Surface Forces in Particle Technology: Wet Systems

Abstract

Surface forces play a fundamental role in particle processing as they control the stability, adhesion, friction and rheology of particulate systems and information on all of these can be obtained from an analysis of the normal forces measured between particles. Therefore particle processing at all stages can be informed by knowledge of the forces between the constituent particles. For wet particles systems, the interaction forces between two particles can rarely be predicted from theory, but rather requires experimentation or direct measurement. This requires that the surfaces used have the same as surface properties as the particles. In practice this is rarely possible, as surface force measurements require surfaces with extremely low roughness and precise geometry and the majority of materials do not conform to these requirements. To address these challenges we produce surfaces of low roughness and controlled chemistry using Atomic Layer Deposition (ALD) and are developing methods to calculate and understand the influence of surface roughness on the measured forces. Here we report the forces between hafnia surfaces produced by ALD and show that like ALD produced titania surfaces and silica surfaces, the expected van der Waals forces at high pH are not manifest, suggesting that most real surfaces have unexpectedly repulsive surface forces at high pH and small separations. This will fundamentally alter how these particulate systems behave when being processed, reducing the adhesion and the friction and enhancing the stability compared to the expected interaction from DLVO theory.

The fabrication of TiO2 supported on slag-made calcium silicate as low-cost photocatalyst with high adsorption ability for the degradation of dye pollutants in water

“…It is assumed that TiO 2 small nanoparticles are physically adsorbed onto the PCS and SCS via the Van der Waals forces among particles and the interaction between Ti-OH and Mi-OH (M = Ca, Si and Al etc.) species on the support surfaces[20][21][22][23].…”

SERS and DFT study of 5F‐PB‐22

“…This explains the negative zeta potential and also a surface species that is capable of hydrogen bonding. The Derjaguin, Landau, Verwey, and Overbeek (DLVO) theory can be used to explain the stability of the HPAg colloid. The DLVO theory represents the interaction potential as a superposition of van der Waals and electric double‐layer forces.…”

The Role of Citric Acid in the Stabilization of Nanoparticles and Colloidal Particles in the Environment: Measurement of Surface Forces between Hafnium Oxide Surfaces in the Presence of Citric Acid

“…The low friction is evidenced by the lack of hysteresis between the approach and retraction force data. 55 This generally results in dense flocs (as opposed to open flocs formed by diffusion-limited aggregation which occurs when particles strongly adhere with high rolling friction). Also, the particles are readily redispersed if the ionic strength of the solution is reduced or if shear forces are exerted due to the low adhesion.…”

“…Note that this calculation does not include the reduction in the dispersion forces that takes place for particles less than 100 nm in radius. 55 If this effect were included, the secondary minimum would be even shallower. This shows that nanoparticles with citrate adsorbed are stable at high ionic strengths under conditions where larger colloidal particles are unstable and highlights the extreme stability conferred on nanoparticles by the adsorption of citrate.…”