KINETIC STRUCTURES FOR GLASS-TRANSITION IN A MODIFIED 2D FREDRICKSON MODEL

Butler Harrowell pictures (BHP) are presented for a modified Fredricks on 2d-50 x 50 lattice model in a large temperature interval above and below the onset temperature. The fraction of ''mobile'' (spin down) si tes in equilibrium is also numerically calculated as a function of tem perature. The results are discussed with respect to a characteristic l ength of glass transition and to exhaustion of fluctuating free volume at about half of the onset temperature. The contributions from alpha cooperativity and accidental combinations of local beta modes to the c haracteristic length cannot clearly be separated from the BHPs alone. Below the a onset temperature a cellular pattern is obtained with less mobile cell walls and islands of mobility within. Comparison with an analytical onset model and with cooperativities from heat capacity spe ctroscopy experiments on polymers results in the conclusion that one m onomeric unit of a real glass former corresponds to an array of severa l or even many sites. (C) 1998 Elsevier Science B.V. All rights reserv ed.