Emulsion Polymerization

At O.S.P.R.E., a lot of our research has to do with emulsion polymerizations. This often includes teaching people what an emulsion polymerization is. To help us "spread the word" about emulsion polymerization, we have developed a "Java applet" which depicts some of the more straightforward aspects of emulsion polymerization. This applet was coded by Chris Badeen. What follows is a description of a typical emulsion polymerization. Clicking on the highlighted words in this text enables further explanations and a still shot of the relevant part of the applet to be shown.

A typical conventional emulsion polymerization recipe will consist of water, emulsifier, monomer and initiator. Water serves as both a transport and heat transfer medium. An emulsifier is a hydrocarbon chain with one end being hydrophobic and the other, hydrophilic. If the concentration of emulsifier is high enough, the hydrophobic ends of several emulsifiers (usually about 50 to 100) form aggregates known as micelles. The emulsifier serves as a stabilizer for polymer particles and monomer droplets. That is, the hydrophobic ends will attach to the particles while the hydrophilic ends will remain in the water phase. The charges on these emulsifiers forms what is known as an electrical double layer which prevents the particles from coagulating. In other words, the emulsifier serves to keep the particles suspended in the water. The micelles can also be the location of particle nucleation. Monomer is present in the reaction in the form of large droplets. These droplets act as a reservoir of monomer. The monomer in the droplets diffuses through the water phase and into the micelles due to thermodynamic reasons. Initiator is added to the reaction mixture and dissociates into two radicals in the presence of heat. The initiator radicals are extremely reactive and readily react with any monomer in the water phase. The monomer in the water phase continues to add to the radical until the chain grows long enough such that its solubility in water is exceeded. The oligomeric radical chain (multiple monomeric units) is now hydrophobic enough to enter a polymer particle or enter a micelle to nucleate a new particle. This is known as micellar nucleation. Another form of nucleation, homogeneous nucleation, can occur but is not included in our animation.

Thus, the conventional emulsion polymerization will occur in three stages. The first stage involves the nucleation (birth) of polymer particles. This can occur by either micellar or homogeneous nucleation (the latter mode is not included in our animation). The second stage involves the growth of the particles until the monomer droplets disappear. The third and final stage begins with the disappearance of the monomer droplets and continues until the end of the reaction.

On with the show. Note that the various elements in the animation are not to scale. That is the monomer droplets appear to be a lot smaller than they should be. Click on the target to launch the applet! Note that it may take a few moments to load, depending on the speed of your system.

There are three versions of the applet available depending on what internet browser you are using:

For users of Microsoft Internet Explorer with the Java JIT (just-in-time compiler) disabled and Netscape versions prior to 4.5 click on this target:

For users of Microsoft Internet Explorer version 4 only (JIT does not have to be disabled) (not recommended for Netscape users) click on this target:

For users of Netscape 4.5, and Microsoft Internet Explorer with the JIT disabled click on this target:

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