Nonlinear Growth of Polyelectrolyte Multilayers: Chain Dynamics and Film Structure

本项目的重点是控制功能聚合物涂层的结构。例如，这种涂层可用于生物医学或光学应用。例如，可以在多阶段、时间分辨方案中局部递送药物的涂层，或者可以作为更好的抗反射光学涂层前体的结构聚合物薄膜。为了支持这些先进的应用，(a)涂层应该能够通过环保工艺轻松沉积在各种表面上，(b)它们的结构应该容易由沉积程序和条件控制。逐层（LbL）技术是一种独特的方法，通过完全在水中沉积的过程，可以在几乎任何表面上创建厚度可控的保形涂层。然而，挑战在于如何控制涂覆膜内聚合物分子的混合，以保持膜层的分层。本项目将探索各种分子和沉积参数对薄膜分层的影响，以实现通过更少步骤沉积的结构化薄膜。先进的仪器技术将用于拍摄多层结构、含水量和薄膜机械性能如何被操纵的快照。重要的是，这个项目将为参与的研究生、本科生和高中生创造一个肥沃的训练场地。PI目前是“材料科学女性”（WIMS）组织的学术顾问，该组织积极参与许多外展活动，从校园参观和女童子军和高中生的示范，到访问当地学校，目的是鼓励和吸引女性和少数民族5-7年级的学生从事科学和工程方面的职业。第二部分：技术概述控制动力学和层接层（LbL）聚电解质薄膜结构的能力是聚电解质多层膜（PEM）先进生物医学和光学应用的核心。特别感兴趣的是具有明确和控制内部分层的薄膜。然而，非线性生长的LbL薄膜（nl -LbL）沉积在更大的厚度上，因此在许多应用中是非常理想的，受到分子混合的影响。本研究旨在(a)揭示NL-PEM薄膜生长过程中聚合物链扩散的机制，(b)建立广泛的NL-PEM薄膜的分子相互作用、动力学和顺序之间的相关性，以及(c)利用这些知识来控制NL-PEM的结构，并制定构建分层和梯度LbL薄膜的策略。该项目将包括通过离子配对或氢键合成定义明确的聚基-聚酸（PB-PA）对。在PEM组装过程中，以及在组装后的步骤中，将研究链间动力学。中子反射法（NR）将用于跟踪聚合物链在薄膜厚度上的扩散，原位椭偏法用于测定薄膜含水量，纳米压痕法用于探索薄膜在构建过程中的机械性能。在组装后的步骤中，NR将用于解决内部分层，并在图案光漂白后荧光恢复（FRAP）研究组装链的横向迁移率。这些知识将用于合理地构建具有可编程密度、含水量、电荷平衡和渗透率的薄膜。它还将使合理设计的扩散屏障和NL-PEM膜内的水含量梯度成为可能，从而使膜成为可用于保形抗反射涂层的基质，或通过改进功能分子的渗透性控制来进行顺序药物输送。

PART I: NON-TECHNICAL SUMMARY This project focuses on controlling the structure of functional polymer coatings. Such coatings could be used, e.g., for biomedical or optical applications. Examples might be coatings that can deliver drugs locally in a multi-stage, time-resolved protocol, or structured polymer films that can serve as precursors for better anti-reflective optical coatings. To support these advanced applications, (a) the coatings should be able to be easily deposited on a variety of surfaces via an environmentally friendly process, and (b) their structure should be easily controlled by the deposition procedure and conditions. The layer-by-layer (LbL) technique is a unique method which, through a deposition process entirely in water can create conformal coatings of controlled thickness on virtually any surface. The challenge, however, is to control the mixing of polymer molecules within the coated film to preserve film layering. This project will explore the effect of various molecular and deposition parameters on film layering, with the goal of achieving structured films which can be deposited through fewer steps. Advanced instrumental techniques will be used to take snapshots of how multilayered structures, water content, and film mechanical properties can be manipulated. Importantly, this project will create a fertile training ground for the participating graduate, undergraduate and high-school students. The PI is currently the academic advisor of the "Women in Materials Science" (WIMS) organization, which is strongly involved in many outreach activities, ranging from on-campus tours and demonstrations for Girl Scouts and high-school students to visits to local schools with the goal of encouraging and engaging female and minority 5-7th graders to pursue careers in science and engineering.PART II: TECHNICAL SUMMARYThe ability to control dynamics and the structure of layer-by-layer (LbL) polyelectrolyte films lies at the heart of advanced biomedical and optical applications of polyelectrolyte multilayer (PEM) films. Of specific interest are films with defined and controlled internal stratification. Yet nonlinearly growing LbL films (NL-LbLs) which deposit at larger thicknesses and therefore are highly desirable for many applications, suffer from molecular intermixing. This proposal aims to (a) uncover the mechanism of polymer chain diffusion within NL-PEMs during film growth, (b) establish correlations between molecular interactions, dynamics, and order for a broad range of NL-PEM films and (c) use this knowledge to control structure of NL-PEMs and develop strategies for constructing stratified and gradient LbL films. This project will involve synthesizing well-defined polybase-polyacid (PB-PA) pairs associated through ionic pairing or hydrogen-bonding. Interchain dynamics will be studied during PEM assembly, as well as at a post-assembly step. Neutron reflectometry (NR) will be used to track diffusion of polymer chains across the film thickness, in situ ellipsometry to determine film water content, and nanoindentation to explore film mechanical properties during film construction. At the post-assembly step, NR will be applied to resolve internal stratification, and fluorescence recovery after pattern photobleaching (FRAP) to study lateral mobility of assembled chains. This knowledge will then be used to rationally construct films with programmable density, water content, charge balance, and permeability. It will also enable rationally designed diffusional barriers and gradients of water content within NL-PEM films, in order to achieve films useful as matrices for conformal antireflective coatings or for sequential drug delivery via improved control of permeability of functional molecules.