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Optimization of the fiber/matrix interface and integration of a photochromic molecule in the fiber/matrix system
(Wydawnictwo Politechniki Łódzkiej, 2022) Aden, Mahad Barre; Rault, François; Salaün, Fabien
Molecules and supramolecular that are capable of undergoing structural rearrangements when subjected to an external stimulus have attracted a great deal of attention as they can represent a new way to design smart textiles. Azobenzenes are stable molecules in both the isomeric states, i.e., open and closed forms. By mimicking nature, one of the most significant challenges in the realization of switches is to integrate multiple and independent reactive units in a single molecular system allowing to couple a photochromic activity with a mechanical activity to obtain a photo mechanically activatable system. Among the different inputs, photons have been considered as one of the most promising for application in the textile field. This study aims to explore the possible ways to integrate a diarylethene (DTE) either in the core of the fiber or on its surface to create a photoactive textile structure. The integration of DTE by melt spinning into a poly (methyl methacrylate) matrix has demonstrated the feasibility of the process. Nevertheless, even if a photosensitive effect has been observed, the low quantity of molecules coupled with the thermal constraints do not make this process feasible on a larger scale. To overcome this problem, it was considered to integrate the DTE in a functional coating formulation by dispersing them in a polyurethane matrix with a coating step. This part of the study focuses mainly on the fiber/matrix adhesion mechanisms to determine the best couples in terms of adhesion. The results obtained after the pull-out test showed that the polyamide/polyurethane couple has the highest work of adhesion compared to the polypropylene or polyethylene terephthalate ones.
Preparation of PVDF nanofibers by optimizing solvent properties: improved solvent viscosity and evaporation rate
(Wydawnictwo Politechniki Łódzkiej, 2022) He, Zhongchen; Rault, François; Mohsenzadeh, Elham; Lewandowski, Maryline; Salaün, Fabien
PVDF nanofibers have been intensively investigated in wearable energy harvesting because of their flexibility and piezoelectric properties. In this study, we prepared PVDF nanofibers by the electrospinning method. Different solvents like DMF and DMF/acetone with the ratio of 6/4, 5/5, and 4/6 were selected to adjust the solvent properties. SEM, FTIR, and DSC characterizations were used to characterize the morphology, structure, and β phase content of PVDF nanofibers. The results demonstrate that the electrospun PVDF nanofibers produced by using DMF/acetone have predominantly a fibre structure and increased β phase compared to electrospun samples using DMF alone as solvent. PVDF nanofibers fabricated by using DMF/acetone with a ratio of 4/6 exhibit the maximum content of β phase and the highest value of piezoelectric coefficient (d33).