A deep insight into the polystyrene chain in cyclohexane at theta
temperature: molecular dynamics simulation and quantum chemical
calculations
S Rasouli and MR Moghbeli and SJ Nikkhah, JOURNAL OF MOLECULAR MODELING,
25, 195 (2019).
DOI: 10.1007/s00894-019-4078-4
Molecular characteristics of an atactic polystyrene (aPS) chain with
different lengths in a theta solvent, cyclohexane at 307.65K, were
studied via molecular dynamics (MD) simulation. The interaction energy
of the aPS dilute solution models and Flory-Huggins (FH) interaction
parameter were calculated to investigate the effect of the chain
molecular weight on its compatibility with the solvent molecules. The
simulation results illustrated that increasing the chain length
increased the interactions between the chain and the solvent molecules.
The chain dimensions via calculating the radius of gyration (R-g) and
end-to-end distance, , were measured. Mean square displacement
(MSD) and diffusivity coefficient of the chains were calculated to
determine their dynamic behavior. The results exhibited that two factors
of the chain movability and size were important for the diffusion in
oligomeric state. Additionally, viscosity of the resultant dilute
solutions was calculated via nonequilibrium molecular dynamics
simulation (NEMD). Moreover, the steric hindrance of the chains was
determined by radial distribution function (RDF) analysis. The
calculated characteristics of the chain and solution viscosity results
showed a good agreement with experimental published works. Measurement
of the potential field of cyclohexane-cyclohexane and aPS-cyclohexane
pairs was also based on their potential field via quantum chemical
calculations to determine the special orientation of the solvent
molecules to each other and to the polymer segments, respectively The
equilibrated dilute solution model of polystyrene in cyclohexane at
theta temperature (the red and yellow balls represent carbon and
hydrogen atoms, respectively. The cyclohexane molecules are illustrated
in line style in the box), (b) the electrostatic potential field around
an optimized structure containing two cyclohexane molecules, and (c)
around the sole cyclohexane molecule and polystyrene with two repeating
units (carbon and hydrogen atoms are represented in green and yellow,
respectively).
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