Kikuchi Mao, Hara Mitsuo, Nagano Shusaku, Ebe Hinako, Matsui Jun
Graduate School of Science and Engineering, Yamagata University, 1-4-12 Kojirakawa-Machi, Yamagata 990-8560, Japan.
Faculty of Engineering and Design, Kagawa University, Hayashi-Cho, Takamatsu, Kagawa 761-0396, Japan.
J Phys Chem B. 2024 Aug 8;128(31):7681-7689. doi: 10.1021/acs.jpcb.4c03123. Epub 2024 Jul 24.
In this paper, we describe the formation of an ordered structure in a copolymer thin film through hydration, which subsequently transitions to a different ordered structure upon dehydration. A statistical copolymer of poly(-octadecyl acrylamide--hydroxymethyl acrylamide) with a comonomer content ratio of 1:1, denoted as p(ODA50/HEAm50), was synthesized via free radical copolymerization. We prepared a thin film of this copolymer on a solid substrate and annealed it at 60 °C under humid conditions. This treatment formed a side-chain segregated lamellar (SCSegL) structure, in which the ODA and HEAm units are oriented perpendicularly to the polymer backbone and opposite each other. Increasing the annealing temperature to 90 °C led to a transition to a side-chain mixed lamellar (SCMixL) structure, where the ODA and HEAm units are also oriented perpendicularly to the polymer backbone but in both directions. The quartz crystal microbalance (QCM) data indicate that p(ODA50/HEAm50) exhibits LCST-like behavior with a transition temperature of approximately 50 °C. We conclude that the formation of the SCSegL structure at 60 °C is due to pronounced segregation between the water-adsorbed HEAm groups and the hydrophobic ODA. Conversely, dehydration at 90 °C reduces the segregation forces, forming the SCMixL structure, which exhibits lower strain. These results demonstrate that the p(ODA50/HEAm50) film undergoes an order-to-order transition driven by the hydration-dehydration process. Additionally, we found that changes in the lamellar structure significantly alter the swelling properties of the film.
在本文中，我们描述了共聚物薄膜通过水合作用形成有序结构，随后在脱水时转变为另一种有序结构。通过自由基共聚合成了一种共聚单体含量比为1:1的聚（十八烷基丙烯酰胺 - 羟甲基丙烯酰胺）统计共聚物，记为p(ODA50/HEAm50)。我们在固体基板上制备了这种共聚物的薄膜，并在潮湿条件下于60°C进行退火处理。这种处理形成了侧链分离层状（SCSegL）结构，其中ODA和HEAm单元垂直于聚合物主链且彼此相对取向。将退火温度提高到90°C会导致转变为侧链混合层状（SCMixL）结构，其中ODA和HEAm单元同样垂直于聚合物主链，但在两个方向上排列。石英晶体微天平（QCM）数据表明，p(ODA50/HEAm50)表现出类似最低临界溶液温度（LCST）的行为，转变温度约为50°C。我们得出结论，60°C时SCSegL结构的形成是由于水吸附的HEAm基团与疏水性ODA之间明显的分离。相反，90°C时的脱水降低了分离力，形成了应变较低的SCMixL结构。这些结果表明，p(ODA50/HEAm50)薄膜经历了由水合 - 脱水过程驱动的有序到有序的转变。此外，我们发现层状结构的变化显著改变了薄膜的溶胀性能。
