THE THETA-CONDITION FOR LINEAR POLYMER-CHAINS IN CONTINUOUS SPACE AND3 DIMENSIONS

Configurational properties of isolated flexible linear chains of lengt hs in the range 72 less than or equal to N less than or equal to 576 h ave been investigated close to the theta regime by continuous space si mulations using a configurational bias Monte Carlo algorithm. The poly mer model consisted of beads interacting through a nontruncated Lennar d-Jones potential and connected by a Gaussian distribution of link vec tors. We use two criteria in order to characterize departures from ide al behavior at finite N, first the ratio of the mean squared end-to-en d distance and the mean squared radius of gyration, and second the end -to-end vector distribution. Both the criteria lead, within the statis tical errors, to the same prediction for the theta temperature as N--> infinity; the ratio criterion gives k(B)T(theta)(rat)/epsilon=4.167+/- 0.035 and the distribution criterion gives k(B)T(theta)(dis)/epsilon 4 .184+/-0.035, in close agreement with previous estimates for the same model. Deviations from ideal behavior were found to be independent of whether the finite number of beads constitute a whole chain or merely an inner part of a much larger chain. The N-dependencies of several co nfigurational properties including the moments of the end-to-end distr ibution and the asphericity have been examined at the N-->infinity the ta temperature. Nonideal effects are manifest in different ways depend ent on the property being considered. For instance the radius of gyrat ion shows a slight contraction effect which diminishes with increasing chain length and which shows remarkable quantitative agreement with t he prediction of tricritical renormalization group theory, while the e nd-to-end distribution shows slight expansion effects. It is suggested that each property emphasizes nonideal effects in slightly different ways. (C) 1996 American Institute of Physics.