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

被油和水部分润湿的颗粒在油/水界面吸附是众所周知的。这种界面吸附的颗粒可以稳定油水的乳状液，这种乳状液称为皮克林乳状液。我们试图将皮克林乳液的想法移植到聚合物系统中：特别是创建由两种不混溶的均聚物相和界面吸附颗粒组成的稳定形态。以前我们已经表明，颗粒很容易吸附在各种聚合物之间的界面上，即使一小部分（远低于1 vol. %）的颗粒也会极大地影响液滴/基质聚合物共混物的形态。此外，当颗粒在界面处足够拥挤时，它们会将界面堵塞成固体状，从而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在非混相聚合物共混物中的作用。我们假设吸附在两种不混相均聚物界面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（圆柱形或片层状）的形态，以及产生一种新型的层状结构。研究计划：实验将在均聚物模型对（可交联聚异戊二烯（PI）和聚二甲基硅氧烷（PDMS））上进行，并对表面改性以吸附在PI/PDMS界面的二氧化硅颗粒进行实验。现场流动可视化实验将在剪切流动条件下进行，以表征形貌。通过将PI交联，洗去未交联的PDMS，然后对颗粒负载界面进行SEM，进行非原位颗粒级成像。在初步研究中，我们将设计流动方案，诱导颗粒在界面处快速吸附，并诱导它们在界面处聚集，造成界面干扰。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。因此，研究的核心是验证上述关于形态控制的假设。颗粒对流动诱导形态的影响将作为PI和PDMS的相对体积，颗粒负载和颗粒润湿性的函数进行检查。粒子控制形貌尺寸的能力和它们通过界面干扰稳定各向异性形貌的能力将被检验。最后，在高颗粒负载时，当颗粒倾向于在剪切流动中形成层时，我们将检查这些颗粒层是否可以模板PI/PDMS交替片层形态。知识优势：该提案将三个不同领域的知识结合在一起：油水系统中的界面吸附颗粒，聚合物/聚合物界面中的聚合物相容剂，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，颗粒在聚合物体系中作为界面调节剂，类似于嵌段共聚物相容剂。这种颗粒增容剂具有实现形态控制的潜力，远远超出了传统嵌段共聚物增容剂的可能性。在本研究过程中，我们还将解决几个实际和基本的问题，如如何在界面上快速吸附颗粒，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中，并且该提案在这个方向上走得更远。更广泛的影响：该提案将开发一种新的机制来精确控制聚合物共混物的形态，并开发一种新型的颗粒模板形态，该形态由两种不混相聚合物在每个界面上具有颗粒的交替层组成。一名研究生和几名本科生将接受培训。PI将为工程师开发一个新的为期一小时的关于润湿现象的本科模块，将动手实验与理论讨论结合起来。这是一系列软物质模块的一部分，将会公开发布。

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.