I wonder why you are not providing sufficient information in the question. I am answering for your question based on my presumption.

There is no point in adding surfactants after the reaction is done. They should be added to the precursor.

CTAB is a cationic surfactant and SDS is an anionic surfactant. The type of surfactant has many roles to play depending on the process chemistry. It appears that you are particular about the crystallite size of the compound that you preparing by hydrothermal synthesis. Addition of surfactants will certainly influence the crystal size. The crystallite size of the synthesized compound depends on the type of surfactant, cationic or anionic and, its concentration. At lower concentrations, surfactants adsorb on the growing crystal faces and prevent agglomeration of the crystals. In such instances, the crystallite size will be decreased. If the concentration of surfactant is higher than its critical micelle concentration (cmc), then the surfactants tend to form a micelle and the crystallite size will be different (probably higher)

Your question is not clear. Please be specific.

Dear Sankara TSn Sir,

I have prepared a material through hydrothermal synthesis which has the size in microns.If I add any surfactant like CTAB or SDS ,what will be the effect of surfactant on this material?And when shall I add this surfactant(to the precursor or after the reaction is done)..

I wonder why you are not providing sufficient information in the question. I am answering for your question based on my presumption.

There is no point in adding surfactants after the reaction is done. They should be added to the precursor.

CTAB is a cationic surfactant and SDS is an anionic surfactant. The type of surfactant has many roles to play depending on the process chemistry. It appears that you are particular about the crystallite size of the compound that you preparing by hydrothermal synthesis. Addition of surfactants will certainly influence the crystal size. The crystallite size of the synthesized compound depends on the type of surfactant, cationic or anionic and, its concentration. At lower concentrations, surfactants adsorb on the growing crystal faces and prevent agglomeration of the crystals. In such instances, the crystallite size will be decreased. If the concentration of surfactant is higher than its critical micelle concentration (cmc), then the surfactants tend to form a micelle and the crystallite size will be different (probably higher)

I agree with Sankara Narayanan Tsn, the answer given is very nice. I would only add one precaution to your experiment though. CTAB can significantly increase the pressure inside a hydrothermal bomb, so be careful when adding it to your precursors. I am not sure if SDS behaves the same way, but it might.

If you intend to decrease/control the particle size, there are several impact factors that could be considered in a synthesis in addition to the surfactants, such as the precursor concentration, heating rate, reaction temperature...

Addition of surfactants is indeed a simpler and easier route.

Dear Alexander , can u please explain me, how the CTAB will increase the pressure inside the hydrothermal bomb? Could u please explain me the mechanism when it is added to a material.... :)

Dear Satish, CTAB is a powdery material, when it is added to they hydrothermal bomb, it occupies space, reducing the volume of the bomb available to fill with your solvent and precursors. CTAB, as mentioned by Sankara, is a cationic surfactant that adsorbs to the surface of your material, aiding in passivating the surface and stopping crystal growth. Under certain conditions and with certain materials CTAB can also selectively adsorb onto particular crystal facets, resulting in anisotropic or directed growth of your material. I feel that it is important to note here that hydrothermal is a excellent synthesis method, however, it can be fairly difficult to obtain the desired crystallinity or morphology of your product. CTAB is not the only surfactant out there and the use of a different surfactant may result in a better synthesis for your product.

Thank u all

please help me .....

How can i choose the best surfactant for dispersing the AL2O3 nanoparticle in Ethanol ?

i have this surfactant : Sorbitan Oleat ( Span 80 ) - Tween 80 - Triton X100 - PEG 600-PEG400 -SDS -SDBS -Oleic acid

It's important to know what kind of 'material' are you talking about. Surfactants are amphiphilic molecules; so they tend to localize at interfaces, e.g. they are absorbed onto surfaces. Also, 'material' properties such as hidrophobicity, or electric charge, as well as the medium (electrolytes, pH,..) will determine the surfactant behaviour. Then, you can choose the most appropriate for your process.

Dear Hamid,

Are you asking which surfactant will be best for making the aluminum oxide, or for coating already made aluminum oxide particle?

Dear Sankara Sir, thanks for ur answer. But I could see some sides with this CTAB. At some concentration of this surfactant , I could get phase pure compound and at the concentration lower than this and above than this ,I could see side phases. If it only localizes at interfaces then this should not happen know? Does this CTAB is reacted with the starting materials here?