Sun Xiaokang, Liu Kai, Zhao Nie, Bian Fenggang, Yang Chunming, Huang Yuying
College of Materials Science and Engineering, Xiangtan University, Xiangtan 411105, Hunan Province China.
Shanghai Synchrotron Radiation Facility, Shanghai Advanced Research Institute, Chinese Academy of Sciences, 239 Zhang Heng Road, Pudong New District, Shanghai 201204, China.
J Phys Chem B. 2022 Feb 24;126(7):1625-1632. doi: 10.1021/acs.jpcb.1c09443. Epub 2022 Feb 10.
Directed self-assembly of block copolymers (BCPs) is widely investigated for its potential application in surface patterning. The self-assembly kinetics of BCP based on modified layers is the key to realizing structural control for obtaining highly ordered lamellar grains. In this study, morphological evolution of PS--PMMA films during the thermal-induced self-assembly process was investigated via the in situ grazing-incidence small-angle X-ray scattering (GISAXS) technique. In the first heating stage, reorientation of lamellar grains occurred as the temperature increased above the glass transition temperature. Then, a fast increase in the lamellar repeat period was observed, which is considered as a phase separation process. Whereas the size of the lamellar grain ξ was observed to have rapidly increased in the stage wherein the temperature was held at 230 °C, the was almost constant. This result indicates that the formation of ordered structure in PS--PMMA films was mainly determined by two periods: phase separation of block molecules followed by growth of grains in the nanodomain. In addition, it was interesting that the better-order nanodomains were obtained with thermal annealing at a faster heating rate. These findings suggest that accomplishing ordered structure control in a large area could be realized via the design of a proper heating profile.
嵌段共聚物（BCP）的定向自组装因其在表面图案化方面的潜在应用而受到广泛研究。基于改性层的BCP自组装动力学是实现结构控制以获得高度有序层状晶粒的关键。在本研究中，通过原位掠入射小角X射线散射（GISAXS）技术研究了热诱导自组装过程中PS-PMMA薄膜的形态演变。在第一个加热阶段，随着温度升高到玻璃化转变温度以上，层状晶粒发生重新取向。然后，观察到层状重复周期迅速增加，这被认为是一个相分离过程。而在温度保持在230°C的阶段，层状晶粒尺寸ξ迅速增加，而层间距几乎保持不变。该结果表明，PS-PMMA薄膜中有序结构的形成主要由两个阶段决定：嵌段分子的相分离，随后是纳米域中晶粒的生长。此外，有趣的是，以较快加热速率进行热退火可获得更好有序的纳米域。这些发现表明，通过设计适当的加热曲线可以实现大面积有序结构的控制。
