Monte Carlo study of geometric, thermodynamic properties and flexibility of hydrocarbon chain molecules

One of the main problems of condensed matter physics is investigation of interconnections between chemical structures and physical properties of various molecules. The hydrocarbon chain molecules play an important role in natural systems. They are widely used in different fields of technology. In this paper, Monte Carlo simulation of 65 hydrocarbon chain molecules CH3-(CH2) a-(CH=CH-CH2)d-(CH2)b-CH3 (where a, b, d are integer) was carried out. Sets of N = 16, 18, 20, 22 (where N = a + b + 3d + 2 is carbons number), d = 0, 1,..., 6 (where d is cis double bonds number) are studied; temperature T = 293, 303 and 313 K. All studied molecules were treated in unperturbed state, torsion angles were generated using importance sampling technique in 0 - 360 deg range and three-wise interdependence of torsions along the chain. As a result, the equilibrium flexibility, conformational heat capacity, relative fluctuations of square radius of gyration, and square end-to-end distance of each molecule were calculated in the simulations. Dependencies of the properties on the molecule structure parameters were analyzed. The set of regularities, including correlations between flexibility and relative fluctuations of geometric dimensions, were found. An interpretation of obtained dependencies based on experimental data of characteristics of internal rotation in the chains, was proposed. The obtained data provide further insight into interconnections between the structure and properties of considered molecules.