Local conformation of poly(methyl methacrylate) at nitrogen and water interfaces
Local conformation of poly(methyl methacrylate) at nitrogen and water interfaces
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DOI：
10.1039/b9py00227h
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发表时间：
2010-04
影响因子：
4.6
通讯作者：
Y. Tateishi;Naoki Kai;H. Noguchi;K. Uosaki;T. Nagamura;Keiji Tanaka
中科院分区：
文献类型：
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作者：
Y. Tateishi;Naoki Kai;H. Noguchi;K. Uosaki;T. Nagamura;Keiji Tanaka
通过红外 - 可见和频产生（SFG）光谱研究了聚甲基丙烯酸甲酯（PMMA）链在氮气（N₂）和水界面处的局部构象。尽管迄今为止已经报道了PMMA在N₂界面处C - H区域的SFG光谱，但峰的归属并不一致。因此，我们首先使用三种不同的氘代PMMA以及普通的质子化PMMA薄膜对SFG峰进行了准确的归属，这些薄膜在高于玻璃化转变温度的条件下长时间充分退火。在N₂界面处，存在诸如α - 甲基、酯甲基和亚甲基等疏水官能团。α - 甲基沿平行于界面的方向取向，而酯甲基和亚甲基垂直于界面取向。通过模型计算有助于对PMMA在N₂界面处官能团取向进行定量讨论。一旦PMMA薄膜与水接触，PMMA侧链的羰基就会朝向水相，与水分子形成氢键，导致酯甲基迁移到薄膜内部区域。同时，亚甲基在水界面处变得随机取向和/或部分迁移到内部区域。有趣的是，α - 甲基仍然存在于水界面处，沿平行方向取向。PMMA在水中的最外层区域可以由亚纳米尺度的亲水和疏水区域组成。水分子在疏水区附近自身形成氢键，导致水分子形成类似冰的结构。然而，与亲水区相邻的水分子与羰基形成氢键。
The local conformation of poly(methyl methacrylate) (PMMA) chains at the nitrogen (N2) and water interfaces was studied by infrared-visible sum-frequency generation (SFG) spectroscopy. Although SFG spectra in the C–H region for PMMA at the N2 interface have been hitherto reported, the peak assignments are not in accord with one another. Thus, we first made accurate assignments of SFG peaks using films, which had been well annealed at a temperature above the glass transition temperature for a long time, of three different deuterated PMMAs as well as normal protonated PMMA. At the N2 interface, hydrophobic functional groups such as α methyl, ester methyl and methylene groups were present. While the α methyl group was oriented along the direction parallel to the interface, ester methyl and methylene groups were oriented normal to the interface. Quantitative discussion concerning the orientation of the functional groups of PMMA at the N2 interface was aided by a model calculation. Once the PMMA film contacted water, the carbonyl groups of the PMMA side chains were oriented to the water phase to form hydrogen bonds with water molecules, resulting in the migration of ester methyl into the internal region of the film. Concurrently, the methylene groups became randomly oriented at the water interface and/or in part migrated into the internal region. Interestingly, the α methyl groups still existed at the water interface oriented along the parallel direction. The outermost region of PMMA in water can consist of hydrophilic and hydrophobic domains with sub-nanometre scale. Water molecules H-bond to themselves near the hydrophobic domains, leading to the formation of an ice-like structure of water molecules. However, water molecules adjacent to the hydrophilic domains H-bond with carbonyl groups.