A non-invasive method to directly quantify surface heterogeneity of porous materials

Abstract

It is extremely challenging to measure the variation of pore surface properties in complex porous systems even though many porous materials have widely differing pore surface properties at microscopic levels. The surface heterogeneity results in different adsorption/desorption behaviors and storage capacity of guest molecules in pores. Built upon the conventional Porod’s law scattering theory applicable mainly to porous materials with relatively homogeneous matrices, here we develop a generalized Porod’s scattering law method (GPSLM) to study heterogeneous porous materials and directly obtain the variation of scattering length density (SLD) of pore surfaces. As SLD is a function of the chemical formula and density of the matrix, the non-invasive GPSLM provides a way to probe surface compositional heterogeneity, and can be applied to a wide range of heterogeneous materials especially, but not limited to, porous media and colloids, using either neutron or X-ray scattering techniques.

Probing the Core–Shell Organization of Nanoconfined Methane in Cylindrical Silica Pores Using In Situ Small-Angle Neutron Scattering and Molecular Dynamics Simulations

“…The point at which the contrast between the silica matrix and adsorbed CD 4 becomes zero such that I(Q) = 0 62,63 also known as the contrast matching point or zero average contrast occurs at 898.4 and 1012.2 bar in MCM-41 and SBA-15 pores, respectively. 64 It is interesting to observe a higher zero average contrast pressure for MCM-41, despite the smaller pore size compared to SBA-15, which can be attributed to the lower gas partitioning into the smaller pores. stand the partitioning of methane into the pore and the adsorption of the partitioned gas molecules on the pore surface, the density profile of CH 4 along the axis parallel to the pore length (z axis) is calculated from MD simulations and averaged over the last 10 ns to ensure that the profiles are at equilibrium (see Figure 5).…”

“…Further, the amplitude of the maximum intensity I ( Q max ), plotted as I ( Q max ) 1/2 versus CD 4 SLD, showed a linear dependence upon the SLD (see Figure ). The point at which the contrast between the silica matrix and adsorbed CD 4 becomes zero such that I ( Q ) = 0 , also known as the contrast matching point or zero average contrast occurs at 898.4 and 1012.2 bar in MCM-41 and SBA-15 pores, respectively . It is interesting to observe a higher zero average contrast pressure for MCM-41, despite the smaller pore size compared to SBA-15, which can be attributed to the lower gas partitioning into the smaller pores.…”

Relating chemical composition, structure, and rheology in alkali‐activated aluminosilicate gels

“…Scaling of q −3 has also been attributed to porosity in dense suspensions such as cement hydrates and in solids including shale rocks 58‐60 . Our model is chosen to physically represent the gel particles as the scattering objects rather than the pores due to the dilute nature of the system, but other interpretations may exist to describe complementary aspects of the system.…”

Technical Aspects of the Pore Structure in Shale Measured by Small-Angle and Ultrasmall-Angle Neutron Scattering: A Mini Review

“…Recently, Liu et al developed a method to quantify surface heterogeneity of porous materials. , This method also assumes that all of the pore are accessible to external fluids because it relies on contrast variation. By variation of the SLDs of the fluid, such as increasing the pressure of CD 4 , several scattering curves are obtained.…”

“…When the experimental data are fitted with IR (ρ f ), a surface-averaged SLD and a normalized mean square variation of the SLD (Δ H 2 ) are obtained. A smaller Δ H means that surface chemistry over the entire interface in the material is more homogeneous. , …”