Nanoconfinement Effect on Surface Tension: Perspectives from Molecular Potential Theory

Abstract

Liquid–vapor surface tension (ST) in nanopores attracts great attention in many industries because of the prosperity of nanoscience and nanotechnology. Here, considering the important emerging new physical phenomena induced by nanoconfinement effects, including curvature-dependent and shift-critical temperature (T c)-dependent effects, the anomalous variation of ST in nanopores is captured from the molecular potential perspective. Furthermore, a simple analytical model is proposed to determine the ST in nanopores by correlating these two effects with an easily accessible parameter, that is, normalized pore dimension, which is the ratio of the pore radius to Lennard-Jones size parameter. The model is validated to be reliable for determining the STs of different substances both in the bulk phase as well as nanopores through comparison with the experimental results and molecular simulations. Our results show that the reduction of ST induced by the nanoconfinement effects is visible when the pore diameter is within tens of nanometers, and the reduction is more sensitive as the pore size decreases. In detail, the curvature-dependent effect is remarkable in the pores with diameters ranging from a few nanometers to tens of nanometers. Moreover, a simply generalized formula is obtained to determine the curvature-dependent effect and the Tolman length for different substances. The shift-T c-dependent effect is not only related to the pore dimension but also depends on the temperature. As the pore size decreases, the critical temperature of confined fluids diverges significantly from the bulk values. While at high temperatures, the range of pore size impacted by the shift-Tc-dependent effect is enlarged. Additionally, the nanoconfined STs of different substances are calculated and compared. Overall, the new model captures the underlying physics behind the variation of STs in nanopores and can determine the nanoconfined STs reasonably. Moreover, the simple formulation of the model is beneficial to the practical applications in many chemical engineering processes, such as chemical separation, nucleation phenomenon, and capillary condensation.

A Laboratory Approach on the Hybrid-Enhanced Oil Recovery Techniques with Different Saline Brines in Sandstone Reservoirs

“…According to their results, complex interactions of pore morphology and wettability would be a significant controlling parameter for the displacement efficiency, both in heterogeneous and homogenous porous media [39]. Feng et al (2020) considered that the non-confinement influence contained a shift critical temperature and curvature dependent effect on nanopores. They found that the non-confinement effect on the nanometer pore sizes (it would be more sensitive especially with a decrease in pore sizes) had reduced the surface tension [40].…”

“…Feng et al (2020) considered that the non-confinement influence contained a shift critical temperature and curvature dependent effect on nanopores. They found that the non-confinement effect on the nanometer pore sizes (it would be more sensitive especially with a decrease in pore sizes) had reduced the surface tension [40].…”

Effect of Pore Structure on Slippage Effect in Unsaturated Tight Formation Using Pore Network Model

“…Where is the disjoining pressure of water film on flat surface, Pa; is potentials of the solid-water and water-gas interfaces respectively, V; is the 𝑘 coefficient for the strength of structural force, N/m 2 ; the characteristic length of 𝜆 water molecules, m. The values of these parameters are displayed in Table 1 with reference to previous work [43] . Here, we assumed interfacial tension as a constant value, and its dependence [44,45] on other variables will be included in our future work. As shown in this table above, the thickness of water film is a function of pore radius and humidity.…”

Model for Interfacial Tension of Nanoconfined Lennard-Jones Fluid

“…46−49 Generally, the elements of the confinement effect are imbedded into the EOS for the phase equilibrium calculation of fluids in nanoscale domain, among which the IFT is determined by coupling the parachor model with the EOS model. 1,4 For example, Yang et al extended the classical PR EOS for unconventional reservoir fluids by incorporating critical property shift and capillary pressure, while the IFT was calculated by the extended parachor model. 46 Therefore, this kind of method is not accurate enough both for the IFT and the phase equilibrium estimation because the parachor model is empirical and does not take the confinement effect into consideration.…”

“…As a prime parameter in basic formulations of many processes, including nucleation, imbibition, etc., IFT has attracted great attentions due to its wide and practical applications, such as chemical reactions, energy storage, heterogeneous catalysis, biological membrane operations, and in particular, oil and gas productions in conventional/unconventional reservoirs. − When the pore size is on the nanoscale, the confinement effect becomes strengthened, and the thermodynamic properties and interfacial behavior of nanoconfined fluids are quite different from that of the bulk counterparts. − Therefore, macroscopic expressions of the IFT cannot be employed directly, and the influences of curvature and wall–fluid interaction must be considered in theoretical studies.…”