Role of Non-Equilibrium Pinned Layers on the Thermodynamics of Confined Polymer Blends

这项工作将明智地将实验和理论结合起来，探索已知在润湿基材处形成的钉扎聚合物层对受限聚合物混合物的表观热力学的作用。这项研究的目的是研究这一问题，因为最近利用各种辅助工具对受限聚合物共混物的相行为进行的实验表明，相分离温度几乎不受限制条件下的影响。这些结论与现有的平衡态理论在性质上是不一致的，后者一致地预言了禁闭时相混合态的强烈稳定化。由于平衡情景似乎不能解释这些结果，可以推测，实验结果源于一个众所周知的事实，即在实验的时间范围内，可润湿基材附近的熔体链有效地固定在这一边界上。因此，很自然地，剩余的非钉扎链的表观热力学受该钉扎层的存在的影响，从而提供了一种使实验结果合理化的方法。这项研究将使用稀薄的聚合物混合物和填充纳米颗粒的聚合物混合物来详尽地探索这一猜测。小角中子散射和准弹性中子散射实验将与理论和模拟相辅相成，以描绘这种钉扎聚合物层的存在，并深刻理解其对聚合物混合物上层相行为的影响。这些活动与两门新课程的开发紧密相关，这两门课程的标题分别为“纳米材料导论”和“复杂流体的多尺度建模”，这两门课程将提供给大四的本科生。PI还将与特洛伊的少年博物馆合作，开发针对K-12儿童的IMAX风格的电影，讲述聚合物的行为，特别是在表面附近。%聚合物材料可用于各种薄膜应用，如涂料、润滑剂、阻挡涂层、纳米光刻和拟议的光电设备。这项拟议的研究推测，在宏观时间尺度上固定的近表面层深刻地影响了受限聚合物的热力学性质。这些钉扎层还可以强烈地改变这些薄膜的结构，从而改变其机械、热和电性能。这些结论如果得到证实，可能会影响聚合物在当前和未来各种应用中的设计和使用。教育和外展活动的对象是从幼儿园到高级毕业生的学生：这些活动将强调基础表面科学和聚合物在日常生活中的重要性。

This work will judiciously combine experiments and theory to probe the role of pinned polymer layers, which are known to form at wetting substrates, on the apparent thermodynamics of confined polymer mixtures. This research is motivated to study this issue since recent experiments on the phase behavior of confined polymer blends, which utilize a variety of complementary tools, suggest that the phase separation ["binodal"] temperatures are hardly affected on confinement. These conclusions are in qualitative disagreement with existing equilibrium theories, which uniformly predict a strong stabilization of the phase mixed state on confinement. Since equilibrium scenarios do not appear to explain these results, it is conjectured that the experimental findings arise from the well known fact that melt chains in the immediate vicinity of a wettable substrate are effectively pinned to this boundary over the time scale of the experiments. It then naturally follows that the apparent thermodynamics of the remaining, non-pinned, chains are affected by the presence of this pinned layer, thus providing a means of rationalizing the experimental results. This research will use thin polymer mixtures and polymer blends filled with nanoparticles to exhaustively probe this speculation. Small angle neutron scattering and quasi-elastic neutron scattering experiments will be complemented with theory and simulations, to delineate the existence of this pinned polymer layer, and to incisively understand its consequences on the phase behavior of an overlayer of a polymer blend. These activities are strongly coupled to the development of two new courses, titled "Introduction to Nanomaterials" and "Multiscale Modeling of Complex Fluids," which will be offered to senior undergraduate students. The PI will also partner with the Junior Museum in Troy to develop IMAX style movies, aimed at K-12 children, on the behavior of polymers, especially in the vicinity of surfaces.%%%Polymeric materials find use in a myriad of thin film applications, such as paints, lubricants, barrier coatings, in nanolithography and in proposed optoelectronic devices. The proposed research conjectures that a near-surface layer, which is pinned on macroscopic time scales, profoundly affects the thermodynamic properties of confined polymers. These pinned layers could also strongly alter the structure and hence the mechanical, thermal and electrical properties of these thin films. These conclusions, if verified, could impact the design and use of polymers in these wide variety of current and future applications. The educational and outreach activities target students from kindergarten to the advanced graduate: these activities will stress the importance of fundamental surface science and polymers in everyday life.***