Solid bridging (e.g., due to ambient-temperature sintering and solid-solid diffusion) often occurs between dried nanoparticles.
My questions is: Upon the "physical" contact between two nanoparticles in water as they are trapped in the primary energy well, would solid bridges be formed between them? Why or why not?
This is of particular relevance to identifying possible (mechanical or chemical) routes that could be used for declustering (if possible) hard particle aggregates.
Omar Z. Sharaf
Van der Waals (always attractive) forces exist in aqueous environments and give rise to aggregate formation. See:
Adhesion and cohesion http://tinyurl.com/zwb2wlh
The issue though is that particles in a liquid interact at the slipping plane and not as hard billiard ball type entities and with the correct concentration of additive or change of pH can be made to repel. Drying or removal of water, though, will cause this solid bridging.
Comminution in a medium of high surfactant and ionic stabilizers can slowly produce nano-sized particles, but the issue with small particles is that they either flex and bend with applied energy (the rate determining step is separation) or fracture is followed by recombination and an equilibrium is set up. The term 'comminution limit' is important to understand. Sonication will disprupt agglomerates (loose)
Particle aggregates (hard) can only be separated by chemical means and the process of stress corrosion milling allows these areas of weakness between particles in an aggregate to be dissolved. More in:
Dispersion and nanotechnology
https://www.brainshark.com/malvern/vu?pi=zHSznNgprz5chz0
and:
Controlling powder bulk density by optimizing particle size and shape distribution
https://www.brainshark.com/malvern/vu?pi=271602698&b=1&tx=120486&c1=22
Omar Z. Sharaf
Van der Waals (always attractive) forces exist in aqueous environments and give rise to aggregate formation. See:
Adhesion and cohesion http://tinyurl.com/zwb2wlh
The issue though is that particles in a liquid interact at the slipping plane and not as hard billiard ball type entities and with the correct concentration of additive or change of pH can be made to repel. Drying or removal of water, though, will cause this solid bridging.
Comminution in a medium of high surfactant and ionic stabilizers can slowly produce nano-sized particles, but the issue with small particles is that they either flex and bend with applied energy (the rate determining step is separation) or fracture is followed by recombination and an equilibrium is set up. The term 'comminution limit' is important to understand. Sonication will disprupt agglomerates (loose)
Particle aggregates (hard) can only be separated by chemical means and the process of stress corrosion milling allows these areas of weakness between particles in an aggregate to be dissolved. More in:
Dispersion and nanotechnology
https://www.brainshark.com/malvern/vu?pi=zHSznNgprz5chz0
and:
Controlling powder bulk density by optimizing particle size and shape distribution
https://www.brainshark.com/malvern/vu?pi=271602698&b=1&tx=120486&c1=22
Thank you for clearing that up, Dr. Alan F Rawle.
"Brownian motion at room temperature in small (“nano”) primary sized particles typically smaller than 100 nm is sufficient to cause solid bridging between adjoining particles in close contact due to van der Waals attraction." [A. F. Rawle, “Micron sized nano-materials,” Powder Technology, vol. 174, no. 1–2, pp. 6–9, May 2007]
Does this apply to nanoparticles dispersed in a liquid?
If yes, then how can we confirm the existence of solid bridges between nanoparticles in a liquid?
I would think that any solid bridges observed from SEM/TEM micrographs could simply be an artifact of the droplet-drying process during sample preparation.
Exactly Prof. Alan F Rawle and this is how particles are stable in aqueous environment. Even we can speak about electrostatic repulsion that predominates in several colloidal solutions.
Omar Z. Sharaf
If the conditions (pH and charge, ionic concentration etc) allow the particles to touch in suspension (i.e. they're not interacting at the slipping plane) then solid-solid diffusion can occur and solid bridging is the outcome as sure as night follows day.
You are correct that artifacts of sample preparation will be shown in electron microscopy. And everything under a TEM is an artifact of sample preparation and particle selection.
Agnishwar Girigoswami strictly, particles dispersed have higher or lower kinetic stability but are thermodynamically unstable (not to confuse with gravitational separation).
Colloidal solutions are thermodynamically stable (polymer solutions, 'micro''emulsions', micellar solutions). Colloidal dispersions are different. https://www.researchgate.net/project/nanoparticle-solutions-search-for-a-perpetuum-mobile-there-are-no-particle-solutions-only-particle-dispersions
- Badges
- Science topic
- Similar topics
- Chemistry
- Nanotechnology
- Nanostructured Materials
- Nanoparticles