Colloid Interaction Energies for Surfaces with Steric Effects and Incompressible and/or Compressible Roughness

Abstract

Colloid aggregation and retention in the presence of macromolecular coatings (e.g., adsorbed polymers, surfactants, proteins, biological exudates, and humic materials) have previously been correlated with electric double layer interactions or repulsive steric interactions, but the underlying causes are not fully resolved. An interaction energy model that accounts for double layer, van der Waals, Born, and steric interactions as well as nanoscale roughness and charge heterogeneity on both surfaces was extended, and theoretical calculations were conducted to address this gap in knowledge. Macromolecular coatings may produce steric interactions in the model, but non-uniform or incomplete surface coverage may also create compressible nanoscale roughness with a charge that is different from the underlying surface. Model results reveal that compressible nanoscale roughness reduces the energy barrier height and the magnitude of the primary minimum at separation distances exterior to the adsorbed organic layer. The depth of the primary minimum initially alters (e.g., increases or decreases) at separation distances smaller than the adsorbed organic coating because of a decrease in the compressible roughness height and an increase in the roughness fraction. However, further decreases in the separation distance create strong steric repulsion that dominates the interaction energy profile and limits the colloid approach distance. Consequently, adsorbed organic coatings on colloids can create shallow primary minimum interactions adjacent to organic coatings that can explain enhanced stability and limited amounts of aggregation and retention that have commonly been observed. The approach outlined in this manuscript provides an improved tool that can be used to design adsorbed organic coatings for specific colloid applications or interpret experimental observations.

Coupled impact of proteins with different molecular weights and surface charges on TiO2 mobility

“…Shakiba et al also reported that the adsorption of BSA on the TiO 2 surface was a monolayer coating, 74 and BSA caused steric hindrance and enhanced TiO 2 transport. 75 When the BSA concentration increased from 2 to 16 mg L −1 , the thickness of the corona layer gradually increased, and the thicknesses of the BSA adsorption layers were 4.7, 4.8, 5.4, and 5.8 nm, respectively (Fig. 3g), which were obtained by Ohshima's soft particle theory (Fig.…”

“…The reason might be that when the protein was adsorbed onto the TiO 2 surface, the roughness of the sand surface resulted in compressible roughness and reduced the energy barrier and primary attraction potential between TiO 2 and quartz sand. 75 Thus, the steric repulsion was largely reduced. Therefore, OVA-coated TiO 2 possessed the largest mobility because it had the most negative surface charge and the strongest electrostatic repulsion between TiO 2 and the sand surface.…”

Eco-Corona Dictates Mobility of Nanoplastics in Saturated Porous Media: The Critical Role of Preferential Binding of Macromolecules

“…Moreover, the grafting of carboxyl groups would facilitate polar interactions (e.g., H-bonding and Lewis acid–base interactions) with the polar components of humic substances and EPS. ,− Thus, the macromolecules accumulated on HOOC-PS were likely less hydrophobic (and more polar) than those on PS. It has been reported that hydrophobic macromolecules (e.g., proteins) tend to take a compact configuration in aqueous solutions, whereas the more hydrophilic ones are relatively disordered and flexible. − Compared with the more condensed macromolecules, the disordered and flexible ones may result in greater elastic repulsion between the nanoplastics and sand grains . Previous studies have shown that polymers with longer chains would result in greater steric hindrance, compared with the shorter ones. − Moreover, the polar segments tend to protrude into the aqueous phase as loops and tails, which would lead to greater steric repulsion, irrespective of the total adsorption density .…”

Luminescence-enhanced conjugated polymer dots through thermal treatment for cell imaging

“…It may be speculated that water ionization intensifies at high temperature, which weakens the electric double layer of Pdots, and then weakens the repulsion of Pdots, and nano-sized agglomeration occurs. 46–49…”

“…It may be speculated that water ionization intensifies at high temperature, which weakens the electric double layer of Pdots, and then weakens the repulsion of Pdots, and nano-sized agglomeration occurs. [46][47][48][49] The morphology of Pdots was also studied by transmission electron microscopy (TEM). The typical TEM images of PFO-Pdots are shown in Fig.…”