Pore connectivity effects on the internal surface electric charge of mesoporous silica

Abstract

Nano-scale confinements within mesoporous systems develop overlapping electric double layers (EDL) such that the existing theoretical models cannot predict the electric potential distributions and resulting surface charges. In addition, ionic conditions undergo local variation through connections between the pore voids and pore throats. For the first time in literature, we studied the charging behavior of mesoporous silica in terms of the pore to throat size ratio (R pt ) to characterize the pore connectivity effects, in addition to porosity (є) and pore size (H). Both local and average surface charge densities inside mesoporous silica were examined by varying these parameters systematically. Results showed that the magnitude of surface charge density decreased with increasing EDL overlap and decreasing connectivity effects. We formulized this behavior and developed an extended model to predict mesoporous silica's internal charge as a function of porosity, pore size, and pore to throat size ratio.

Slip Effects on Ionic Current of Viscoelectric Electroviscous Flows through Different Length Nanofluidic Channels

“…The coupled behavior of the local ionic concentration in the electrolyte solution and the surface dissociation/association reactions creates the surface charge. This spontaneous phenomenon is commonly simulated by charge regulation models ,− in the literature. In the case of silica channel walls, the resulting surface charge can be evaluated through the following equations. K A and K B in eq are the equilibrium constants of surface reactions shown in eqs and .…”

Roughness Effects on the Surface Charge Properties of Silica Nanoparticles

“…In such a case, the development of surface charge and the resulting EDL are coupled; 47,48 also called "Charge Regulation (CR)," this physicochemical nature of surfaces was first identified by Ninham and Parsegian 49 and later observed by multiple experiments in surface force measurements using colloids 50,51 and AFM. 52,53 Since then, researchers have attempted to apply CR into calculations by using active charge models as boundary conditions to resolve the surface charging of silica nanochannels, 48,54−57 nanopores, 58−61 mesoporous systems, 62,63 and nanoparticles. 19,64,65 Using this systematic approach, we characterized the surface charging of SNPs for the case of flat surface condition without any roughness.…”

Pore Size and Porosity Dependent Zeta Potentials of Mesoporous Silica Nanoparticles

“…The above-described surface charging mechanisms can only be calculated by considering the natural surface physicochemistry through surface charge regulation (CR) models incorporated with Poisson–Nernst–Planck (PNP) equations. , CR was first identified by Ninham and Parsegian and later observed by multiple experiments in surface force measurements by colloids , and AFM. , Since then, researchers have attempted to apply CR in calculations using active charge models as boundary conditions to resolve surface charging of silica nanochannels, − nanopores, − mesoporous systems, , and nanoparticles. ,, Using this systematic approach, we characterized surface charging of SNPs and presented that the SNP surface charge depends on the size of the nanoparticle . Just recently, we also described the effect of surface roughness/patterning on the surface charge of SNPs and planar surfaces where surface charge shows local variation and the average of it becomes different than predictions for a flat surface condition.…”

“…42,43 CR was first identified by Ninham and Parsegian 44 and later observed by multiple experiments in surface force measurements by colloids 45,46 and AFM. 47,48 Since then, researchers have attempted to apply CR in calculations using active charge models as boundary conditions to resolve surface charging of silica nanochannels, 49−51 nanopores, 52−57 mesoporous systems, 58,59 and nanoparticles. 34,43,60 Using this systematic approach, we characterized surface charging of SNPs and presented that the SNP surface charge depends on the size of the nanoparticle.…”