This self protocol covers some of the most important parameters and steps involved in solution blow spinning of polymeric nano composite fibers including polymer molar mass selection of thermodynamically appropriate solvents, polymeric concentration in solution, incorporation of nano materials, carrier gas pressure, and working distance. SPS is a relatively new technique that offers great versatility with respect to the polymer solvent system and the end product. Furthermore, it can be used to rapidly deposit formal fibers onto both planar and non-planar substrates and create sits or webs of fibers of both the nano and microscale diameters.
The goal of this work is to provide guidance to develop tunable and flexible polymeric fiber nano composites that can be used as alternatives for typical binder materials found in body armor applications by incorporating nano particles in the fiber's polymer elastomer matrix. Currently, there are no commercially available systems or standard operating procedures to perform a solution blow spinning on tuneable polymeric nano composite fibers. The demonstration of our particle and apparatus could help others to effectively develop their own process for their application.
To begin, transfer the desired amount of the dry polymer into a clean 20 milliliter borosilicate glass vial using a small spatula. Place the vial into the chemical fume hood and add approximately 10 milliliters of tetrahydrofuran to achieve a 200 milligrams per milliliter concentration. Then close the vial and place it on the mixer or rotator.
Add dry iron oxide nanoparticle powder into a clean 20 milliliter glass vial. Then add 10 milliliters of tetrahydrofuran into the vial and close it. Thoroughly agitate the sample on the vortex mixer until the nanoparticles become invisible at the bottom of the vial and then sonicate the sample for approximately 30 minutes with a two to five minute interval between each sonication, to ensure the complete dispersion of the nanoparticles, and to avoid the sample heating.
Add the polymer into the nanoparticle dispersion inside the chemical hood and seal the vial. Then mix it on the rotator at 70 RPM for 60 minutes at room temperature until the polymer completely dissolves. Adjust the height and angle of the airbrush to align with the center of the glass microscope slide attached to the collector and secured in place.
Ensure the gas cylinder is properly secured to its wall mount, and connect the gas inlet of the airbrush to the nitrogen pressurized gas cylinder. Turn on the main valve of the gas cylinder and slowly adjust the pressure to achieve the desired flow. Then close the main valve.
Secure the substrate on the collector using the equipped vice and adjust the height of the collector to align perpendicular to the spray direction and pattern of the airbrush to deposit the material on the substrate. Identify the optimal working distance by sliding the collector to its furthest position away from the airbrush nozzle. Transfer the polymer nanoparticle solvent mixture into a dissolved gas analysis borosilicate glass syringe equipped with a stainless steel needle.
Remove any air bubbles from the sample by holding the syringe with the needle pointing up and tapping the syringe gently then slowly depress the plunger to displace any excess air. Detach the needle, attach the syringe to the syringe pump unit and secure the syringe. Connect the PTFE tubing coming from the outlet of the syringe to the appropriate inlet on the airbrush and select the desired injection rate from the syringe pump unit menu.
Open the main valve on the nitrogen gas cylinder for the nitrogen gas to flow through the airbrush and initiate the spraying process by starting the syringe pump unit to dispense the polymer nanoparticle solvent mixture. Observe the spraying pattern and ensure that there are no clogs. Incrementally increase or decrease the injection rate until the solution is spraying freely.
Adjust the position of the collector for solvent evaporation by sliding it towards the airbrush until the desired amount of the material is deposited on the substrate. Then stop the syringe pump unit and close the main valve of the nitrogen gas cylinder. At the critical concentration the dissolved polymer coils start to overlap each other and cause entanglement.
The calculated and experimentally predicted values of the critical concentration were similar. Therefore, a polymer concentration above the critical concentration was used for the solution blow spinning process. The effect of different polymer concentrations on the fiber mat morphology was studied, and it was observed that undesired polymer beads were present at lower and near the critical overlap polymer concentrations.
Pristine and morphologically smooth fibers were obtained at polymer concentrations above the critical concentration. At low magnification the fiber mat generated from a high polymer concentration showed the presence of individual and cylindrically shaped fibers with minimal beads or fiber welding. Higher magnification confirms the absence of polymer beads.
The effect of gas pressure on fiber morphology was also studied. As pressure increases the fiber diameter decreases while very high pressure results in large polymer beads and welded fibers. The presence of iron oxide nanoparticles within the polymer fibers was determined using back scattered electron analysis.
The elemental analysis further indicated the presence of iron oxide nanoparticles Selection of an appropriate solvent, as well as the molar mass of the polymer in its concentration and solution are some of the most critical parameters that can dictate success or failure of this protocol. The methods described in this protocol can be applied to develop polymeric fiber nano composites for various other fields and applications including biomaterials, polymer based conductive materials, filtration devices, and others.
