MONTE-CARLO SIMULATION OF TETRAHEDRAL CHAINS .6. LINEAR AND STAR-BRANCHED POLYMERS NEAR TO THETA-CONDITIONS

By use of the pivot algorithm; star-branched chains with F = 4, 8 and 12 arms of length n and linear chains (F = 2) are generated on a tetra hedral lattice (I 20 less-than-or-equal-to nF less-than-or-equal-to 3 840). By taking into account non-bonded nearest-neighbour interactions (each contact contributes an energy PHI . kT to the total energy of t he configuration) a variation of the thermodynamic quality of the solv ent is simulated by a variation of the energy parameter PHI in the ran ge -0,425 to -0,525. The energy parameter PHI(THETA) = -0,475, charact eristic of theta conditions, was evaluated by use of an intramolecular criterion (proportionality between mean-square dimensions and total c hain-length) and confirmed by a crossover scaling analysis. Theta dime nsions are found to be larger than those of nonreversal random walks, the deviation growing with increasing number of arms.