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  1. #1
    Photo Engineer's Avatar
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    Stirring, mixing and homogenizing

    In response to some questions here are some loose "definitions" for emulsion making.

    Stirring is accomplished most simply by a magnetic stirring bar and a magnetic stirrer but it can be accomplished manually with a spoon or spatula. In gelatin, a magnetic stirrer is good from up to about 700 rpm with a good point being 300 rpm and a volume from 100 - 500 ml.

    Mixing is accomplished most commonly by a propeller on a shaft and is most efficient at about 100 - 5000 rpm and volumes up to 5 L. You must be careful not to beat air into your emulsion.

    Homogenizing is at the upper end of mixing and if the homogenizer has a loose enough gap between the rotor and stator (bigger than the emulsion or say 10 - 20 microns) then it can be used as a "mixer" for emulsion making. However, this gap is critical as a narrow gap can break or shear crystals and fog the emulsion. Generally a homogenizer has a gap of 1 micron or thereabouts and is used to make photographic dispersions of insoluble materials in gelatin. In this latter case a surfactant is needed. There is no limit on size of solution to be homogenized depending on the container used and the size of the rotor/stator. I have used them from test tube size up to liters with the right equipment. Speeds vary up to 25000 rpm or higher. These are dangerous units that can cause severe injury and also they can even overheat the solution being worked with or can shatter glass containers.

    See here for a state of the art rotor/stator homogenizer: http://www.ikausa.com/rotor-stator.htm

    PE
    Last edited by Photo Engineer; 09-11-2010 at 06:41 PM. Click to view previous post history. Reason: Added reference

  2. #2
    dwross's Avatar
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    Thank you, Ron, for taking the time and care to post this information.
    d

  3. #3
    Sirius Glass's Avatar
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    Thanks, now I am all mixed up!

    Steve
    Warning!! Handling a Hasselblad can be harmful to your financial well being!

    Nothing beats a great piece of glass!

    I leave the digital work for the urologists and proctologists.

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    See here for a state of the art rotor/stator homogenizer: http://www.ikausa.com/rotor-stator.htm

    PE[/QUOTE]

    This thing look just like the grinder my father (the chef) used to grind up raw beef liver for leberknoodles. I still have two just like it.
    Bill

  5. #5
    AgX
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    I'm mixed up too...

    So far I thought that stirreng is just a way of mxing.
    Now I learn that stirring and mixing are just grades of... Of what? Of blending?

  6. #6
    Photo Engineer's Avatar
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    Stirring may not mix the ingredients depending on condition. Or, it may just be moving the liquid in a continuous circle with no real change in the up or down direction. Mixing implies an intermingling of ingredients whereas stirring does not. Both use just a rotor. Homogenizing blending imply shearing forces as well that can change any particle size present if set up that way, or it may imply simply dispersing the ingredients forcefully.

    The three are not necessarily identical, but many of the effects involved are the same. Mixing does not imply any shearing or blending force, nor does it involve heat. A blender may generate quite a lot of heat and may boil the liquid(s) involved. So, there is also a difference in speed.

    PE

  7. #7
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    Is 'vortex mixing' used in commercial emulsion making?
    - Ian

  8. #8
    Photo Engineer's Avatar
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    Quote Originally Posted by Hexavalent View Post
    Is 'vortex mixing' used in commercial emulsion making?
    Ian;

    No, they are not used due to the generally small sample size that vortex mixing can handle.

    PE

  9. #9
    Sirius Glass's Avatar
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    PE,

    You are getting me stirred up!

    Steve
    Warning!! Handling a Hasselblad can be harmful to your financial well being!

    Nothing beats a great piece of glass!

    I leave the digital work for the urologists and proctologists.

  10. #10
    dwross's Avatar
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    I was hoping your OP was a jump-off to a more detailed discussion. You are very good at salting the forum that way (and I totally approve), but so far I'm not seeing the kind of follow-up information I was expecting. If 'stirring', 'mixing', and 'homogenization' are meant as vocabulary words, I'd love it if you could add them to your sticky thread, A short dictionary of emulsion making and coating terms. It's my observation/opinion that this forum is getting very bulky and hard to mine for usable information.

    If you intended more discussion, I'll poke into some potential details. 1) What "insoluble materials" does one typically need to disperse into an emulsion with an homogenization rotor? and 2) Are you saying that a properly selected and implemented rotor can be used to change the grain size distribution of an emulsion that had been originally precipitated with uniform-sized grains? (And if so, to what end? More precise grain size control? Or, a way to economize on vat set-ups and emulsion runs?)

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