Oil soluble Ba SO_4@Si O_2-OTMS nanoparticles were prepared by a sol-gel and in-situ surface modification method. The morphology and structure of the as-prepared Ba SO_4@Si O_2-OTMS nanoparticles were analyzed by transmission electron microscopy, X-ray diffraction, and Fourier transform infrared spectrometry. The thermal stability of Ba SO_4@Si O_2-OTMS nanoparticles was evaluated by thermogravimetric analysis, and its effects on the lubrication performance and rheological behavior of an oil-based drilling ...