J. Iran. Chem. Soc., Vol. 8, No. 2 June 2011, pp.574~579.

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Investigation of Phase Transition in the One-Dimensional Phospholipids Model by Combinatorial Factor Method

S. Ranjbar* and S. Taslimian

Chemistry College, Razi University, 67149-67346, Kermanshah, Iran

     In this study, using a one-dimensional phospholipids model, we have introduced an exact combinatorial factor method for the investigation of order-disorder in the phospholipids lattice. Our assumption was that the lattice was composed of six groups, and for simplicity, we assumed that the total energy of the lattice can be considered as the rotational energy of gauche molecules and the nearest neighbor interactions between trans molecules. Using the combinatorial factor method (CFM), the total energy and the corresponding constrains, the Helmholtz free energy was minimized. Finally, the thermodynamic properties of the one-dimensional lattice including the internal energy, entropy, and heat capacity were determined, exactly. The results show that, adopting such a model and under specific conditions, a phase transition, similar to the one in Onsager transition, takes place.

Keywords: Phase transition, Combinatorial factor method, Phospholipids model, Helmholtz free energy, Order-disorder

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