Relaxation of Slow Glassy Interphases in Polymeric Systems

非技术总结将使用两种独特的技术研究两种模型聚合物体系中的玻璃态界面：用于测量体积和热膨胀系数的膨胀率测定法和用于测量热容和其他重要热性能的超快量热法。 这些互补技术将用于确定几种纳米结构材料中界面相的尺寸、性质和动态行为。 例如，半结晶聚合物将被研究，因为这些材料由结晶和非结晶域组成。 两个区域之间的纳米级界面也是如此，其性质对于理解整体材料行为非常重要。 通过表征这种界面的研究结果将提供一个基本的理解纳米结构材料的技术应用，包括但不限于在结构复合材料和纳米/微电子学的应用。该项目包括培养一名研究生、一名博士后研究员和一名本科生研究员，从事聚合物物理、热分析、界面行为和纳米结构材料的研究。 将大力吸收少数民族学生和女学生。 该项目将包括对K-12学生的宣传，包括为TTU方案“科学-这是女孩的事”为初中女生组织几个为期一周的材料模块。 将研究两种具有缓慢松弛玻璃态界面的模型聚合物系统，即半结晶聚对苯二甲酸乙二醇酯（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颗粒界面处的不动玻璃态层。 玻璃界面的性质和弛豫动力学将作为PET系统中的形态的函数和作为纳米颗粒系统中的接枝密度、接枝链长度和二氧化硅含量的函数进行研究。膨胀和纳米量热实验的目的是确定的长度尺度，玻璃化转变温度（Tg），和Tg的宽度为刚性或“不动”的中间相，与刚性或“不动”相关联的节段弛豫时间的温度依赖性，并在半结晶聚合物的情况下，作为材料形态的功能的结构恢复和结晶之间的相互作用和竞争。 一个独特的温度扰动实验将被实施，以允许在等温老化实验期间在半结晶系统中区分结构恢复和结晶，并允许在毛状纳米颗粒系统中量化固定化表面层厚度的变化。该奖项反映了NSF的法定使命，并被认为值得通过使用基金会的智力价值和更广泛的影响进行评估来支持审查标准。

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.