ISS: GOALI: Nonequilibrium Processing of Particle Suspensions with Thermal and Electrical Field Gradients

胶体颗粒是直径大约在1纳米到1微米之间的颗粒。它们可以被看作是建筑材料的块，就像形成分子和晶体的原子一样。在胶体晶体中，颗粒在从纳米到毫米或更大的长度范围内有序地组织成周期性结构。胶体晶体的研究受到几个因素的推动。它们可以用来回答与材料组装相关的基本问题，并且它们在电子学，光子学和生命科学中有许多潜在的应用。然而，在地球上观察到的丰富多样的胶体晶体结构受到重力作用的影响，这导致颗粒沉降，并可能导致周围流体的运动。在这项研究中，一组研究人员将在地球上的正常重力实验和国际空间站（ISS）的微重力实验中研究胶体晶体的形成。这些实验将揭示重力和外力对粒子组装的重要作用。最终，研究人员将更好地了解如何操纵外力来创建胶体晶体，以便在地球和太空中进行高分辨率3D打印。粒子悬浮液中亚稳相和玻璃相的形成机制将在国际空间站进行研究，并在地球上进行比较。胶体粒子悬浮液是利用长时间微重力的合理候选者，因为(i)它们对广泛的地面和空间应用很重要，（ii）它们在粒子水平上具有宏观粒子输运和结构转换之间耦合的共同特征，（iii）迄今为止尚未对在地球实验中观察到的悬浮液中结构形成的基本特征做出充分的解释。虽然用于地面和微重力实验的时间和设备有限，但研究小组计划在许多这些领域产生影响，因为他们新使用了场梯度来操纵颗粒密度，这是悬浮液的控制参数。因此，不是使用许多不同的样品来获得感兴趣的颗粒密度范围，而是将单个样品安排在样品池中的场梯度中以覆盖该范围。由于悬浮实验中粒子密度是直接通过显微镜测量的，因此不需要先验的梯度剖面知识。实验包括设置场梯度和观察产生的结构，然后局部混合一个已知密度的区域，观察它的玻璃化或结晶。悬浮液流变学的一些知识将来自混合过程的观察，但定量数据将来自通过跟踪颗粒热运动的微流变学测量。在这些研究中，胶体悬浮液与真实时空微观观察的使用使它们对各级学生的教学特别有吸引力。我们已经并将继续参与利用空间主题来提高STEM兴趣和技能的教育项目，与教育专业人员合作，将项目工作转化为有利于初高中学生的课程计划，并让高中生和本科生参与实验室工作，以及培训和教育本科生和研究生。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。

Colloidal particles are particles with diameters between approximately 1 nanometer and 1 micron. They can be considered as blocks for building materials, like atoms for forming molecules and crystals. In colloidal crystals, the particles are organized in periodic structures with ordering on a range of length scales from nanometers to millimeters or larger. Research on colloidal crystals is motivated by several factors. They can be used to answer fundamental questions related to the assembly of materials, and they have many potential applications in electronics, photonics, and life sciences. However, the rich variety of colloidal crystal structures observed on earth are influenced by the effects of gravity, which leads to particles settling and may lead to motion of the surrounding fluid. In this study, a team of researchers will study colloidal crystal formation in both normal gravity in Earth-based experiments and in microgravity on the International Space Station (ISS). These experiments will reveal the important roles that gravity and external forces play on particle assembly. Ultimately, the researchers will obtain a better understanding of how to manipulate external forces to create colloidal crystals for high resolution 3D printing on Earth and in space. Mechanisms for formation of metastable and glassy phases in particle suspensions will be studied in the ISS and for comparison on Earth. Colloidal particle suspensions are the logical candidates to take advantage of long duration microgravity because (i) they are important for a wide range of terrestrial and space applications, (ii) they share the common feature of coupling between macroscopic particle transport and structure transformations at a particle level and (iii) an adequate explanation for basic features of structure formation in suspensions observed in Earth experiments has not been made to date. Although the time and equipment available for both ground and microgravity experiments is limited, the team of researchers plans to have an impact in many of these areas due to the novel use of field gradients to manipulate the particle density, which is the control parameter for suspensions. Thus, instead of using many different samples to access the interesting range of particle densities, a single sample will be arranged in a field gradient in the sample cell to cover this range. As the particle density is directly measured by microscopy in suspension experiments, a priori knowledge of the gradient profile is not required. The experiments involve setting up the field gradients and observing the resulting structures and then locally mixing a region of known density to watch it glassify or crystallize. Some knowledge of the suspension rheology will come from observations of mixing processes, but quantitative data will come from microrheology measurements through tracking particle thermal motion. The use of colloidal suspensions with real space-time microscopic observations in these studies makes them particularly attractive for teaching students at all levels. We have and will continue to participate in education programs that use space themes to improve interest and skills in STEM, to work with educational professionals to translate the project work to lesson plans for the benefit of students in middle and high school grades and to engage high school and undergraduate students in laboratory work as well as to train and educate undergraduate and graduate students.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.