Dear Prof.

We have a oil matrix that nanocomposite base carbon nanotubes presence in it as a suspension. After increasing temperature carbon nanotubes aggregate in it.

Dear Hassan,

Are the carbon nanotubes stabilised by anything? Additives, surfactants, polymers etc?

NO

We do not add any additive. On my CNTs is functionalize with COOH.

Only COOH without any additive, surfactants

Best regards

My guess is that you are encountering a 'theta temperature' phenomenon. i.e. the 'solubility' of your nanotubes decreases with an increase in temperature as a result of poor compatability between surface -CO2H groups (simplistically) and your oil matrix. Hard to say without knowing what your matrix is. Aggregation of colloidal partciles at elevated temperatures is well known for high solids contents (typically >35%). For a start this refs may be a useful introduction to colloidal/nanoparticle aggregation:

Temperature-Dependent Nanostructure of an End-Tethered Octadecane Brush in Tetradecane and Nanoparticle Phase Behavior

Aaron P. R. Eberle,† Norman J. Wagner,*,† Bulent Akgun,‡,§ and Sushil K. Satija‡

Langmuir 2010, 26(5), 3003–3007

Particularly the Introduction with a number of references to temperature induced aggregation.

Regards,

Simon

My view is that, as the temperature of the system increases, the number of collisions among the nanoparticles increases and thereby the aggregation increases. I have noticed a lot of literature citations regarding the rise in metal nanoparticle aggregation as a result of increase in concentration which has been attributed to multiplying the number of particle collisions, e.g. "Chekli et al., (2013) Assessing the aggregation behaviour of iron oxide nanoparticles under relevant environmental conditions using a multi-method approach".

In addition, as in your study there may be a decrease in the viscosity of the solution due to the rise in the temperature, the number of collisions of nanoparticles can be multiplied as well.

Thanks Prof. Aleem for your kind appreciation. Actually, I am just a PhD candidate not a professor. 

Kind regards,

Peyman