Improved Calculation of Polymer Liquid-Gas Phase Transitions through Coarse-Grained Molecular Dynamics

Industrial applications for polymers, such as fuels, polymeric actuators, and supercritical foams, require a detailed understanding of their liquid-gas phase transitions. However, experimental studies of these transitions in long-chain polymers are constrained by thermal degradation at high temperatures. For example, the coexistence conditions for long polyethylene chains typical of industrial applications remain experimentally unexplored.  Traditional computational approaches, including Monte Carlo and atomistic molecular dynamics (MD), struggle to capture phase behavior at longer chain lengths and higher densities. To address this, we employ the integral equation coarse-grained (IECG) potential  based on a solution to the Ornstein-Zernike equation, enabling our CG system to overcome the energy barrier associated with phase transitions in polyethylene chains of N=16 (C₁₆H₃₄) and beyond. This model reproduces experimental and Monte Carlo results for thermodynamics and phase boundaries of intermediate-length polyethylene chains and extends unique predictive capability to phase transitions in longer chains. This approach offers a promising computational framework for exploring polymer phase behavior in regimes inaccessible to both experiment and traditional simulations.