چكيده به لاتين
In this study, the molecular dynamics (MD) simulation were used to determination and investigation of the molecular characteristics of Atactic polystyrene (aPS) chains at different molecular weight and its behaviors in toluene solvent at 288.15 K (good solvent) and cyclohexane solvent at 307.65 K (theta solvent), respectively. In order to investigate the chain compatibility with the solvent, the interaction energies and parameters were calculated for each system in the dilute concentration. The obtained results indicated that by increasing the aPS chain repeating units, the non-bond interactions between the solute and solvent molecules became more, which caused the interaction energy to be more negative. Also, the calculated interaction parameters in aPS/toluene at 298.15 K (0.314±0.004) and aPS/cyclohexane at 307.65 K (0.474±0.005) were approved that the toluene and cyclohexane solvent (at mentioned temperature) is good and theta solvent for aPS molecule, respectively. Additionally, the variations of the chain dimensions with changing of the chain molecular weight were evaluated by calculation of the radius of gyration (Rg) and the end to end distance of chains. For examining the dynamic behavior of the chains in the solutions, the mean square displacement (MSD) and the diffusivity coefficient of the chains were calculated. According to the results, in low molecular weight, the two factors of the chain movability and the chain size are very important on chain dynamics behavior. Moreover, calculation of the chains radial distribution function (RDF) in solutions illustrated that, in chain with the number of repeating units (N) 94 the steric hindrance of the chain is the highest, which caused the solvent molecules cannot be close to the chains backbone well, while the chains with N=14 and N=17 have the lowest steric hindrance in toluene and cyclohexane solvent, respectively. In addition, solutions viscosity was calculated by performing non-equilibrium molecular dynamic simulation (NEMD). The obtained results from MD simulations have the good agreement with the experimental results, which confirm the accuracy of the applied simulation method to characterize the solution. Also, the MD simulation was used to consideration of the effect of aliphatic co-monomer on the dynamics behavior of the random co-polymer of polystyrene with 1-Octen co-monomer in toluene solvent (at 298.15 K).
