### Abstract

The dynamical and equilibrium properties of a strongly coupled chain of charged particles (polyampholyte) submerged in an immobile viscous medium are studied using the molecular dynamics simulations. The polyampholyte relaxes to an equilibrium conformation typically in 300ω_{pe}
^{-1} due to folding of the chain for low temperatures, and expands several times faster for high temperatures, where ω_{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 root-mean-squared size of the polyampholytes 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 crossover point of the regimes is 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 results agree well with the Flory theory in the high and medium temperature regimes. The densely packed 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.

Original language | English (US) |
---|---|

Pages (from-to) | 5798-5808 |

Number of pages | 11 |

Journal | Physical Review E - Statistical Physics, Plasmas, Fluids, and Related Interdisciplinary Topics |

Volume | 56 |

Issue number | 5 SUPPL. B |

State | Published - Nov 1997 |

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### ASJC Scopus subject areas

- Physics and Astronomy(all)
- Condensed Matter Physics
- Statistical and Nonlinear Physics
- Mathematical Physics

### Cite this

*Physical Review E - Statistical Physics, Plasmas, Fluids, and Related Interdisciplinary Topics*,

*56*(5 SUPPL. B), 5798-5808.

**Molecular dynamics study of the structure organization in a strongly coupled chain of charged particles.** / Tanaka, Motohiko; Grosberg, A. Yu; Pande, V. S.; Tanaka, Toyoichi.

Research output: Contribution to journal › Article

*Physical Review E - Statistical Physics, Plasmas, Fluids, and Related Interdisciplinary Topics*, vol. 56, no. 5 SUPPL. B, pp. 5798-5808.

}

TY - JOUR

T1 - Molecular dynamics study of the structure organization in a strongly coupled chain of charged particles

AU - Tanaka, Motohiko

AU - Grosberg, A. Yu

AU - Pande, V. S.

AU - Tanaka, Toyoichi

PY - 1997/11

Y1 - 1997/11

N2 - The dynamical and equilibrium properties of a strongly coupled chain of charged particles (polyampholyte) submerged in an immobile viscous medium are studied using the molecular dynamics simulations. The polyampholyte relaxes to an equilibrium conformation typically in 300ωpe -1 due to folding of the chain for low temperatures, and expands several times faster for high temperatures, where ωpe 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 root-mean-squared size of the polyampholytes in these regimes is scaled, respectively, as Rg∼N1/2, (NT)1/3, and N0.3T0.8-1.0, where N is the number of monomers on the chain and T the temperature. The crossover point of the regimes is characterized by the unique values of the monomer distance 2Rg/N1/3, being insensitive to the length and stiffness of the chain. The present results agree well with the Flory theory in the high and medium temperature regimes. The densely packed 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.

AB - The dynamical and equilibrium properties of a strongly coupled chain of charged particles (polyampholyte) submerged in an immobile viscous medium are studied using the molecular dynamics simulations. The polyampholyte relaxes to an equilibrium conformation typically in 300ωpe -1 due to folding of the chain for low temperatures, and expands several times faster for high temperatures, where ωpe 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 root-mean-squared size of the polyampholytes in these regimes is scaled, respectively, as Rg∼N1/2, (NT)1/3, and N0.3T0.8-1.0, where N is the number of monomers on the chain and T the temperature. The crossover point of the regimes is characterized by the unique values of the monomer distance 2Rg/N1/3, being insensitive to the length and stiffness of the chain. The present results agree well with the Flory theory in the high and medium temperature regimes. The densely packed 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.

UR - http://www.scopus.com/inward/record.url?scp=0000744751&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=0000744751&partnerID=8YFLogxK

M3 - Article

VL - 56

SP - 5798

EP - 5808

JO - Physical Review E - Statistical, Nonlinear, and Soft Matter Physics

JF - Physical Review E - Statistical, Nonlinear, and Soft Matter Physics

SN - 1539-3755

IS - 5 SUPPL. B

ER -