Wearable solar radiation sensors based on ionic hydrogels are facilely prepared to simultaneously monitor the radiation dose for the production of vitamin D and the prevention of sunburn. Tetramethylethylenediamine (TEMED) is neutralized with acrylic acid (AA) to obtain tetramethylethylenediamine acrylate (TEMEDA), which is further polymerized with acrylamide by a free radical reaction. By simply adding MB or NR during the polymerization, the final obtained ionic hydrogels can indicate solar radiation. Due to the extent of discoloration, the discoloration speed of MB and NR is correlated to the radiation dose. This wearable sensor can indicate the solar radiation dose required by the human body to synthesize vitamin D through the discoloration of the ionized hydrogel of MB, whereas those with NR are able to illustrate the threshold of radiation dose that causes potential skin hurt. Therefore, the benefit and drawback of solar radiation can be well balanced by optimizing the exposure time to solar irradiation. In addition, polyurethane cross-linked with a thermoresponsive coating is used as band for this wearable sensor. Due to the hydrophilicity below its transition temperature, the cross-linked band possesses the easy cleaning capability of stains after the daily wear. Such type of wearable sensor can be broadly used for monitoring the solar radiation, especially in outdoor activities.

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2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO)-mediated oxidized cellulose nanofiber (TEMPO-CNF)/poly (vinyl alcohol) (PVA) suspension can be used to prepare composite. Therefore, understanding the viscoelastic property of TEMPO-CNF/PVA suspension is necessary. The analysis of the rheological dates from steady and dynamic rheology indicates that the suspension is pseudoplastic fluid with thixotropic behavior. When the concentration of PVA is in the dilute regime, the gel like behavior of the suspensions turns to liquid like state with the increasing frequency. Such behaviors are related to the entangled network among cellulose fibrils and the hydrogen bond interaction between TEMPO-CNFs and PVA. When the concentration of PVA is in semidilute and entangled regime, the suspensions show liquid character, because the viscosity of the suspensions are mainly determined by the entanglement of PVA molecules in homogeneous state. Furthermore, the TEMPO-CNF/PVA membranes were prepared by solution casting method. The Fourier transform infrared spectroscopy and atomic force microscope data proved the interaction between TEMPO-CNFs and PVA. This research reveals the importance of PVA concentration on the fluid characters of TEMPO-CNF/PVA suspensions, providing the approach to adjust the viscosity of TEMPO-CNF suspensions.

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