@article{bouza_colina_olivera-fuentes_2005, title={Parameterization of molecular-based equations of state}, volume={228}, ISSN={["1879-0224"]}, DOI={10.1016/j.fluid.2004.08.043}, abstractNote={Despite significant advances in the development and formulation of molecular-based (MB) equations of state (EOS), their practical use has been limited, at least in part, by unavailability of the fluid-specific constants. In this work, we explore the possibility and consequences of obtaining the MBEOS parameters of a fluid directly from its critical constants Tc, Pc and acentric factor ω, as is done with cubic EOS. Four different models are used as examples: perturbed hard chain theory in original (PHCT) and simplified (SPHCT) forms, Huang–Radosz version of the statistical associating fluid theory (SAFT), and the augmented van der Waals theory as implemented in the Boublík–Alder–Chen–Kreglewski (BACK) EOS. For each model, the scaled critical and saturation properties are computed and approximated by polynomial expansions. Using these, the molecular parameters can be related to the macroscopic properties Tc, Pc and ω. In this way it is not necessary to fit the EOS parameters to extensive experimental data, because the parameters obtained are fully equivalent to those generated from complex minimization techniques. In particular, the BACK EOS, parameterized in terms of Tc, Pc, ω and critical compressibility factor Zc, gives excellent representation of the entire phase envelope. An alternative approach is also suggested where the experimental critical volume Vc and ω are matched, and a simple one-dimensional search is used to minimize the average absolute deviation of saturation pressures. The techniques presented in this work provide a simple way to estimate MBEOS parameters for a wide variety of fluids, and can be readily extended to other MBEOS.}, journal={FLUID PHASE EQUILIBRIA}, author={Bouza, A and Colina, CM and Olivera-Fuentes, CG}, year={2005}, month={Feb}, pages={561–575} }
@article{colina_gubbins_2005, title={Vapor-liquid and vapor-liquid-liquid equilibria of carbon dioxide/n-perfluoroalkane/n-alkane ternary mixtures}, volume={109}, ISSN={["1520-6106"]}, DOI={10.1021/jp046612d}, abstractNote={Perfluoroalkanes have numerous applications (e.g., in the medical field and the chemical industry), and their high affinity for carbon dioxide makes them attractive as surfactants and cosolvents. Although research in this area has grown in the past few years, very little phase-equilibrium data is available in the open literature for these systems. In this work, we present, for the first time, predictions of vapor-liquid and vapor-liquid-liquid equilibria of binary and ternary systems of carbon dioxide/n-perfluoroalkane/n-alkane. Our results are based on the SAFT-VR EOS (statistical associating fluid theory of variable range, equation of state), and we study the influence of temperature, pressure, composition, and chain length on the phase diagram. The predicted phase diagrams are based on temperature-independent binary interaction parameters, and no ternary parameters are introduced. Comparisons to the available experimental and molecular simulation data show that the predicted diagrams should provide a good representation of the phase equilibria.}, number={7}, journal={JOURNAL OF PHYSICAL CHEMISTRY B}, author={Colina, CM and Gubbins, KE}, year={2005}, month={Feb}, pages={2899–2910} }
@article{colina_galindo_blas_gubbins_2004, title={Phase behavior of carbon dioxide mixtures with n-alkanes and n-perfluoroalkanes}, volume={222}, ISSN={["1879-0224"]}, DOI={10.1016/j.fluid.2004.06.021}, abstractNote={The phase behavior of mixtures containing carbon dioxide, n-alkanes and n-perfluoroalkanes is studied using the statistical associating fluid theory for potentials of variable attractive range (SAFT-VR). The molecules are modeled as fully flexible chains of tangentially bonded attractive spherical segments of hard-core diameter σ. The attractive interactions are treated via square-well potentials of depth ε and range λ. The pure component intermolecular parameters for carbon dioxide and the n-alkane molecules were determined in previous works by fitting to vapor pressures and saturated liquid densities; the same procedure is followed in this work to determine the parameters for the n-perfluoroalkane molecules. The optimized conformal parameters (σ and ε) are rescaled with the experimental critical point of each of the pure components. A set of transferable mixture parameters is presented, which provide a good description of the mixtures phase behavior, and additionally offer an insight into the higher solubility of n-perfluoroalkanes in carbon dioxide as compared to the solubility of n-alkanes.}, number={2004}, journal={FLUID PHASE EQUILIBRIA}, author={Colina, CM and Galindo, A and Blas, FJ and Gubbins, KE}, year={2004}, month={Aug}, pages={77–85} }
@article{striolo_colina_gubbins_elvassore_lue_2004, title={The depletion attraction between pairs of colloid particles in polymer solution}, volume={30}, ISSN={["0892-7022"]}, DOI={10.1080/0892702042000197649}, abstractNote={NVT Monte Carlo simulations were used to assess the effective interaction between pairs of colloid particles dissolved in non-adsorbing polymer solutions. The polymers were represented as freely-jointed-hard-sphere chains composed of 10, 20, or 30 segments. The size of the interacting colloid particles was similar to or smaller than the radius of gyration of the polymers. Results show a short-range colloid–colloid depletion attraction. At low polymer concentration, this attraction slowly decays to zero at increasing separations. At higher polymer concentration, the depletion attraction is coupled to a mid-range repulsion, especially for solutions of short, stiff polymers. From the simulated forces, osmotic second virial coefficients were computed for colloids as a function of polymer concentration. The calculated osmotic second virial coefficients exhibit a non-monotonic dependence on polymer concentration, in qualitative agreement with experimental results. The simulated colloid–colloid potentials of mean force were used, within a perturbation theory, to calculate fluid–fluid and fluid–solid coexistence curves. The colloids are treated as a pseudo one-component system, and the polymers in solution are considered only through the effective pair potential between the dissolved colloids. When long flexible polymers are dissolved in solution, the phase diagram for small colloid particles shows a fluid–fluid coexistence curve at low colloid packing fraction, and a fluid–solid coexistence curve at higher packing fraction. As the size of the colloid particles increases, the molecular weight of the polymer decreases, or the polymer concentration in solution increases, the fluid–fluid coexistence curve becomes metastable with respect to the fluid–solid coexistence curve.}, number={7}, journal={MOLECULAR SIMULATION}, author={Striolo, A and Colina, CM and Gubbins, KE and Elvassore, N and Lue, L}, year={2004}, month={Jun}, pages={437–449} }
@article{walker_colina_gubbins_spontak_2004, title={Thermodynamics of poly(dimethylsiloxane)/poly(ethylmethylsiloxane) (PDMS/PEMS) blends in the presence of high-pressure CO2}, volume={37}, ISSN={["1520-5835"]}, DOI={10.1021/ma034920o}, abstractNote={Processing polymer blends in the presence of high-pressure carbon dioxide (CO2) affords numerous advantages over organic solvents and is becoming a commercially viable and environmentally responsible alternative in the development of new multicomponent materials. A prerequisite to such processing is a fundamental understanding of how high-pressure CO2 influences the phase behavior of polymer blends. In this work, we use high-pressure spectrophotometry to measure the cloud point (Tcp) of poly(dimethylsiloxane)/poly(ethylmethylsiloxane) (PDMS/PEMS) blends as a function of CO2 pressure (P) in the vapor phase. Results obtained here at different blend compositions indicate that values of Tcp for this upper critical solution temperature (UCST) blend (i) generally increase with increasing pressure and (ii) collapse onto a master curve of ΔTcp(P) for pressures up to about 35 MPa. These data are analyzed by the Sanchez−Lacombe equation of state to ascertain the temperature dependence of an effective interaction pa...}, number={7}, journal={MACROMOLECULES}, author={Walker, TA and Colina, CM and Gubbins, KE and Spontak, RJ}, year={2004}, month={Apr}, pages={2588–2595} }
@article{colina_olivera-fuentes_siperstein_lisal_gubbins_2003, title={Thermal properties of supercritical carbon dioxide by Monte Carlo simulations}, volume={29}, ISSN={["0892-7022"]}, DOI={10.1080/0892702031000117135}, abstractNote={We present simulation results for the volume expansivity, isothermal compressibility, isobaric heat capacity, Joule-Thomson coefficient and speed of sound for carbon dioxide (CO 2 ) in the supercritical region, using the fluctuation method based on Monte Carlo simulations in the isothermal-isobaric ensemble. We model CO 2 as a quadrupolar two-center Lennard-Jones fluid with potential parameters reported in the literature, derived from vapor-liquid equilibria (VLE) of CO 2 . We compare simulation results with an equation of state (EOS) for the two-center Lennard-Jones plus point quadrupole (2CLJQ) fluid and with a multiparametric EOS adjusted to represent CO 2 experimental data. It is concluded that the VLE-based parameters used to model CO 2 as a quadrupolar two-center Lennard-Jones fluid (both simulations and EOS) can be used with confidence for the prediction of thermodynamic properties, including those of industrial interest such as the speed of sound or Joule-Thomson coefficient, for CO 2 in the supercritical region, except in the extended critical region.}, number={6-7}, journal={MOLECULAR SIMULATION}, author={Colina, CM and Olivera-Fuentes, CG and Siperstein, FR and Lisal, M and Gubbins, KE}, year={2003}, month={Jun}, pages={405–412} }
@article{colina_lisal_siperstein_gubbins_2002, title={Accurate CO2 Joule-Thomson inversion curve by molecular simulations}, volume={202}, ISSN={["0378-3812"]}, DOI={10.1016/S0378-3812(02)00126-7}, abstractNote={We present simulation of the Joule–Thomson inversion curve (JTIC) for carbon dioxide using two different approaches based on Monte Carlo (MC) simulations in the isothermal–isobaric ensemble. We model carbon dioxide using a two-center Lennard–Jones (LJ) plus point quadrupole moment (2CLJQ) potential. We show that a precision of four significant figures in ensemble averages of thermodynamic quantities of interest is needed to obtain accurately the JTIC. The agreement between the experimental data, Wagner equation of state (EOS) and our simulations results indicates that the 2CLJQ potential represents an excellent balance between simplicity and accuracy in modeling of carbon dioxide. Additionally, we calculate the JTIC using the BACKONE EOS (that uses the same intermolecular potential as in our simulations) and show that the BACKONE EOS performs very well in predicting the JTIC for carbon dioxide.}, number={2}, journal={FLUID PHASE EQUILIBRIA}, author={Colina, CM and Lisal, M and Siperstein, FR and Gubbins, KE}, year={2002}, month={Nov}, pages={253–262} }
@article{colina_hall_gubbins_2002, title={Phase behavior of PVAC-PTAN block copolymer in supercritical carbon dioxide using SAFT}, volume={194}, ISSN={["1879-0224"]}, DOI={10.1016/S0378-3812(01)00789-0}, abstractNote={Statistical associating fluid theory (SAFT) is an equation of state that can be used to calculate the phase behavior of mixtures comprised of components that exhibit wide disparities in molecular size, such as solvent–polymer mixtures. In this paper, we model the phase behavior of a PVAC-PTAN block copolymer composed of a CO2–phobic polyvinyl acetate (PVAC) and a CO2–philic poly(1,1,2,2-tetrahydroperfluorooctyl acrylate) (PTAN) in supercritical carbon dioxide (scCO2) using SAFT. SAFT is a molecular-based equation that is designed to account for effects of molecular association, chain flexibility, repulsive and dispersion interactions. The group contribution approach of Lora et al. was used to obtain the physical SAFT parameters for PVAC and PTAN polymers. PTAN was modeled as a non-associating polymer while PVAC was modeled with two association sites per molecule. Cloud curves of CO2–PVAC, CO2–PTAN and of the PVAC-b-PTAN–CO2 system were predicted, and good agreement was obtained with the experimental data available. Additionally, critical micellar densities (CMD) appear to be successfully predicted for the PVAC-b-PTAN–CO2 system using a criteria based in the variation of osmotic pressure with surfactant concentration. This was made possible by the ability of SAFT to handle long chain and association interactions.}, number={2002 Mar 30}, journal={FLUID PHASE EQUILIBRIA}, author={Colina, CM and Hall, CK and Gubbins, KE}, year={2002}, month={Mar}, pages={553–565} }
@article{colina_olivera-fuentes_2002, title={Predicted inversion curve and third virial coefficients of carbon dioxide at high temperatures}, volume={41}, ISSN={["0888-5885"]}, DOI={10.1021/ie010367s}, abstractNote={The shape of the Joule−Thomson inversion curve of a fluid at high temperatures is shown to be directly related to its second and third virial coefficients. Experimental values and empirical correlations of the third virial coefficient of carbon dioxide are used to resolve a previously observed conflict between inversion curves obtained from different equations of state for this fluid. In particular, third virial coefficients predicted from the Pitzer−Sterner equation of state are shown to be in error, resulting therefore in an incorrect inversion curve.}, number={5}, journal={INDUSTRIAL & ENGINEERING CHEMISTRY RESEARCH}, author={Colina, CM and Olivera-Fuentes, C}, year={2002}, month={Mar}, pages={1064–1068} }
@article{colina_turrens_gubbins_olivera-fuentes_vega_2002, title={Predictions of the Joule-Thomson inversion curve for the n-alkane series and carbon dioxide from the Soft-SAFT equation of state}, volume={41}, ISSN={["0888-5885"]}, DOI={10.1021/ie010382x}, abstractNote={In this work, we use a molecular based equation of state, the Soft-SAFT equation, to predict complete Joule−Thomson inversion curves for carbon dioxide and the n-alkane series, including heavy n-alkanes up to octatetracontane (n-C48H98). Comparisons with available experimental and correlation data, for carbon dioxide and the lighter n-alkanes, show good quantitative agreement. We observe a strong dependence of the inversion curve on the set of molecular parameters used in the calculations, especially near the inversion point and in the high-temperature region. The equation is able to predict the general trend of inversion curves even for extreme conditions, with reduced pressure, Pr = P/Pc, values up to 40, and reduced temperatures, Tr = T/Tc, of almost 5.}, number={5}, journal={INDUSTRIAL & ENGINEERING CHEMISTRY RESEARCH}, author={Colina, CM and Turrens, LF and Gubbins, KE and Olivera-Fuentes, C and Vega, LF}, year={2002}, month={Mar}, pages={1069–1075} }