-
Author(s):
M. Tanaka, A.Yu Grosberg, V.S. Pande and T. Tanaka
-
Title:
Molecular Dynamics and Structure Organization inStrongly-Coupled Chain of Charged Particles
Date of publication:
July 1997
-
Key words:
Coulomb System, Structure Organization, Phase Transition
-
Abstract:
The dynamical and equilibrium properties of a strongly-coupled chain of charged particles (polyampholyte) submerged in a viscous medium are studied using the molecular dynamics simulations. The polyampholyte relaxes to an equilibrium conformation typically in 300 omega_pe^-1 due to folding of the chain for low temperatures, and expands several times faster for high temperatures, where omega_pe is the plasma frequency. Three regimes with distinct conformations as stretched, oblate and spherical are observed under the Coulomb force at high, medium and low temperatures, respectively. The change in the conformations is considered to minimize the free energy through the electrostatic potential. The gyration radius in these regimes is scaled, respectively, as R_g ~ N^1/2, (NT)^1/3 and N^0.3 T^(0.8-1.0) where N is the number of monomers on the chain and T the temperature. The regime boundaries are characterized by the unique values of the monomer distance 2R_g/N^1/3, being insensitive to the length and stiffness of the chain. The present molecular dynamics agrees well with the Flory theory in the high and medium temperature regimes. The densely-packed frozen state at low temperatures is first obtained here without the use of the lattice model. The transition among the different regimes under the Coulomb force is exactly reversible. However, the transition under the cooperation of the Coulomb force and the attractive short-range force exhibits a hysteresis against successive changes in temperature.
-
|
