TiO2 Nanocontainers Coconstructed Using Polymers and Corrosion Inhibitors for Anticorrosion Reinforcement of Waterborne Epoxy Coatings.

Stimulus-responsive coatings can provide active corrosion protection in response to environmental changes, but they have not reached their anticipated application prospects because of the intricate preparation processes of hollow materials and methods for loading corrosion inhibitors. Herein, polyaniline molybdate corrosion inhibitor and polydopamine-wrapped titanium dioxide nanocontainers (named TiO2/PANI-MoO42-/PDA) are synthesized via a simple three-step electrostatic assembly technique. Introducing TiO2/PANI-MoO42-/PDA nanocontainers in smart waterborne epoxy (WEP) coatings affords the latter with high barriers and long-term corrosion protection. The successful deposition of each layer on the TiO2 nanocontainer surface was validated via Fourier transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy, and X-ray photoelectron spectroscopy. Release test results show that the molybdate corrosion inhibitor exhibits notable pH-responsive activity under acidic conditions and slow release in neutral environments, which improves the corrosion resistance of coatings. The addition of synthetic nanocontainers greatly improves the impermeability of WEP coatings. The charge transfer resistance of WEP/TiO2/PANI-MoO42-/PDA coatings is 1.79 × 1011 Ω cm2 after 30 day immersion in a 3.5 wt % NaCl solution, which is 3.32 × 105 times higher than that of WEP coatings. WEP/TiO2/PANI-MoO42-/PDA coatings remain uniform and reliable, even after 50 days of salt spray exposure. The excellent corrosion protection of WEP/TiO2/PANI-MoO42-/PDA coatings is attributed to (1) the enhanced dispersion and compatibility of PDA in the coating for nanocontainers, (2) the combination of phenolic hydroxyl groups of PDA and Fe, which inhibit corrosion activity on the exposed metal surface, and (3) the on-demand release of the MoO42- inhibitor, which provides sustained passivation protection. This work proposes a strategy to simplify the preparation of responsive long-term anticorrosion coatings and extend their service lives.

Effect of Powder on Tribological and Electrochemical Properties of Nylon 66 and Ultra-High Molecular Weight Polyethylene in Water and Seawater Environments.

Polymer materials are used increasingly in marine machinery and equipment; their tribological properties and effect on the water environment have garnered significant attention. We investigate the effect of water or seawater environment containing powder on tribology and electrochemistry of polymer materials. A friction test involving nylon 66 (PA66) and an ultrahigh molecular weight polyethylene (UHMWPE) pin-disc (aluminum alloy) is performed in seawater or water with/without polymer powder, and the solution is analyzed electrochemically. The results show that the tribological properties of the UHMWPE improved by adding the powder to the solution, whereas the PA66 powder demonstrates abrasive wear in a pure water environment, which elucidates that the synergistic effect of powder and seawater on UHMWPE reduces the wear, and the synergistic effect of pure water and powder aggravates the wear. The results of electrochemical experiments show that after adding powder in the friction and wear tests, the powder can protect the pin by forming a physical barrier on the surface and reducing corrosion, and the changes are more obvious in seawater with powder in it. Through electrochemical and tribological experiments, the synergistic effect of solution environment and powder was proved.

Molecular dynamics simulation of shock-induced microscopic bubble collapse.

Shock waves and micro-jets generated during the process of bubble collapse lead to cavitation damage on the surface of materials in hydraulic machinery equipment parts, which is attention. However, research on the dynamics of bubble collapse is still unclear. In this work, molecular dynamics (MD) simulations are used to study the compression and collapse processes of microscopic bubbles under the impact of different velocities for water molecules. The velocities of the shock wave, time of bubble collapse and shock pressure of collapse were obtained. Results showed that higher the impact velocity, shorter is the time of bubble collapse and the higher velocity of the micro-jet. After the bubble collapse, the micro-jet will form secondary water hammer shocks and a greater shock pressure. The water structure appears to undergo a phase change (ice-VII structure) when the velocity of water molecules is 1.0 km s-1. The shock induces the bubble collapse and the micro-jet significantly increases the chemical activity of water molecules; the degree of ionization of water molecules increases with the shock velocity. In addition, the Hugoniot curve of the shock velocity obtained by molecular dynamics simulations are in good agreement with the experimental data.

Molecular dynamics simulation of microscopic friction mechanisms of amorphous polyethylene.

Determining the nature of the microscopic mechanism of tribological properties by experimental methods for a polymer material surface/interface in the sliding friction process is a challenge. Molecular dynamics simulations were conducted by sliding a rigid indenter over the amorphous polyethylene. The results show that the friction is mainly composed of plough force and adhesion force. The average friction of adhesive contact is greater than that of frictionless contact because of the adhesion effect. The difference of average friction between adhesive contact and frictionless contact increases with increasing indentation depth because of the plough force effect. The elastic deformation of amorphous polyethylene in the cohesive zone is related to van der Waals interaction energy, whereas the plastic deformation was mainly dominated by bond angle energy and dihedral energy of the molecular chain for amorphous polyethylene. Molecular chains of amorphous polyethylene extend along the sliding direction and agglomerate along the indentation direction. The flexibility of the molecular chains increases with the increase of temperature and facilitates the molecular chains returning more easily to their original state.

Design and Development of Lubricating Material Database and Research on Performance Prediction Method of Machine Learning.

Long developing period and cumbersome evaluation for the lubricating materials performance seriously jeopardize the successful development and application of any database system in tribological field. Such major setback can be solved effectively by implementing approaches with high throughput calculation. However, it often involves with vast number of output files, which are computed on the basis of first principle computation, having different data format from that of their experimental counterparts. Commonly, the input, storage and management of first principle calculation files and their individually test counterparts, implementing fast query and display in the database, adding to the use of physical parameters, as predicted with the performance estimated by first principle approach, may solve such setbacks. Investigation is thus performed for establishing database website specifically for lubricating materials, which satisfies both data: (i) as calculated on the basis of first principles and (ii) as obtained by practical experiment. It further explores preliminarily the likely relationship between calculated physical parameters of lubricating oil and its respectively tribological and anti-oxidative performance as predicted by lubricant machine learning model. Success of the method facilitates in instructing the obtainment of optimal design, preparation and application for any new lubricating material so that accomplishment of high performance is possible.