Despite recent advances in the stimuliresponsive composites for oil storage and smart lubrication, achieving the high oil storage and recyclable smart-lubrication remains a challenge. Herein, a novel cobweb-like structural system consisting of oil warehouse and transportation system was designed and prepared and it shows high capacity of oil storage and recyclable smart-lubrication. Hollow SiO 2 microspheres grated of KH550 and porous polyimide (PPI) were used as oil warehouse and pipeline, respectively, to build the smart system. Because of the novel structure, the composites can keep both high oil-content and oil-retention. Applying stimuli on materials resulted in lubricants releasing on the contact surface which can reduce the friction and wear during sliding. However, removing stimuli, the capillary force induced the sucking back of lubricant into the interior of composites through interconnected small pores of PPI. On the basis of high oil storage and stimuli-responsive performance, the composites can be used for recyclable smart-lubrication. The composites showed remarkable lubricating properties (coefficient of friction 0.056 and Ws 3.55 × 10 −7 mm 3 N −1 m −1 ) when the content of KHSM (hollow silica microspheres grated of KH550 (3-Aminopropyltriethoxysilane)) was 1.5 wt % by subjecting it to macroscopic pin-on-disc friction tests. Therefore, cobweb-like structural composites with oil warehouse and transportation system hold the promise for formulating of high oil storage and recyclable smart-lubrication.
Integrating good strength and toughness, high thermostability, and easy processability into one shape memory polymers is highly desirable yet challenging. Herein, we demonstrate an approach to fabricate high temperature shape memory polymer based on polyhexahydrotriazines (PHT) cross-linked polyimide oligomers. The obtained thermosets with enhanced thermal and mechanical properties can comparable to well-established high molecular weight polyimide. The thermoset with molecular weight of polyimide oligomer as low as 8 kg/mol (PI 8k -PHT) exhibit the tensile strength, fracture toughness, and elastic modulus of 90 MPa, 69 MJ/m 3 , and 2059 MPa, respectively. The PI 8k -PHT show good shape memory effect at 210 °C with shape fixity above 98% and shape recovery above 90%, and their temporary shapes quickly recover to original within 4 s under thermal stimulus. Besides, utilizing the partially cured prepregs sheets and further compression molding methods, the block or surface micropatterned shape memory composites can be facilely obtained.
Two-dimensional (2D) lamellar materials have unique molecular structures and mechanical properties, among which molybdenum disulfide (MoS 2) and graphitic carbon nitride (g-C 3 N 4) with different interaction forces served as reinforcing phase for polytetrafluoroethylene (PTFE) composites in the present study. Thermal stability, tribological and thermomechanical properties of composites were comprehensively investigated. It was demonstrated that g-C 3 N 4 improved elastic deformation resistance and thermal degradation characteristics. The addition of g-C 3 N 4 significantly enhanced anti-wear performance under different loads and speeds. The results indicated that PTFE composites reinforced by g-C 3 N 4 were provided with better properties because the bonding strength of g-C 3 N 4 derived from hydrogen bonds (H-bonds) was stronger than that of MoS 2 with van der Waals force. Consequently, g-C 3 N 4 exhibited better thermomechanical and tribological properties. The result of this work is expected to provide a new kind of functional filler for enhancing the tribological properties of polymer composites.
In this article, the relationship of complexity, diversity, and uncertainty between components and tribological properties of friction materials based on a Monte Carlo-based artificial neural network (MC-ANN) model was predicted precisely. Meanwhile, the grey relational analysis was applied to figure out weight of factors, optimize formulation design, and calculate nonlinear dependency of ingredients. The accuracy of model was studied by comparing experimental and simulated values on the basis of statistical methods (root-mean-squared error). It was found that the model exhibited an excellent performance in predicting and fitting effect. Moreover, comprehensive analysis of weight indicated that nano-SiO 2 and mica exerted a significant role in improving the friction stability and wear resistance. According to different contents of each ingredient, the corresponding friction coefficient and specific wear rate could be obtained by virtue of a well-trained MC-ANN model without experiments, which saved a lot of time and money. It can be expected that the results of this work will extend the current research and pave a route for further in-depth studies of friction materials.
In this article, thermosetting polyimide (TPI) composites based on two ideal ingredients (graphite/graphene‐like carbon nitride, g‐C3N4) were designed with different fibers and their tribological performance was comprehensively investigated at different high temperatures. It was found that the synergistic effect between solid lubricants graphite blended with g‐C3N4 and reinforced fibers on friction and wear performance. Extremely lower friction and wear behavior of TPI composite is attained with aramid pulps (APs) at high temperatures. More importantly, an obvious transition of wear rate and friction took place with aramid pulps under 200°C. When the cross‐sections of the transfer films were analyzed using focused ion beam transmission electron microscopy (FIB‐TEM) and X‐ray photoelectron spectroscopy (XPS), it was found that graphite and g‐C3N4 combined with APs led to simultaneous improvement in load‐carrying capability of TPI matrix and durability of tribofilms subjected to complex physical and chemical reaction. Our work discloses a route for developing the TPI composite exposed to high temperatures with extremely lower friction and wear rate.
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