Crystal Isomorphism and Nanodomain Approach toward Novel Ferroelectric Crystalline Polymers

技术摘要：在半结晶极性聚合物中观察到了新的铁电行为，即窄的单极化和双极化回路，并有望用于先进的电气应用。基于最近从基于聚（偏二氟乙烯）的无规共聚物的发现，提出在铁电晶体内部具有大体积共聚单体的重复单元同构是扩大链间距离和钉扎纳米尺寸铁电畴（即，纳米结构域）。本研究利用铁电纳米畴的同晶钉扎假说，合理设计了新型的铁电尼龙共聚物，并验证了其工作机理。首先，将合成具有各种n-尼龙共聚单体的尼龙11无规共聚物，以使晶体中的酰胺基团错配，破坏氢键相互作用以增强铁电性。第二，N-或C-甲基化将进一步用于尼龙11无规共聚物中，以扩大链间距离并促进更快的偶极切换。第三，纳米畴将在铁电尼龙晶体中被物理地（通过较大的共聚单体）或化学地（通过UV可交联的共聚单体）钉扎以实现窄的极化回路。如果成功，这项研究不仅将证实钉扎纳米畴导致新型铁电行为的机制，而且还将为各种电活性应用提供更好的聚合物材料。非技术总结：具有高场响应的电活性聚合物是智能软材料，对于电能存储、智能致动器/人工肌肉和能量收集等众多电气应用非常有吸引力。然而，与电活性陶瓷材料相比，目前的电活性聚合物显示出较差的电场响应。尽管聚合物具有上级加工性、轻质和低成本的特性，但这损害了它们在实际应用中的使用。本项目在最新研究成果的推动下，通过合理的聚合物设计、合成和电性能表征，实现半结晶极性聚合物电响应性的纳米限制效应。如果成功的话，这些新型电活性聚合物将能够实现超高压电场响应，上述应用将变得切实可行，造福社会。除了科学研究活动，该项目还为少数民族和代表性不足的高中生以及本科生和研究生青年专业人员提供了一个广阔的教育和培训平台。一个互动反馈教育主题，涉及教师，研究生，本科生和高中生，将实施和强调整个拟议的项目，以提高公众对纳米科学和聚合物技术的认识。

TECHNICAL SUMMARY:Novel ferroelectric behaviors, namely, narrow single and double polarization loops, have been observed in semicrystalline polar polymers and are promising for advanced electrical applications. Based on recent finding from poly(vinylidene fluoride)-based random copolymers, it is proposed that repeating-unit isomorphism having bulky comonomers inside ferroelectric crystals is an effective strategy to expand interchain distance and pin nanosized ferroelectric domains (i.e., nanodomains). In this proposal, the hypothesis of pinned nanodomains via crystal isomorphism is employed to rationally design new ferroelectric nylon copolymers and testify the working mechanism. First, nylon 11 random copolymers with various n-nylon comonomers will be synthesized to mismatch amide groups in the crystal, disrupting hydrogen-bonding interactions for enhanced ferroelectricity. Second, N- or C-methylation will be further employed in nylon 11 random copolymers to expand the interchain distance and facilitate faster dipole switching. Third, nanodomains will be pinned either physically (by larger comonomers) or chemically (by UV-crosslinkable comonomers) in ferroelectric nylon crystals to realize narrow polarization loops. If successful, this study will not only confirm the mechanism of pinned nanodomains responsible for novel ferroelectric behaviors, but also provide better polymeric materials for various electroactive applications.NON-TECHNICAL SUMMARY:Electroactive polymers with high field response are smart soft materials, which are highly attractive for numerous electrical applications in electrical energy storage, smart actuators/artificial muscles, and energy harvesting. However, comparing with electroactive ceramic materials, current electroactive polymers show inferior electric field responses. This impairs their usage in practical applications, despite the superior processability, light weight, and low-cost characteristics for polymers. Stimulated by recent research results, this project aims to realize a nanoconfinement effect on electric responsiveness of semicrystalline polar polymers via rational polymer design, synthesis, and electrical property characterization. If successful, these novel electroactive polymers will be able to achieve ultrahigh electric field responses and the above-mentioned applications will become practically feasible to benefit society. In addition to the scientific research activities, this project also provides a broad education and training platform for minority and under-represented high school students, and undergraduate and graduate young professionals. An interactive feedback educational theme, involving faculty members, graduate students, undergraduates and high school students, will be implemented and emphasized throughout the proposed project to enhance the awareness of nano-science and technology of polymers in the general community.