NIRT: Molecular Brushes as Components for Nanomechanical Devices

本提案是响应“纳米尺度科学与工程”（NSF 00-119）招标而提交的。微型致动器在短响应时间内产生大的菌株，是纳米和生物技术的兴趣所在。它们可用于制造微流体泵、微型机车和微操纵器。人们普遍认为，从单个大分子中可以制备出非常高效和快速的致动器。由灵活的主链和密集接枝的侧链组成的圆柱形刷状分子是可能的候选者，因为它们可以根据周围环境的变化和外场的影响改变其长度。提出了利用具有刺激响应形状的软圆柱体作为开发纳米机械器件的多功能平台。最有趣的应用之一是分子刷阵列，其一端系在固体基底上，并在入射光下改变其构象。这些层将被设计成产生表面浮雕光栅，沿着衬底平面传播，并传输不同的流体、小颗粒，最终传输生物细胞。为此，在毛刷的化学结构中要么引入红外吸收染料，要么引入光敏偶氮苯和螺吡喃基团。与气管纤毛类似，被束缚的分子会以一种协调的方式来回跳动，并推动覆盖在上面的物质向某个方向移动。该项目将解决三个基本问题：(i)控制电刷分子长度的分子和外部参数是什么？（ii）毛刷分子收缩/伸展时产生的力是什么？（三）系留电刷在偏振光作用下的动态特性是什么？PI将通过采取以下步骤来实现回答这些重要问题的目标。首先，他们将制备一系列定义良好的刷子，并研究侧链长度、接枝密度和光异构基团对刷子分子长度的具体影响。其次，他们将通过原子力显微镜和磁镊子单轴拉伸单个分子和拴在一起的单层分子，研究它们的机械特性。实验研究将得到电刷构象理论分析的支持。第三，建立了结合原子力显微镜的光学装置，对表面浮雕光栅的形貌和衍射效率进行了原位研究。这将允许测量双刷单层的访问和松弛时间，并监测覆盖物质的运输。这个跨学科的项目将基于精确的化学、严格的物理和生物学概念。它为学生提供了一个掌握这些基础学科的绝佳机会，同时获得纳米技术前沿的经验。

0103307SheikoThis proposal was submitted in response to the solicitation "Nanoscale Science and Engineering" (NSF 00-119). Miniature actuators, which produce large strains at short response times are of interest for nano- and biotechnologies. They can be used to construct micro fluidic pumps, tiny locomotives, and micromanipulators. It is generally believed that extremely efficient and fast actuators can be prepared from single macromolecules. Cylindrical brush molecules consisting of a flexible backbone and densely grafted side chains are possible candidates because they can change their length in response to variations in their surrounding environment and the effect of an external field. It is proposed to use soft cylinders with a stimuli-responsive shape as a multifunctional platform for the development of nanomechanical devices. One of the most interesting applications is envisioned for an array of molecular brushes, which are tethered with one end to a solid substrate and change their conformation under incident light. The layers will be designed to generate surface-relief-gratings, which propagate along the substrate plane and transport different fluids, small particles, and ultimately biological cells. For this purpose, either IR-absorber dyes or photosensitive azobenzene and spiropyran moieties will be introduced in the chemical structure of brushes. Similar to tracheal cilia, the tethered molecules will beat back and forth in a coordinated way and propel overlaying substances in a certain direction.The project will address three fundamental questions:(i) What are the molecular and external parameters controlling the length of brush molecules?(ii) What is the force developed during contraction/extension of brush molecules?(iii) What are the dynamic properties of the tethered brushes under the effect of polarized light?The PI's will achieve their goals of answering these important questions by taking the following steps. First, they will prepare a series of well-defined brushes and investigate the specific effects of the side chain length, the grafting density, and the photoisomerizable groups on the length of brush molecules. Second, they will study mechanical properties of individual molecules and tethered monolayers by stretching them uniaxially with an atomic force microscope and magnetic tweezers. The experimental studies will be supported by theoretical analysis of brush conformations. Third, an optical set-up combined with an atomic force microscope will be built for in-situ investigation of the morphology and the diffraction efficiency of the surface relief grating. This will allow the measurement of the access and relaxation times of the double-brush monolayer, and the monitoring of the transport of the overlaying substances.This interdisciplinary project will be based on precise chemistry, rigorous physics, and biological concepts. It presents a perfect opportunity for students to master several of these fundamental disciplines and at the same time gain experience at the cutting edge of nanotechnology.