Microbubble Fabrication of Concave-porosity PDMS Beads

The overall goal of this procedure is to fabricate millimeter sized microporous polymer beads with concave morphologies. This procedure is designed to produce polymeric high surface area to volume materials. These materials could be used either for separation science or as substrates for new energy materials.

The main advantage of this technique is that we use salt concentrations in the aqueous phase of our emulsion to adjust the bead morphologies. Generally, individuals who are new to this method may struggle because maintaining the temperature throughout sonication is extremely crucial. To begin mass an appropriate amount of salt to produce 10 milliliters of 0.03 molar solution weigh 1.02 grams of vinyl terminated polymethyl SUBOXANE or PDMS by slowly pouring it over a stir rod and into a 20 milliliter sealable glass vial.

Resting on a zeroed scale, then pipette 1.02 milliliters of N heptane to the vial. Add two drops of non ionic surfactant to the vial, followed by 0.3 milliliters of salt solution and 0.45 milliliters of deionized water. After sealing the glass vial by screwing the lid on tightly, shake vigorously for 60 seconds to initiate the emulsion before beginning sonication.

To construct a water bath ator apparatus, fill the ator with water up to the minimum fill line. Add 250 milliliters of tap water to a 400 milliliter beaker. Fill the 400 milliliter beaker with ice so that the water level is just at the rim.

Place this beaker inside the water bath sonicate. Check the fill line on the sonicate and adjust if needed. Then place a ring.

Stand directly beside the water bath sonicate. Using two ring stand clamps. Position them so that one arm is extended out perpendicular to the ring stand, and the other one is extended towards the water bath pointing downwards into the beaker filled with ice water.

Attach another clamp to the rings. Stand with a thermometer down in the 400 milliliter beaker so that the temperature can be monitored throughout the occasion. To perform the emulsification procedure, place the emulsion containing vial so that it is fully submerged in the 400 milliliter beaker by securing it into the clamp, protruding down into the beaker.

Temperature control the emulsion prior to cross-linking is the single most important step. If clumps are present in the solution, the solution is not homogenous before cross-linking that will damage the emulsion and solids will not form. Turn on the sonicate and set the sonication time for seven minutes.

Because the emulsion is very heat sensitive, ensure that the temperature inside the beaker is between zero and five degrees Celsius throughout the sonication. Start sonication once the temperature inside the beaker is desirable. After seven minutes of sonication, remove the vial and gently shake or swirl for one minute holding the top of the vial to eliminate any clumps that might form In the emulsion.

Dispose the contents of the beaker, then refill it with 250 milliliters of water and add ice to fill within one centimeter of the top of the beaker. Repeat the sonication steps for a total of eight, seven minute sonication periods or until the sonication appears to be homogeneous and no clumps are present. Store the emulsion at room temperature.

Pipette 5.4 milliliters of trixi silene into a test tube and place the tube in a test tube rack under the hood for later use working under the hood. Place a ring stand with an attached clamp extended directly over the opening of a 400 milliliter beaker filled with ice water. This will be the ice bath for the addition of Tri Oxy.

Then fill an 800 milliliter beaker with approximately 700 milliliters of tap water and place it on a hot plate on the other side of the ring stand. Attach a clamp with a thermometer to the ring stand so the temperature of the water inside the 800 milliliter beaker can be monitored. Maintain a temperature of 75 to 85 degrees Celsius inside the 800 milliliter beaker.

Produce the surfactant solution by dissolving 0.5 grams of sodium esal sulfate in 375 milliliters of water. Add approximately 10 milliliters of surfactant solution to a clean, empty test tube. Attach another clamp to the ring Stand with a surfactant test tube secured such that its liquid level is below the surface of the water inside the 800 milliliter beaker.

Allow 10 minutes for thermal equilibration play. Place the emulsion vial in the clamp over the ice water beaker inside the hood. Position the PDMS mixture in the clamp so that the vial contents are below the surface of the water.

The addition of trixi silene causes an exothermic reaction, so the emulsion must be kept cold in order to maintain its structure slowly pour the test tube containing trixi silene into the glass vial in a continuous stream Over a period of approximately 10 seconds, the addition of trixi silene initiates an exothermic reaction and the release of caustic hydrogen chloride gas. Do not stir the contents while adding the trixi. After adding trixi completely, gently stir the contents with a glass stir rod while wearing a heat protective glove.

Wait for two minutes or until gas stops evolving from the vial following crosslinking. There is no phase separation visible in the sample. If clumps are present, seal the vial and shake rigorously for 20 seconds while holding the vial by the lid.

When pipetting the emulsion, it is extremely important that the emulsion hit the surfactant solution as a drop. Otherwise, a bead will not form even. So it is important that the emulsion be pipetted quickly.

That way the the emulsion doesn't congeal inside of the pipette. Use a clean glass pest your pipette to draw the cross-linked emulsion from the glass vial. Add the cross-linked emulsion dropwise to the surfactant solution into the test tube.

Taking as little time as possible in between drops while wearing heat protective gloves, take the test tube out of the clamp and pour its entire contents into the filtration apparatus under the hood. After filtering for five minutes, remove the filter paper from the filter. Transfer the filtered solids onto a watch glass and separate beads for overnight drying under the hood.

To clean the beads, pour them into a clean filtering apparatus and use a plastic wash bottle filled with deionized water to rinse the beads gently moving them around slightly to ensure all the beads are rinsed. Let the beads dry for one hour by placing them on a watch glass under the hood. Use a wash bottle filled with hexanes to rinse the beads using the same method as was used for water.

After the beads are completely dry, place them in a small sealable glass vial and store at room temperature. For future youth. Place a strip of double-sided carbon conductive tape on top of the stub onto which the beets will be mounted using scissors trim around the stub to ensure no tape hangs over the edges, place a piece of filter paper under the stub on a flat surface.

Remove the top layer from the tape so that the adhesive underside is exposed. Gently pour the beads over the stub. Some beads will stick to the tape, but most will bounce off and land on the filter paper or the beads that stayed on the filter paper back into the vial.

Repeat if necessary washing any beads that become contaminated to ensure the beads are secure on the stub. Use a bulb syringe and lightly blow very closely to the st surface. Pour more beads over the stub if only a few adhered to the tape.

Ensure that all beads are secure before placing the stub into the SEM chamber and evacuating it. Once the samples have been mounted properly, they are now ready to undergo scanning electron microscopy analysis as described in the text protocol representative SEM. Images of beads arising from emulsions with different electrolyte conditions are shown here.

Beads produced without the addition of any electrolyte to the aqueous layer are characterized by exclusively convex porosity. The other beads, surfaces shown are of beads produced by addition of electrolyte resulting in different morphologies for each metal ion. Those produced with platinum chloride, zinc chloride, and sodium chloride show different morphologies including the substantial addition of concave pores due to microbubble formation as indicated in the circled area.

Higher resolution images of beets produced with no electrolyte and with zinc chloride are shown without the addition of electrolyte. Spherical substructures are generally larger and more closely packed than with the addition of zinc chloride, which contributes significantly to the increase in the surface area to volume ratio. Bru nower, Emmett Teller analysis of the beads found that the surface area to volume ratio of beads produced using zinc chloride was over 30 times that found without electrolyte providing a drastic increase in the area available for surface interactions Once mastered, this technique can be accomplished in approximately 90 minutes when done properly by viewing this video.

I hope you've gotten a good understanding of how to produce high surface area to volume polymeric beads by incorporating a small amount of salt into the aqueous phase of your emulsion While attempting this procedure. It is extremely important that the emulsion be maintained at a low temperature throughout sonication, especially prior to cross-linking. There must be no clumps present in the emulsion Following the procedures outlined in this video.

You can use other techniques like BET analysis in order to determine the actual quantitative surface area to volume of your beads. Don't forget that working with Tri Oxy Silene can be hazardous and precautions such as keeping the sash on the hood almost all the way down upon the addition of Tri Oxy silene to the primary emulsion should be taken Since its development. This technique has provided researchers in analytical chemistry and material science with the opportunity to produce separations materials for things like chromatography applications and substrates for new energy applications.