Particles at polymer/polymer interfaces: Interfacial phenomena and morphology control in immiscible polymer blends

09329091众所周知，部分被油和水润湿的Velankar颗粒会吸附在油/水界面上。这种界面吸附的颗粒可以稳定油和水的乳状液，这些乳状液被称为皮克林乳状液。我们试图将Pickering乳液的这一想法移植到聚合物系统中：特别是创建由两个不相容的均聚物相和界面吸附颗粒组成的稳定形态。以前我们已经证明，颗粒很容易吸附在各种聚合物之间的界面上，即使是一小部分(远低于1vol.%)的粒子对液滴/基质聚合物共混物的形态有很大影响。此外，当颗粒在界面上足够拥挤时，它们会将界面堵塞到类似固体的状态，以防止界面张力驱动的形态变化。在这里，我们提出了一个全面的实验研究界面活性粒子的影响，在不相容的聚合物共混。我们假设吸附在两个不相容的均聚物界面上的颗粒可以用来控制共混物的形态，特别是它们可以控制形态的大小，产生高度各向异性(柱状或片状)的形态，以及产生一种新型的层状结构。研究建议：实验将在一对模型对的均聚物(可交联性聚异戊二烯(PI)和聚二甲基硅氧烷(PDMS))和二氧化硅颗粒上进行，这些颗粒被修饰为吸附在PI/PDMS界面上。在剪切流条件下，将进行现场流动可视化实验，以表征其形态。粒子尺度成像将通过交联PI，洗去未交联的PDMS，然后对颗粒界面进行扫描电子显微镜(SEM)进行异地进行。在最初的研究中，我们将设计流动协议，诱导颗粒在界面上快速吸附，并诱导它们在界面处聚集，导致界面堵塞。我们还将检查颗粒是否在界面上聚集或扩散，以及它们是否降低了界面张力。本研究的核心是对上述形态控制假说进行检验。颗粒对流动诱导形态的影响将作为PI和PDMS的相对体积、颗粒负载量和颗粒的润湿性的函数来考察。我们将考察颗粒控制形态大小的能力，以及它们通过界面干扰稳定各向异性形态的能力。最后，在高颗粒含量下，当颗粒在剪切流动中倾向于形成层状时，我们将检验这些颗粒层是否可以形成PI/PDMS交替的层状形态。智力优势：这一建议统一了三个不同领域的知识：油/水体系中的界面吸附颗粒，聚合物/聚合物界面上的聚合物相容剂，以及聚合物共混物中的流动诱导形态。这些想法结合在一起，开发出颗粒相容剂颗粒，以类似于嵌段共聚物相容剂的方式在聚合物体系中充当界面改进剂。这种颗粒相容剂具有实现远远超过传统嵌段共聚物相容剂的形态控制的潜力。在这项研究过程中，我们还将解决几个实际和基本的问题，如如何快速将颗粒吸附到界面上，以及颗粒是否降低了聚合物界面的界面张力。最后，PI已经成功地将几个概念从油/水系统移植到聚合物系统，这一提议在这个方向上走得更远。广泛的影响：这一提议将开发一种新的机制来精确控制聚合物共混物的形态，并开发一种由两个不相容的聚合物交替层组成的新型颗粒模板形态，每个界面上都有颗粒。将培训一名研究生和几名本科生。PI将为工程师开发一个长达一小时的关于润湿现象的新的本科水平模块，将动手实验与理论讨论相结合。这是关于软物质的一系列模块的一部分，这些模块将公开提供。

09329091 Velankar Particles that are partially wetted by oil and water are well known to adsorb at oil/water interfaces. Such interfacially adsorbed particles can stabilize emulsions of oil and water, and these emulsions are called Pickering emulsions. We seek to transplant this idea of Pickering emulsions to polymeric systems: specifically to create stable morphologies composed of two immiscible homopolymer phases and interfacially adsorbed particles. Previously we have shown that particles readily adsorb at the interface between a variety of polymers, and that even a small fraction (well under 1 vol. %) of particles can greatly affect the morphology of droplet/matrix polymer blends. Furthermore, when particles are sufficiently crowded at the interface, they jam the interface into a solid like state that prevents interfacial tension driven changes of the morphology. Here we propose a comprehensive experimental study of the effects of interfacially active particles in immiscible polymer blends. We hypothesize that particles that adsorb at the interface between two immiscible homopolymers can be used to control the morphology of the blend, in particular they can control the sizescale of the morphology, create highly anisotropic (cylindrical or lamellar) morphologies, as well as generate a new type of layered structure.Research Proposal: Experiments will be conducted on a model pair of homopolymers,(crosslinkable polyisoprene (PI) and polydimethylsiloxane (PDMS)), and silica particles that are surfacemodified to adsorb at the PI/PDMS interface. In situ flow visualization experiments will be conducted under shear flow conditions to characterize the morphology. Particle scale imaging will be performed ex situ by crosslinking the PI, washing away the uncrosslinked PDMS, and then conducting SEM of the particle laden interface. In initial research, we will devise flow protocols that induce the particles to rapidly adsorb at the interface, and induce them to crowd at the interface to cause interfacial jamming. We will also examine whether particles aggregate or spread on the interface, and whether they reduce the interfacial tension. The core of the research then is to test the above hypothesis about morphology control. The effect of particles on the flow induced morphology will be examined as a function of the relative volumes of the PI and PDMS, the particle loading, and the wettability of the particles. The ability of the particles to control the sizescale of the morphology and their ability to stabilize anisotropic morphologies by interfacial jamming will be examined. Finally, at high particle loadings when the particles tend to form layers in shear flow, we will examine whether these particle layers can template a PI/PDMS alternating lamellar morphology.Intellectual merit: This proposal unites knowledge in three different areas: interfacially adsorbed particles in oil/water systems, polymer compatibilizers at polymer/polymer interfaces, and the flow induced morphology in polymer blends. These ideas are combined together to develop particulate compatibilizers particles that act as interfacial modifiers in polymeric systems in a fashion similar to block copolymer compatibilizers. Such particulate compatibilizers have the potential for achieving morphology control far beyond what is possible with conventional block copolymer compatibilizers. During the course of this research, we will also address several practical and fundamental issues such as how to rapidly adsorb the particles on the interface, and whether particles reduce the interfacial tension of polymeric interfaces. Finally, the PI has had success with transplanting several concepts from oil/water systems to polymeric systems, and this proposal goes considerably further in that direction.Broader impact: This proposal will develop a new mechanism to precisely control the morphology of polymer blends, and develop a new type of particle templated morphology composed of alternating layers of two immiscible polymers with particles at each interface. One graduate student and several undergraduates will be trained. The PI will develop a new hour long undergraduate level module on wetting phenomena for engineers combining hands on experiments with theoretical discussion. This is a part of a series of modules on soft matter that will be made available publicly.