Pore structure and glass transition temperature of nanoporous poly(ether imide)

The effect of nanopores on the glass transition temperature (T_g) of poly(ether imide) was studied with differential scanning calorimetry. Nanoporous poly(ether imide) samples were obtained through the phase separation of immiscible blends of poly(ether imide) and polycaprolactone diol and by the removal of the dispersed minor phase domains with a selective solvent. Microscopy and statistical methods were used to characterize the pore structure and obtain the pore structure parameters. The pore size was found to depend on the processing time and the initial blend composition, mainly because of phase-coarsening kinetics. A decrease in T_g was observed in the nanoporous poly(ether imide) in comparison with the bulk samples. The change in T_g was strongly influenced by the pore structure and was explained by the percolation theory. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 3546–3552, 2006     

Monte Carlo Simulation of the Structures and Dynamics of Amorphous Polyethylene Nanoparticles

Monte Carlo simulations of amorphous polyethylene (PE) nanoparticle have been performed on the second nearest neighbor diamond lattice by including short and long‐range interactions. A droplet can be either obtained from equilibrated PE bulk or from nanofiber snapshots by modifying periodic boundary conditions. The presence of attractive long‐range interactions gives cohesion to the nanoparticle. PE nanoparticles, which contain up to 72 chains of C₁₀₀ and have the radius ˜5.0 nm, have been produced and equilibrated on the 2nnd lattice. In these droplets, the density profiles are hyperbolic, with end beads being more abundant than middle beads at the surface. There are orientational preferences at the surface on the scale of individual bonds and whole chains. Comparison of nanoparticles with different sizes, which contain different numbers of chains, does not indicate any significant differences in local and global equilibrium properties – for thickness in the range 5.8 to 7.4 nm. Surface energies are calculated directly from the on‐lattice energetics. The mobility of the chain in the droplet at the level of individual chords or an entire chain is greater than in the bulk, and the mobility increases as the size of the droplet decreases.