Topological shape transitions of colloidal membranes

非技术摘要：阐明薄平板折叠成复杂三维结构的规则对从物理学、材料科学到生物学的广泛领域具有根本意义。例如，具有暴露边缘的平坦2D双层折叠成无边缘3D囊泡的过程对于跨细胞膜的运输以及开发药物递送的新方法是必不可少的。然而，使用纳米尺寸的脂质双层来可视化和量化这种折叠过程目前还不可行。本计画将利用脂双层与胶体单层膜之间的类比，来定量测试囊泡形成与其他折叠过程的基础模型。胶体膜将允许人们测量所有参数，并直接用光学显微镜观察折叠过程，达到传统材料不可能达到的程度。除了可视化封闭囊泡的形成，研究小组还将研究平板折叠成拓扑上更复杂的数学结构的过程，如链状结构和陀螺状结构。与此同时，该团队将开展外展活动，重点是（1）为研究生和本科生提供跨学科科学的严格培训，（2）鼓励代表性不足的群体从事STEM相关领域的工作，（3）提高公众对科学研究对更广泛社区重要性的认识。该项目将积极支持本科生的研究，并将建立在招收来自不同背景的学生的良好记录。他们还将继续参与Cal-Bridge计划，这是一个由NSF资助的计划，其使命是增加进入物理学博士课程的少数民族和女性学生的人数。最后，他们每年还将参加当地中小学的六次外展活动，以促进科学教育。技术摘要：胶体膜是由一个棒状长度的厚的液体状单层排列的单分散棒组成的，它提供了一个独特的机会来探索平面内剪切模量消失的薄片的基本方面。到目前为止，研究主要是检查胶体膜的行为，在政权，他们仍然是平坦的2D结构。当前项目的目标是阐明2D胶体膜折叠成不同的和拓扑上不同的3D架构的基本规律。提出了三个具体目标。在第一个目标中，他们将开发基于主动和被动波动的技术来测量胶体膜的平均和高斯弹性模量，这是确定从最小能量状态弯曲膜所需的能量成本的现象学常数。在第二个目标中，他们将调整胶体膜的微观成分，以研究平坦胶体膜固有的不稳定性和自发折叠成复杂结构的机制。在一个方向上，它们将降低胶体膜的弯曲刚度，以诱导平坦的2D膜折叠成无边缘的3D囊泡，并可视化和量化这种转变的途径。在一个互补的方向，他们将探索的制度是掺杂胶体膜与可混溶的短棒诱导形成显着多样性和拓扑复杂的表面与负高斯曲率。使用最先进的成像技术，他们将阐明驱动这些不稳定性的分子机制。在最后的目标，他们将开发强大的实验工具，使时空外部控制的膜曲率，从而允许一个积极干预正在进行的折叠过程和指导形成的拓扑组装的预定最终shape.This奖反映了NSF的法定使命，并已被认为是值得通过评估使用基金会的智力价值和更广泛的影响审查标准的支持。

Non-technical abstract:Elucidating the rules by which thin flat sheets fold into complex three dimensional structures is of fundamental interest to a broad range of fields ranging from physics, and materials science to biology. For example, the process by which a flat 2D bilayer with exposed edges folds into an edgeless 3D vesicle is essential for transport across cellular membranes and also for developing new methods of drug delivery. However, visualizing and quantifying such folding processes using nanometer-sized lipid bilayers is currently not feasible. This project will use an analogy between lipid bilayer and colloidal monolayer membranes to quantitatively test foundational models of vesicle formation and other folding processes. Colloidal membranes will allow one to measure all the parameters and directly visualize the folding process with optical microscopy, to a degree that is not possible with conventional materials. Besides visualizing closed vesicle formation the team will also study processes by which flat sheets fold into topologically more complex mathematical structures, such as catenoids and Gyroid-like structures. In parallel, the team will pursue outreach activities focused on (1) providing rigorous training in interdisciplinary sciences to graduate and undergraduate students, (2) encouraging underrepresented groups to pursue work in STEM related fields, (3) and raising general awareness of the importance of scientific research to broader communities. This project will actively support undergraduate research and will build on a strong record of recruiting students from diverse backgrounds. They will also continue their involvement with the Cal-Bridge program, a NSF-funded program whose mission is to increase the number of underrepresented minority and female students entering doctoral program in physics. Finally, each year they will also participate in about half a dozen outreach activities at local elementary and middle schools in order to promote science education.Technical abstract: Colloidal membranes, which are comprised of one-rod-length thick liquid-like monolayer of aligned monodisperse rods, offer a unique opportunity to explore fundamental aspect of thin sheets with vanishing in-plane shear modulus. So far, studies have mainly examined the behavior of colloidal membranes in the regime were they remain flat 2D structures. The goal of the current project is to elucidate the fundamental laws by which 2D colloidal membranes fold into diverse and topologically distinct 3D architectures. Three specific aims are proposed. In the first aim they will develop active and passive fluctuations-based techniques to measure the mean and Gaussian elastic moduli of colloidal membranes, the phenomenological constants that determine the energetic cost required to bend a membrane from its minimum energy state. In the second aim they will tune microscopic constituents of colloidal membranes to investigate regimes were flat colloidal membranes are inherently unstable and spontaneously fold into complex structures. In one direction they will reduce the bending rigidity of colloidal membranes to induce folding of flat 2D membranes into edgeless 3D vesicles and visualize and quantify the pathways of this transition. In a complementary direction they will explore the regime were doping colloidal membranes with miscible short rods induces formation of remarkably diverse and topological complex surfaces with negative Gaussian curvatures. Using state of the art imaging technique they will elucidate the molecular mechanisms that drive these instabilities. In the final aim they will develop robust experimental tools that will enable spatiotemporal external control of the membrane curvature, thus allowing one to actively intervene in the ongoing folding processes and guiding formation of topological assemblages of predetermined final shape.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.