A Monte Carlo simulation of a single short polyelectrolyte chain immersed in a dielectric continuum solvent with screened Coulombic interactions is described. Two main effects are involved in the coil→rod conformational transitions that have been observed when the temperature is decreased: a new thermal effect and a screening effect. The pure thermal effect is resolved by simulating a bare fully ionized polyion with Coulombic interactions at various T. With decreasing T, the radius of gyration exhibits a crossover from a self-avoiding walk configuration to a rod-like shape. This phenomenon is explained by fundamental thermodynamic considerations. The screening effect at various temperatures, has been investigated for several ‘‘salt’’ concentrations using a screened Coulomb potential instead of a pure Coulomb one. Configurational properties such as the mean square end-to-end distance 〈R2〉, the mean square radius of gyration 〈S2〉, the average of the ratio of the means 〈S2〉/〈R2〉, the mean reduced electrostatic energy 〈UN/NkT〉, and the reduced mean electrostatic energy fluctuations Cν/Nk at various concentrations and temperatures were studied. Our results show that, at low salt concentration where C<0.001 M, the chain behaves like a bare polyelectrolyte chain at all temperatures (no screening at all). At high salt concentration, C>1 M, the chain is fully screened and exhibits a self-avoiding walk configuration at all temperatures, so that the thermal effect cannot be observed. At intermediate salt concentrations, 0.001 M<C<1 M, the chain is partially screened, exhibiting the coil to rod-like transition but with less extension under decreasing temperature. No increase in the effective screening due to temperature decrease is observed under these conditions, despite the decrease in κ−1, the Debye–Hückel screening length.

An interesting connection between the mean straight length 〈ls〉 and the defined average number of kinks 〈nkink〉 in a polyelectrolyte chain configuration is found and described. 〈nkink〉 is found to be the dominant parameter throughout the entire range of the Bjerrum length λ and very sensitive to salt concentration. Identification of λm where (nkink values for various chain lengths coincide, as a percolation threshold is suggested. Considering the kink as a bond, it is found to be much more significant than the contacts described in a previous article as a new type of bonds. It is shown that the family of the physical statistical bonds includes not only contacts but also kinks. The kink fraction in a chain and the effective screening of 〈nkink〉 are defined and described for various values of λ. Through the use of these new parameters, pronounced size effects appear clearly. A connection between polymer systems and molecular cluster systems is proposed.

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At present there exists two types of Monte Carlo techniques by which polymer conformations may be simulated. The most widely used methods are the "static" methods 1 .:! whereby equilibrium samples of polymer chains are generated. Alternatively one may employ relaxation methods 3 -5 to study not only equilibrium config-urations but also chain dynamics. To date the most comprehensive computer study of polymer relaxation on a lattice has been made by Verdier etal. 3 using a Simple kinetic scheme for single bead motion which simulates the Brownian motion of a real chain. For the normal random walk case Verdier's results agree with predic-

A dynamic Monte Carlo method for the relaxation of a polyion in the presence of its counter ions is reported. A lattice model incorporating long range interaction of a Coulombic and excluded volume nature is considered. Results are listed for the configurational energy 〈UNI/NIkT〉, as well as the mean square end-to-end distance 〈R2N〉, and the mean square radius of gyration 〈S2N〉, for short chains.