Monte Carlo simulations of polyethylene (PE) melts and thin films have previously been performed on the second nearest neighbor diamond (2nnd) lattice by including short and long range interactions. A fiber can be obtained from equilibrated thin film snapshots by increasing another (normal to thin film plane) periodic side to infinity. There is only one effective periodic boundary condition in the simulation. The presence of attractive long range interactions gives cohesion to the fiber. PE fibers, which contain up to 72 chains of C99 and have the radius ≈ 5.0 nm, have been produced and equilibrated on the 2nnd lattice. In these fibers, the density profiles are hyperbolic, with end beads being more abundant than the middle beads at the surface. There are orientational preferences at the surface on the scale of individual bonds and whole chains. Comparison of fibers with different thickness, which contain different number of chains, does not indicate any significant differences in local and global equilibrium properties – for thickness in the range 5.6 to 7.6 nm. Surface energies are calculated directly from the on‐lattice energetics and presented as a function of the fiber radius
Atomistic local structure of potassium ion adsorbed in hydrated montmorillonite (MMT) was investigated based on a combination of an extended X-ray absorption fine structure (EXAFS) spectroscopy and classical molecular dynamics (MD) simulation. The accuracy of the representative MMT atomistic model with PCFF-INTERFACE force field was validated. MD-simulated EXAFS spectra were calculated from trajectories of hydrated MMT atomic coordinates and the results were in satisfactory agreement with corresponding experimental EXAFS spectra. Interlayer spacing determined by X-ray diffraction was consistent with the mono-layer hydrated MMT structure. The first coordination shell of K ? ion in monohydrated MMT was formed by 5 water oxygen atoms at an average K-O W distance of 2.85 Å and the second coordination shell of 6 oxygen atoms from both sides of the closest silicate tetrahedral sheet at K-O MMT = 3.41 Å . For hydrated K ? -MMT, MD and EXAFS results confirm that K ? counter ions form the inner-sphere surface complex and that the adsorbed sites were located with the vicinity edge of a basal oxygen hexagonal cavity in the silicate tetrahedral sheets of MMT. For higher-layer hydrated MMT, K ? ions can form surface complexes that are inner-sphere, outersphere, and transient diffuse-layer species depending on the number of intercalated water in the clay. Water molecules are of less ordered arrangement in the monohydrated MMT due to the confinement effect from the clay surface. K ? counter ions in the single layer hydrates are almost trapped within the cavities of the basal planes surface.
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