Nonsolvents cause swelling at the interface with poly(methyl methacrylate) films
Nonsolvents cause swelling at the interface with poly(methyl methacrylate) films
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DOI：
10.1021/la702132t
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发表时间：
2008-01-01
期刊：
影响因子：
3.9
通讯作者：
Nagamura, Toshihiko
中科院分区：
文献类型：
--
作者：
Tanaka, Keiji;Fujii, Yoshihisa;Nagamura, Toshihiko
通过镜面中子反射率（NR）沿垂直于界面的方向研究了在水、己烷和甲醇（这些是全氘代聚甲基丙烯酸甲酯（dPMMA）的“非溶剂”）中旋涂在基底上的dPMMA薄膜的密度分布。与原始的dPMMA - 空气界面相比，dPMMA与这些液体的界面是弥散的；dPMMA与水的界面宽度比与己烷的宽。有趣的是，在水中，dPMMA薄膜除了弥散层外，还由一个溶胀层和内部区域组成，内部区域也含有水。dPMMA与己烷的界面比与水的界面更清晰。尽管在己烷中的dPMMA有轻微的溶胀层迹象，但溶剂分子没有显著渗透到薄膜中。另一方面，在甲醇中，dPMMA薄膜的整个区域都显著溶胀。为了保持质量，非溶剂使薄膜溶胀伴随着薄膜厚度的增加。通过NR估算的薄膜厚度变化与使用原子力显微镜（AFM）直接观察的结果非常吻合。还根据AFM测量的力 - 距离曲线研究了dPMMA在与液体界面附近的模量。模量在靠近薄膜最外层区域时降低。界面区域模量降低的程度与吸收到薄膜中的液体量一致。
Density profiles of a perdeuterated poly(methyl methacrylate) (dPMMA) film spin-coated on a substrate in water, hexane, and methanol, which are "nonsolvents" for dPMMA, were examined along the direction normal to the interface by specular neutron reflectivity (NR). The interfaces of dPMMA with the liquids were diffuse in comparison with the pristine interface with air; the interfacial width with water was thicker than that with hexane. Interestingly, in water, the dPMMA film was composed of a swollen layer and the interior region, which also contained water, in addition to the diffused layer. The interface of dPMMA with hexane was sharper than that with water. Although there were slight indications of a swollen layer for the dPMMA in hexane, the solvent molecules did not penetrate significantly into the film. On the other hand, in methanol, the whole region of the dPMMA film was strikingly swollen. To conserve mass, the swelling of the film by the nonsolvents is accompanied by an increase in the film thickness. The change in the film thickness estimated by NR was in excellent accord with the results of direct observations using atomic force microscopy (AFM). The modulus of dPMMA in the vicinity of the interfaces with liquids was also examined on the basis of force-distance curves measured by AFM. The modulus decreased closer to the outermost region of the film. The extent to which the modulus decreased in the interfacial region was consistent with the amount of liquid sorbed into the film.