Preparation of Hollow Polystyrene Particles and Microcapsules by Radical Polymerization of Janus Droplets Consisting of Hydrocarbon and Fluorocarbon Oils

The overall goal of this procedure is to prepare hollow polymer particles using a simple radical polymerization with mutually immiscible oils. This method can help expand the availability of fluorinated compounds, which have been poorly utilized recently, since the European Union banned the use of fluorinated surfactants in 2006. The main advantage of this technique is that the immiscibility between hydrocarbon and fluorocarbon oils plays an important role for the fabrication of hollow polymer particles.

Because this method can provide insight into molecular interactions between hydrocarbon oil and fluorocarbon oil, it can also be applied to another hydrocarbon monomer like methyl methacrylate. We first had the idea for this method when we studied molecular interactions between hydrocarbons and fluorocarbons. Visual demonstration of this method is critical, as the process in forming polymer particles depends on the polymerization time.

To begin, prepare a five millimolar of an aqueous SDS solution by dissolving 14.5 milligrams of SDS in 10 milliliters of high-purity water. Then add 0.9 grams of the SDS solution, 1.5 grams of styrene, and 0.6 grams of PFO to a 10-milliliter glass vial, and add a stir bar. Place the solution onto a stir plate.

Stir the mixture at 1, 150 RPM for 60 minutes at room temperature. Then raise the temperature to 80 degrees Celsius, and continue stirring for an additional 60 minutes. Add 3.9 milligrams of potassium peroxodisulfate, two milligrams of pyrene, 1.5 grams of styrene, 0.6 grams of PFO, and 0.9 grams of the five millimolar of the aqueous SDS solution into a 10-milliliter glass vial with a stir bar.

Then seal it with a rubber septum. Next turn on a nitrogen supply. Slowly bubble nitrogen gas into the solution through a needle for 30 minutes to deoxygenate the mixture.

As before, place the mixture on a stir plate at room temperature, and stir at 1, 150 RPM for 60 minutes. Then turn on the heater, and stir the mixture at the same rate for an additional 30 minutes at 80 degrees Celsius. When finished, transfer the cloudy part of the solution into a test tube.

Then add 30%of an aqueous ethanol solution to completely terminate the polymerization reaction. Next sonicate the emulsion for 10 minutes to wash the resultant polymer particles. When finished, centrifuge the polymer particles from suspension for 10 minutes at 2, 300 times gravity.

To obtain the polystyrene particles, remove the resulting supernatant solution from the test tube. Then add three milliliters of water to the resultant solids in the test tube. Sonicate again for 10 minutes, and then spin down the particles for 10 minutes at 2, 300 times gravity.

Repeat the washing procedure until no more foam is generated from the supernatant solution. Following the final wash, evaporate the remaining water in a desiccator to obtain the hollow polystyrene particles. Add one milligram of the dried hollow polystyrene particles, four milliliters of water, and a stir bar to a 10-milliliter glass vial.

Sonicate the mixture for 10 minutes to disperse the hollow particles in the water. Then add 0.1 milliliters of toluene to the water. Disperse the particles and stir them for one hour at 100 RPM.

Afterwards transfer the liquid to a test tube. Finally centrifuge the liquid for 10 minutes at 2, 300 times gravity to isolate the microcapsules. When the spin is complete, remove the supernatant from the test tube to be left with the hollow polymer particles.

In the emulsions, the continuous phase is aqueous SDS. This phase is indicated by the green color, which corresponds to aqueous fluorescent calcein. Therefore oil and water type emulsions are formed.

Additionally emulsions containing the oil-soluble coumarin 102 reveal that a PFO droplet is located at the interface between water and a styrene droplet. To measure the average size of the final hollow polystyrene particles, scanning electron microscopy is effective. Using this method, the average diameter estimated from SEM observations was 1.3 micrometers, the average hole size is 800 nanometers, and the average volume of the hole was found to be 0.9 micrometers cubed.

Once mastered, this technique can be done in about two hours if it's performed properly. While attempting this procedure, it's important to pay close attention to the polymerization time. After its development, this technique paved the way for researchers in the field of physics and material science to explore numerous shape particles and the optical properties as well as drug carriers and delivery systems.

After watching this video, you should have a good understanding of how to fabricate hollow polymer particles using droplets consisting of hydrocarbon and fluorocarbon oils. Don't forget that working with styrene can be extremely hazardous, and the precautions, wearing a lab coat, gloves, and safety glasses, should always be taken while performing this procedure.