Review on factors affecting nanofluids surface tension and mechanism analysis

[Display omitted] •Research on the surface tension of nanofluids was comprehensively summarized.•The effects of nanoparticles, temperature, and surfactants on surface tension were studied.•The impact mechanisms of various factors on surface tension were investigated.•The relationship between the surface tension and wettability was proposed. Nanofluid has become a hot topic in scientific research because of its excellent thermal and physical properties. Surface tension is an important parameter for describing boiling process. Nevertheless, compared with other properties, studies on nanofluids surface tension are still relatively scarce. This paper reviews the research progress on the surface tension of nanofluids, and deeply analyzes the influence mechanisms of various factors for the first time, including the concentration, properties, and size of nanoparticles, the concentration of surfactants, temperature, microwave irradiation, voltage, and stability. Nanoparticles have a complex influence on the surface tension. Comparing existing research results, it is found that hydrophilic nanoparticles tend to increase surface tension in polar solvents, whereas hydrophobic nanoparticles tend to diminish the value of surface tension. Through the study of hybrid nanofluids, it is found that the dominant influence on the surface tension of the fluid is exerted by the higher concentration of nanoparticles. The impact of surfactants and temperature on the surface tension of nanofluids are generally consistent: higher surfactant concentrations or higher temperatures lead to lower surface tension values. In the final part of this review, from the perspective of the correlation between multiple influencing factors and experimental and theoretical methodologies, this article proposes the challenges and future research directions pertaining to the study of nanofluids surface tension.