EAGER: A New Class of Self-Assembled Photorheological Fluids

1062123 Raghavan光流变（PR）流体是其流变或流动性质（例如其粘度）可通过用光照射而显著改变的那些流体。这种流体的先前配方需要使用复杂的有机分子，例如光响应表面活性剂或聚合物。然而，合成这些复杂分子的难度和成本阻碍了这一领域的研究。需要低成本的PR流体，其可以仅使用简单的市售纳米级两亲性分子制备。如果这种液体是可用的，它可能会对各种科学和工程学科产生变革性影响。在一个成功的CAREER项目的基础上，PI提议探索一类新的光可逆PR流体，该流体可以通过不同波长的光照射从低粘度可逆地转化为高粘度。最重要的是，所提出的流体将仅使用两种市售分子：阳离子表面活性剂和偶氮苯衍生物。EAGER项目的结果可能代表了刺激响应流体领域的概念突破。初步的数据将提供一个框架，一个更大的系统研究光可逆PR流体，水和非水。智力优势：所提出的水性PR流体预计将基于称为“蠕虫状胶束”的自组装纳米结构，其性质将受到偶氮苯光异构体结合程度的影响。用一种波长的光照射预期会拉长这些胶束，从而产生流体粘度的增加。相反，在不同波长的光下照射预期会缩短胶束，从而引起流体粘度的下降。PI假设光异构体平面性的偏差决定了其结合效力。该提案将探讨在稳态和动态（振荡）剪切的流变学响应的PR流体之前，期间和之后，在不同波长的光照射。这些结果将与使用小角中子散射（SANS）和低温透射电子显微镜（cryo-TEM）的微观结构研究相关联。总而言之，这项研究有望为这些新型液体的行为提供一个连贯的科学图景。更广泛的影响：与其他刺激响应系统相比，PR流体代表了一种新鲜而令人兴奋的技术。该项目将通过提供一系列简单、可逆的系统，帮助PR流体“进入主流”，这些系统可以在任何实验室使用低成本的市售分子制备。PR流体的潜在应用包括微流体阀，微型机器人和减阻流体;一旦更多的科学家开始探索这些系统，其他应用可能会出现。此外，从这项工作中获得的光响应自组装的基本见解可以扩展到胶束以外的结构。该项目还将支持马里兰州大学PI系一名学生的研究生培训和教育。

1062123RaghavanPhoto-rheological (PR) fluids are those whose rheological or flow properties such as their viscosity can be dramatically altered by illumination with light. Previous formulations of such fluids have necessitated the use of sophisticated organic molecules such as photo-responsive surfactants or polymers. However, the difficulty and cost involved in synthesizing these complex molecules has hampered research in this field. There is a need for low-cost PR fluids that can be prepared using only simple, commercially available nano-scale amphiphilic molecules. If such fluids were available, it is likely to have a transformative effect on a variety of scientific and engineering disciplines. Building on a successful CAREER project, the PI proposes to explore a new class of photo-reversible PR fluids that can be reversibly transformed from low to high viscosity by irradiation with different wavelengths of light. Most importantly, the proposed fluids will only use two commercially available molecules: a cationic surfactant and an azobenzene derivative. The results of this EAGER project are likely to represent a conceptual breakthrough in the field of stimuli-responsive fluids. The preliminary data will provide a framework for a larger systematic study on photo-reversible PR fluids, both aqueous and non-aqueous. Intellectual Merit: The proposed aqueous PR fluids are expected to be based on self-assembled nano-structures called "wormlike micelles", the properties of which will be impacted by the extent of binding of the azobenzene photoisomer. Irradiation with one wavelength of light is expected to elongate these micelles and thereby produce an increase in fluid viscosity. Conversely, irradiation at a different wavelength of light is expected to shorten the micelles and thereby induce a drop in the fluid viscosity. The PI hypothesizes that deviations from planarity of the photoisomer dictate its binding efficacy. This proposal will explore the rheological response of the PR fluids in steady and dynamic (oscillatory) shear before, during, and after irradiation with light at different wavelengths. The results will be correlated with microstructural studies using small-angle neutron scattering (SANS) and cryo-transmission electron microscopy (cryo-TEM). Altogether, the study is expected to yield a coherent scientific picture for the behavior of these novel fluids. Broader Impact: Compared to other stimuli-responsive systems, PR fluids represent a fresh and exciting technology. This project will help to bring PR fluids "into the mainstream" by offering a range of simple, reversible systems that can be prepared in any laboratory using low-cost commercially available molecules. Potential applications for PR fluids include microfluidic valves, microscale robots, and drag-reducing fluids; additional applications are likely to arise once more scientists begin to explore these systems. Also, fundamental insight on light-responsive self-assembly from this work could be extended to structures other than micelles. This project will also support the graduate training and education of a student in the PI's department at University of Maryland.