The solid phase thermal decomposition and nanocrystal effect of hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) via ReaxFF large-scale molecular dynamics simulation.

The solid phase thermal decomposition and nanocrystal effect are extremely important to understand the ignition, combustion, reaction growth and buildup to detonation under shock wave action. To explore the basic mechanism at the atomic level and understand the interaction among nanocrystal lattices, molecules, and intermediates during the solid phase decomposition, ReaxFF large-scale molecular dynamics simulation at 1000-3000 K was demonstrated on the solid phase of nanocrystalline RDX with a size in the range of 5-12 nm. Based on the analysis of the RDX decay and chemical species, we found that the whole decomposition process can be divided into the solid-affected stage and the following less-condensed phase stage. From the results of NO2 diffusion and high frequency reaction statistics for the nanocrystal effect on the RDX decay, intermediate diffusion was found to be strongly associated with the chemical pathway. In addition, it was found for the first time that the thermal decomposition of RDX originates from the inside of the nanocrystal instead of its surface. Furthermore, a promising uniform energy distribution mechanism transfer by vibration inside the nanocrystalline RDX was demonstrated. The detailed information derived from this study can aid in the thorough understanding of the size effect on the chemical kinetics of nanoexplosives, especially for thermal decomposition and reaction growth.

Investigation of High-Speed Erythrocyte Flow and Erythrocyte-Wall Impact in a Lab-on-a-Chip.

To better understand erythrocyte high-speed motion, collision characteristics, and collision-induced hemolysis probability in rotary blood pumps, a visual experimental investigation of high-speed erythrocyte flow and erythrocyte-wall collision in a lab-on-a-chip was performed. The erythrocyte suspension was driven by a microsyringe pump connected to the microchip, and the erythrocyte flow and erythrocyte-wall impact process were observed and imaged by an optical microscope and a high-speed camera. Two types of microchips with different impact surfaces (flat and curved) were employed. The motion and deformation features before and after collision were studied in detail. The results show that erythrocytes not only move along the flow direction in the flow plane but also rotate and roll in three-dimensional space. Erythrocytes keep discoid shape during the movement in the straight channel, but their deformations during collision are mainly classified into two types: erythrocyte structure is still stable and the erythrocyte performance can be ensured to a certain extent in the TypeA deformation, while the TypeB deformation makes the membrane more likely to fracture on the stretched side, increasing the probability of hemolysis. Furthermore, the movements and deformations of the erythrocytes after collision are analyzed and classified into two types: bouncing and slipping. Moreover, a simulation method for the flow in microchip was performed and validated through a comparison of the streamlines and experimental erythrocytes tracks, which can be further employed to predict the high-speed blood flow, associated with collision process in mechanical blood pump.