You have diluted your nanotubes (empty or with something attached?) with a surfactant solution if I have understand right.

Depends on the kind of surfactant you have used aggregation it is possible. If you have use for example an ionic surfactant with a short aliphatic chain, this could neutralize the electric charge of your nanotubes letting them to aggregate.

I suggest you to use non-ionic surfactants with a high HLB such as Tween 80 in low concentrations and perform some measurements about the Z-potentials. An increase in your Z-potential  far from 0 would give you an elestrostatic repulsion of you nanotubes having a stabilization of them in solution. On the other hand, the use of long aliphatic chain surfactans would give you steric repulsion helping also with the stabilization.

Settle or not depends on size, density difference and effective viscosity. Do not know your system, but deagglomerated CNT dispersions exhibit high viscosity already at 1 %. Maybe you dilute and deagglomerated CNT have enough space to settle freely. Further possibility in different situation would be depletion flocculation due to surfactant micelles.

carbon nanotube materials are of non-ionic materials. however, surfactants have generally ionic heads. for instance superplasticizers are of anionic surfactants and have negative heads. thus, surfactants could not adsorb on the carbon nanotubes and due to inconsistency between the type of surfactant and carbon nanotubes, agglomeration happens. It is recommended to use a non-ionic surfactant for this purpose.

sincerely yours

Hesam Madani

Hesam,

anionic surfactants adsorb well on CNT`s

e.g. https://www.researchgate.net/publication/228856666_Dispersion_of_Single-Walled_Carbon_Nanotubes_in_Aqueous_Solutions_of_the_Anionic_Surfactant_NaDDBS

Article Dispersion of Single-Walled Carbon Nanotubes in Aqueous Solu...

Dear Titus,

I didnt know that. So, We could use different types of superplasticizers as dispersants for nanotubes in  water.