Novel Mixed Brushes with Tunable Internal Structures of Various Length Scales

该奖项是根据2009年《美国复苏和再投资法案》(Public Law 111-5)资助的。技术摘要：采用实验和理论相结合的方法，拟议的研究旨在提供对新型混合聚合物刷子系统热力学的基本理解，即由相互不相容的横向可移动、弱聚电解质和中性聚合物链组成的混合刷子。这种新型的混合刷子系统提供了以前无法获得的机会(I)通过两种链类型之间的长程受挫横向相分离来产生各种长度尺度的介观表面图案，以及(Ii)产生表面性质可在带电状态和非带电状态之间切换的功能界面。这些性能只有通过这种具有横向可移动接枝点的可电离聚合物和中性聚合物的独特组合才能实现，具有巨大的潜力，可用于以下领域的先进技术目的：(I)用于先进制造二维纳米/微结构的功能表面图案化；(Ii)生物医学传递和检测。了解控制混合电刷行为的热力学对于进一步开发这些技术应用是至关重要的。这项研究的具体目标是建立和了解模型混合刷子系统的主要热力学性质，包括(A)二维相行为，(B)相分离区域结构，(C)侧向刷子可压缩性和(D)链构象，在空气-水界面使用混合两嵌段共聚物构建的混合刷子系统。我们将利用荧光/原子力显微镜成像、压力-面积等温线和中子/X射线反射率测量等综合实验技术来研究这种混合刷子体系，以确定刷子的分子特征(即聚合物相对分子质量、刷子组成和链接枝密度)和溶液静电环境(即介质的pH和离子强度)如何影响混合刷子系统的上述性能。这些实验研究将得到自洽场(SCF)理论研究的补充，以建立对实验结果的一致和理论上的合理理解。非技术总结：拟议研究的智力价值在于，通过实验和理论的独特结合，这项研究将提供对这种新型混合聚电解质刷子系统的相行为和结构的有用理解。从这项研究中获得的知识也将对发展对受挫相分离的普遍理解具有重要意义。在从生物细胞膜到二维电子系统的各种材料中广泛观察到的现象。拟议活动的更广泛影响是深远的。用混合聚电解质和中性聚合物刷子配制材料表面代表了一种新的范式，作为一种通用方法学，适用于包括纳米/微制造和生物医学技术在内的各种先进技术，拟议的研究将为这些领域的进一步技术发展提供必要的基础材料科学基础。拟议的研究将在一个多学科、协作和智力激发的环境中为研究生和本科生提供综合培训，以学习下一代聚合物/软材料科学家所需的技能。拟议研究的各个方面将用于加强聚合物和纳米医学领域的课程。

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).TECHNICAL SUMMARY:Using a combined experimental and theoretical approach, the proposed research aims to provide fundamental understanding of the thermodynamics of novel mixed polymer brush systems, namely, the mixed brushes composed of laterally-mobile, weak polyelectrolyte and neutral polymer chains that are mutually incompatible. This novel mixed brush system offers previously unavailable opportunities (i) to produce mesoscopic surface patterns of various length scales by long-range-frustrated lateral phase separation between the two chain types and (ii) to create functional interfaces with surface properties switchable between charged and non-charged states. These properties, achievable only with this unique combination of ionizable and neutral polymers with laterally-mobile grafting points, have enormous potential to be used for advanced technological purposes in such areas as (i) functional surface patterning for advanced fabrication of two-dimensional nano/microstructures and (ii) biomedical delivery and detection. Understanding of the thermodynamics that governs the behavior of the mixed brushes is essential to furthering the development of these technological applications. The specific objectives of this research are to establish and understand the key thermodynamic properties, including (a) two-dimensional phase behavior, (b) phase-separated domain structures, (c) lateral brush compressibility and (d) chain conformations, of a model mixed brush system constructed using mixed diblock copolymers at the air-water interface. This mixed brush system will be studied using combined experimental techniques of fluorescence/AFM imaging, pressure-area isotherm and neutron/x-ray reflectivity measurements, to establish how the brush molecular characteristics (i.e., polymer molecular weights, brush composition, and chain grafting density) and the solution electrostatic environment (i.e., pH and ionic strength of the medium) influence the above-mentioned properties of the mixed brush system. These experimental investigations will be complemented by self-consistent field (SCF) theoretical studies to establish a consistent and theoretically sound understanding of the experimental results.NON-TECHNICAL SUMMARY:The intellectual merit of the proposed research is that, by using a unique combination of experiment and theory, this research will provide a useful understanding of the phase behavior and structures of this new class of mixed polyelectrolyte brush system. The knowledge gained from this research will also have great implications for developing a generalized understanding of the ?frustrated phase separation? phenomena widely observed in various materials ranging from biological cell membranes to two-dimensional electronic systems. The broader impacts of the proposed activities are far reaching. Formulating the surface of a material with a mixed polyelectrolyte and neutral polymer brush represents a new paradigm applicable, as a generic methodology, to a wide variety of advanced technologies, including nano/micro fabrication and biomedical technologies, and the proposed research will provide the fundamental materials science groundwork necessary for further technological development in these areas. The proposed research will provide integrated training for graduate and undergraduate students in a multidisciplinary, collaborative and intellectually stimulating environment to learn skills necessary for the future generation of polymer/soft materials scientists. Aspects of the proposed research will be used to enhance curricula in the areas of polymers and nanomedicine.