Vapor Phase Deposition of Electroactive Poly(3,4-ethylenedioxythiophene) onto Electrospun Commodity Polymer Nanofibers

This research investigates the use of chemical vapor deposition for the preparation of Poly(3, 4-ethylenedioxythiophene)coated electrospun polyacrylonitrile nanofibers to create porous materials for applications in biomedicine, water purification, and catalysis. Key challenges include preventing fiber bridging at high oxygen concentrations, optimizing washing to remove residual iron chloride without polymer loss, and maintaining fiber integrity during PEDOT deposition. Nanofibers were coated with the electroactive polymer, Poly(3, 4-ethylenedioxythiophene)using chemical vapor deposition with iron chloride serving as an oxidant.

The study demonstrate the impact of different iron chloride concentration on PEDOT deposition on the PAN coupons. Chemical vapor deposition of electroactive polymers produces uniform coatings on complex geometries, is scalable, and is environmentally friendly as it avoids the need for the use of solvents. Our findings optimize iron chloride oxidant concentration for uniform PEDOT deposition on PAN nanofibers, enhancing the mechanical properties of the nanofibers.

Thereby advancing applications in water purification, energy storage, and biomedical scaffolds. To begin, assemble the electrospinning setup, ensuring that the high voltage power supply, syringe pump, and a 20-gauge needle with a flat tip are connected to a grounded collector. Make sure that the electrospinner is used in a fume hood or connected to ventilation ducting to minimize exposure to solvent vapors.

Cover the metal collection drum with wax paper for easy fiber retrieval and minimal cross-contamination between samples. Fill the syringe with the PAN solution, then use a 0.8 millimeter inner diameter PTFE tube with luer adapters to connect it to the spinneret needle. Next, set the flow rate of the syringe pump to 0.04 milliliters per minute.

Apply a voltage of 18.9 kilovolts between the spinneret and the grounded collector and set the collector to rotate at 1, 200 revolutions per minute. Allow the charged jet to initiate from the spinneret where it solidifies into continuous nanofibers as the solvent evaporates. Next, after 4.5 hours, dry the PAN sheet mat in a vacuum desiccator at temperature for 72 hours to remove any residual solvent or water absorbed.

Cut the dried fiber mats into 2 by 2 centimeter coupons with a pair of scissors. Note the positions of the coupons with respect to the direction of drum rotation. Then, organize coupons into groups of triplicates to ensure consistency.

For the vacuum system, fit an enclosed steel container with a glass lid lined with a silicone gasket to assemble the chemical vapor phase deposition system. Equip the system with one valve connecting the vacuum pump and another for controlled release of vacuum. Now, connect a vacuum pump to the system to reduce the pressure in the chamber.

Position the container on a hot plate capable of reaching temperatures up to 250 degrees Celsius for thermal management during the deposition process. To assemble the vapor phase deposition racks, first develop deposition racks according to the specified designs. Now, connect the vertical legs with horizontal rods at the top and bottom to form a hollow cube-like structure for stability.

Wind three horizontal copper wires around the legs to create three tiers or levels for hanging the coupons. Wrap four vertical legs made of stainless steel in aluminum foil to construct the Generation 1 or G1 deposition rack. Ensure that the G1 rack is compact, fits within the processing chamber, and allows for easy assembly and disassembly.

Construct the Generation 2 or G2 setup using stainless steel for durability and corrosion resistance. Design the G2 rack with a circular base and top plate connected by four vertical rods for stability and support. Equip the vertical rods with adjustable clamps to allow customization of the height between the base and top plate.

Then, install a circular wire mesh tray made of stainless steel for hanging coupons. Weigh the PAN coupons. Then, soak them in aqueous ferric chloride solutions of varying concentrations ranging from 1 molar to 5 molar for 30 minutes.

Transfer the coupons onto low lint paper wipes to facilitate osmotic drying. Replace the wipes twice during the drying process. Now, wrap the coupons in wipes and place them inside a fume hood for 24 hours to complete the first stage of the drying process.

Weigh the PAN coupons after 24 hours and record the weight loss. Hang the PAN coupons by hooking them onto the metal wire tray. Next, place a 500 milliliter beaker containing dry calcium chloride desiccant at the bottom of the setup.

Position the entire setup inside a vacuum chamber. Turn on the pump to initiate the vacuum and leave the vacuum valve open for continuous air removal. Monitor the weight loss of the coupons at intervals of 1 hour, 2 hours, 3 hours, 24 hours, 48 hours, and 72 hours.

For PEDOT deposition, hook and hang the PAN coupons on the coupon rack assembly. Suspend the coupons inside the vacuum system along with an open glass container holding approximately 4 grams of the monomer EDOT. Adjust the hot plate temperature to 55 degrees Celsius.

Now, open the valve between the chamber and the vacuum pump and evacuate the chamber until the desired vacuum is achieved. Then, close the valve, leaving the chamber under vacuum. Allow the vapor deposition process to occur for 2 hours.

After 2 hours, open the vacuum release valve to retrieve the PEDOT-coated coupons. Drying of ferric chloride-soaked PAN coupons resulted in a gradual weight reduction over time, stabilizing after 72 hours with higher ferric chloride concentrations leading to greater initial weight gain. The coupons showed an increase in weight gain proportionate from 146%at 1 molar ferric chloride concentration to 400%at 5 molar concentrations.

During PEDOT vapor phase deposition, weight gain increased with ferric chloride concentration with the highest increase of 470%observed at 5 molar before washing. Washing PEDOT-coated coupons reduced weight gain due to removal of iron salts and unreacted EDOT with retained weight gain ranging from 73%at 1 molar to 267%at 5 molar.