In the past decade, flexible electronics have attracted significant research attention due to their distinct features and emerging applications in numerous fields such as, flexible displays, implantable sensors, and energy storage systems, among other applications. Due to the development of flexible electronics, this paper details the substrates employed to produce flexible electronic devices, given that substrates generally govern the overall device properties. The increase in research attention can be attributed to the use of films as flexible substrates, which enable the implementation of numerous design strategies and engineering methodologies, thus leading to extensive advances in the manufacturing quality and prospect of flexible electronics in various applications. This paper provides a comprehensive review of the significance of substrates in flexible wearable electronics over the past decade, such as, the substrate properties requirements, processing classification, important flexible devices, and applications, including sensing, energy storage, and other electronic devices.

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In the present study, multi‐walled carbon nanotubes (MWCNTs) were sulfonated by 1,3‐propane sultone and distillation–precipitation polymerization, respectively, and then incorporated into chitosan (CS) to prepare CS/MWCNTs composite membranes for fuel cell applications. CS/MWCNTs membranes show better thermal and mechanical stability than pure CS membrane due to the strong electrostatic interaction between the SO3H groups of MWCNTs and the NH2 groups of CS, which can restrict the mobility of CS chain. The sulfonated MWCNTs provide efficient proton hopping sites (SO3H, SO3− …. 3+HN), thereby resulting in the formation of continuous proton conducting channels. The composite membranes with 5 wt % of MWCNTs modified by two different ways show a proton conductivity of 0.026 and 0.025 S·cm−1, respectively. In conclusion, CS/MWCNTs membrane is a promising proton exchange membrane for fuel‐cell applications. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47603.

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In this study, we incorporated commercially available p‐toluene sulfonic acid coated boehmite nanofillers (commercially known as OS1) into the chitosan (CS) matrix to fabricate CS–OS1 nanocomposite membranes with a high proton conductivity for fuel‐cell applications. These nanocomposite membranes were characterized by Fourier transform infrared spectroscopy, energy‐dispersive X‐ray spectroscopy, X‐ray diffraction analysis, scanning electron microscopy, and thermogravimetric analysis. Their mechanical properties, water uptake, ion‐exchange capacity, and proton conductivity were also determined. The results show that the incorporation of OS1 to CS chains can inhibit the mobility of CS chains and, hence, enhance the thermal stability and mechanical properties of CS–OS1 nanocomposite membranes. The composite membrane with 5 wt % OS1 showed a proton conductivity of 0.032 S/cm; this was almost equal to that of commercially available Nafion 117. We concluded that CS–OS1 nanocomposite membranes have potential for fuel‐cell applications. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 46904.