Any solid-liquid mixing process can be divided into two main steps: Breaking of the solid agglomerates or aggregates which is called the dispersion step and the distribution of the broken particles (or individual particles) in the matrix.

The first step generally depends, mostly, on the strength of the agglomerates (which depends on the size of the individual particles and the cohesive energy(=2*surface energy) between the particles),the transfer of the stress from matrix to the agglomerates (which depends on the interaction of matrix-particle that can also be examined by the surface energy of the components) and the applied stress (which depends on the type of the flow field (shear or elongational) and the strain rate).

In the case of dispersion, the agglomerate breakup can occur either by dividing into smaller pieces or by erosion mechanism (sometimes is called the peeling mechanism) and both of these mechanisms are time dependent. Depending on the ratio of the agglomerate strength to the effective applied stress, either mechanism or both may contribute in the dispersion.

The second step depends mainly on the flow characteristics (flow type and strain rate) and mixing time.

Back to your question, during mixing and after certain mixing time, depending on the other parameters, you reach a pleateau in the agglomerate (or aggregate) size and the dispersion cannot be enhanced by increasing mixing time. In another word, if you plot agglomerate size versus mixing time you will see a drop (due to agglomerate breakup) followed by a final plateau. So if you have not reached the plateau, mixing time can enhance the dispersion. Beside these facts, you may also see a decrease in the particle size by what can be called Fatigue mechanism! So if your agglomerate strength is slighly stronger than what the effective applied stress can breakup, increasing mixing time may result in Fatigue effect and may enhance slightly the dispersion.

The same argument stands for the distribution. In another word, after certain mixing time, you will reach a pleateau in the level of the distribution. You should consider that such plateau does not necessarily mean uniform distribution and it depends on the flow characteristics.

Ultrasonic may helps. However the frequency and the time exposed to sonic may damage the sample. We have use sonic to disperse CNTs and graphite in polymeric matrices and shown that sonic help to disperse the filler without damaging the system.

Any solid-liquid mixing process can be divided into two main steps: Breaking of the solid agglomerates or aggregates which is called the dispersion step and the distribution of the broken particles (or individual particles) in the matrix.

The first step generally depends, mostly, on the strength of the agglomerates (which depends on the size of the individual particles and the cohesive energy(=2*surface energy) between the particles),the transfer of the stress from matrix to the agglomerates (which depends on the interaction of matrix-particle that can also be examined by the surface energy of the components) and the applied stress (which depends on the type of the flow field (shear or elongational) and the strain rate).

In the case of dispersion, the agglomerate breakup can occur either by dividing into smaller pieces or by erosion mechanism (sometimes is called the peeling mechanism) and both of these mechanisms are time dependent. Depending on the ratio of the agglomerate strength to the effective applied stress, either mechanism or both may contribute in the dispersion.

The second step depends mainly on the flow characteristics (flow type and strain rate) and mixing time.

Back to your question, during mixing and after certain mixing time, depending on the other parameters, you reach a pleateau in the agglomerate (or aggregate) size and the dispersion cannot be enhanced by increasing mixing time. In another word, if you plot agglomerate size versus mixing time you will see a drop (due to agglomerate breakup) followed by a final plateau. So if you have not reached the plateau, mixing time can enhance the dispersion. Beside these facts, you may also see a decrease in the particle size by what can be called Fatigue mechanism! So if your agglomerate strength is slighly stronger than what the effective applied stress can breakup, increasing mixing time may result in Fatigue effect and may enhance slightly the dispersion.

The same argument stands for the distribution. In another word, after certain mixing time, you will reach a pleateau in the level of the distribution. You should consider that such plateau does not necessarily mean uniform distribution and it depends on the flow characteristics.

What kind of polymer and filler are you talking about?

Basheer, I think it is very important to know how is your system. It is not the same to mix short fibers or small particles into a melt polymer or polymeric solution. In each case you will get particular dispersion or distribution of your filler. Here, you have read the comments and all of them are for particular system, someone in solution and other in melt polymer. Could you tell us, how is your system? In order to improve the discussion. Thanls. 

Thanks a lot for all

I am using melt compounding . thanks

Dear Basheer

first of all you should recognize parameters affected distribution and dispersion.

for dispersion, shear rate is the main parameter. so each parameters which increased shear rate would increased dispersion too. such as back pressure in extruder, kneading element in screw and some others.

but about distribution;time of mixing would increased distribution but it should be noticed that time has a limited affect.

In extruders, L/D is the most important parameter for distribution. higher L/D means better distribution.

if you need any more explanation, please inform me.

Maziar

There is an entire chapter (Chapter 5) dedicated to the Preparation of filled polymer systems in the following book:

Aroon V. Shenoy, Rheology of Filled Polymer Systems, Kluwer Academic Publishers, Netherlands (1999).

In section 5.4, there is a detailed discussion on the compounding /mixing variables that affect the quality of the mix.  Some variables are more sensitive to changes than others. It is important to study and identify these variables and understand their sensitivity so that the compounding /mixing can be carried out under optimum conditions.  Variables affecting compounding operations could be machine variables (mixer type, rotor geometry) or operating variables (mixing time, rotor speed, ram pressure, chamber loading, mixing temperature, order of ingredient addition). You will have to study and understand the effect of each of these variables for your specific filler – polymer matrix combination to find the optimum conditions to achieve the proper level of dispersion and distribution of filler into the polymer.  You will get the necessary hints on how to go about this by reading Chapter 5 of the book.

THak you all

Ultrasonic may helps . How easy/fast the dissolution and dispersion and distribution of fillers into polymers . I am thinking that does the polymer molecular weight of affecting the dispersion and distribution.

Comixing and Ultrasonic may help!