Microscopic equations of state of polyethylene: Hard-chain contribution to the pressure

Journal Article · Thu Jan 14 23:00:00 EST 1993 · Journal of Chemical Physics; (United States)

DOI:https://doi.org/10.1063/1.464280· OSTI ID:6948196

Yethiraj, A ^[1]; Curro, J G ^[2]; Schweizer, K S ^[1]; McCoy, J D ^[3]

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1. Department of Materials Science and Engineering and Materials Research Laboratory, University of Illinois, 1304 West Green Street, Urbana, Illinois 61801 (United States)
2. Sandia National Laboratories, Albuquerque, New Mexico 87185 (United States)
3. Materials and Metallurgical Engineering Department, New Mexico Institute of Mining and Technology, Socorro, New Mexico 87801 (United States)

The athermal contribution to the pressure of polyethylene is investigated via integral equations and mean field generalized Flory-type theories. The molecules are modeled as fused-hard-sphere chains with fixed bond lengths and bond angles; torsional rotations are treated via the rotational isomeric state approximation with literature values for the [ital trans]--[ital gauche] energies. The hard sphere diameter is obtained by matching structure factor predictions of the polymer reference interaction site model (PRISM) theory for hard chains to data from wide-angle scattering experiments. In all, five hard chain equations of state are investigated: three via different thermodynamic routes in the PRISM theory, and two via different extensions (to fused-sphere chains) of the generalized Flory-dimer (GFD) theory. The integral equation approaches consist of a free energy charging'' route, the compressibility route, and the wall'' route (where the pressure is obtained from the density profile of the fluid at a hard wall). The two GFD approaches correspond to different choices for the reference monomer and dimer fluids required in the theory. Each of the five equations of state results in significantly different predictions for the pressure. The predictions of the various equations relative to each other are nearly independent of chain length, and this allows us to draw conclusions for polymeric fluids (where simulation results are not available) by testing the performance of the equations for diatomics (where simulation results are available). We thus speculate that the charging route overestimates the pressure, the compressibility route underestimates the pressure, and the GFD and wall equations of state are the most accurate.

• DOE Contract Number: AC04-76DP00789
• OSTI ID: 6948196
• Journal Information: Journal of Chemical Physics; (United States), Journal Name: Journal of Chemical Physics; (United States) Vol. 98:2; ISSN JCPSA6; ISSN 0021-9606
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360606* -- Other Materials-- Physical Properties-- (1992-)
ALKANES
BOND ANGLE
BOND LENGTHS
CHEMICAL REACTIONS
DIMENSIONS
ENERGY
ENERGY LEVELS
EQUATIONS
EQUATIONS OF STATE
EXCITED STATES
FREE ENERGY
HARD-SPHERE MODEL
HYDROCARBONS
INTEGRAL EQUATIONS
LENGTH
MEAN-FIELD THEORY
ORGANIC COMPOUNDS
ORGANIC POLYMERS
PHYSICAL PROPERTIES
POLYETHYLENES
POLYMERIZATION
POLYMERS
POLYOLEFINS
PRESSURE DEPENDENCE
ROTATIONAL STATES
THERMODYNAMIC PROPERTIES
TORSION