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Complexes like iron (II)-triazoles exhibit spin crossover behavior at ambient temperature and are often considered for possible application. In previous studies, we implemented complexes of this type into polymer nanofibers and first polymer-based optical waveguide sensor systems. In our current study, we synthesized complexes of this type, implemented them into polymers and obtained composites through drop casting and doctor blading. We present that a certain combination of polymer and complex can lead to composites with high potential for optical devices. For this purpose, we used two different complexes [Fe(atrz)3](2 ns)2 and [Fe(atrz)3]Cl1.5(BF4)0.5 with different polymers for each composite. We show through transmission measurements and UV/VIS spectroscopy that the optical properties of these composite materials can reversibly change due to the spin crossover effect.
Electrospun polymer fiber mats feature versatile applications in tissue engineering, drug delivery, water treatment and chemical processes. The orientation of fibers within these mats is a crucial factor that significantly influences their properties and performance. However, the analysis of fiber samples using scanning electron microscopy (SEM) has limitations such as time consumption, fixed assembly, and restricted field of vision. Therefore, a fast and reliable method for qualitative measurements of fiber orientation is required. Mueller matrix polarimetry, a well-established method for measuring orientation of chemical and biological species, was employed in this case. We investigated the effect of four important parameters of the electrospinning process, namely collector speed, applied voltage, needle-to-collector distance, and solution concentration, on fiber orientation using Mueller matrix polarimetry thus extending the range of parameters analyzed. Measurements were performed using two extreme values and a central optimized value for each fabrication parameter. Changes in matrix values were observed for each fabrication parameter, and their correlation with fiber orientation was analyzed based on the Lu-Chipman decomposition. The results were compared with SEM images, which served as the ground truth, and showed overall good agreement. In the future, the analysis of electrospun polymer fibers can be done by using Mueller matrix polarimetry as alternative to current technology and fabrication parameters, including solution concentration for the first time in this context and the production can quickly be adjusted based on the outcome of the measurements
