GEOMETRIC ANALYSIS OF DIFFUSION PATHWAYS IN GLASSY AND MELT ATACTIC POLYPROPYLENE

被引:118
作者
GREENFIELD, ML [1 ]
THEODOROU, DN [1 ]
机构
[1] UNIV CALIF BERKELEY,DEPT CHEM ENGN,BERKELEY,CA 94720
关键词
D O I
10.1021/ma00072a026
中图分类号
O63 [高分子化学(高聚物)];
学科分类号
070305 ; 080501 ; 081704 ;
摘要
Glassy and melt atactic polypropylene microstructures obtained via energy minimization and Monte Carlo simulation are subjected to geometric analysis (Delaunay tessellation followed by volume and connectivity analysis) in order to determine the clusters of sites where a hard sphere penetrant of radius 0-2.5 A can reside. A variety of cluster volumes are found for each penetrant radius, and typical clusters are visualized for methane, helium, and two hypothetical penetrants of smaller radius. Peaks are observed in the distribution of cluster volumes, representing characteristic hole sizes induced by local packing. The cluster root-mean-square radius of gyration and average accessible volume decrease monotonically for penetrants larger than helium. A hypothetical penetrant of radius ca. 0.9 angstrom can percolate the polymer structure, whereas the same size penetrant is trapped in a random close-packed (rcp) configuration of spheres with diameter commensurate with the polymer segments. Clusters accessible to small penetrants are used to isolate probable pathways for diffusion, and the connectivity of the network of clusters is quantified. Visualization of thermal fluctuations of clusters shows two kinds of mobility. In the melt, polymer fluctuations induce rapid cluster rearrangement. In the glass, clusters retain their identity, while thermal fluctuations infrequently open and close diffusion pathways between them. A methodology for applying this work to full energy-based calculations of diffusivity in the glass using multidimensional transition-state theory is introduced.
引用
收藏
页码:5461 / 5472
页数:12
相关论文
共 54 条
[1]  
[Anonymous], 1987, COMPUTER SIMULATION
[2]   SPACE AVAILABLE TO SMALL DIFFUSANTS IN POLYMERIC GLASSES - ANALYSIS OF UNOCCUPIED SPACE AND ITS CONNECTIVITY [J].
ARIZZI, S ;
MOTT, PH ;
SUTER, UW .
JOURNAL OF POLYMER SCIENCE PART B-POLYMER PHYSICS, 1992, 30 (05) :415-426
[3]  
ARIZZI S, 1990, THESIS MIT
[4]  
Bird R B., 2007, TRANSPORT PHENOMENA
[5]  
BOONE TD, 1992, POLYM PREPR AM CHEM, V33, P513
[6]   MOLECULAR PACKING AND DIFFUSION IN POLYISOBUTYLENE [J].
BOYD, RH ;
PANT, PVK .
MACROMOLECULES, 1991, 24 (23) :6325-6331
[8]   INTERSTICES, DIFFUSION DOORWAYS AND FREE-VOLUME PERCOLATION STUDIES OF A DENSE RANDOM PACKED ATOMIC-STRUCTURE [J].
CHAN, SL ;
ELLIOTT, SR .
JOURNAL OF NON-CRYSTALLINE SOLIDS, 1990, 124 (01) :22-33
[9]   FREE-VOLUME DISTRIBUTIONS OF AN EPOXY POLYMER PROBED BY POSITRON-ANNIHILATION - PRESSURE-DEPENDENCE [J].
DENG, Q ;
JEAN, YC .
MACROMOLECULES, 1993, 26 (01) :30-34
[10]   MOLECULAR PROPERTIES OF AMORPHOUS HIGH POLYMERS .2. AN INTERPRETATION OF GASEOUS DIFFUSION THROUGH POLYMERS [J].
DIBENEDETTO, AT .
JOURNAL OF POLYMER SCIENCE PART A-GENERAL PAPERS, 1963, 1 (11) :3477-&