Ugur Yahsi

Equation of state of poly(dimethylsiloxane) melts

The pressure-volume-temperature (PVT) properties of three commercial samples of poly(dimethylsiloxane) are studied experimentally and theoretically in the temperature range 25-150°C and for pressure to ∼ 3 kbar. The Tait equation is employed to represent the data at elevated pressure. Isothermal compressibilities are computed for the three samples. The melt data are analyzed in terms of the Simha-Somcynsky hole theory, and scaling parameters of pressure, volume, and temperature are obtained. Satisfactory agreement between theory and experiment is found over the entire range of experimental pressures.

Viscous behavior of linear and three-branch alkanes: Linking the equilibrium and transport theories

A new model for zero-shear viscosity, η, is proposed. The model combines the Simha-Somcynsky (SS) statistical thermodynamic theory of liquids with the Eyring Significant Structure (ESS) transport theory. Using the new model, a successful linearization of the experimental viscosity vs. hole fraction data was obtained. A comparison between the new model and Utrackis relation, In η = α 0 + α 1 /(h + α 2 ) was also made. The former was found to be more successful for both linear and nonlinear structures, provided that an appropriate choice of the degrees of freedom of normal and activated states was made. The proportionality constant of the activation energy and transmission coefficient were also calculated for each species.

Statistical thermodynamics of hydrocarbon fluids: scaling parameters and their group contributions

We have analysed the equation of states (eos) data for five series of compounds in terms of the Simha–Somcynsky hole theory and, in this manner, obtained graph-averaged temperature, volume and pressure scaling parameters. The eos data were obtained some time ago, when several series of hydrocarbon oligomer fluids with systematically varied structures were synthesized and their eos and Newtonian viscosities determined over broad ranges of temperature and pressure. By means of suitable decomposition equations, individual group attraction energy and repulsion volume quantities have now been derived. These compounds include saturated and unsaturated rings. The approach taken also yields results for branched alkanes. However, the results diverge from what would be expected from those found for the linear species. Simple linearities between group self-interaction repulsion volumes and Bondis van der Waals volumes, and correlations of energy parameters with group-derived cohesive energy estimates are observed. The results obtained can form a basis for equation of state predictions and encourage applications of the methodology to further structures. Finally, the results lead to ideas for the investigation of correlations between rheological and thermodynamic equations of state.

Equation of State of Alkane and Alkylbenzene Liquids: A Test of the Group Contributions of Scaling Parameters for Physical and Chemical Mixtures

The equation of state (EOS) data for physical and chemical mixtures have been studied in terms of the Simha–Somcynsky hole theory. In a previous paper, individual group attraction energy and repulsive volume quantities necessary for the description of interactions between the chemical constituents of alkanes and alkylbenzene were proposed. The previous method has now been extended to physical mixtures of alkanes and alkane–alkylbenzene through suitable decomposition equations for physical and chemical mixtures. A comparison of the theoretical EOS data, predicted by means of the proposed scaling parameters, and the experimental data is in reasonable agreement. The results confirm a basis for the EOS predictions and promote applications of the methodology to further systems.