Molecular dynamics simulation of temperature and pressure effects on the intermediate length scale dynamics and zero shear rate viscosity of cis-1,4-polybutadiene: Rouse mode analysis and dynamic structure factor spectra
✍ Scribed by Georgia Tsolou; Vagelis A. Harmandaris; Vlasis G. Mavrantzas
- Publisher
- Elsevier Science
- Year
- 2008
- Tongue
- English
- Weight
- 935 KB
- Volume
- 152
- Category
- Article
- ISSN
- 0377-0257
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✦ Synopsis
A well-relaxed atomistic configuration of a 32-chain C 128 cis-1,4-polybutadiene (cis-1,4-PB) system has been subjected to long (on the order of a few microseconds) molecular dynamics (MD) simulations in the NPT ensemble using the united-atom forcefield introduced by Smith et al. [G. Smith, D. Bedrov, W. Paul, A molecular dynamics simulation study of the alpha-relaxation in a 1,4-polybutadiene melt as probed by the coherent dynamic structure factor, J. Chem. Phys. 121 (2004) 4961-4967] on the basis of quantum chemistry calculations. This allowed us to study the temperature and pressure dependences of the Rouse-mode relaxation spectrum of cis-1,4-PB over a wide range of temperature (ranging from T = 430 K down to 165 K) and pressure (from P = 1 atm up to 3.5 kbar) conditions. Results are presented for: (a) the time decay of the autocorrelation function of the normal coordinates (Rouse modes), (b) the single chain intermediate coherent dynamic structure factor, S coh (q, t), and (c) the intermediate incoherent dynamic structure factor, S inc (q, t), for different values of the wavevector q. By mapping our MD simulation results onto the Rouse model, we have been able to extract a prediction for the zero shear rate viscosity of the simulated cis-1,4-PB system as a function of temperature and analyze its fragile character. In agreement with our previous MD simulation studies on the same system [G. Tsolou, V.A. Harmandaris, V.G. Mavrantzas, Atomistic molecular dynamics simulation of the temperature and pressure dependences of local and terminal relaxations in cis-1,4-polybutadiene, J. Chem. Phys. 124 (2006) 084906-1-11] and in contrast to what is experimentally observed [see, e.g., G.