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Investigation of the electrospinnability of polymer solutions using tubeless siphoning Textile Engineering, Chemistry and Science Taslim Ur Rashid, Wendy E. Krause, Russell E. Gorga Department of Textile Engineering, Chemistry and Science, Wilson College of Textiles, North Carolina State University Materials and methods ¾ Electrospinning is a unique technique for fabrication of nanofibers ¾ Constant elongational flow of polymer solution is maintained from a reservoir ¾ An extensional force is applied by high electrical voltage ¾ A conductive substrate, normally grounded, serves as a collector 1. Effect of concentration of PEO solution (400k) on siphon height 1. Effect of concentration of PEO solution (400k) on siphon height of concentration of PEO Results and discussion Motivation and objectives ¾ Siphon height increases significantly with increasing MW of PEO ¾ Siphon height for PEO 5000k is four times higher than that of PEO 400k ¾ Different maximum siphon heights concentration for different MW of PEO (400k: 2%, 900k: 2%, 5000k: 1.5% ¾ Siphon heights for all runs (3-5) are remarkably consistent 2. Effect of molecular weight ¾ Maximum siphon height was observed for 2% (w/w) solution ¾ Siphonable range : 0.25-6% (w/w) ¾ Pipette with diameter at or above 0.66 mm shows maximum siphon height ¾ Consistency of data for multiple runs (3-5) is remarkable 5. Correlation between siphonable range and electrospinnable range C 0 C* C e * Siphonable range Beaded fiber Uniform fiber Electrospinnable range A. Electrospinnability of PEO solutions (MW: 400k) B. Electrospinnability of PEO solutions (MW: 900k) C. Electrospinnability of PEO solutions (MW:5000k) 2% solution: Beaded fibers 4% solution: Beaded fibers 6% solution: Uniform fibers 2% solution: Beaded fibers 3% solution: Beaded fibers 5% solution: almost uniform fibers (fewer beads) 2% solution: Beaded fibers 3% solution: Beaded fibers 5% solution: Uniform fibers 4. Electrospinnability of PEO solutions A. 2% solution B. 2% solution C. 2% solution A. 4% solution B. 3% solution C. 5% solution A. 6% solution C. 3% solution B. 5% solution ¾ PEO solution exhibits tubeless siphoning within the range of 0.25 and 6% ¾ ‘Jelly fish’ structure along siphon column at 2% for PEO 400k and 900k, and 1.5% for PEO 5000k ¾ No siphoning was possible at 6% for PEO 400k and 900k, and 5% for PEO 5000k ¾ For PEO 400k and 900k: beaded fiber at concentration 2-5% bead free fibers at or above 6% ¾ For PEO 5000k: beaded fiber at concentration 1.5-4% bead free fibers at 5% Future work ¾ Correlation between siphonable range and electrospinnable range for other water-soluble polymers such as polyacrylamide (PAM) and PAM-co-DADMAC ¾ Effect of addition of salts, surfactants, and PEG, temperature, pressure and solvents on tubeless siphoning ¾ Measuring extensional viscosity of polymer solutions from maximum siphon height measurement ¾ Using backlight imaging technique to correlate siphon pattern with solution concentration and pipette diameter References ¾ Electrospinning is a unique technique for fabrication of nanofibers ¾ Constant elongational flow of polymer solution is maintained from a reservoir ¾ An extensional force is applied by high electrical voltage ¾ A conductive substrate, normally grounded, serves as a collector Electrospinning ¾ Electrospinnable range specific to polymer ¾ Specific to molecular weight ¾ Polymer solution concentration ¾ Costly way of determining electrospinnable range 2. Challenges of electrospinning A B C Taylor cone ¾ Ruiter, F. A. A., Alexander, C., Rose, F. R., & Segal, J. I. (2017). Biomedical Materials, 12(5), 055009. ¾ Shabani, E., Rashid, T. U., Gorga, R. E., & Krause, W. E. (2020). Polymer Testing, 92, 106865. ¾ Chao, K. K., & Williams, M. C. (1983). Journal of Rheology, 27(5), 451-474. ¾ Thoppey, N. M., Gorga, R. E., Bochinski, J. R., & Clarke, L. I. (2012) Macromolecules, 45(16), 6527-6537. ¾ Fong, H., Chun, I., & Reneker, D. H. (1999). Polymer, 40(16), 4585-4592. ¾ Liu, X., Baldursdottir, S. G., Qu, H., Christensen, L. P., Rantanen, J., & Yang, M. (2015). Nordic Rheology Society Annual Transactions, 23, 225-229. Fig. A typical needle electrospinning setup 1. Electrospinning of polymer solution Fig. Tubeless siphoning of polyethylene oxide (PEO) solution Tubeless siphoning ¾ Tubeless siphoning, a unique property of non-Newtonian fluid, is a pure extensional flow ¾ Unlike Newtonian fluid, siphoning action continues even when the siphon nozzle is raised above the free surface of the fluid ¾ Viscoelastic stresses, resulting from stretching of the polymer molecules in solution, support the weight of the column 1. Tubeless siphoning of polymer solution 2. Factors influence Tubeless siphoning ¾ Molecular weight and concentration of polymer solution ¾ Entanglement of the polymer chains in the solution ¾ Applied extensional force Fig. SEM images of electrospun fibers of PEO solution A: PEO 400k, B: PEO 900k, C: PEO 5000k 0.43 mm Pipette 0.58 mm Pipette 0.66 mm Pipette 0.87 mm Pipette 1.91 mm Pipette ¾ Tubeless siphoning for a polymer solution also possible for a definite range of concentration ¾ Both the electrospinning process and tubeless siphoning involve high extensional flow ¾ Electrospinning is possible for a concentration range of a specific polymer Polymer concentration Electrospinnable Too high viscosity and entanglement Too low entanglement Two high concentration too high chain entanglement to draw the solution n t Two high concentration too high chain entanglement to form a siphon column t Two low concentration lack of chain entanglement Does not form siphon column l D ¾ Establishing a correlation between siphonable range and electrospinnable range for a polymer solution with different molecular weight ¾ Predicting electrospinnability of a polymer solution from tubeless siphoning ¾ Reducing the costly process of determining electrospinnability Objective of this work Two low concentration lack of chain entanglement Does not form continuous fiber l D 1. Tubeless siphoning of PEO solutions Fig. Tubeless siphoning setup for PEO solution with the arrangement of backlight imaging technique ¾ A series of concentrations (0.05 -10 w/w %) of PEO solutions with MW 400k, 900k, and 5000k were investigated ¾ Backlight imaging technique was used for measuring the siphon height for each solutions 2. Electrospinning of PEO solutions ¾ A needle electrospinning setup was used for electrospinning of all PEO solutions ¾ A constant flow rate, high electric voltage, and needle tip-to-collector distance were maintained Process parameters of electrospinning Flow rate (ml/h) Voltage (kV) Needle tip-to-collector distance (cm) 0.5 15 14 Pipette diameter (mm) Cross sectional area in m 2 (10 -7 ) Force in N (considering pressure -0.60 bar) 0.43 1.457 0.0087 0.58 2.628 0.0158 0.66 3.413 0.0205 0.87 5.959 0.0358 1.91 28.673 0.1720 Force at pipette tip Fig. Suction pressure: a -0.60 bar, pipette diameter: 0.87 mm 3. Siphonable range of PEO solutions Fig. PEO 400k, suction pressure: a - 0.60 bar, pipette diameter: 1.91 mm Jell fish formation region Jell fish formation ¾ Jelly fish formation for PEO solutions with concentration at or above 2 % for PEO 400k and 900k, and 1.5 % for PEO 5000k ¾ Siphon height decreases significantly at jelly fish formation region ¾ No siphoning at concentration 6 % for PEO 400k and 900k, and 5 % for PEO 5000k ¾ PEO solution exhibits tube nd 6 % ¾ ‘Jelly fish’ structure along siphon column at 2 % for PEO 400 k and 900 k, and 1 . 5 % for PEO 5000 k ¾ No siphoning was possible at 6 % for PEO 400 k and 900 k, and 5 % for PEO 5000 k ¾ For PEO 400 k and 900 k : beaded fiber at concentration 2 - 5 % bead free fibers at or above 6 % ¾ For PEO 5000 k : beaded fiber at concentration 1 . 5 - 4 % bead free fibers at 5 % Future work ¾ Correlation between siphonable range and electrospinnable range for other water - soluble polymers such as polyacrylamide (PAM) and PAM - co - DADMAC ¾ Effect of addition of salts, surfactants, and PEG, temperature , pressure and solvents on tubeless siphoning ¾ Measuring extensional viscosity of polymer solutions from maximum siphon height measurement ¾ Using backlight imaging technique to correlate siphon pattern with solution concentration and pipette diameter References ¾ Ruiter, F F F A . A . , Alexander, C . , Rose, F F F R . , & Segal, J . I . ( 2017 ) 7 . Biomedical Materials, 12 ( 5 ), 5 055009 . ¾ Shabani , E . , Rashid, T T T U . , Gorga, R . E . , & Krause, W . E . ( 2020 ) 0 . Polymer Testing, 92 , 106865 . ¾ Chao, K . K . , & Williams, M . C . ( 1983 ) 3 . Journal of Rheology, 27 ( 5 ), 5 451 - 474 . ¾ Thoppey , y y N . M . , Gorga, R . E . , Bochinski , J . R . , & Clarke, L . I . ( 2012 ) 2 Macromolecules, 45 ( 16 ), 6 6527 - 6537 . ¾ Fong, H . , Chun, I . , & Reneker , r D . H . ( 1999 ) 9 . Polymer, 40 ( 16 ), 6 4585 - 4592 . ¾ Liu, X . , Baldursdottir , r r S . G . , Qu, H . , Christensen, L . P . P P , Rantanen , J . , & Yang, M . ( 2015 ) 5 . Nordic Rheology Society Annual Transactions, 23 , 225 - 229 . less siphoning within the range of 0 . 25 an Conclusions Polymer Jelly fish formation (%) No siphoning (%) Beaded fiber (%) Uniform fiber (%) PEO 400k 2 6 2 6 PEO 900k 2 6 2 6 PEO 5000k 1.5 5 2 5 5. Correlation between siphonable range and electrospinnable range C 0 C* C e * Siphonable range Beaded fiber Uniform fiber Electrospinnable range A. Electrospinnability of PEO solutions (MW: 400k) B. Electrospinnability of PEO solutions (MW: 900k) C. Electrospinnability of PEO solutions (MW:5000k) 2% solution: Beaded fibers 4% solution: Beaded fibers 6% solution: Uniform fibers 2% solution: Beaded fibers 3% solution: Beaded fibers 5% solution: almost uniform fibers (fewer beads) 2% solution: Beaded fibers 3% solution: Beaded fibers 5% solution: Uniform fibers 4. Electrospinnability of PEO solutions A. 2% solution B. 2% solution C. 2% solution A. 4% solution B. 3% solution C. 5% solution A. 6% solution C. 3% solution B. 5% solution Fig. SEM images of electrospun fibers of PEO solution A: PEO 400k, B: PEO 900k, C: PEO 5000k Polymer Jelly fish formation (%) No siphoning (%) Beaded fiber (%) Uniform fiber (%) PEO 400k 2 6 2 6 PEO 900k 2 6 2 6 PEO 5000k 1.5 5 2 5 spinnability of PEO solutions Results and discussion
