Sachin K C

You actually have aggregation in nanosystems caused by van der Waals attraction and solid-solid diffusion. You end up, in a powder, with a collection of post- and sub-micron aggregates (tight; chemically bound) and agglomerates (loose). General rules are the keep the system in colloidal/liquid form and never dry or filter. For atomized systems then again avoid trapping the particles and collecting the powder. For a little more information see these webinars:

• Dispersion and nanotechnology https://tinyurl.com/y2wfzed7
• Adhesion and cohesion http://tinyurl.com/zwb2wlh

When you've viewed both, please don't hesitate to pose further questions.

Dear Sachin

Perform the ultrasonic process at each step of the synthesis process and also use a centrifuge to separate the synthesized powder.

Of course, the type and structure of the powder is also important.

Dear Sachin,

To reduce the agglomeration, you should use vigorous stirring during the preparation.

In order to have well separated nano-particles, it is wise to use capping agents during synthesis of nano-particles. However it may affect the other properties of nano-particles.So be careful what you need primarily.

Inderjeet Singh - Sir, can please suggest some good capping agents

S.s. Metwally - Sir, is there any specific rpm range which has to be maintained. We are maintaining around 300 rpm. Is that sufficient ?

Alan F Rawle - Sir, we need the end product in powder form. Nano particles in powder form are found to be agglomerated. Is there any possibility of making the end product free from agglomeration ?

Mahdi mirzaei-moghadam - Sir, we have adopted ultra sonication process. It has reduced the size of agglomeration. From SEM images it is evident that prominent agglomeration are still existing. If the duration of sonication is extended, will the agglomeration size reduce? Will it affect any other property of nano particle?

You are faced with the usual chemical-technological problem of how to preserve the properties and macrostructure of the obtained substance till use (I believe that you receive the substances in nanoform for future use, and not for the museum). For example, a story is known how in the 19th century pure metal tin ingots were sent to Russia from Europe. What did customers receive, given that the cars were in East-European winter? Other example, a bag of cement or even ordinary salt a few weeks after opening does not contain powder, but conglomerate.

Dr. Alan F Rawle is right, nanoscale exists only in colloidal system (but I would not exaggerate the role of diffusion at room temperature, but this is a topic for another discussion). Those, you need to make a study of the state of your substance versus time, as nanoform (both in powder form and in suspension) and its structure and properties change over time (usually this is a curve similar to an exponential with reaching a constant value in the region of large times).

That is, you must answer the questions:

- Is colloidal system with nanocomponent stable during storage? (For example, I stored aluminum oxide in nanoform in an aqueous suspension for several years, its properties did not change, despite sedimentation)?

- Which solvent is most suitable for creating such a suspension (taking into account the technological and economic factors of production, storage, transportation and intended use)?

- Is it possible to "restore" the nanoform of a substance after drying of the initial suspension (agglomeration occurs) and storage (transportation)? What methods should be used to re-create nanoforms (for example, ultrasound, or just enough intensive mixing)?

- What are the optimal storage conditions? Is it necessary to use polymer bags filled with an inert (inactive or dry) gas? For example, I used once for storing the substance 3 layer plastic sealed bags filled with dry nitrogen (this is much cheaper than argon, not to mention helium). Just keep in mind that ordinary polyethylene is completely “leaky” and gases pass through these micro-holes quite quickly ...

Of course, all these studies should be carried out in close contact with the consumer (a whole bunch of problems arise there).

Hi

Use surfactents while preparing nano particles. Oleic acid is an cheap and best organic surfactant. Even soap also a good surfactant.

Dear Sachin,

I think 300 rpm is not enough for preparing nano-sized material, you should use mechanical stirring >600rpm. This is used for a specific preparation method not for all methods.