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Nanofluids have become of interest in recent years thanks to their improved thermal properties, which make them especially interesting for microchannel heat sink applications. In this study, we prepared two aqueous nanofluids based on reduced graphene oxide (rGO) decorated with manganese dioxide (MnO2) at a concentration of 0.1 wt.%. The difference between the two nanofluids was in the preparation of the reduced graphene oxide decorated with MnO2. In the first case, the manganese salt was mixed with ascorbic acid before GO reduction with NaOH, and in the second case, the GO reduction with NaOH occurred under ascorbic acid. Ascorbic acid not only plays the role of a non-toxic and ecofriendly reducing agent but also acts as an important parameter to control the reaction kinetics. The structural, microstructural and spectral characterizations of the MnO2/rGO nanocomposite were conducted via X-ray diffractometry (XRD), Raman spectroscopy, FT-IR, TEM, SEM and EDS analyses. Moreover, the synthesized MnO2/rGO nanocomposites were utilized as nanofluids and their stability, thermal conductivity and rheological behaviors were studied. The thermal conductivity of the MnO2/rGO and MnO2AsA/rGO nanofluids was 17% and 14.8% higher than that of water for the average temperature range, respectively, but their viscosity remained statistically equal to that of water. Moreover, both nanofluids presented Newtonian behavior in the analyzed shear rate range. Therefore, both MnO2/rGO and MnO2AsA/rGO nanofluids are promising alternatives for use in applications with micro- and millichannel heat sinks.

This article focuses on agar biopolymer films that offer promise for developing biodegradable packaging, an important solution for reducing plastics pollution. At present there is a lack of data on the mechanical performance of agar biopolymer films using a simple plasticizer. This study takes a Design of Experiments approach to analyze how agar-glycerin biopolymer films perform across a range of ingredients concentrations in terms of their strength, elasticity, and ductility. Our results demonstrate that by systematically varying the quantity of agar and glycerin, tensile properties can be achieved that are comparable to agar-based materials with more complex formulations. Not only does our study significantly broaden the amount of data available on the range of mechanical performance that can be achieved with simple agar biopolymer films, but the data can also be used to guide further optimization efforts that start with a basic formulation that performs well on certain property dimensions. We also find that select formulations have similar tensile properties to thermoplastic starch (TPS), acrylonitrile butadiene styrene (ABS), and polypropylene (PP), indicating potential suitability for select packaging applications. We use our experimental dataset to train a neural network regression model that predicts the Young's modulus, ultimate tensile strength, and elongation at break of agar biopolymer films given their composition. Our findings support the development of further data-driven design and fabrication workflows.

Carbon-based nanomaterials have a high thermal conductivity, which can be exploited to prepare nanofluids. Graphene is a hydrophobic substance, and consequently, graphene-based nanofluid stability is improved by adding surfactants. An attractive alternative is the decoration of reduced graphene oxide (rGO) with metallic materials to improve the thermal conductivity without affecting the stability of nanofluids. This study focuses on the synthesis and characterization of rGO/Ag (0.1 wt.%) aqueous nanofluids. Moreover, the effects of the Ag concentration (0.01−1 M) on the thermal conductivity and viscosity during the synthesis of rGO/Ag composite are analyzed. The nanofluid thermal conductivity showed increases in relation to the base fluid, the most promising being 28.43 and 26.25% for 0.1 and 1 M of Ag, respectively. Furthermore, the nanofluids were Newtonian in the analyzed range of shear rates and presented a moderate increase (<11%) in viscosity. Aqueous nanofluids based on rGO/Ag nanocomposites are a potential alternative for applications as heat transfer fluids.