Hello Ismalia Aliyu,

I hope this can help you: Apart from agglomeration one of the reasons for mechanical properties decrease is when you reach the "mechanical" percolation threshold. At this point interactions (electrical, physical and chemical) drastically change electrical properties and at a nano level also mechanical be affected, and are mostly related to graphene dispersion on the matrix. There are several books and papers mentioning that concept, I have a book from Sadasivuni et. al. called Graphene Based Polylmer Nanocomposites in Electronics. You can also read about Graphene/elastomer nanocomposites by Papageourgiou et. al. in Carbon journal. https://doi.org/10.1016/j.carbon.2015.08.055

Bests,

Dear Ismaila, 

When we prepare a cmposite material of any type we all use the mixture law which simply as follow:

Pc= Pm. Vm + Pr. Vr

Where Pc is any property for the composite material ejther physical, chemical,.... etc. Pm, Pr is any property for the matrix and reinforcement respectively. Vm, Vr is the volume fraction of matrix and reinforcement respectively. Means the final property of the composite material is equal to the sum of the properties of both matrix and reinforcement multiplied by their volume fractions (some times we use the weight fraction Wt% instead of the volume fraction). Vr some times reach to a point where it has no effect on the properties or in some bad cases it may have a bad effect on the properties of the composite material as happened with you at 1% concentrate this is what we called the critical volume fraction, which we have to avoid, so you can use a lower concentration. 

Secondly when we reinforced with a nano material we always try not to exceed 1% or even not to reach it. Personally when I work on a nano reinforcement material I prefere 0.5% and lower, since all the nano materials have a large specific area which ensures a good dispersion within the matrix phase hence a good mechanical properties. 

With all my best wishes

@ Baydaa,

Thank you very much for your contribution.

But I think you do not understand my question. Agreed, when you reinforce with nano material, once reach a composition the property drops or does not provide improvement. The question is why does this happen. One answer is agglomeration. I am familiar with this. I am looking for another reason.

Also in your second point, you said that nano materials have large specific area ensuring good dispersion. Then there should be no agglomeration at low concentration such as 1 wt %.

Finally, I do not believe that you can fix the amount of optimum reinforcement as 0.5 wt % for all materials. for any combination of matrix and reinforcement you have, you have to investigate the optimum composition.

Once again thank you

Dear Ismalia, 

Accept my thanks too. Here is some ideas I hope you will find them useful for your work. 

Beside agglomeration, there is alot of things that will happen during the addition and interaction between the graphene and the polymer matrix, have you tried to get the FTIR, XRD, and UV spectra for your specimen to detect the difference in constraction before and after the addition of graphene to the polymer matrix,  espacially in bond length, streching of bonds, rotation of the bond, and other phenomenas that take place during the specimen preperation?.

I cant agree with you when you say 1% of nano material is a low concentration, reinforcing with nano materials is just like doping in semiconductors where a tiny amount measured in part per million (ppm) can transfere an insulator material like (Si) into a condutive material, this example is also true in nano materials espacially graphene. May be there if you mention the preperation method of your specimen we can indurstand more about your result. 

Finally I am sorry if I give you a miss leading information, I take 0.5% as an example only we can use as much as we want of volume fractions till we get the pest compositon. 

With all my best wishes

Dear Ismaila,

What kind of polymer matrix (Thermoset, thermoplastic or elastomer?) are you incorporating your graphene into? The interaction between your graphene and polymer is critical and also how the graphene is positioned in your polymer matrix. Orientation can play a role and also the graphene concentration does influence this, as has been mentioned by Baydaa Abdul-Hassan.

Furthermore, weight percentage is not necessarily directly related to volume percentage. If your concentration is too high, then you can have where your graphene platelets can "slip" due to insufficient interaction with the polymer matrix. When your filler starts to exceed your polymer volume, then you can start to experience this slipping or decline in mechanical properties.

Anyway, hope this helps.

Louis van Rooyen

Thank you both for your contributions

I am using sonication and stirring to make the powder composite. After that, I consolidate the composite by hot pressing. and the polymer is thermoplastic. I did the XRD of the prepared composite powder and found that the peak intensities were decreasing steadily with the amount of concentration. I think the peak shift was not significant, about 0.5 degree. Note that the graphene peak did not show in the XRD spectra of the composites.

Can you give examples of published papers to support what both of you have explained earlier.

i would like to see papers in which it is reported that at all concentrations, there was no agglomeration, but property deteriorate due to the increase in concentration due to, for example, low interfacial bond, or e.t.c.

Hello Ismalia Aliyu,

I hope this can help you: Apart from agglomeration one of the reasons for mechanical properties decrease is when you reach the "mechanical" percolation threshold. At this point interactions (electrical, physical and chemical) drastically change electrical properties and at a nano level also mechanical be affected, and are mostly related to graphene dispersion on the matrix. There are several books and papers mentioning that concept, I have a book from Sadasivuni et. al. called Graphene Based Polylmer Nanocomposites in Electronics. You can also read about Graphene/elastomer nanocomposites by Papageourgiou et. al. in Carbon journal. https://doi.org/10.1016/j.carbon.2015.08.055

Bests,

In addition to recommendation of the answer by Jorge Mario Patiño Acevedo,

I think that the problem of agglomeration my hide itself sometimes. I recommend dilution of the polymer matrix with carefully selected unharmful dilute, mixing with graphene, and let the dilute to evaporate. According to my experience, this will notably gives better results.

@Jorge

Thank you very much for your input. Can you please give a further explanation on what you mean by this statement.

"and are mostly related to graphene dispersion on the matrix"

by dispersion, are you saying that percolation threshold is a function of dispersion. meaning to say that when dispersion becomes non uniform, percolation threshold is reached?. if you say yes, then this may be against my question. I am looking for instances/references in which it is observed that all composition gave uniform dispersion. however mech property dropped due to x or y or z.

Hi Ismalia,

I mean that interactions are related to dispersion, but percolation threshold definitly is not. Instead percolation threshold is deeply related to concentration of graphene, and later to orientation of the nanoplatelets if that´s the case.

Bests,