Roughness Effects on the Surface Charge Properties of Silica Nanoparticles

Abstract

The surface charge property of silica nanoparticles plays a key role in their function. Previous studies assumed surface charge as a homogeneously distributed constant material property, independent of the nanoparticle size and surface condition. Instead, this study considered surface chemistry as a function of local ionic conditions (Charge Regulation) to calculate the local surface charges around a rough nanoparticle, as an extension to our earlier study (J. Phys. Chem. C 2014, 118 (4), 1836−1842). For the current surface heterogeneity in the form of concave and convex circles, the surface charge showed a distinct local variation: decrease due to the electrical double layer (EDL) overlap in the valleys and increase due to curvature effects on the hills of the surface structure. The average of local surface charges decreased with the decrease of the roughness size (D R ), depending on the particle size (D P ) and pH. We characterized the variation of the average surface charge by a nondimensional group we formed as a measure for the EDL overlap and curvature effects [(D R /λ) × (D R /D P )]. Based on this, we devised a phenomenological model as an extension to the existing flat surface theory, which can successfully predict the average surface charge around a rough/patterned nanoparticle as a function of the particle size, roughness size, and pH.

Size and roughness dependent temperature effects on surface charge of silica nanoparticles

“…This surface pattern allows surface structures to be controlled by simply varying the single quantity D R and perform a parametric study by systematically varying it. Furthermore, the charging mechanisms developing on the circular pattern are similar to the flat surface nanoparticles previously studied [44] and validated with our earlier work [45]. The liquid phase is considered as KCl (i.e.…”

“…Such local variation of electric charge as a function of the surface nano topology was observed by a few studies through AFM measurements [41] and numerical simulations [42,43] over planar surfaces. Recently, we studied the charge of SNPs and planar surfaces with varying size of surface nanopatterns/roughness [44,45]. While lower and higher charges were observed at the pits and the tips of surface pattern, the average of local surface charges became lower than the theoretical predictions.…”

“…While lower and higher charges were observed at the pits and the tips of surface pattern, the average of local surface charges became lower than the theoretical predictions. Based on the numerical calculations, phenomenological models were developed as an extension to the existing flat surface theory to predict the average surface charge on a nano patterned flat surface and SNP as a function of the surface pattern size, ionic concentration and pH, and particle diameter [44,45].…”

Biostimulation and toxicity: The magnitude of the impact of nanomaterials in microorganisms and plants

“…Roughness and porosity constitute two of the physical properties of pristine or functionalized NMs that increase the surface area of the NM [69] , the distribution of charges on the surface of the NM [70] , and, therefore, the ability to adsorb organic molecules in the corona [71] . The corona, apparently because of the complex and rough topography of the NM surface, has been found not to form a continuous coverage, allowing exposure of some regions of the NM surface [72] .…”

“…The corona, apparently because of the complex and rough topography of the NM surface, has been found not to form a continuous coverage, allowing exposure of some regions of the NM surface [72] . These exposed regions are believed to, through hydrophobicity and hydrophilicity processes, modify the hydrodynamic properties of the NMs, the adsorption force of organic molecules to the surface of the NM [27] and the way of interaction with cell walls and membranes [70] , [73] .…”