dorsal/arxiv
View SchemaDynamics of n-alkanes: Comparison to Rouse Model
| Authors | Maurizio Mondello, Gary S. Grest, Edmund B. Webb III, P. Peczak, Scott T. Milner |
|---|---|
| Categories | |
| ArXiv ID | physics/9802022 |
| URL | https://arxiv.org/abs/physics/9802022 |
| DOI | 10.1063/1.476619 |
Abstract
The crossover to Rouse-like behavior for the self-diffusion constant D, the viscosity $\eta$, and the equilibrium structural statistics of n-alkanes $(6 \le n \le 66)$ is studied numerically. For small n the chains are non-Gaussian and the mean squared end-to-end distance $R^2$ is greater than $R_G^2$, where $R_g^2$ is the mean squared radius of gyration. As n increases, $R^2/R_G^2 \to 6(1+b/n)$, where b depends on the interaction model. At constant density, the Rouse model is used to extract the monomeric friction coefficient $\zeta$ and the viscosity $\eta$ independently from the diffusion constant D and the longest relaxation time $\tau_R$. $\zeta_D$ extracted from D is nearly independent of chain length while $\zeta_\tau$ obtained from $\tau_R$ is much larger than $\zeta_D$ for small n. The viscosity measured in a non-equilibrium molecular dynamics simulation is closely approximated by the value of $\eta$ determined from $\tau_R$ while $\eta$ inferred from D is smaller for small n. For $n\agt 60$, the two estimates for both $\zeta$ and $\eta$ agree as predicted from the Rouse model. D calculated from three interaction models is studied for increasing $n$ and compared to experimental data.
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"abstract": "The crossover to Rouse-like behavior for the self-diffusion constant D, the\nviscosity $\\eta$, and the equilibrium structural statistics of n-alkanes $(6\n\\le n \\le 66)$ is studied numerically. For small n the chains are non-Gaussian\nand the mean squared end-to-end distance $R^2$ is greater than $R_G^2$, where\n$R_g^2$ is the mean squared radius of gyration. As n increases, $R^2/R_G^2 \\to\n6(1+b/n)$, where b depends on the interaction model. At constant density, the\nRouse model is used to extract the monomeric friction coefficient $\\zeta$ and\nthe viscosity $\\eta$ independently from the diffusion constant D and the\nlongest relaxation time $\\tau_R$. $\\zeta_D$ extracted from D is nearly\nindependent of chain length while $\\zeta_\\tau$ obtained from $\\tau_R$ is much\nlarger than $\\zeta_D$ for small n. The viscosity measured in a non-equilibrium\nmolecular dynamics simulation is closely approximated by the value of $\\eta$\ndetermined from $\\tau_R$ while $\\eta$ inferred from D is smaller for small n.\nFor $n\\agt 60$, the two estimates for both $\\zeta$ and $\\eta$ agree as\npredicted from the Rouse model. D calculated from three interaction models is\nstudied for increasing $n$ and compared to experimental data.",
"arxiv_id": "physics/9802022",
"authors": [
"Maurizio Mondello",
"Gary S. Grest",
"Edmund B. Webb III",
"P. Peczak",
"Scott T. Milner"
],
"categories": [
"physics.chem-ph",
"cond-mat.stat-mech"
],
"doi": "10.1063/1.476619",
"title": "Dynamics of n-alkanes: Comparison to Rouse Model",
"url": "https://arxiv.org/abs/physics/9802022"
},
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