Following this, 200-ps constant mole, pressure, and temperature (NPT) runs were conducted at the same temperature and zero pressure in three directions using the Nosé-Hoover thermostat and barostat [30, 31]. The bulk systems were subsequently cooled down to 50 K at a rate of 4.75 K/ps with zero external pressure under NPT ensemble. After a short NPT run for 50 ps at 50 K, the systems are heated to 600 K with a rate of 1.1 K/ps, and the density of the bulk systems were monitored during the heating process. The systems were subsequently cooled down from 600 to

200 K at a rate of 2 K/ps. Finally, two steps of relaxation were performed under Kinase Inhibitor Library NPT and NVT ensembles with 100 ps each to obtain samples for mechanical load simulations. These MD models are henceforth referred to as the bulk MD models. Figure 1 Unit molecular find more network structure and schematic depiction of PE particles. (a) Unit molecular network structure of polyethylene (PE). A networked

molecule C2200 is decomposed into branched and linear molecules via bond breaking at cross-linking CP-690550 order points. The number of united atoms in each linear segment is indicated. The beads at the ends of as-generated branched and linear molecules are hence re-defined (from CH to CH3 bead). (b) Schematic depiction of the preparation of ultrafine nanoscale PE particles. PE molecules are packed into a spherical Sinomenine shape via shrinking under hydrostatic pressure. The as-generated nanoparticle is able to maintain the spherical shape under full relaxation. Each simulated bulk or particle system consists of 66,000 beads in total. Coloring of beads is based on the molecule number. MD models of PE nanoparticles were constructed as shown in Figure 1b. The periodic boundary conditions of the bulk MD models were removed in all directions, and a spherical wall was introduced to encircle all the beads. The beads falling outside the circle will be dragged into the circle. The spherical wall was able to exert a force onto each atom with the magnitude defined by: (2) where K is a specified force constant which is given

to 5.0 kcal/(moleÅ2), r is the distance from the bead to the center of the sphere, and R is the radius of the sphere. The negative magnitude of the force in Equation 2 indicates that the force acts towards the center of the sphere. Therefore, higher pulling forces are applied to beads far away from the edge of the sphere. The radius of the sphere was reduced to densify the polymer as described by: (3) where R and R 0 are the instantaneous and initial radius of the spherical wall, respectively, S is a positive constant, and n has progressive values of positive integers corresponding to elapsed time of the simulation (i.e., n = 1, 2, 3, …). For the simulations described herein, S was 0.99 and n increased by a value of 1 for every 5 ps of simulation time.