Magnetorheological fluid (MRF) is a widely used smart material that suffers from sedimentation. Since sedimentation is unavoidable, it is crucial to study and improve the redispersibility of MRFs. However, previous redispersibility testing methods have problems, such as complicated operation and low precision. Simultaneously, a simple and effective method is urgently needed for high-precision modeling of MRF sedimentation to test the rheological properties of settled MRFs at different depths. After systematically analyzing the redispersion problem, this paper proposes decoupling the energy required for redispersing settled MRFs into two parts, which are related to different factors. These two parts are the energy required to separate the agglomerated particles (related to the MRF formula) and that to redisperse the settled MRF uniformly vertically against gravity (related to the solid concentration and packing limit). The energy that separates the agglomerated particles is proportional to the shear stress of slowly shearing the corresponding agglomerated samples, i.e., the yield stress. Thus, this paper proposes a simple microdamage quasi-static indentation method to measure the yield stresses of settled MRFs at different depths to characterize the redispersibility of the corresponding MRFs. Herein, this method is applied to study the mechanisms of the influences of surfactants, thixotropic agents, and their networks on the redispersibility of MRFs. The results indicate that a well-dispersed plate-like thixotropic agent network can effectively improve redispersibility, while surfactants with poor compatibility degrade redispersibility. In summary, this redispersibility test method will greatly facilitate studies of MRFs, such as optimizing the formulas and establishing sedimentation models.
Coating microdamage and interfacial corrosion are inevitable for the metal/coating system during service, leading to the premature failure of the equipment and posing significant safety hazards. However, challenges remain regarding the achievement of early detection of corrosion and the visual monitoring of damage. Herein, a novel polymeric coating system exhibiting robust capabilities for corrosion sensing and visualization has been developed through the combination of meticulously designed nanosensors. These nanosensors were synthesized utilizing a zeolitic imidazolate framework that is infused with phenanthroline (Phen) corrosion probes. The onset of metal corrosion at the interface of coating damage can be promptly sensed and reflected by an apparent orange-red color, attributing to the formation of Phen-Fe 2+ coordinates. The impermeability and corrosion resistance of the epoxy coating have been greatly improved through introducing the synthesized nanosensors. This straightforward yet powerful strategy based on elaborate nanosensors, offering a new perspective for design of multifunctional and long-life protective materials.
Liu Wolong,Zhang Jiupeng,Liu Qi,Pei Jianzhong,Zhu Cunzhen,Liu Peng
Micro-damages always occur and accumulate in asphalt pavement materials under the effects of temperature, vehicle loads and other factors during service. Accordingly, self-healing microcapsules could be added into asphalt binder and repair micro-damages to prevent damage extension in
time. In this study, the emulsified rejuvenator and melamine-urea-formaldehyde resin (MUF) were selected as the core and cyst wall materials, respectively, and in-situ polymerization method was applied to synthesize the novel microcapsules. The effects of emulsifier dosage and curing
time were revealed on the particle size, dispersion, surface morphology and coating properties, and the optimum process parameters were determined for microcapsules. Then, the micro morphology, molecular structure, and thermal stability were further investigated to determine the optimal preparation
of the microcapsules. Finally, the linear amplitude sweep (LAS) test was performed to evaluate the self-healing efficiency of the asphalt binder with different dosages of prepared microcapsule, and the optimal dosage of microcapsules was determined as 0.5%.
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