Crossover behavior in dilute polymer solutions: Square-well chains

Lue, L.; Kiselev, S. B.

doi:doi:10.1063/1.479816

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The alanine dipeptide free energy surface in solution

Molecular dynamics (MD) simulations have been used to determine the two dimensional free energy surface of the alanine dipeptide in solution. The intramolecular dipeptide interactions were described by the CHARMM22 force field. Three models of solvation were considered; (i) a simple scaling of electrostatic interactions, (ii) solvation energies determined by finite difference Poisson–Boltzmann calculations, and (iii) inclusion of explicit TIP3P solvent molecules. All three solvation models produ...

The application of the energy landscape model to polymers

The energy landscape model of the glass transition has received increasing attention, due to its potential for providing a thermodynamic interpretation of the dynamics of glass-forming liquids. Herein, the idea that the temperature-dependence of the dynamics near the glass temperature (“fragility”) can be related to thermodynamic properties is tested for polymers. Previously, for several homologous series, we found deviations from a proposed correlation between fragility and the heat capacity in...

Monte Carlo simulations for model polymer chains composed of hard spheres with square-well attractions were performed to find a precise relation between the parameters of a crossover theory and the parameters of the square-well chain. For sufficiently large bond lengths, there was a direct relation between the effective parameters of the crossover theory and the second- and third-virial coefficients of the square-well atoms. For the systems under study, the theta temperature is close to the Boyle temperature of the disconnected monomers, is mainly dependent on the details of the monomer–monomer interactions, and is only weakly dependent on the bond length of the chain. Above the theta temperature, the crossover theory is in good agreement with the simulation data. Near the theta point, the main effect of tricritical corrections is a shift in the critical amplitudes. Other effects are extremely small. The simulation data are consistent with the tricritical crossover theory. However, more precise data are needed to quantitatively test the tricritical crossover theory. © 1999 American Institute of Physics.