Athermal stiffness blends: A comparison of Monte Carlo simulations and integral equation theory
- Department of Materials Science and Engineering, Polymer Science Program, Pennsylvania State University, University Park, Pennsylvania 16802 (United States)
- Department of Materials Science & Engineering, and Materials Research Laboratory, University of Illinois, Urbana, Illinois 61801 (United States)
Off-lattice Monte Carlo computer simulations and numerical polymer reference interaction site model (PRISM) integral equation calculations were performed to quantitatively probe the origins of entropic corrections to Flory--Huggins theory for athermal polymer blends with stiffness disparity. This model system is of interest since it has been recently proposed for describing commercially relevant hydrocarbon polymer mixtures. The novelty of the simulations is that the chemical potential changes on mixing for both components are evaluated. We have considered mixing under constant density conditions, and find surprisingly that the stiffer component is stabilized on blending, while the flexible component is characterized by a positive interaction or {chi} parameter. The net effective single {chi} parameter describing these blends, however, is close to zero suggesting that they are completely miscible over a wide range of stiffness disparities and chain lengths. PRISM theory is found to be in good agreement with the simulations for both structural and mixing thermodynamic properties. While purely entropic nonrandom mixing effects could be relevant in determining system thermodynamics, the dominant contribution to the chemical potential changes on mixing arise from equation-of-state (EOS) effects since the two pure components and the mixture are at different pressures when examined at the same density. The EOS contribution to the mixing free energy for small stiffness mismatch is shown to be quantitatively reproduced through an extension of the generalized Flory approach. Through the use of PRISM theory we find that athermal, nonlocal entropy-driven phase separation can occur for long enough chains and high enough stiffness disparity.
- Research Organization:
- University of Illinois
- DOE Contract Number:
- FG02-91ER45439
- OSTI ID:
- 146761
- Journal Information:
- Journal of Chemical Physics, Journal Name: Journal of Chemical Physics Journal Issue: 21 Vol. 103; ISSN JCPSA6; ISSN 0021-9606
- Country of Publication:
- United States
- Language:
- English
Similar Records
Microscopic solubility-parameter theory of polymer blends: General predictions
Application of integral equation theory to polyolefin liquids and blends