RII Track-4: NSF: Understanding Microstructure Evolution in Stimuli-Responsive Yield-Stress Fluid-Assisted 3D Printing: Linking Microstructures to Macroscale Rheological Properties

最近，一种创新的三维(3D)打印方法被提出并开发出来，用于制造任意结构的零件。在该方法中，3D结构在独特的液体支撑浴中自由打印，具有可由打印条件或工作环境控制的所需属性。虽然这种方法具有比目前许多3D打印方法更好的打印能力，但独特的支撑浴材料的工作机理仍然不清楚，这阻碍了这种3D打印方法的进一步发展。本项目旨在研究一种具有代表性的热敏支撑浴材料在不同温度和印刷条件下的微观结构变化。该项目的成果可以指导更多支撑浴的设计，并从根本上解释支撑浴内印花的工作机理。这项拟议的研究将通过加快3D打印技术的发展来提升美国的制造能力，从而产生深远的社会影响。此外，该项目将通过各种活动促进内华达州从K-12到毕业的学生的教育，包括动手的K-12实验室活动、涉及研究模块的课程，以及在里诺内华达大学指导来自代表性不足背景的学生。研究基础设施改进Track-4 EPSCoR研究人员(RII Track-4)项目将为内华达大学雷诺分校(UNR)的一名助理教授提供奖学金，并为一名研究生提供培训。刺激响应型屈服应力流体是在常规屈服应力材料的基础上发展起来的，它可以通过对施加的剪应力和外部刺激的响应来改变流变性/行为。这种双重响应性使刺激响应型屈服应力流体有望用于支持浴辅助3D打印，因为通过施加外部刺激以获得所需的流变性，可以在打印过程中很容易地添加支持浴材料，并在打印后将其移除，从而使打印具有任意结构的3D结构在技术上是可行的。然而，到目前为止，微观结构演化和宏观流变性变化之间的相互关系仍然难以捉摸。因此，本项目的首要目标是通过纳米材料表征、数学建模、分子动力学模拟和流变测试，从根本上了解具有代表性的屈服-应力流体-Pluronic F127-纳米粘土纳米复合材料在不同应力和温度条件下的微观结构演变。为了实现这一目标，将追求两个综合的研究目标：(1)通过纳米材料表征技术和数学建模来表征/建立Pluronic F127-纳米粘土纳米复合材料的静态微结构模型；(2)通过分子动力学模拟和流变性能测试来探索温度和应力诱导的微结构演化。完成这些目标将建立一个将微观结构与支持浴材料的宏观流变性联系起来的范例，促进未来3D打印应用中更先进的刺激响应型屈服应力流体的开发。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。

Recently, an innovative three-dimensional (3D) printing method has been proposed and developed to fabricate parts with arbitrary architectures. In this method, a 3D structure is freeform printed within a unique liquid support bath with desired properties that are controllable by either printing conditions or working environments. Although this method presents a better printing capability than many current 3D printing approaches, the working mechanisms of unique support bath materials are still elusive, which has hampered the further development of this 3D printing method. The project aims to investigate the microstructure changes of a representative thermosensitive support bath material at different temperatures and printing conditions. The achievements of this project can guide the design of more support baths as well as fundamentally explain the working mechanisms of printing within a support bath. The proposed research will have a profound societal impact by accelerating the development of 3D printing technology to enhance the manufacturing capability in the United States. In addition, the project will promote the education of students from K-12 to graduate in the State of Nevada through diverse activities, including hands-on K-12 lab activities, research module-involved curricula, and mentorship of students from underrepresented backgrounds at the University of Nevada, Reno. This Research Infrastructure Improvement Track-4 EPSCoR Research Fellows (RII Track-4) project would provide a fellowship to an Assistant professor and training for a graduate student at the University of Nevada Reno (UNR). Stimuli-responsive yield-stress fluids, developed on the basis of regular yield-stress materials, can change rheological properties/behaviors by responding to both applied shear stress and external stimuli. This dual-responsiveness makes stimuli-responsive yield-stress fluids promising for support bath-assisted 3D printing because a support bath material can be easily added during printing and removed after printing by applying external stimuli to achieve desired rheological properties, making it technically feasible to print 3D structures with arbitrary architectures. However, the interrelationships between microstructure evolution and macroscale rheology change of stimuli-responsive yield-stress fluids have so far remained elusive. Thus, the overarching goal of this project is to fundamentally understand the microstructure evolution of a representative stimuli-responsive yield-stress fluid—Pluronic F127-nanoclay nanocomposite—under different stress and temperature conditions through nanoscale material characterization, mathematical modeling, molecular dynamics simulation, and rheological testing. To achieve this goal, two integrated research objectives will be pursued: (1) characterize/establish static microstructure models in Pluronic F127-nanoclay nanocomposite via nanoscale material characterization techniques and mathematical modeling; and (2) explore temperature- and stress-induced microstructure evolutions via molecular dynamics simulation and rheological property testing. Completing the objectives will establish a paradigm for linking microstructures to macroscale rheological properties of support bath materials, promoting the development of more advanced stimuli-responsive yield-stress fluids for 3D printing applications in the future.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.