As written in 'advanced body armour using shear thickening fluids', Wagner suspended silica particles (diameter of 446 nm) in ethylene glycol at a volume fraction of approximately 0.57. Suppose the density of the silica particles to be around 1.8 g/cc, then the silica suspension Wagner prepared would have about 70 wt% of silica particles! Does anyone know how he managed to suspend so many particles in a small amount of ethylene glycol?
I've read some paper that Wagner referenced to but still couldn't understand how he managed to achieve that.
It's explained here:
https://science.howstuffworks.com/liquid-body-armor1.htm
Thanks for the information, John. However, the article did not contain information regarding how they prepared such a colloidal suspension. It seems impossible to me to use normal stirring methods (such as mechanical stirring, magnetic stirring, ultrasonic dispersion) to mix particles in a liquid up to 70 wt%. I'm curious about the method they've used to prepare the suspension. John Francis Miller
70%wt is fairly simple for dense particles in a typical liquid. 70%vol is a different story.
e.g., for zinc oxide, as 50%wt dispersion is the same as 15%vol.
Thanks John.
If I want to prepare a particle dispersion at 70 vol%, what method should I use? Or is it impossible to make a particle dispersion at such a high volume percentage?
You could make it at a lower volume fraction and then:
1. Let it sediment/centrifuge, remove enough of the supernatant and then redisperse
2. Evaporate off the liquid - e.g., in a rotary evaporator.
70% is pushing it for an ideal system of spheres (you run up against the limit of hexagonal close packing). You make get there with irregular particles.
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