CAREER: Self-Assembled Light-Sensitive Fluids with Tunable Rheological Properties

“智能”可调流体的基本原理是，人们可以通过紫外线或可见光范围内的光照射来调节含有光活性成分的两亲系统的自组装。PI建议使用这一概念来引起流体流变特性的可逆和剧烈变化。流变转变包括：(a)将低剪切粘度转换1000倍或更高；(b)将流变行为类型从剪切减薄转换为剪切增厚；(c)试样响应从弹性固体切换到粘性液体。PI提出了三种设计这种光流变（PR）流体的策略。前两种策略涉及表面活性剂的蠕虫状胶束的自组装。在这些情况下，光化学转化减少了胶束的轮廓长度或诱导了从线性胶束到分支胶束的转变，这两者都有助于显著降低流体粘度。第三种策略涉及在添加远旋缔合聚合物后形成囊泡凝胶，即囊泡的自组装网络。光照射将囊泡破坏成球形胶束，从而将样品转化为低粘度液体。本研究的基本目标是密切研究这些流体的自组装、微观结构和流变学之间的关系。利用光调节自组装将允许对这些机械问题进行新颖的实验研究。更广泛的影响：光流变（PR）流体为可调流变提供了一种新的选择，并且可能具有实际应用价值。它们的纳米级结构和均匀性将使它们特别适合用于微流体或其他新兴的微尺度技术。利用光来调节流变性，将在亚毫米长度尺度上提供一定程度的空间控制，这是其他方法难以实现的。这项研究还将与以复杂流体为中心的教育、指导和外展活动相结合。PI提议开设一门新的选修课程，内容涉及复杂流体、自组装和软纳米结构，目的是将聚合物和胶体等传统学科的概念统一起来。在这门课程中，他将尝试传授基于其固有介观结构的复杂流体的理解，他将强调化学和生物系统之间的联系。指导活动将针对有才华的本科化学工程师，特别是女性和少数族裔，与研究生一起研究自组装的PR流体。该系多元化的学生群体将有助于这样的招生工作。PI还建议使用各种复杂的流体，包括家用材料和可调的PR系统，创建简单而吸引人的演示，这些演示可以带到马里兰州公立学校的K-12科学教室。这些演示的图片和影片也将在互动网页上播放。

Raghavan, SirnivasaU of Maryland - College Park"CAREER: Self-Assembled Light-Sensitive Fluids With Tunable Rheological Properties" The principle underlying "smart" tunable fluids is that one can tune the self-assembly of amphiphilic systems containing a photoactive component by light irradiation in the UV or visible range. The PI proposes to use this concept to cause reversible and dramatic changes in the rheological properties of the fluid. Rheological transitions include: (a) switching the low-shear viscosity by a factor of 1000 or higher; (b) switching the type of rheological behavior from shear-thinning to shear thickening; and (c) switching sample response from elastic solid to viscous liquid.The PI proposes three strategies for engineering such photorheological (PR) fluids. The first two strategies involve the self-assembly of wormlike micelles from surfactants. In these cases, a photochemical transformation decreases the micellar contour length or induces a transition from linear to branched micelles, both of which serve to dramatically reduce the fluid viscosity. The third strategy involves the formation of a vesicle gel, i.e., aself-assembled network of vesicles, upon addition of a telechelic associating polymer.Light irradiation disrupts the vesicles into spherical micelles, thus converting the sampleinto a low-viscosity liquid. The fundamental goals in this study are to closely investigatethe correlation between self-assembly, microstructure, and rheology in all these fluids.The use of light to tune self-assembly will permit novel experimental studies into thesemechanistic issues.Broader Impact:Photorheological (PR) fluids offer a new alternative for tunable rheology and are likely to have practical applications. Their nanoscale structure and homogeneous nature will make them especially suitable for exploitation in microfluidics or other emerging microscale technologies. The use of light to tune rheology will provide a degree of spatial control on submillimeter length scales that is difficult to achieve by other means.The research also will be integrated with educational, mentoring and outreach activities centered on the subject of complex fluids. The PI proposes to develop a new elective course on Complex Fluids, Self-Assembly and Soft Nanostructures, with the aim of unifying concepts from traditional subjects like polymers and colloids. In this course, he will attempt to impart an understanding of complex fluids based on their inherentmesoscopic structure, and he will highlight the links between chemical and biological systems. The mentoring activities will target talented undergraduate chemical engineers, especially women and minorities, to work with graduate students in studying the self-assembled PR fluids. The diverse student body in the department will facilitate such recruitment efforts. The PI also proposes to create simple and appealing demonstrations using various complex fluids, both household materials as well as the tunable PR systems, that can be taken to K-12 science classrooms in Maryland public schools. Pictures and movies of these demonstrations will also be featured on an interactive web page.