Translational and Rotational Target Effect onElectrospun NanofibersJosé A. Cruz-Arzón1, Edwin J. Alvarado2Department of Biology, University of Puerto Rico at Cayey, PR1Department of Mathematics-Physics, University of Puerto Rico at Cayey, PR1A B S T R A C TUsing PEO stock solution, non-aligned nanofibers can be formed. The electrospinning technique makesthe formation of these fibers more bearable by using electrical conductivity. Independently if the fibers are aligned ornot, the metallization by Sputtering can be helpful because it adds less oxidation to the fibers, allowing them to beseen under the electronic microscope. The shells formed by this process of Sputtering are what researchers arelooking for, because they have the ability of performing a specific function such as gas sensing. The electronicmicroscope also helps in the characterization and analysis of the Nanofibers and more important the shells. If onewants to study the shells want to be studied in details, the calcination process can be a way of evaporating the fibersto characterize only the shells previously metalized. This abstract seems incomplete to me because I do not see theobjective of the researchor the hypothesis, the methodology, the results, the conclusions, and the futuredirectionnecessary in any abstract of primary research.IntroductionNanofibers are fibers that one of their dimensions hasa diameter of 100nm or less. These Nanofibers are usedbecause of their high surface-to-volume ratio thatallowscertain substances and particles to attach to its surface in orderto perform a specific function. Their physicochemicalproperties and high porosity allow the fibers to have a highchemical reactivity with the particles attached to it, and anyother substance or chemical. These fibers have to first beprepared using a solution-based method in order to produce afiber. PEO Nanofibers are a good example; they are madebased on a solution of 95% water and ethanol and 5% weight/weight of the solute PEO. The solution has to be spun inorder to create a fiber. In this case, electrospinning is used toproduce the PEO nanofibers (Deitzel et al. 2001).The electrospinning technique was reinforced on1930 as a simple and versatile method for making fibers ofpolymer solutions with the specified diameter (Katta et al.2004). Other types of spinning involve melt spinning, solutionspinning, and gel state spinning. The electrospinningtechnique uses a power supply to provide electricity so thesolution, placed inside a syringe, runs using electrical charges.A negatively charged electrode would be attached to thesyringe, and a positively charged electrode to a collector whichhas a substrate that is going to catch the fibers when theydeposit. The size of a syringe’s tip is going to create a slowacceleration at the beginning, and then when it comes outfrom the tip, a fast acceleration creates a fiber deposited on thesubstrate. In this case, the substrate used is Silicon, because itcan be used to study conductivity and oxidation of the fibers.
Yet, there are two methods in which the fibers can be formedby electrospinning, the aligned electrospinning method andthe non-aligned electrospinning. Basically, they both work thesame way, but the aligned electrospinning posses a movingcollector which has rotational and translational movement soit can create more organized and aligned fibers for futurecharacterization. The objective was to determine the effect ofthat aligned electrospinning on the fibers. The non-alignedelectrospinning just has a static collector. So the hypothesisstates that having rotational and x-translational target willproduce uniform fibers.Certain other processes are involved in making agood fiber for their usage. In case that the fibers cannot beseen under an electronic microscope because of their highoxidation thanks to electron bombing of the microscope, thefibers have to go through a metallization process. A metal,palladium, is deposited on the fiber inside a Vacuum Chamberto avoid oxidation. Also, this metal forms a shell which can beused for further studies in the field.Nanofibers in this case are used as templates for theformation of palladium shells which can be used for studies onthe sensing of certain gases such as Hydrogen.Electrospinning also provides a variety of possibilities for theformation of fibers. Collagen fibers are also synthesized usingelectrospinning, but the collagen fiber is the material used forBiomedical Applications, like the regeneration of thehydroxyapatite in bones (Mathews et al. 2002). DNAnanofibers can be also be created using electrospinning, tostudy their sequences in details.Materials and MethodsThe original solution planned to be used in thisexperiment was PVA and Zn (Ac) 2 solution.However, dueDue to a possible contamination due tothrough humidity, thesolution was changed to a PEO stock solution (Deitzel et al.2001). Before beginning to use any other equipment, the useof gloves is compulsory to avoid further contamination of thefibers or any other samples. The electrospinning chamber usedwas the non-aligned electrospinning chamber, because thealigned fibers were already synthesized. A Vacuum Chamberwas used to metalize the fibers with palladium for the futurecreation of shells. The Scanning Electron Microscope wasused to characterize the aligned and non-aligned fibers andanalyze the formation of shells on the fibers. LAt last of all, anoven was used to calcinate the fibers and leave only the shellsfor research of their capability as hydrogen sensors.ElectrospinningApproximately 1.5ml of the PEO stock solution wasplaced inside a syringe. The syringe was then placed inside theelectrospinning chamber with the negative electrode attachedto it, and the positive electrode attached to the substrate onthe target. The power supply was turned on at 20.0 KV at arate of 0.5 ml/hr. It took tTwo hours were have to be waitedfor the solution to deposit itself on the substrate creating theNanofibers.Sputtering or MetallizationThe sample including the Silicon substrate and thefibers, were placed inside the Vacuum Chamber to start themetallization process by sputtering. The chamber wasis set toa Base Pressure of 1.6 x 10-5torr, a Deposition Pressure of13mtorr and a power of 25 W. A magnet and a power sourcetogether formed an electromagnetic field, which hadsfreeelectrons in constant motion within it. The electrons begain tocollide with highenergy ions of argon, which wasis chemicallyinert, creating plasma surrounding the target which containedsthe metal, palladium. The collisions of electrons and ionsmadke the material of palladiumto eject and startdepositingitself all over the inner surface of the chamber. Sincethe substrate, containedningsilicon and PEO fibers, are facingthe target, more palladiumwasisdepositeding on the fibersample. This process isoccuroccurred ring in a span of 2minutes. After the deposition process finisheds, it wasisimportant to remember to create a vacuum, and fill thechamber with nitrogen to balance the pressure from the
outside,justbeforeopeningthechamber.Characterization of the fibersThe characterization of the fibers wasisdonemadeunder an electronic microscope. The fibers were analyzedusing a magnification of 600×, 900×, 1,500×, 2,000×, 8,000×,12,000×, and 22,000×.CalcinationThe fibers were calcinatedfor 2 hours at 325 ºC,causing evaporating the fibers to evaporateand thus isolatingthe palladium shells. After the calcinations, the shells wereanalyzed again under the microscope.Fig.2 Palladium shells after calcination (SEM micrograph at 2,000×)ResultsThe electrospinning process was done successfully,and with the PEO fibers, no contamination occurred. Thenon-aligned fibers were done using the established parameters(20.0V and 0.50 mL/h). Using the pressures established in theSputtering process, the palladium material was deposited onthe fibers inside the Vacuum Chamber. Using the electronicmicroscope, the objective was accomplished.,Rrotational andtranslational movement of the collector produceds uniformand more organized fibers. With the calcinations stepcompleted, the fibers used as a template were evaporated,leaving the palladium shells for future characterization.These shells were seen under a microscope. ,concludingthat shells were formed by the calcinations process lettingfurther research on the shells (This last part is not clear.Yet, since you are concluding it should appear inthediscussion section.).DiscussionNon-aligned PEO fibers were produced to beused as a template for further sensing of gases such ashydrogen. One of the characteristics of palladium is that it hasa great affinity for gases, especially hydrogen, so the palladiumshells formed by the metallization of PEO fibers can be a greatmaterial for gas sensing. As a conclusion, the aligned PEOfibers could work better for the formation of shells than thenon-aligned fibers, because they are more organized anduniform, allowing the deposition of palladium to be moresuccessful. Further research of the characteristics of thealigned and non-aligned fibers could open doors forimprovements to the electrospinning technique for better fiberproduction, and therefore fortothe better formation of shellsthat may be used for different kinds of functions that includenot only gas sensing, but also certain biomedical applications.ReferencesKatta P, Alessandro M, Ramsier R D, Chase GG. 2004.Continuous electrospinning of aligned polymernanofibers onto a wire drum collector. Nano Lett[Internet]. 4(11):2215-8.Matthews JA, Wnek GE, Simpson DG, Bowlin GL. 2002.Electrospinning of Collagen Nanofibers.Biomacromolecules [Internet]. 3(2):232–8Deitzel JM, Kleinmeyer JD, Hirvonen JK, Beck Tan NC.2001. Controlled Deposition and Collection ofElectro-spun Poly (ethylene oxide) Fibers. ARL[Internet]. 2415: 9-27