Collaborative Research: Role of Polymer Sequence on Penetrant Transport in Charged Brushes

通过将聚合物接枝到表面而产生的分子级刷子可用于控制表面的性质，包括其电荷、润湿性、渗透性以及对环境条件（如盐浓度）的响应。原则上，聚合物刷涂表面对于药物输送、化学分离过程和水净化等重要应用具有潜在的变革性技术。选择性地控制小分子和颗粒进出刷子的运输对于这些应用是必要的，但是这样做的能力仍然是一个持续的挑战，因为很难调整刷子的结构。该研究项目将通过设计组成聚合物刷的单体序列来控制刷的构象及其对环境条件的响应。该团队将把工程刷的结构与小分子和颗粒在静态和流动条件下如何通过它们联系起来。这项研究将通过了解带电聚合物的序列如何影响渗透剂的运输来解决一个关键的知识空白，从而改进用于水和生物药物净化的膜涂层。项目团队将通过当地会议（包括德克萨斯州软物质会议）将这些结果传播给休斯顿石化、生物医学和材料行业的科学家和工程师。与此同时，他们将在休斯顿都会区用多种语言制作有关水净化的教育外展视频，并在休斯顿能源节上为公众展示实际操作演示。这个项目的目的是发展聚合物序列对带电聚合物电刷内传输的影响的基本理解。来自休斯顿附近两所大学的团队成员将整合在序列控制聚合物合成（马塞尔-赖斯大学），中子散射应用于刷子（康拉德-休斯顿大学）和最先进的显微镜技术（马塞尔和康拉德）方面的互补专业知识，以解决三个具体目标：(1)确定聚合物序列对电刷性能的影响；(2)确定渗透剂和带电聚合物电刷动力学之间耦合的机制；(3)了解流动对带电聚合物电刷中非平衡渗透剂传输的影响。蛋白质工程方法将用于合成序列控制的带电聚合物，并进行同位素标记，用于掠入射小角中子散射（GI-SANS）和中子反射率（NR）实验，以测量平衡和非平衡条件下的电刷构象和高度。渗透传输系数将使用共聚焦和全内反射荧光相关光谱（TIR-FCS）来测量，利用垂直灵敏度来区分刷内和刷外的传输，并根据聚合物基质和多孔介质中的扩散和分散理论进行测试。总之，这些研究将为电荷间距和分数对带电刷中渗透剂扩散和流动驱动输运的作用提供新的见解，这将为设计先进的响应表面铺平道路。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Molecular-scale brushes, created by grafting polymers to surfaces, can be used to control the properties of the surface, including its charge, wettability, permeability, and response to environmental conditions such as salt concentration. In principle, polymer brush-coated surfaces are potentially transformative technologies for important applications in drug delivery, chemical separation processes, and water purification. Selectively controlling the transport of small molecules and particles into and out of the brush is necessary for these applications, but the ability to do so remains a persistent challenge because it is difficult to tune the structure of the brush. This research project will develop a route to control brush conformation and its response to environmental conditions by engineering the sequence of monomers that compose the polymer brush. The team will relate the structure of the engineered brushes to how small molecules and particles move through them under static and flow conditions. This research will address a critical knowledge gap by providing understanding of how the sequence of charged polymers affect the transport of penetrants, leading to improved membrane coatings for water and biologic drug purification. The project team will disseminate these results to scientists and engineers in Houston’s petrochemical, biomedical, and materials industries through local meetings, including the Texas Soft Matter Meeting. In parallel, they will develop educational outreach videos on water purification in multiple languages spoken in the Houston metro area, and present hands-on demonstrations for the general public at the Houston Energy Festival.The objective of this project is to develop fundamental understanding of the influence of polymer sequence on transport within charged polymer brushes. Team members from two nearby universities in Houston will integrate complementary expertise in sequence-controlled polymer synthesis (Marciel – Rice University), neutron scattering applied to brushes (Conrad – University of Houston), and state-of-the-art microscopy techniques (Marciel and Conrad) to address three specific aims: (1) determine the role of polymer sequence on brush properties, (2) identify mechanisms that dictate coupling between penetrant and charged polymer brush dynamics, and (3) understand the effects of flow on out-of-equilibrium penetrant transport in charged polymer brushes. Protein engineering methodologies will be used to synthesize sequence-controlled charged polymers with isotopic labelling for grazing-incidence small angle neutron scattering (GI-SANS) and neutron reflectivity (NR) experiments to measure brush conformation and height in equilibrium and out-of-equilibrium conditions. Penetrant transport coefficients will be measured using confocal and total internal reflection fluorescence correlation spectroscopy (TIR-FCS), exploiting vertical sensitivity to distinguish transport inside and outside brushes and tested against theories for diffusion and dispersion within polymer matrices and in porous media. Together, these studies will provide new insight into the role of charge spacing and fraction on the diffusive and flow-driven transport of penetrants in charged brushes, which will pave the way for the design of advanced responsive surfaces.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.