Nowadays, porous materials are widely used for different applications, e.g., water purification or depollution, heterogeneous catalysis, drug delivery, etc. Optimizing these applications relies on the in-depth understanding of the specific properties of confined fluids. The confinement induces various effects on a fluid adsorbed inside a porous material. First, there is a tremendous interface between the fluid and the porous material. It is such a huge interface that offers the high efficiency for heterogeneous catalysis. Obviously, the interaction between the fluid and the pore wall results in a surface tension for such an interface. Surface tension is a venerable scientific concept and its study goes back to Thomas Young, Laplace and Gibbs. Different but equivalent definitions of surface tensions exist, e.g., the derivative of a thermodynamic potential with respect to the interface area, or the excess surface Gibbs free energy per surface area. When a fluid is confined in nanopores, one can question about the validity of thermodynamics for such small systems since it is a theory for macroscopic systems. Recently, it is revealed that the above two definitions do not give the same results and it is necessary to introduce the new concept of differential and integral surface tensions. One significant contribution of my Ph.D. work is the finding of simulation evidences which validate the prediction of distinct differential and integral surface tensions for nanoscale systems.
My dissertation includes four chapters: 1) Introduction; 2) Simulation evidence of two surface tensions for fluids confined in nanopores; 3) A generalized scaled particle theory; 4) Conclusions.
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