How to select a medium for making emulsions
I have to credit Mark Osterman for getting me to move on this one. I've known it for years, but just don't think about it. I use gelatin exclusively, but others want to use another vehicle (polymer) for making or coating their emulsion and there is a simple qualitative way to test to see if using this new material is possible.
First, make up a solution of about 4 molar Silver Nitrate in a dropper bottle. Then make up, a 4 molar solution of Sodium Chloride in the polymer that you wish to test. The polymer should be at 5 - 10% by weight.
In a 3rd container make up 4 molar Sodium Chloride in 10% gelatin.
In another container, make up just 4 molar Sodium Chloride in water.
Now, gently add about 1 ml of the AgNO3 to the NaCl and observe the results. A white solid forms that rather quickly falls to the bottom of the beaker of NaCl. This is what happens in the worst case.
Repeat this using the NaCl + Gelatin solution and you will see a creamy white material form and remain suspended in the gelatin. This is the best case.
Repeat with the experimental polymer and see where it falls in terms of the material formed. Qualitatively, you will be able to determine if your new polymer is closer to Gelatin or nothing at all and will then be able to judge its suitability in precipitation.
Now, using the Gelatin + salt and Polymer + salt solutions, use your favorite coating method and see how well the polymer compares with gelatin for coating quality. After dry, harden the coatings by your favorite methods, or those suggested for the polymer, and then dip the sheets into water at 80F and see how well the coatings respond to pseudo processing.
Using your fingertips, gently rub the wet coatings to see if they can withstand mild abrasion.
Use what works best.
There you have it, a simple qualitative test of any polymer for suitability in making or coating emulsions. Obviously, some will pass but be unsuitable and others that are suitable will fail these tests, but these tests can serve as a general starting point to help.