I am working with 10% PAN/DMF solution for making nanofibers. The problem is that the fibers are formed in the air gap before reaching the collector and after sometime the cone will be disappeared. I increased and decreased voltage, gap distance and flow rate but they did not work. Any idea about this matter?
Increase the separation between the needle and collector. For this purpose you have to increase the potential difference proportionately.
What is the humidity level , is the rig enclosed in a vacume, whats the temperature like. How many needles are you using, what guage is it, Have you tried using a different guage, There could be a dozen factors as to why this is happening. I would also like some input from Marc Simmonet ( Electrospinning consultant, if I may say ) here as he will have more insight on electrospining.
Hi. In my opinion the best ways to prevent this problem are:
1. Please reduce humidity and temperature of environment
2. Adjust voltage in lowest grade
3. Adjust flow rate in lowest rate
4. Clean head of needle during spinning to prevent solidification
The ES is taking place in a not completely closed box under the hood. The temperature is around 23 C and the humidity is around 65%. We use one needle (gauge 20) in horizontal configuration.
Hello,
I may assume that your PAN has a molecular weight of 150,000 g/mol. (i.e. 10wt% PAN solution in DMF would have a viscosity of around 0.3 Pa.s).
Regarding the problem that you've got, it is the high level of RH% that causes this issue. That's because DMF is a solvent of PAN while water is not, then when the humidity is too high, the system (polymer +solvent + nonsolvent) passes to the so called "meta-stable region" where phase separation takes place. This leads to reduce the evaporation rate of DMF and the surface tension of the jet will still higher. Consequently, a competition between Rayleigh instability and bending instability will occur. Meanwhile, under the influence of the electric field intensity (kV/cm) the jet accelerates and no enough time is available for the jet to reduce its surface tension. Overall, a continuous wet jet is yielded.
Thus, the first think to do is to reduce the relative humidity. If you work in a humid environment, you can control the RH by enclosing the booth and then using a reasonable quantity of silica particles to adsorb and then to reduce the humidity.
you may set the electrospinning parameters as follows:
* Feed-rate : 0.2 ml/min
* Voltage : 11-13 kV
* Working distance: 20 cm
*Relative humidity: around 30 %RH
Another point, you may assure the homogeneity of your solution!!
As per my suggestion, it seems that there is no problem in applied voltage, viscosity and humidity condition, but you should focus on the drum collector speed and needle to collector distance. Also, in your case, it seems that nanofibers evolve through needle tip, but if your collector speed is not precise then there will be no uniformity in charge on the surface of the drum collector. If the drum collector speed is high then collection of fiber will be disturbed due to uneven charge distribution, this makes fibers to form between the tip and the collector but it won’t get deposited properly on the collector. Hence , concentrate on drum collector speed , gradually tune the speed of the drum , soon you will notice a change in the deposition of fiber, also try to reduce the distance less than 15 cm ( this parameter is very important and vary as per the individual samples ) , all the best.
Thanks to everyone.
Dear Vikram, Dear Sliman, I am working with static collector, not a rotating drum. Therefore I think the problem is with RH.
Do you have any idea about the proper gauge for this spinning?
Dear Mehrdad ,
In such case , i agree with the answer given by [ Sliman Almuhamed ] , these factor will decide your requirement . Specifically, the homogeneity of solution, gauge of needle should be fine tuned along with RH . Also , just for precautionary step , kindly check the moisture content in your solvent , procedures are available for purification of DMF.
you have to concentrate,
1.viscosity of ur soln
2.distance between needle and collector
3.voltage
4.flow rate
Dear Mehrdad,
I'm using a 22 G needle for 10wt% PAN solution in DMF !!
Best regards
I would go for a mixture of DMF with a non solvent. Lets say 1:10 v:v.
Dear Friends, I increased the concentration to 12 % and reduced the RH to 40-50 %.
I also switched to rotating drum instead of stationary collector and now everything is quite OK.
Thanks everybody
I had also face the same problem.This problem occurred due to high RH%.
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