Direct Observation of Two-Step, Stratified Crystallization and Morphology in Conjugated Polymer Thin Films
Direct Observation of Two-Step, Stratified Crystallization and Morphology in Conjugated Polymer Thin Films
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DOI：
10.1021/acs.macromol.2c02439
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发表时间：
2023-04
期刊：
影响因子：
5.5
通讯作者：
Jesse Kuebler;Tucker Loosbrock;J. Strzalka;Lucia Fernandez-Ballester
中科院分区：
文献类型：
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作者：
Jesse Kuebler;Tucker Loosbrock;J. Strzalka;Lucia Fernandez-Ballester
在厚度= 20 - 250 nm的聚（3-己基噻吩）（P3HT）薄膜冷却过程中直接观察到两步分层结晶过程：自由表面的薄层（<20 nm）比体结晶温度（TC，体）高~ 25°C，而薄膜的其余部分（即底层）在TC，体附近结晶。对有和没有自由表面的薄膜的原位测量明确地将高温结晶归因于表面诱导过程，这与在空气-聚合物界面形成大双折射结构和高度定向的边缘晶体有关。相比之下，在较薄的薄膜中，块状下层的结晶主要是边缘取向的晶体，而在较厚的薄膜中，晶体变得越来越各向同性。当< 20 nm时，自由表面效应占主导地位，只观察到高温结晶。这些结果突出了熔融结晶在特定电子应用中定制薄膜厚度的形态和取向的潜力。
A two-step stratified crystallization process has been directly observed during cooling of poly(3-hexylthiophene) (P3HT) thin films of thicknessh= 20–250 nm: a thin (<20 nm) layer at the free surface crystallizes ∼25 °C higher than the bulk crystallization temperature (TC,bulk), whereas the rest of the film (i.e., the underlayer) crystallizes nearTC,bulk. In situ measurements of films with and without a free surface unequivocally ascribe the high-temperature crystallization to a surface-induced process, which correlates with the formation of large birefringent structures and highly oriented edge-on crystallites at the air–polymer interface. In contrast, crystallization of the bulk-like underlayer leads to mostly edge-on-oriented crystallites in thinner films and becomes increasingly isotropic in thicker films. Forh< 20 nm, free-surface effects dominate and only high-temperature crystallization is observed. These results highlight the potential of melt crystallization to tailor morphology and orientation across thin film thickness for specific electronic applications.