Gabriele Sadowski

Application of perturbation theory to a hard-chain reference fluid: an equation of state for square-well chains

An equation of state for square-well chain fluids is developed applying the second-order perturbation theory of Barker and Henderson to a hard-chain reference fluid. The structural information required in the perturbation theory is incorporated using an expression for the radial distribution function of the reference chain fluid proposed by Chiew. The equation of state is simplified by fitting polynomials in density and simple functions of segment number to the original perturbation expressions of first-and second-order. The equation of state is extended to mixtures by applying one-fluid mixing rules and is tested against molecular simulation data of homonuclear chain molecules and mixtures from the literature.

Modeling the Solubility of Pharmaceuticals in Pure Solvents and Solvent Mixtures for Drug Process Design

The knowledge of the solubility of pharmaceuticals in pure solvents and solvent mixtures is crucial for designing the crystallization process of drug substances. The first step in finding optimal crystallization conditions is usually a solvent screening. Since experiments are very time consuming, a model which allows for solubility predictions in pure solvents and solvent mixtures based only on a small amount of experimental data is required. In this work, we investigated the applicability of the thermodynamic model perturbed-chain statistical associating fluid theory (PC-SAFT) to correlate and to predict the solubility of exemplary five typical drug substances and intermediates (paracetamol, ibuprofen, sulfadiazine, p-hydroxyphenylacetic acid, and p-aminophenylacetic acid) in pure solvents and solvent mixtures.

Modeling of polymer phase equilibria using Perturbed-Chain SAFT

Abstract The Perturbed-Chain SAFT equation-of-state is applied to binary and ternary mixtures of polymers, solvents and gases. Using a temperature-independent interaction parameter kij for each binary system, the Perturbed-Chain SAFT equation-of-state gives good correlations of the appropriate phase behavior over wide ranges of conditions. Copolymers or polymers with short-chain branching can be described using the copolymer version of PC-SAFT. In this version, the chain segments are allowed to differ in size and in attractive forces. Using this concept, copolymers like poly(ethylene-co-propylene) and poly(ethylene-co-vinyl acetate) could be modeled using the knowledge of the homopolymer properties and only one additional parameter which describes the attractive interactions between the unlike copolymer segments. Comparisons to the original SAFT model reveal an improvement of the proposed model.

Solvent-sensitive reversible stress-response of shape memory natural rubber.

We found that constrained shape memory natural rubber (SMNR) generates mechanical stress when exposed to solvent vapor. When the solvent vapor is removed, the material reprograms itself. This process is reversible and the stress answer is proportional to the solvent vapor concentration. Further, the stress answer is specific to the solvent.

Compatible solutes: Thermodynamic properties and biological impact of ectoines and prolines

Compatible solutes like ectoine and its derivatives are deployed by halophile organisms as osmolytes to sustain the high salt concentration in the environment. This work investigates the relation of the thermodynamic properties of compatible solutes and their impact as osmolytes. The ectoines considered in this work are ectoine, hydroxyectoine, and homoectoine. Besides solution densities (15-45°C) and solubilities in water (3-80°C), component activity coefficients in the aqueous solutions were determined in the temperature range between 0 and 50°C. The latter is important for adjusting a certain water activity and therewith a respective osmotic pressure within a cell. The characteristic effect of ectoines is compared to that of prolines, as well as to that of incompatible solutes as salts and urea. The experimental results show that the influence on the activity (coefficient) of water is quite different for compatible and incompatible solutes: whereas compatible solutes cause decreasing water activity coefficients, incompatible solutes lead to an increase in water activity coefficients. Based on this quantity, the paper discusses the impact of various osmolytes on biological systems and contributes to the explanation why some osmolytes are more often and at other temperatures used than others. Moreover, it was found that the anti-stress effect of an osmolyte is weakened in the presence of a salt. Finally, it is shown that the thermodynamic properties of compatible solutes can be modeled and even predicted using the thermodynamic model PC-SAFT (Perturbed-Chain Statistical Associating Fluid Theory).

Thermodynamic Phase Behavior of API/Polymer Solid Dispersions

To improve the bioavailability of poorly soluble active pharmaceutical ingredients (APIs), these materials are often integrated into a polymer matrix that acts as a carrier. The resulting mixture is called a solid dispersion. In this work, the phase behaviors of solid dispersions were investigated as a function of the API as well as of the type and molecular weight of the carrier polymer. Specifically, the solubility of artemisinin and indomethacin was measured in different poly(ethylene glycol)s (PEG 400, PEG 6000, and PEG 35000). The measured solubility data and the solubility of sulfonamides in poly(vinylpyrrolidone) (PVP) K10 and PEG 35000 were modeled using the perturbed-chain statistical associating fluid theory (PC-SAFT). The results show that PC-SAFT predictions are in a good accordance with the experimental data, and PC-SAFT can be used to predict the whole phase diagram of an API/polymer solid dispersion as a function of the kind of API and polymer and of the polymers molecular weight. This remarkably simplifies the screening process for suitable API/polymer combinations.

Supercritical antisolvent fractionation: measurements in the systems monodisperse and bidisperse polystyrenecyclohexanecarbon dioxide

As a model system for new polymer-separation processes utilizing compressed gases the system polystyrene cyclohexane carbon dioxide with monodisperse polymers ( M w / M n = 1.09) was investigated experimentally at temperatures up to 250°C and pressures up to 160 bar. Small amounts of carbon dioxide shift the lower critical solution temperature (LCST) to dramatically lower temperatures. When looking at the pressure-concentration representation there is a striking similarity between the effect of temperature and the effect of gas content on the shape of the two-phase region. Pressure has a pronounced effect on the chain partitioning of polystyrenes of different molecular weights in the two liquid phases as determined by gel permeation chromatography. The results are discussed in the context of industrial application.

Modeling of aqueous poly(oxyethylene) solutions. 2. Mesoscale simulations.

We extend our work on aqueous solutions of poly(oxyethylene) oligomers H-(CH2-O-CH2)n -H (POEn). On the basis of atomistic simulations of trimer and decamer solutions (first part of this series of papers), different sets of coarse-grained implicit-solvent potentials have been constructed using the iterative Boltzmann inversion technique. The comparison of structures obtained from coarse-grained simulations (gyration radii, end-to-end distances, radial distribution functions) with atomistic reference simulations and experiments shows that the state-specific potentials are transferable both to a wide concentration range, if the same molecule size is considered, and to at least 2 orders of magnitude larger molecules (in terms of molecular mass). Comparing the performance of different mesoscale potentials, we find different applicability ranges in terms of molecule sizes. The experimental gyration radii for chains comprising up to 1500 monomers are reproduced almost quantitatively by the decamer-fitted potentials with dihedral interactions included. The trimer-fitted potentials reproduce experimental chain dimensions of up to some hundred monomers but seem to become metastable beyond a certain chain length, as we evidenced some chain collapses. Relaxation of large-scale features is 1-2 orders of magnitude faster in the mesoscale simulations than in the atomistic simulations. The diffusion behavior in dependence of concentration is captured correctly when the decamer potential is applied to the decamer itself. For all other chain lengths, we find that time mapping from coarse-grained to atomistic trajectories has to be determined separately for each concentration. Overall, diffusion is 1-2 orders of magnitude faster on the mesoscale, depending considerably on the Lowe-Andersen thermostat parameters. The CG simulations provide an overall speed-up of about 3 orders of magnitude.

Solubility of Sugars and Sugar Alcohols in Ionic Liquids: Measurement and PC-SAFT Modeling

Biorefining processes using ionic liquids (ILs) require proper solubility data of biomass-based compounds in ILs, as well as an appropriate thermodynamic approach for the modeling of such data. Carbohydrates and their derivatives such as sugar alcohols represent a class of compounds that could play an important role in biorefining. Thus, in this work, the pure IL density and solubility of xylitol and sorbitol in five different ILs were measured between 288 and 339 K. The ILs under consideration were 1-ethyl-3-methylimidazolium dicyanamide, 1-butyl-3-methylimidazolium dicyanamide ([bmim][DCA]), Aliquat dicyanamide, trihexyltetradecylphosphonium dicyanamide, and 1-ethyl-3-methylimidazolium trifluoroacetate. Comparison with the literature data was performed, showing good agreement. With the exception of [bmim][DCA], the solubility of these sugar alcohols in the other ILs is presented for the first time. The measured data as well as previously published solubility data of glucose and fructose in these ILs were modeled by means of PC-SAFT using a molecular-based associative approach for ILs. PC-SAFT was used in this work as it has shown to be applicable to model the solubility of xylitol and sorbitol in ILs (Paduszyński; et al. J. Phys. Chem. B 2013, 117, 7034-7046). For this purpose, three pure IL parameters were fitted to pure IL densities, activity coefficients of 1-propanol at infinite dilution in ILs, and/or xylitol solubility in ILs. This approach allows accurate modeling of the pure IL data and the mixture data with only one binary interaction parameter k(ij) between sugar and the IL or sugar alcohol and the IL. In cases where only the pure IL density and activity coefficients of 1-propanol at infinite dilution in ILs were used for the IL parameter estimation, the solubility of the sugars and sugar alcohols in the ILs could be predicted (k(ij) = 0 between sugar and the IL or sugar alcohol and the IL) with reasonable accuracy.

Finite and infinite dilution activity coefficients in polycarbonate systems

Measurements of activity coefficients at infinite dilution in bisphenol-a-polycarbonate were carried out for a series of alkanes (C8,C9,C10,C12), alcohols (C3 C10) and aromatics (toluene, ethylbenzene, propylbenzene, o-, m-, p-xylene, chlorobenzene, o-dichlorobenzene) at 160°C, 180°C and 200°C using the inverse gas chromatography. Applying a gravimetric method, the solubilities of different solvents (chlorobenzene, toluene, ethylbenzene, m-xylene, p-xylene and mesitylene) in the same polymer were measured. To model the absorption data the SAFT equation of state was used. For this purpose the pure-component parameters of the polymer had to be adjusted to the binary data of one polycarbonate-solvent system. Using these parameters for the polymer, the experimental data of the other systems could be described well, too.