Progress 10/01/10 to 09/30/13
Outputs
Target Audience: A broad range of stakeholders and target audiences were addressed over the course of this project. The general public was were reached via general press and media participation including ‘Futurescape’ television program ‘cheating time’ episode on the Science Channel and the Cornell Chronicle. The scientific community, fellow researchers in the field and colleagues were reached via peer reviewed journal articles and presentations at scientific meetings. Government entities including both houses of Congress and the Department of Defense were addressed during briefings for Congressional staffers, poster presentation at DoD stake holder meetings and responses to RFI (request for information) calls. Changes/Problems:
Nothing Reported
What opportunities for training and professional development has the project provided? Three graduate research assistants completed Masters level projects under this project. These students reviewed literature, wrote research proposals, learnedtechniques for and conducted laboratory experiments and wrote both theses and peer reviewed journal articles based on their work. Two undergraduates have also been trained and conducted independent research on the proposed project. One student has completed an honors thesis and the second has been accepted into the honors program. One undergraduate student wrote an internal College of Human Ecology research proposal which was funded to support her summer research on this project. How have the results been disseminated to communities of interest? Results have been disseminated via peer reviewed journal articles, presentations at professional meetings, congressional briefings, and general audience presentations, via television and via print/internet media. What do you plan to do during the next reporting period to accomplish the goals?
Nothing Reported
Impacts
What was accomplished under these goals?
Two types of electrically active polymeric fibers were investigated; piezoelectric fibers which can generate or respond mechanically to current and conducting fibers. The seamless integration of flexible piezoelectric fibers as a component of a fabric would allow motion sensing as well as kinetic energy harvesting in ‘smart textiles’. Connecting these fibers with a flexible conductor increases the potential for textile based smart materials. Polyvinylidene fluoride is a piezoelectric polymer that readily forms microfibers via electrospinning. PVDF nanofibers were electrospun from solution in dimethylacetamide (DMAC)/ acetone mixed solvent at temperatures ranging from 25oC to 55oC with a goal of maximizing the beta crystalline phase which has piezoelectric properties. Between 12 and 18wt% of Poly (vinylidene fluoride) (PVDF) was dissolved in the solvent (14v% to 50v%) and nonsolvent mixture(50v% to 86v%). The solvent capable of dissolving PVDF pellets is DMAc and the acetone is latent solvent which requires high temperature to dissolve PVDF. Acetone which has high volatility was added to improve the electrospinning process by changing viscosity of solution and evaporation of solvent. Its effect on viscosity and evaporation influenced by the polymer concentration and the spinning temperature is responsible to produce different fiber morphology and crystalline phases. Fiber diameter ranges from 0.1 to 3.6μm. Smallest fibers are found when the spinning solution combines lower PVDF concentration as 12 or 14wt% and higher volume percent of acetone, 83 or 86v%, regardless of spinning temperature. Although finest fibers with best fiber morphology are found at high volume percent of acetone, those fibers do not possess high %beta crystallinity as there is no correlation between fiber morphology and the crystallinity. However, those fibers which exhibit high %beta crystallinity also presente uniform fibers without solvent left or beads. Obtained by XRD, %total crystallinity and %beta crystallinity have correlation so fibers with high crystallinity could have high piezoelectric properties. Total crystallinity measured by XRD has a maximum of 52% when the fibers are spun from the solution of 12wt%PVDF and solvent of 80v%acetone and 20v%DMAc at 55 oC. The same solution produces the fibers with maximum beta crystallinity 35%. The maximum 35% beta crystallinity is also achieved under other spinning conditions. Analyzing XRD results from different composition concludes that there are many ways to increase %beta crystallinity. Investigating combined effect of acetone and concentration at different spinning temperature shows significantly different results at different temperature. At different temperature, %beta crystallinty correspond differently to the combined effect and the simplest way is to use spinning temperature of 55 degrees C with 80v%acetone in the solvent. With this combination, many concentrations can maximize %beta crystallinity. %Total crystallinity was also investigated by DSC although there is no correlation with the data from XRD. Heat flow shows large cold crystallization peak for solution with low volume percent of acetone. This states that fibers from those solutions were not able to crystallize fully during the electrospinning process. For better understanding of spinning, rheometer was used. The study proves that the influence of the acetone on both viscosity and evaporation. The comparison with fiber morphology points the limitation of acetone to decrease viscosity on concentration and the limitation of concentration to slow evaporation rate on the volume percent of acetone. The rheology also indicates the link between spinnable condition and chain entanglement measured by storage modulus. While interaction between three variables creates complication to identify the conditions to maximize %beta crystallinity, also investigating many factors suggests several ways to improve formation of beta crystallinity. Few conditions have been located to produce fibers with high piezoelectric properties and theses conditions also produces good fiber morphology.%beta crystallinity of theses fibers can be increased further using other methods and the uniform fibers with the high piezoelectric properties can be applied in many ways. As-spun fibers were then poled by exposing them to 90 °C and 10 kV for 1.5 hours, orienting the β crystallite dipoles perpendicular to the fiber surface. Crystallinity and piezoelectricity of PVDF microfibers were further enhanced by the addition of up to 0.25 wt% carbon nanotubes to the spinning dope. At higher concentrations the aggregation of nanotubes tended to cause beading in the fiber jet, diminishing the elongational forces enhancing β crystallinity and thereby decreasing voltage output for a given displacement. Improving nanotube dispersion within the polymer solution and improving fiber morphology could overcome this limit on nanotube concentration and further enhance piezoelectricity in these materials. The effect of solvents on the morphology and conductivity of poly (3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) nanofibers is investigated. Conductive PEDOT:PSS nanofibers are electrospun by dissolving a fiber forming polymer, polyvinyl alcohol (PVA), in an aqueous dispersion of PEDOT:PSS. The conductivity of PEDOT:PSS nanofibers is enhanced 15-fold by addition of DMSO and almost 30-fold by addition of ethylene glycol to the spinning dopes. This improvement is attributed to the change in the conformation of the PEDOT chains from the coiled benzoid to the extended coil quinoid structure as confirmed by Raman spectroscopy, X-Ray Diffraction (XRD), and Differential Scanning Calorimetry (DSC) results. Scanning Electron Microscopy (SEM) images show that less beady and more uniform fiber morphology could be obtained by incorporation of ethylene glycol in to the spinning dopes.Conducting nanofibers of Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)/Polyvinyl Alcohol (PEDOT:PSS/PVA) were fabricated at room temperature and via electrospinning with diameters ranging from 100 to 300nm. The nanofibers were irradiated with Gamma and X–rays for varying lengths of time and the change in conductivity was evaluated. Raman and Electron Spin Resonance spectroscopy of X-ray irradiated nanofibers were obtained to determine the mechanism of conductivity degradation. A decrease in molecular ordering as well as chain scission via chain cross-linking and free radical formation are the two most likely mechanisms for change in conductivity. These nanofibers are promising candidates for use in highly sensitive, real-time electrically based sensor for radiation detection.
Publications
- Type:
Journal Articles
Status:
Published
Year Published:
2013
Citation:
Schrote, K. and M.W. Frey, Effect of irradiation on poly (3, 4-ethylenedioxythiophene): poly (styrenesulfonate) nanofiber conductivity. Polymer, 2013. 54: 737-742.
- Type:
Journal Articles
Status:
Accepted
Year Published:
2014
Citation:
Pehlivaner Kara, M.O.; M.; Frey, M.W., The effects of solvents on the morphology and conductivity of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) nanofibers, Journal of Applied Polymer Science, in-press.
- Type:
Journal Articles
Status:
Other
Year Published:
2014
Citation:
Boban, M.; Park, S.Y.; Harden, J.; Jakli, A.; Frey, M.W.; Piezoelectric electrospun polyvinylidene fluoride/carbon nanotube composite microfibers,; in preparation.
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2013
Citation:
Boban, M.; Park, S.Y.; Frey, M.W.; Piezoelectric electrospun polyvinylidene fluoride/carbon nanotube composite microfibers, The Fiber Society National Meeting Program and Abstract Book, 10/2013, Clemson, SC.
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Progress 10/01/11 to 09/30/12
Outputs
OUTPUTS: Optimization of Poly Vinylidene Fluoride (PVDF) nanofibers for piezoelectric response continued. Carbon nanotubes were added to PVDF solutions and electrospun into nanofibers using conditions previously identified as maximizing the beta crystalline phase. Fibers were then characterized for structure, crystallinity and piezoelectric response. Measurements of mechanical response to an applied current were made at the Liquid Crystal Institute at Kent State University. Measurements of current generated in response to mechanical deformations were made in the Frey laboratory at Cornell University. Addition of carbon nanotubes increased both the beta crystalline phase of PVDF and the piezo electric response of the nanofibers. As a second component for fiber based electrical systems, conductive nanofibers were prepared from poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS) using PVA as a fiber forming carrier polymer. Conducting polyvinyl alcohol (PVA) nanofibers with diameters ranging from 100 nm to 300 nm were fabricated by an electrospinning method from spinning dopes of the dissolved PVA polymer in aqueous dispersionof PEDOT:PSS. Using a chemical cross-linking agent, glutaraldehyde (GA), water insoluble conducting PVA nanofibers were obtained through an in-situ crosslinking of PVA polymer during electrospinning. The cross-linked conducting nanofibers maintained fiber morphology after a soaking in water and exhibited high conductivity (4-8 S m−1). To create PVA nanofibers that were both conducting and had a persistent negative surface charge, Poly(methyl vinyl ether-altmaleic anhydride) (PVMA) polymer was added to the spinning dope. Organic conducting PVA nanofibers with or without negatively charged surfaces will potentionally be used to create highly sensitive, real-time electrically based sensors for biological and chemical species and for radiation detection. To characterize radiation sensitivity, the nanofibers were irradiated with Gamma and X-rays for varying lengths of time and the change in conductivity was evaluated. Raman and Electron Spin Resonance spectroscopy of X-ray irradiated nanofibers were obtained to determine the mechanism of conductivity degradation. A decrease in molecular ordering as well as chain scission via chain cross-linking and free radical formation are the two most likely mechanisms for change in conductivity. These nanofibers are promising candidates for use in highly sensitive, real-time electrically based sensor for radiation detection. Results to date were presented at the joint AATCC/Fiber Society/National Textile Center meeting in Charleston, SC on October 10-12, 2011, at the CCMR ICP Symposium at Cornell University in Ithaca, NY on May 22, 2012, at the ACS NERM in Rochester, NY on October 3, 2012 and at the National Textile Center meeting in Boston, MA on November 7-9, 2012. PARTICIPANTS: Ms. Sun Young Park - M.S. thesis research Dr. Daehwan Cho - post doctoral research associate Ms. Kaitlin Schrote - M.S. thesis research, Ms. Mereyem Pehlivaner - M.S. thesis research. Mr. Mathew Boban, B.S. Honors Thesis research. Mr. Jordan Adamek, M.S. thesis research Mr. Nick Hoepker, Ph.D. candidate At the Liquid Crystal Institute, Kent State University, Prof. J.L. West, and Prof. A. Jakli TARGET AUDIENCES: The target audience for this research is expanding to include groups and individuals interested in smart textiles, renewable energy generation and radiation detection. Capabiities for generating and transporting current or creating a mechanical response to an applied current are expected to have a applications in areas including: producing electical energy/current from ambient motion or vibrations including wind, or incorporating stimulous/response capabilities into textiles via textile fibers rather than applied wire or electronics. The radiation sensitivity of the conducting fibers leads to a simple and potentially inexpensive radiation monitoring and signalling device based on a blown fuse type circuit. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
Impacts
Piezoelectricity Measurement Apparatus: An improvised testing setup was created to confirm the piezoelectric response of the fiber samples. The purpose of the device was to provide a controlled periodic mechanical impulse to a sample incorporated into a flexible cantilever such that a voltage response could be read with an oscilloscope. A small 5V solenoid (ZHO-0420S-05bA4.5, SparkFun Electronics) with a spring-return shaft is held within an acrylic frame that also holds the sample above the piston. The solenoid is controlled by an Agilent 33210A Function/Arbitrary Waveform Generator with a 2V square wave via an amplification circuit consisting of a Darlington pair of two Fairfield TIP31C medium power NPN transistors, Heathkit IP-2718 bench power supply, and a flyback diode (1N4745 16V Zener diode) to protect the power supply. The output from the sample was recorded with an Agilent DSO-X 2012A digital storage oscilloscope via a Tektronix P2200 probe, and exported to CSV files on a USB flash drive for further analysis. Sample preparation for this test involved the creation of small cantilevers suitable for mounting into the testing apparatus. For each sample, two 30mm by 6 mm strips of PVDF fibers on aluminum foil were cut from a 6 cm x 6 cm piece onto which fibers had been collected for 20 min. The fiber meshes were approximately 100 micrometer thick. The two strips were then placed with the fiber surfaces on the inside, ensuring good adherence between surfaces, as foil which is merely placed onto a dry fiber surface tends to peel away. The doubling of the fiber layer thickness also should enhance the piezoelectric response, making data collection easier. The aluminum/fiber/aluminum layer was placed within a cellulose acetate film (cut from an overhead transparency) coated with double sided tape to protect the fiber mesh and give the assembled sensor the necessary stiffness to return to the neutral position after actuation. Some excess aluminum was allowed to protrude from the end on either side of the PVDF film, allowing connection to the oscilloscope. Copper tape was added to these contacts to improve the durability of the contacts throughout multiple tests. Mirau Interferometry: A more precise characterization of the piezoelectric characteristics of the fabric samples will be performed by collaborators at the Liquid Crystal Institute (LCI) at Kent State University, Ohio via Mirau interferometry, a technique that involves applying a voltage to sample placed between two conductive glass slides coated with indium tin oxide, and measuring the displacement via interference patterns in a beam of light reflected off the upper surface.
Publications
- Cho,D.,Hoepker,N., and Frey,M.W., (2012) Fabrication and characterization of conducting polyvinyl alcohol nanofibers, Materials Letters, 68:293-295.
- Pehlivaner, M., and Frey, M.W., (2012) The effects of solvents on the morphology and conductivityin PEDOT:PSS/PVA nanofibers, ACS NERM Program and Abstract Book, Rochester,NY.
- Pehlivaner, M., and Frey, M.W., (2012) The effects of solvents on the morphology and conductivityin PEDOT:PSS/PVA nanofibers, The Fiber Society National Meeting Program and Abstract Book, Boston,MA.
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Progress 10/01/10 to 09/30/11
Outputs
OUTPUTS: By controlling the solution composition and temperature, Poly (vinylidene fluoride) (PVDF) fibers with maximized beta crystal form were prepared by an electro spinning process. PVDF in the beta crystal form has piezoelectric properties. Piezoelectric PVDF nanofibers can be used for power generation or detection circuits in fiber based devices. In order to maximize beta crystal structure, PVDF concentration in solution, solvent composition and temperature were investigated. Increasing PVDF concentration caused an increase in the polymer solution viscosity and eventual gelation. Morphology of the electrospun fibers will be characterized using SEM, XRD and Differential Scanning Calorimeter (DSC). PVDF polymer chains consist of a carbon backbone with every other carbon atom bonded to pairs of hydrogen atoms or pairs of fluorine atoms. In the structure of PVDF, hydrogen atoms are electropositive and fluorine atoms are electronegative. The alpha, anti-parallel conformation, and beta, transverse conformation, are the most common crystalline phases of PVDF chain. Alpha phase is found commonly and it is non-polar molecule that creates no net dipole and hence no piezoelectric effect. The beta phase, which does exhibit the piezoelectric effect, is less common. When PVDF chains are crystallized in the piezoelectric beta phase, all hydrogen atoms are move to one side and fluorine to opposite side. When mechanical stress is applied to the beta phase, hydrogen and fluorine atoms shift relative to each other and generate an electric dipole and field. In order to have power generation property, fibers must have beta phase PVDF crystals. PVDF can also be processed into fibers. Fibers which generate electric charge can be produced using PVDF and can be incorporated into sails, garments, flags, wind socks, upholstery, draperies or tents to generate power from textile objects during their normal use. Additionally, conducting polyvinyl alcohol (PVA) nanofibers with diameters ranging from 100 nm to 300 nm were fabricated by an electrospinning method from spinning dopes containing PVA polymer dissolved in aqueous dispersion of poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS). With the addition of a chemical cross-linking agent, glutaraldehyde (GA), water insoluble conducting PVA nanofibers were obtained. The cross-linked conducting nanofibers maintain fiber morphology after a soaking in water and exhibit high conductivity (4 - 8 Siemens per meter). To create PVA nanofibers that are both conducting and have a persistent negative surface charge, Poly(methyl vinyl ether-alt-maleic anhydride) (Poly(MVE/MA) or PVMA) polymer was added to the spinning dope. Results to date were presented at the joint AATCC/Fiber Society/National Textile Center meeting in Charleston, SC on October 10-12, 2011 PARTICIPANTS: Ms. Sun Young Park - M.S. thesis research Dr. Daehwan Cho - post doctoral research associate Ms. Kaitlin Schrote - M.S. thesis research Ms. Mereyem Pehlivaner - M.S. thesis research TARGET AUDIENCES: New commercial development ventures based on fiber based power generation and sensor device development for medical diagnostics, environmental hazard detection will benefit from this research. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
Impacts
Electrospinning is a simple method for drawing polymer fibers with diameters at nano or micron scale using high voltage supply. Electrospun fibers are semicrystalline and have small diameter. Characteristics of fabrics formed from electrospun fibers includ high porosityexcellent pore interconnectivity and high surface to volume ratio. Also, electrospun fibers can be uniaxailly aligned over several centimeters. Gelation of polymer is driven by the interaction between solvent molecules and polymer chains and the gelation of PVDF can be affected by solvents composition. In this work, a combination of a solvent (DMF) and a non-solvent (acetone) were used to influence gelation in the electrospinning jet and lead to the preferential formation of beta phase PVDF crystals in the final fibers. Increasing the non-solvent proportion in spinning solution also increased the crystallinity of the final fibers. Electrospinning dopes were prepared by dissolving PVA polymers in the aqueous dispersion of PEDOT:PSS. Without using a toxic solvent, the hydrophilic conducting PVA nanofibers were successfully fabricated by optimizing the PVA contents in the aqueous dispersion. To measure the conductivity of the fabricated PVA nanofibers, the fibers were spun on an IDMA electrode and a yarn was formed. The fabricated fibers showed electrical semi-conductivity and charge mobility. Water insoluble conducting PVA nanofibers were obtained through an in-situ crosslinking of PVA polymers by adding a chemical cross-linking agent, glutaraldehyde (GA) in the PVA spinning dopes. The cross-linked conducting fibers showed slightly higher conductance than the pure PVA fibers and maintained good morphology after a soaking test in water. In addition, the conducting PVA nanofibers with functionally negative charges were electrospun using the mixture made with incorporating Poly(MVE/MA) polymers into the PVA/GA solution. The negatively charged nanofibers conducted as well.
Publications
- Cho, D., N. Hoepker, and M.W. Frey, Fabrication and characterization of conducting polyvinyl alcohol nanofibers. Materials Letters, 2012. 68(0): p. 293-295.
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