In almost every article I've read, the nanoparticles are being dispersed in epoxy resin first (not counting the beginning solution). Isn't it easier to disperse in hardener first since its viscosity is way less than the resin?
I would say that in general, you are right.
However, in a number of cases, surface groups of the particles can react with the hardener (e.g. carbon fibres with amines), but not with the epoxy. It then becomes obvious that one must disperse fibres in the epoxy.
Moreover, the hardeners tend to be quite volatile, on the contrary to epoxy resins. When several hours of mixing are required, you would prefer not to have a volatile/harmful compound as "base" material.
In one of these situations, one strategy to reduce the viscosity of epoxy resin is simply to heat it. Some resins may well be heated until 80 °C without noticeable degradation.
Hope this helps!
I would say that in general, you are right.
However, in a number of cases, surface groups of the particles can react with the hardener (e.g. carbon fibres with amines), but not with the epoxy. It then becomes obvious that one must disperse fibres in the epoxy.
Moreover, the hardeners tend to be quite volatile, on the contrary to epoxy resins. When several hours of mixing are required, you would prefer not to have a volatile/harmful compound as "base" material.
In one of these situations, one strategy to reduce the viscosity of epoxy resin is simply to heat it. Some resins may well be heated until 80 °C without noticeable degradation.
Hope this helps!
There is another reason for the generally accepted procedure: high viscosity resin allows to generate high shear rate which leads to better dispersion.
These answers were very enlightening. Thank you so much for your kind helps.
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