的液-液乳液，例如食品，个人护理产品或石油工业中遇到的液-液乳液。本研究获得的流变特性将指导聚合物共混物加工设备的设计。很大一部分的研究将由本科生完成。产品设计模块将提供给各地的教师，可能会影响其他化学工程部门的产品设计教学方法。可行性：PI在这里涵盖的研究课题中具有广泛的知识和实验技能。所有必要的实验资源要么是可用的，要么将在本研究期间购买。本署全力支持教育计划所建议的课程改革。

ABSTRACT - 0448845Motivation: Blending of immiscible polymers is an effective and efficient strategy to obtain materials with unusual properties. Often the desired properties are realized only if the blend has a specific morphology, e.g. a diffusion-barrier material requires that the low-diffusivity component be in the form of lamellae or platelets. An ability to control the morphology is therefore crucial for design of new polymeric materials. The hypothesis of this proposal is that the morphology of immiscible polymer blends can be controlled by addition of polymeric surfactants. Specifically, we propose to exploit the coupling between interfacial flow and surfactant concentration to manipulate the morphology. Research Proposal: The structure obtained from a two-phase blending operation is a result of the interplay between hydrodynamic stresses due to blending, and interfacial stresses due to interfacial tension. The latter make it difficult to obtain small-scale anisotropic morphologies in blends. A well-known effect of added surfactant is to reduce these interfacial stresses by decreasing the equilibrium interfacial tension between the immiscible phases. Less obviously, a coupling between the flow and the concentration of the surfactant on the interface causes deviations of the interfacial tension from its equilibrium value, as well as interfacial tension gradients, along the interface. The focus of this proposal is to quantify these nonequilibrium surfactant effects, and exploit them to control structural evolution. Key elements of the methodology are simple materials and flow fields to help highlight interfacial phenomena, and a surfactant that is generated by an interfacial coupling reaction. The latter ensures that most of the surfactant remains at the interface, and very little dissolves in the bulk. A crucial innovation is the use of fluorescently-tagged surfactants, which allows locating the surfactant in the blend, and measuring the local interfacial tension, by confocal laser scanning microscopy. The mechanisms by which surfactants can achieve unusual morphologies such as dispersed plates, dispersed ribbons, or dual-phase continuity, will be elucidated. Rheological methods to determine the viscoelastic properties of surfactant-laden interfaces will be explored. Education Plan: The education plan addresses the need to shift the undergraduate Chemical Engineering curriculum towards Chemical Product Design. The central educational goal is to introduce product design ideas throughout the curriculum, and not only as an add-on Product Design course. Short modules that can be incorporated into existing classes in Chemical Engineering will be designed to facilitate a curriculum-wide introduction to Chemical Product Design. These will culminate in a newly developed capstone course on Chemical Product Design. In the modules as well as in the course, all case studies will be chosen to emphasize core Chemical Engineering disciplines such as Transport Phenomena and Thermodynamics. Intellectual merit: Polymeric surfactants, (more commonly referred to as "compatibilizers") are routinely used to facilitate blending of immiscible polymers. This proposal is based on the idea that the same surfactants can also be used to manipulate the morphology. The chief scientific advances over past research in this area are that the anisotropy of the structure, and the coupling between the flow and the surfactant on the interface, will be quantified for the first time. This research will offer fundamental insights into the fluid mechanics of multiphase flow and will lay guidelines for using surfactants to control structure in immiscible polymer blends.Broader impact: While the research will be conducted on polymeric systems, the results are applicable to all liquid-liquid emulsions with surfactants, such as those encountered in the foods, personal care products, or oil industries. The rheological properties obtained in this research will guide the design of processing equipment for polymer blends. A significant portion of the research will be performed by undergraduate students. The product design modules, to be made available to instructors everywhere, is likely to influence the pedagogy of product design in other Chemical Engineering departments.Feasibility: The PI has extensive knowledge and experimental skills in the research topics covered here. All necessary experimental resources are either available, or will be purchased during this research. The Department whole-heartedly supports the curricular changes proposed in the education plan.