Relaxation of Slow Glassy Interphases in Polymeric Systems

非技术总结将使用两种独特的技术来研究两种模型聚合体系中的玻璃态中间相：膨胀法测量体积和热膨胀系数，超快量热法测量热容和其他重要的热性能。这些互补的技术将被用来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，我们将研究半结晶聚合物，因为这些材料由晶区和非晶区组成。两个结构域之间的纳米级界面也是如此，它们的性质对于理解整体材料行为非常重要。通过对这种界面相的表征，研究结果将使人们对纳米结构材料在技术上的应用有一个基本的了解，包括但不限于在结构复合材料和纳米/微电子方面的应用。该项目包括培训一名研究生、一名博士后研究员和一名本科生研究聚合物物理、热分析、相间行为和纳米结构材料。将大力吸纳少数民族和女性学生。该项目将包括对K-12学生的外展，包括为TTU为初中女孩举办的“科学--这是女孩的事情”项目组织了几个为期一周的材料模块。技术总结将研究两种具有缓慢松弛玻璃态界面相的模型聚合物体系，即半结晶聚对苯二甲酸乙二酯(PET)中的刚性无定形部分(RAF)和毛状聚苯乙烯接枝二氧化硅纳米颗粒中粒子界面处的静止玻璃层。玻璃化中间相的性质和松弛动力学将作为PET系统中形态的函数以及作为纳米粒子系统中接枝密度、接枝链长和二氧化硅含量的函数来研究。膨胀和纳米量热实验的目的是确定刚性或“静止”中间相的长度尺度、玻璃化转变温度(Tg)和宽度，与刚性或“静止”相有关的链段松弛时间的温度依赖性，以及对于半结晶聚合物，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。将实施一项独特的温度微扰实验，以便在等温老化实验期间区分半晶体系统中的结构恢复和结晶，并允许在多毛纳米粒子系统中量化固定表面层厚度的变化。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势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.