Molecular simulations of the early structural development of normal alkanes with different chain lengths and...

The development of ordered structures upon immediately quenching from 473 K to different crystallization temperatures (Tc = 300 K, 320 K, 340 K, and 360 K) of three n-alkanes (n-eicosane (C₂₀H₄₂), n-tetracontane (C₄₀H₈₂) and n-octacontane (C₈₀H₁₆₂) to accommodate the formation of bilayer, monolayer and the folded-chain configurations, respectively), was quantitatively analyzed by evaluating chain/bond order parameters, interaction energies, conformational statistics, local dynamics, structural pair correlation function, and X-ray scattering profiles. The formation of ordered structures seems to be best at Tc = 340 K. Generally, systems that tend to form the monolayer and folded-chain configurations exhibit the most and the least ordered structures, respectively. Chains in monolayer structures tend to have a larger fraction of trans state, higher anisotropy of bond orientation, slower monomer dynamics, and more densely packed structures than chains in bilayer structures, while longer alkanes with chain-folded structures exhibit the least characteristics of these properties. The nucleation temperature (Tn) can be affected by their structural configuration, with the highest Tn for the monolayer structure. Nevertheless, the melting temperature (Tm) tends to depend solely on the molecular weights of these alkanes, not on their structural configuration.

Monte Carlo (MC) simulation of the coarse-grained (CG) models of three n-alkanes (one CG bead equivalent to an ethylene unit) on the second nearest neighbor diamond (2nnd) lattice with the same periodic box dimension of 5 nm in each size. The energetics of CG models were composed of the Rotational Isomeric State (RIS) model and the Lennard-Jones (LJ) potential energies to represent their intra- and intermolecular interactions, respectively. Structure developments within 100 million Monte Carlo steps (MCS) trajectories were monitored, and data analysis was based on snapshots collected at intervals of 10,000 MCS. All simulations and data analysis were performed using in-house FORTRAN codes with the g77 compiler.