Contact angles and wetting behaviour of single micron-sized particles

Abstract

A 'particle interaction apparatus' based on the technique of atomic force microscopy was constructed that allows us to measure the interaction between single micron-sized particles and the air-water interface. From the force versus distance profiles ('force curves') the contact angle of single microspheres could be determined. This new method for microsphere tensiometry was validated using a variety of materials with contact angles between 20 • and 90 • . Contact angles measured on single microspheres correlated well with those measured on flat substrates of the same materials.The interaction of single silica microspheres with an air bubble in the presence of surfactants (SDS and DTAB) was investigated. Depending on surfactant type and concentration, adhesion or repulsion could be induced. Adhesion forces were found to depend on the applied load, indicating possible adsorption/desorption processes at the particle-bubble interface.We have built a new set-up that combines a particle interaction apparatus with a Langmuir trough and a fluorescence microscope. This will allow study of interactions at the air-water interface in more detail, especially in the presence of a definite surface density of amphiphilic molecules.The interaction of single ZnS spheres with a bubble (modelling flotation of ZnS) was studied at different pH values. The results suggest that the isoelectric point of these spheres exists between pH 7 and 8.

Improving water-injection performance of quartz sand proppant by surface modification with surface-modified nanosilica

“…This means that the encapsulation of the quartz sand by HMDS-modified nano-SiO 2 with a high enough dosage (e.g., 2.5%) endows the quartz sand with a certain degree of hydrophobicity, which should be beneficial to improving the water-injection performance of the quartz sand proppant. Such a significantly increased hydrophobicity of the surface-modified quartz sand proppant is attributed to the formation of a dense superhydrophobic nanoSiO 2 layer on the quartz sand surface, as verified by relevant FESEM observation [24].…”

Unraveling the 3D Localization and Deformation of Responsive Microgels at Oil/Water Interfaces: A Step Forward in Understanding Soft Emulsion Stabilizers

“…This is in stark contrast to hard particles for which differences in the particle− water interfacial energy as a function of pH translates to significant contact angle variations. 40 This is also different from the case of partially deformable core−shell nanoparticles that show a strong pH dependence at air−water interfaces. 41 In conclusion, the complex balance of interfacial and bulk properties highlighted above is completely absent for hard objects.…”

Nanoparticle effects on the water-oil interfacial tension

“…19,46 Solution pH can alter both the surface properties of the nanoparticles (e.g., their 'hydrophobicity'), 47 as well as NP-NP interactions 48 .…”