Relaxation of Slow Glassy Interphases in Polymeric Systems

本文将使用两种独特的技术来研究两种模型聚合物体系中的玻璃界面：测量体积和热膨胀系数的膨胀法和测量热容量和其他重要热性能的超快量热法。这些互补的技术将用于确定几种纳米结构材料中界面的大小、性质和动态行为。例如，半晶聚合物将被研究，因为这些材料由晶体和非晶体域组成。两个畴之间的纳米级间相也是如此，其性质对于理解整体材料行为非常重要。通过对该界面的表征，研究结果将为纳米结构材料的技术应用提供基本的理解，包括但不限于结构复合材料和纳米/微电子技术的应用。该项目包括培养一名研究生、一名博士后和一名本科生，研究方向包括聚合物物理、热分析、界面行为和纳米结构材料。将大力努力纳入少数民族和女学生。该项目将包括向K-12学生推广，包括为TTU的初中女生项目“科学——这是女孩的事情”组织几个为期一周的材料模块。技术概述：本文将研究两种具有慢弛豫玻璃界面的模型聚合物体系，即半晶聚对苯二甲酸乙酯（PET）中的刚性非晶部分（RAF）和毛状聚苯乙烯接枝二氧化硅纳米颗粒中颗粒界面处的不动玻璃层。在PET体系中，玻璃界面相的性质和弛豫动力学将作为形貌的函数，以及作为纳米颗粒体系中接枝密度、接枝链长度和二氧化硅含量的函数进行研究。膨胀测量和纳米量热实验将旨在确定刚性或“不动”界面相的长度尺度、玻璃化转变温度（Tg）和Tg宽度，与刚性或“不动”相相关的节段松弛时间的温度依赖性，以及在半结晶聚合物的情况下，结构恢复和结晶之间的相互作用和竞争作为材料形态的函数。在等温老化实验中，将采用一种独特的温度扰动实验来区分半晶体系中的结构恢复和结晶，并对毛状纳米颗粒体系中固定面层厚度的变化进行量化。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

NON-TECHNICAL SUMMARYThe glassy interphases in two model polymeric systems will be studied using two unique techniques: dilatometry to measure the volume and thermal expansion coefficient, and ultrafast calorimetry to measure the heat capacity and other important thermal properties. These complimentary techniques will be used to determine the size, properties, and dynamic behavior of the interphase in several nanostructured materials. For example, semicrystalline polymers will be studied since these materials consist of crystalline and non-crystalline domains. So will the nanoscale-size interphase between the two domains, whose properties are important for understanding the overall material behavior. Through characterization of this interphase the results of the research will provide a fundamental understanding of nanostructured materials for technological applications including but not limited to applications in structural composites and nano/microelectronics. The project includes the training of one graduate student, one postdoctoral researcher, and an undergraduate researcher in research in polymer physics, thermal analysis, behavior of interphases, and nanostructured materials. A strong effort will be made to include minority and female students. The project will include outreach to K-12 students, including organization of several one-week long materials modules for the TTU program "Science – It's a Girl Thing" for junior high school girls. TECHNICAL SUMMARYTwo model polymeric systems with slowly relaxing glassy interphases will be investigated, namely, the rigid amorphous fraction (RAF) in semicrystalline poly(ethylene terephthalate) (PET) and the immobile glassy layer at the particle interface in hairy polystyrene-grafted silica nanoparticles. The properties and relaxation dynamics of the glassy interphases will be studied as a function of morphology in the PET system and as a function of graft density, graft chain length, and silica content in the nanoparticle system. Dilatometry and nanocalorimetry experiments will aim to determine the length scale, glass transition temperature (Tg), and breadth of Tg for the rigid or "immobile" interphases, the temperature dependence of the segmental relaxation times associated with the rigid or "immobile" phases, and in the case of the semicrystalline polymer, the interplay and competition between structural recovery and crystallization as a function of material morphology. A unique temperature perturbation experiment will be implemented to allow structural recovery to be differentiated from crystallization in the semicrystalline system during isothermal aging experiments and to allow changes in the immobilized surface layer thickness to be quantified in the hairy nanoparticle system.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.