Electrospinning solution viscosity

It is well known that many parameters, such as viscosity, elasticity, conductivity, surface tension and distance between tip and collection screen, can influence the transformation of polymer solutions into nanofibers through electrospinning. Solution viscosity is one of the most important factors. Since both polymers have significantly different molecular weights, four different solutions of N6,6 with various concentrations were prepared. We used a mixed solvent consisting of formic acid and chloroform with the ratio of 75/25 (v/v). Table 4.1 shows the solution viscosities for each concentration of low and high molecular weight N6,6. 

Jun, Z., Hou, H., Schaper, A., Wendorff, J.H., and Greiner, A., 2003. Poly-L-lactide nanofibers by electrospinning influence of solution viscosity and electrical conductivity on fiber diameter and fiber morphology, e-Polymers, paper 9. Available at http //www. e-polymers.org/journal/abstract.cfm.abstractld=401 (accessed September 17, 2007). 

Experiments have shown that a minimum viscosity for polymer solution is required to yield fibers without beads, the solution of the PI.50 sample was determined the best electrospinning solution because of the continuous electrospinning process for this study. 

The relatively low molecular weight of conductive pol miers, decrease in specific viscosity of composites resulted a small nanofiber diameters. Interaction of PPy with matrix creates a decrease in viscosity, and that causes the smaller diameter of nanofibers. Moreover, electrospinning solutions of nanofibers with small average diameters have exhibited higher conductivity. 

The effect of aging time was also mentioned by Alio et al. [140], who qualitatively observed a continuous increment in solution viscosity during electrospinning of a sol containing TEOS and PCL, which highlighted the importance of finding the proper window of operation for spinnability. 

In order to obtain continuous polymer fibres, highly volatile solvents must be used in order to ensure complete evaporation of the solvent before the jet reaches the collector. The temperature and humidity in the electrospinning chamber also impact the rate of solvent evaporation. These, combined with the distance between the tip and the collector, determine whether the obtained polymer fibres are wet or dry, as well as influence their morphology. Fibres obtained at higher temperatures have heen found to have smaller diameters due to reductions in the solution viscosity, while increases in humidity result in the formation of pores in the fihres. Decreases in fibre diameter are also observed when higher voltages and solutions with higher conductivities are used. ... 

Polymer solution parameters are certain variables related to the physical properties of the polymer solution used for electrospinning nanofibers such as polymer concentration, polymer solution viscosity, polymer molecular weight, solution charge density, conductivity, volatility, surface tension, dielectric constant, and dipole moment. These variables are hard to be altered since changing one of those variables would consequently change some of the others. An example of that is the alteration in the polymer solution viscosity upon changing its conductivity (Pham et al. 2006). 

However, it was reported that exaggerated increase in solution viscosity would lead to complete drying of the first polymer droplet at the tip of the spinneret leading to prevention of evolving of the polymer jet and finally blocking the electrospinning process (Demir et al. 2002 Duan et al. 2004 Zong et al. 2002). 

Ffe. 7 a SEM midographs showing the inverse relationship between the polymer solution viscosity used during electrospinning and the amount of beaded regions detected in the corresponding electrospun nanofibers, b, c PCL electrospun nanofibers made from 9 to 5 % PCL solutions, respectively. Adopted from Huang et al. (2003) and Pham et al. (2006)... 

Zeng J, Haoqing H, Schaper A, Wendorff JH, Greiner A (2003) Poly-L-lactide nanofibers by electrospinning—influence of solution viscosity and electrical conductivity on fiber diameter... 

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