Abstract: A model for the freely jointed square well chain fluid is developed based on the thermodynamic perturbation theory of BarkerHenderson,Zhang and Wertheim.The analytic representations of squarewell monomer by Zhang are extended to obtain a series of representations for thermodynamic properties of squarewell chain fluids using the incorporating structural information for squarewell monomer of Wertheim's TPT1 model.The same work has been done using incorporating structural information for the diatomic squarewell fluid of TPTD model.The calculated results of compressibility factor,residual internal energy and constantvolume heat capacity of 4mer,8mer and 16mer chain fluids are tested against the MC results and a careful comparison between the model from TPT1 and that from TPTD has been made.The former agree with MC results much better than the later,especially for internal energy.To obtain the constantvolume heat capacity,NVT MC simulations have been performed.

Key words: Chain-like molecule, Square-well potential, Perturbation theory, 　Thermodynamic property, Monte Carlo simulation