| Summary: |
Liquid-liquid interfaces are found in many separation and reaction processes in chemical engineering. Although the use of two-liquid phase systems is common in the pharmaceutical and chemical industries, their application is normally performed empirically, since little is known about the characteristics of the interfaces in terms of their structure (e.g., composition and molecular orientation), equilibrium thermophysical properties (e.g., interfacial tensions) and dynamics (e.g., interfacial diffusion coefficients). Such properties are particularly important in liquid-liquid extractive systems, multiphase flows and catalysis.
Different experimental techniques are available to characterize liquid interfaces, namely interfacial tension measurements and spectrophotometric methods. However, these techniques are limited by the complexity and buried nature of the interface. Interfacial tension measurements are extremely sensitive to impurities that frequently have a surfactant behavior, thus considerably reducing the interfacial tensions. On the other hand, the use of the above-mentioned optical methods often leads to conclusions that are method dependent, and it is thus very difficult to draw conclusions about the structure of a given interface using a single experimental method. For these reasons, molecular simulation studies are growing in importance as alternative techniques, since they can probe the interface at the molecular level. Recent advances have allowed for consistent estimates of the interfacial tension and have yielded insight into the intrinsic interfacial structure, molecular diffusion parallel and perpendicular to the interface, surface adsorption, molecular orientation, and free energy of transfer of solutes across the interface. Important advances in our knowledge of interfacial processes are expected if one is able to combine the advantages of different experimental characterization methods with those of molecular simulation.
The recent increase  |
Summary
Liquid-liquid interfaces are found in many separation and reaction processes in chemical engineering. Although the use of two-liquid phase systems is common in the pharmaceutical and chemical industries, their application is normally performed empirically, since little is known about the characteristics of the interfaces in terms of their structure (e.g., composition and molecular orientation), equilibrium thermophysical properties (e.g., interfacial tensions) and dynamics (e.g., interfacial diffusion coefficients). Such properties are particularly important in liquid-liquid extractive systems, multiphase flows and catalysis.
Different experimental techniques are available to characterize liquid interfaces, namely interfacial tension measurements and spectrophotometric methods. However, these techniques are limited by the complexity and buried nature of the interface. Interfacial tension measurements are extremely sensitive to impurities that frequently have a surfactant behavior, thus considerably reducing the interfacial tensions. On the other hand, the use of the above-mentioned optical methods often leads to conclusions that are method dependent, and it is thus very difficult to draw conclusions about the structure of a given interface using a single experimental method. For these reasons, molecular simulation studies are growing in importance as alternative techniques, since they can probe the interface at the molecular level. Recent advances have allowed for consistent estimates of the interfacial tension and have yielded insight into the intrinsic interfacial structure, molecular diffusion parallel and perpendicular to the interface, surface adsorption, molecular orientation, and free energy of transfer of solutes across the interface. Important advances in our knowledge of interfacial processes are expected if one is able to combine the advantages of different experimental characterization methods with those of molecular simulation.
The recent increase of environmental concerns has stimulated the use of "green solvents" as alternative media in biphasic liquid systems. Ionic liquids (IL) in particular, whose immense combinations of cations and anions can virtually lead to an optimized design of a task-specific solvent system, have been the focus of several research groups, with applications ranging from reaction, separation or combined reaction/separation processes. This emphasizes the urgent need for the development of methods to adequately characterize liquid-liquid interfaces involving ILs. However, due to their added complexity, the lack of knowledge regarding these systems is even more evident than for conventional water/organic systems.
The importance of liquid-liquid interfaces containing ILs thus justifies the combination of experimental and theoretical studies in order to make the bridge between a molecular level understanding and the macroscopic properties of the interface.
In this proposal, experimental measurements of macroscopic and microscopic properties of liquid-liquid interfaces will be combined with theoretical molecular dynamics simulations in order to complement the understanding of the equilibrium, dynamics and structure of liquid-liquid interfaces.
The strategy to be followed in this project involves the study of a series of water-IL interfaces where the nature (hidrophobicity, polarity, cation and anion size) of the ionic liquid will vary.
Each system will be simultaneously studied experimentally (surface tension measurements and SFG spectroscopy) and theoretically (molecular dynamics). Starting from the global composition of these heterogeneous fluid systems, we expect to arrive to: i) compositions of the equilibrium phases; ii) interfacial tensions; iii) structure and molecular orientation of the interface; iv) diffusion coefficients in the bulk and at the interface; v) solute free energy of transfer between the two equilibrium phases. |