Two‐Step Uniaxial Electrospinning Construction of Up‐Down Structured Janus Fibrous Film With Thermochromic and Magnetic Bifunctionality

Herein, a [thermochromic microcapsules‐45°C (TCM‐45)/polystyrene (PS)]&[CoFe 2 O 4 /PS] up‐down structured thermochromic‐magnetic bifunctional Janus fibrous film (shorted as TMJF) is prepared by a two‐step uniaxial electrospinning technique. The up‐layer of TMJF is TCM‐45/PS fibrous film (denoted as U‐TMJF, i.e., thermochromism layer); the down‐layer of TMJF is CoFe 2 O 4 /PS fibrous film (named as D‐TMJF, i.e., magnetism layer). Due to the up‐down macro Janus partition structure of TMJF, thermochromic substance (TCM‐45) and magnetic substance (CoFe 2 O 4 ) are separated from each other, which fully ensures that the dark‐colored CoFe 2 O 4 has no effect on the thermochromic performance of TCM‐45. When the temperature augments to 45°C, the U‐TMJF color rapidly transforms from blue to white. The film exhibits a more obvious color transition than the counterpart single‐layer blending composite fibrous film. Moreover, due to the advantages of electrospinning, TCM‐45 is completely wrapped in the microfiber, so TMJF still maintains stable thermochromic performance after ultrasonic washing for 100 min. In addition, the saturation magnetization of TMJF varies with the CoFe 2 O 4 NPs content, showing tunable magnetic properties. This simple and particular macro partition design concept lays a theoretical foundation and offers technical support for the fabrication of other functionalized Janus thermochromic flexible fibrous films.