Ma Boo Soo, Lee Jin-Woo, Park Hyeonjung, Kim Bumjoon J, Kim Taek-Soo
Department of Mechanical Engineering, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 34141, Republic of Korea.
Department of Chemical and Biomolecular Engineering, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 34141, Republic of Korea.
ACS Omega. 2022 Jun 1;7(23):19706-19713. doi: 10.1021/acsomega.2c01451. eCollection 2022 Jun 14.
The thermomechanical behavior of a conjugated polymer (CP) in a thin film state has rarely been studied despite the importance of understanding the polymer morphologies and optimizing the thermal processes of organic semiconductors. Moreover, the seamless integration of multilayers without mechanical failures in CP-based electronic devices is crucial for determining their operational stability. Large differences in the coefficients of thermal expansion (CTEs) between the multilayers can cause serious degradation of devices under thermal stress. In this study, we measure the intrinsic thermomechanical properties of poly(3-hexylthiophene) (P3HT) thin films in a pseudo-freestanding state on the water surface. The as-cast P3HT thin films exhibited a large thermal shrinkage (-1001 ppm K) during heating on the water surface. Morphological analyses revealed that the thermal shrinkage of the polymer films was caused by the rearrangement of the polymer chain networks accompanied by crystallization, thus indicating that preheating the polymer films is essential for estimating their intrinsic CTE values. Moreover, the rigidity of the substrate significantly influences the thermomechanical behavior of the polymer films. The polymer films that were preheated on the glass substrate showed nonlinear thermal expansion due to the substrate constraint inhibiting sufficient relaxation of the polymer chains. In comparison, a linear expansion behavior is observed after preheating the films on the water surface, exhibiting a consistent CTE value (185 ppm K) regardless of the number of thermal strain measurements. Thus, this work provides a direct method for measuring in-plane CTE values and an in-depth understanding of the thermomechanical behaviors of CP thin films to design thermomechanically reliable organic semiconductors.
尽管了解聚合物形态和优化有机半导体的热过程非常重要，但共轭聚合物（CP）薄膜状态下的热机械行为却很少被研究。此外，基于CP的电子器件中多层结构的无缝集成且无机械故障对于确定其运行稳定性至关重要。多层结构之间热膨胀系数（CTE）的巨大差异会导致器件在热应力下严重退化。在本研究中，我们测量了聚（3-己基噻吩）（P3HT）薄膜在水表面伪独立状态下的固有热机械性能。铸态P3HT薄膜在水表面加热过程中表现出较大的热收缩（-1001 ppm K）。形态分析表明，聚合物薄膜的热收缩是由聚合物链网络的重排伴随结晶引起的，这表明预热聚合物薄膜对于估算其固有CTE值至关重要。此外，基底的刚性显著影响聚合物薄膜的热机械行为。在玻璃基底上预热的聚合物薄膜由于基底约束抑制了聚合物链的充分松弛而表现出非线性热膨胀。相比之下，在水表面预热薄膜后观察到线性膨胀行为，无论热应变测量次数如何，都呈现出一致的CTE值（185 ppm K）。因此，这项工作提供了一种直接测量面内CTE值的方法，并深入了解了CP薄膜的热机械行为，以设计热机械性能可靠的有机半导体。
