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Molecular structures at the surfaces of self-assembled monolayers and polymer thin films.

机译：自组装单分子层和聚合物薄膜表面的分子结构。

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The present study has focused on in-depth probing of the interfacial molecular structures of two related systems: self-assembled monolayers (SAMs) and thin polymeric films. We have studied the growth mechanism of octadecyltrichlorosilane (OTS) SAMs by probing the alkyl chain conformation using surface-sensitive techniques. Results show that the alkyl chain conformation of OTS monolayers evolves in three stages as monolayer formation progresses. Initially, OTS molecules adsorb from the solution and the surface coverages increase rapidly, yet the alkyl chains within the OTS film still contain disordered gauche conformations. The monolayers then experience a dramatic change from disordered to well-ordered with the alkyl chains adopting an all-trans conformation. Finally, a closely packed OTS monolayer is formed. By correlating sum-frequency (SF) spectroscopy, contact angles, and lateral force microscopy, we found that the adsorption of OTS on fused silica surfaces has two competing growth mechanisms, island growth and uniform growth, and a small amount of water in the deposition solution favors island growth.; We have also studied the molecular orientation of polymer functional groups at the polymer-air, polymer-liquid and polymer-polymer interface. For the first time, we detected SF signals from a polymer-polymer interface. The ester methyl groups on poly(methyl methacrylate) (PMMA) were found to be oriented at the PMMA-polystyrene (PS) interface. In addition to the molecular orientation information that is usually obtained in SF spectroscopy, we have also demonstrated that SF spectroscopy can provide information about the interfacial structure of the polymer blends. From the SF spectra of annealed PS/PMMA blends, their interfacial structure is shown to be laterally discontinuous. Our work in this field opens up a new way to study multicomponent polymeric systems such as polymer blends, copolymers and other binary systems.
机译：本研究的重点是对两个相关系统的界面分子结构的深入研究：自组装单分子膜（SAMs）和聚合物薄膜。我们已经通过使用表面敏感技术探测烷基链构象，研究了十八烷基三氯硅烷（OTS）SAMs的生长机理。结果表明，随着单层形成的进行，OTS单层的烷基链构象分三个阶段发展。最初，OTS分子从溶液中吸收，表面覆盖率迅速增加，但OTS膜中的烷基链仍包含无序的纱状构象。然后，由于采用全反式构象的烷基链，单层经历了从无序到有序的剧烈变化。最后，形成紧密堆积的OTS单层。通过关联和频（SF）光谱，接触角和横向力显微镜，我们发现OTS在熔融石英表面上的吸附具有两个相互竞争的生长机制，即岛状生长和均匀生长，并且沉积物中有少量水解决方案有利于岛屿的发展。我们还研究了聚合物官能团在聚合物-空气，聚合物-液体和聚合物-聚合物界面的分子取向。我们首次检测到来自聚合物-聚合物界面的SF信号。发现聚（甲基丙烯酸甲酯）（PMMA）上的酯甲基位于PMMA-聚苯乙烯（PS）界面。除了通常在SF光谱学中获得的分子取向信息外，我们还证明了SF光谱学可以提供有关聚合物共混物界面结构的信息。从退火的PS / PMMA混合物的SF光谱中，它们的界面结构显示为横向不连续。我们在该领域的工作为研究多组分聚合物体系（例如聚合物共混物，共聚物和其他二元体系）开辟了一条新途径。

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