Thermal Conductivity of Amorphous Polystyrene in Supercritical Carbon Dioxide Studied by Reverse Nonequilibrium Molecular Dynamics Simulations

Abstract

The thermal conductivity of amorphous atactic polystyrene (PS) swollen in supercritical carbon dioxide (sc CO(2)) has been investigated over wide temperature, pressure, and concentration ranges. Nonequilibrium molecular dynamics simulations with a full atomistic force field have been used to calculate the thermal conductivity of neat PS and sc CO(2) as well as of the binary system at different compositions. An analytical interpolation formula for the thermal conductivity of the binary mixture on the basis of PS and CO(2) data has been obtained. Particular attention has been paid to the implications of the quasi-degeneracy and finite-size effects in the simulated polymer system. It has been found that, in addition to the degrees of freedom per volume, the orientation of the carbon-carbon bonds in the backbone relative to the direction of the temperature gradient is important for the heat transport in PS.

Testing the minimum thermal conductivity model for amorphous polymers using high pressure

“…Recently, Algaer and collaborators [35] also reported the pressure dependence of the thermal conductivity of polystyrene obtained via MD simulations. However, in their studies, pressures up to only 60 MPa were investigated, and consequently no dependence on the elastic constants was determined.…”

Molecular Dynamics Calculations of the Thermal Conductivity of Molecular Liquids, Polymers, and Carbon Nanotubes

“…It has been developing through research (9,33) and has been successfully applied to the calculation of the thermal conductivity and shear viscosity of Lennard-Jones liquids (3), molecular fluids (33), polymers (4,9,12), and carbon nanotubes (28). A similar method has been developed by Hafskjold et al (34) In this section we briefly review the original RNEMD method for the calculation of the thermal conductivity.…”

“…For the nonequilibrium methods, the system must be in the linear response regime, that is, the heat flux j z and the temperature gradient (dT /dz) must be proportional. It has been demonstrated in the simulations of molecular liquids as well as of polymers that, as long as system is in the linear response regime, the thermal conductivity deviates only within its error bars for different perturbation periods (4,9,33). Thus, each particular system has to be tested for the linearity of the temperature gradient.…”

“…Starting with the simulation of simple Lennard-Jones liquids (1)(2)(3), theoretical calculations have progressed in the complexity of the materials (4)(5)(6)(7)(8)(9)(10)(11)(12) as well as in the accuracy of the prediction (13,14). This significant development is important from two points of view.…”

“…Calculations become more complicated when one moves from molecular liquids to polymers. The chosen force field plays a bigger role, and small modifications in molecular structure and molecular orientation can lead to uncertainties in thermal conductivity (4,9,12). In contrast, the calculation of thermal conductivities for single-walled carbon nanotubes seems to be robust against the force field and its potential form (27,28).…”