Excluded-volume effects in polymer solutions. 2. Comparison of experimental results with numerical simulation data

The effect of excluded volume on the coil size of dilute linear polymers wa s investigated by off-lattice Monte Carlo simulations. The radius of gyrati on R-g was evaluated for a wide range of chain lengths at several temperatu res and at the athermal condition. The theta temperature and the correspond ing theta chain dimensions were established for the system, and the depende nce of the size expansion factor, alpha(s) = R-g/(R-g)(theta), on chain len gth N and temperature T was examined. For long chains and at high temperatu res, alpha(s) is a function of N/N(s)double dagger alone, where the length scale N(s)double dagger depends only on T. The form of this simulations-bas ed master function compares favorably with alpha(s)(M/M(s)double dagger), a n experimental master curve for linear polymers in good solvents, where M(s )double dagger depends only on polymer-solvent system. Comparisons when N(s )double dagger(T) and M(s)double dagger(system) are reduced to common units , numbers of Kuhn steps, strongly indicate that coil expansion in even the best of good solvents is small relative to that expected for truly athermal solutions. An explanation for this behavior is proposed, based on what wou ld appear to be an inherent difference in the equation-of-state properties for polymeric and monomeric liquids.