| Summary: | 博士 === 國立臺灣科技大學 === 化學工程系 === 100 === ABSTRACT
The present work focuses on the vapor-liquid equilibrium (VLE) measurements for polymeric solutions containing polyethylene glycol (PEG) derivatives and alcohols: polyethylene glycol monolaurate (PEGML) + methanol, PEGML + ethanol, PEGML + 2-propanol, PEGML + 2-butanol, PEGML + tert-butanol, PEGML + 1-pentanol, polyethylene glycol mono-4-octylphenyl ether (PEGOPE) + 2-butanol, PEGOPE + tert-butanol, PEGOPE + 1-pentanol, polyethylene glycol monooleyl ether (PEGMOE) + 2-butanol, PEGMOE + tert-butanol, and PEGMOE + 1-pentanol. For each binary system, four feed compositions were studied over the concentration range from 0.099 to 0.432 of oligomers in mole fractions. With a given feed composition, equilibrium pressures were measured at constant temperatures to obtain p-T-x data. The saturated pressures data are measured at temperatures ranging from (320.0 to 437.1) K by using an autoclave apparatus. The advantages of this apparatus and method are the simplicity and ease of operation for viscous samples like polymer solutions, wide range of temperature and pressure operation, while the accuracy of the data obtained could be matched by other available techniques. The relationship between the saturated pressure and temperature was obtained from the empirical Antoine equation, in which the constants were determined by nonlinear regression. Two activity coefficient models, the universal quasichemical (UNIQUAC) model and the nonrandom two-liquid (NRTL) model, were applied to correlate the experimental data. These two thermodynamic models were further used to calculate solvent activities at various temperatures to observe the deviation from ideal behavior and compare with the values obtained from experimental results.
Additionally, we explore the static and dynamical properties of PEGML in water and in alcohols (methanol, ethanol, 2-propanol, 2-butanol, tert-butanol, and 1-pentanol), through molecular dynamics (MD) simulation by using the Groningen Machine for Chemical Simulation (GROMACS) software package. The binary systems were simulated using the OPLS-AA (optimized potentials for liquid simulations, all-atom) force field for PEGML and alcohol molecules and water was modeled using the SPC/E (extended simple point charge) model. From the isothermal-isobaric (NpT, constant number of particles, constant pressure, and constant temperature), we extracted the densities for simulated systems and compare the values to those from experimental results in order to confirm the validity of the selected force fields. Dynamic aspect of the mixture behavior is inferred from the calculated shear viscosity which was computed by using non-equilibrium molecular dynamics (NEMD) simulations. To gain more insight to the nature of interactions between PEGML molecule and solvents, we analyzed the hydrogen-bonds, the electrostatic (Couloumb) interactions, and the van der Waals (Lennard-Jones) interactions energies extracted from MD simulations. The results were further strengthened by computing the solvation free energy by employing the free energy perturbation (FEP) approach. In this method, the free energy difference was computed by using the Bennet Acceptance Ratio (BAR) method. Moreover, the structural features were simulated in order to gain more understanding of the solution behavior at the molecular level, including the radial distribution functions and the radius of gyration for all the binary systems under investigation.
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