TOPIC：The phase behavior of polymer blends under shear field
SPEAKER：郭洪霞研究员，中科院北京化学研究所
TIME：January 13 (Friday) 9:30 am
LOCATION：Room 528, Chemistry Building A (化学A楼528演讲厅)
INVITER：俞炜 教授 

The phase behavior of polymer blends under shear field

Hongxia Guo

State Key Laboratory of Polymer Physics and Chemistry, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China;

Abstract

Polymer blending is a simple and efficient means to create high performance materials. However, in most cases, the miscibility between different polymers is rather low; homopolymer blends are therefore unstable and tend to macroscopically phase separate into their own domains, which weakens the interfacial adhesion and results in poor mechanical performances. Adding block copolymers or nanoparticles is a straightforward approach to stabilize the immiscible polymers. There has been substantial work on exploring their rich equilibrium phase behavior in the past and a very well understanding has been achieved by today In addition, there is much current interest in nonequilibrium behavior of these complex fluids i.e., under shear flow.

In the present work, we study the phase behavior of sheared ternary systems, which contains symmetric AB block copolymers or nanoparticles with different surface properties and geometric shapes in a symmetric blend of A and B homopolymers. 

We found that the statically stable bicontinuous microemulsions (BuE ) are unstable under shear flow, which can be transformed to the ordered lamellar phase (LAM) or the macroscopically separated phase (2P) depending on the shear rate and the location of phase state relative to the static 2P-BuE boundary as well as surface properties of nanoparticles. Particularly, unlike in the shear-free case, the shear –induced formation of lamellar phase is independent of the shape and dividing surface design of Janus nanoparticles. When comparing among the samples with added block copolymers and added nanoparticles with the amphiphilic characteristics (that is Janus nanoparticles), due to the difference in the interfacial elasticity, the former samples exhibit the sheared-induced parallel to perpendicular orientation transition in lamellar phase upon increasing the shear rate as well as the sheared-induced lamellar-2P transition, while in the latter systems the parallel lamellae remain stable under shear field. These results shed light in unveiling the underlying mechanisms for shear effect on the complex fluids with different morphologies.

Biography

郭洪霞，中国科学院化学研究所高分子物理与化学国家重点实验室研究员，博士生导师。1996年于中国科学院物理研究所获凝聚态物理博士学位，1996.09-2000.09年在中国科学院化学研究所任助理研究员、副研究员, 2000.09-2004.02年在德国马普高分子研究所从事博士后研究， 2004.03-2005.12年，在美国西北大学材料科学与工程系高级研究员。2006年01月回国在中国科学院化学研究所高分子物理与化学国家重点实验室工作，2007年入选中国科学院 “百人计划”人才项目。近年主要从事软物质体系的理论计算与模拟, 在发展有效模型、建立多尺度模拟方法、和开发高性能模拟算法等方面取得了系列重要研究成果，并对高分子及其复杂体系的相行为和动力学、界面性质与界面行为、取向和流变学性质进行了深入研究。近五年来在ACSNano, SoftMatter, nanotechnology, PCCP等核心期刊发表文章50余篇。主持或参加国家自然科学基金项目五项、科技部973项目和国家重点研发计划项目各一项。