Barrier properties of kk-mer packings

• Barrier properties of films, filled by anisotropic particles (kk-mers), are investigated.
• Different variants of dense (DD) and loose (LL) packings on the square lattice are considered.
• Effective medium theory fails to predict the data of computer simulations.
• Diffusion coefficients demonstrate percolation like-behavior for LL packings.
• Anomalous diffusion behavior may reflect spatial organization of kk-mers.

This work discusses numerical studies of the barrier properties of kk-mer packings by the Monte Carlo method. The studied variants of regular and non-regular arrangements on a square lattice included models of random sequential adsorption (RSA) and random deposition (RD). The discrete problem of diffusion through the bonds of a square lattice was considered. The kk-mers were perfectly oriented perpendicular to the diffusion direction and blocked certain fraction of bonds fbfb against diffusion. The barrier efficiency was estimated by calculation of the ratio D/DoD/Do where DD is diffusion coefficient in direction perpendicular to the orientation of kk-mers and DoDo is the same value for diffusion on the square lattice without blocked bonds, i.e., at fb=0fb=0. The value of kk varied from 1 to 512 and different lattice sizes up to L=8192L=8192 lattice units were used. For dense packings (p=1p=1), the obtained D/DoD/Do versus fbfb dependences deviated from the theoretical prediction of effective medium (EM) theory and deviation was the most obvious for the regular non-staggered arrangement. For loose RSA and RD packings, the percolation like-behavior of D/DoD/Do with threshold at fb=p∞fb=p∞ was observed and the data evidenced that their barrier properties at large values of kk may be more effective than those of some dense packings. Such anomalous behavior can reflect the details of kk-mer spatial organization (aggregation) and structure of pores in RD and RSA packings. The contradictions between simulation data and predictions of EM theory were also discussed.