Structure and Dynamics of Polymeric Complex Fluids

非技术摘要两亲性是具有不同亲和力的端基的分子，可以将不相容的流体组织成具有10-100 nm范围内特征结构的所谓复杂流体相。它们在提高石油采收率、活细胞和食品科学等不同领域都有应用。这项研究项目将表征聚合物基复杂流体的行为，目的是严格测试和完善对这些相的理论理解。这反过来将提高我们对如何最好地利用现有的两亲化合物以及如何为实际应用设计更好的两亲化合物的理解。除了时间平均行为外，这些材料中的热波动将使用新兴的X射线光子相关光谱(XPCS)技术来表征。这些研究将阐明涨落如何依赖于所讨论的相的结构和性质，以及如何从观察到的涨落反过来推断这些性质。总体而言，拟议的实验将创造关于两亲性复杂流体的统计物理的新知识。在研究过程中开发的方法将使来自全国各地的科学家能够更好地进行他们自己的XPCS实验。此外，由于XPCS测量探测更短的长度尺度和更短的时间尺度的承诺是新的第四代X射线源基本原理的重要组成部分，包括斯坦福大学的LCLS、康奈尔大学的ERL和布鲁克海文的NSLS-II，因此这项研究将更好地为有关此类设施的方案和技术决策提供信息。最后，它将有助于下一代散射科学家的教育和培训，使他们准备好在现有和未来的X射线和中子源上进行尽可能好的基于设备的科学研究。技术摘要由于自洽平均场理论适用于聚合物体系，基于嵌段聚合物的复杂流体的研究提供了基本上对复杂流体结构、相行为和动力学的第一性原理理解的前景。在先前工作的基础上，揭示了二元嵌段共聚-均聚物共混物中存在基于膜的海绵(L3)和囊泡(L4)相，这项研究将澄清关于这些材料的相行为和结构的几个关键的未解决的问题，包括非谐贡献对膜弯曲自由能的重要性，膜弹性常数可能的依赖于长度的重整化的影响，膜的高斯曲率的作用，以及连续的L3到L4转变所需的条件。除了时间平均行为外，还将使用新兴的X射线光子相关光谱(XPCS)技术来表征平衡动力学，以阐明平衡涨落的动力学如何取决于所讨论的相的结构和性质，以及如何从观察到的动力学反过来推断这些性质。这项研究还将提高开展X射线光子相关光谱实验的能力，使全国各地的科学家能够进行自己的XPCS研究，并将为下一代国家X射线设施的决策提供依据。它还将有助于教育和培训国家的下一代散射科学家，使他们能够在现有和未来的X射线和中子源上进行尽可能最好的基于设施的科学。

*******NON-TECHNICAL ABSTRACT******* Amphiphiles are molecules with end groups that exhibit very different affinities, and can organize immiscible fluids into so-called complex fluid phases with characteristic structures in the 10-100~nm range. They have applications in such diverse areas as enhanced oil recovery, living cells, and food science. This research project will characterize the behavior of polymer-based complex fluids with the goal of rigorously testing and refining theoretical understanding of these phases. This, in turn, will lead to improvements in our understanding of how to make best use of existing amphiphiles and how to design better ones for practical applications. Beyond the time-averaged behavior, thermal fluctuations in these materials will be characterized using the emerging technique of x-ray photon correlation spectroscopy (XPCS). These studies will elucidate how the fluctuations depend on the structures and properties of the phases in question, and how these properties in turn may be inferred from the observed fluctuations. Overall, the proposed experiments will create new knowledge concerning the statistical physics of amphiphilic complex fluids. Methodologies developed during the research will enable scientists from across the country to better pursue their own XPCS experiments. In addition, because the promise of XPCS measurements probing shorter length scales and shorter time scales is an important component of the rationale for new, fourth-generation, x-ray sources, including LCLS at Stanford, the ERL at Cornell, and NSLS-II at Brookhaven, this research will better inform programmatic and technical decisions concerning such facilities. Finally, it will contribute to the education and training of the next generation of scattering scientists, so that they will prepared to do the best possible facility-based science at existing and future x-ray and neutron sources.*******TECHNICAL ABSTRACT*******Because of the applicability of self-consistent mean-field theory to polymer systems, studies of block polymer-based complex fluids offer the prospect of an essentially first-principles understanding of complex fluid structure, phase behavior, and dynamics. Building on prior work that has revealed the existence of membrane-based sponge (L3) and vesicle (L4) phases in binary block copolymer-homopolymer blends, this research will clarify several key, unresolved questions concerning the phase behavior and structure of these materials, including the importance of anharmonic contributions to the membrane bending free energy, the effect of possible length-scale-dependent renormalization of the membrane elastic constants, the role of the membrane's Gaussian curvature, and the conditions required for a continuous L3-to-L4 transition. Beyond the time-averaged behavior, the equilibrium dynamics will also be characterized using the emerging technique of x-ray photon correlation spectroscopy (XPCS), in order to elucidate how the dynamics of equilibrium fluctuations depend on the structures and properties of the phases in question, and how these properties in turn may be inferred from the observed dynamics. This research will also improve the capabilities for carrying out x-ray photon correlation spectroscopy experiments, enabling scientists from across the country to pursue their own XPCS research, and will inform decisions to be made about the next generation of national x-ray facilities. It will also contribute to the education and training of the nation's next generation of scattering scientists, so that they are capable of carrying out the best possible facility-based science at existing and future x-ray and neutron sources.