I was trying to spin a 20%Polystyrene solution (solvent used is DMF). One problem I have been facing recently is electrospraying, When I start the electrospinning process fibers form in the beginning for about half an hour, and then suddenly electrospraying starts happening, sometimes very heavy spraying. Note that I do not change any parameters in between so I am appalled as to what causes the sudden electrospraying. I look forward to any suggestions.
Dear Aisha,
You mentioned that you conduct electrospinning for about half an hour and you did not change any parameters. Consider the effect of insolation of the collector by the deposited fibers. Spraying may occur due to the fact that this isolation of collector causes lovering of the electric field strength. Try change the values of the voltage or maybe stop the process and change the collector for the new one.
Best regards,
Michal W.
Dear Aisha,
You mentioned that you conduct electrospinning for about half an hour and you did not change any parameters. Consider the effect of insolation of the collector by the deposited fibers. Spraying may occur due to the fact that this isolation of collector causes lovering of the electric field strength. Try change the values of the voltage or maybe stop the process and change the collector for the new one.
Best regards,
Michal W.
I think that might just be the cause Michal, appreciate your input, thank you.
Hi Aisha,
I agree with the opinion from Michal, but in my opinion, another possibility, is there any variation of the room conditions like temperature or does the solution change with time? The main difference between electrospraying and electrospinning is the properties of the fluids such as viscosity and viscoelasticity.
Best,
Ting
Thanx for the suggestion Ting, I actually had the same thought regarding temperature. I used a temp of 40C in the setup(DMF has a boiling point of 150C, so I presumed that if I don't apply temp the solvent wouldn't completely evaporate resulting in thick fibers). But, note that the temperature is set from the beginning so if that was causing any changes in viscosity it would be right from the beginning not after some time. Perhaps the prolonged high temperature causes the viscosity to decrease?
Well, I am not sure whether the solution you used is able to change with time. I suggest you can use stirrer to mix it in your experimental process if it is possible. I think non-Newtonian liquids are sometimes sensitive with room conditions. Besides, the collection process is also very important for long time operation.
i agree with Ting Si. check the solubility of the solution. during the spinning time the polymer may tend to deposit if the polymer is not miscible with the solvent. if it happens then it may cause electrospraying.
I think this may be due to incomplete solubilization of the polymer in the electrospinning solvent such that the polymer deposits after some time, thereby decreasing viscosity of the solution. Try leaving your polymer solution overnight for solubilization.
Dear Aisha,
This problem can arise when there is block in the needle which may be formed due to evaporation of solvent or drying of solute. So make the solution homogenous by overnight stirring and try to change the needle diameter to a wider gauge. The rate of pulling force of solution and rate of evaporation by temperature should match.
Check the viscosity of the solution before spinning and after its spraying, from which you can understand the activity of temperature on solution viscosity.
Aisha, I can't say for sure what your problem is. But we also sometimes see electrospinning start to behave strangely over prolonged periods. Though we haven't always been able to tell for sure, usually for us the problem is electrical isolation of the collector and/or buildup of waste fibers elsewhere in the setup (e.g. on the walls of the box we spin in.) Wiping the setup down with some conductive cleaning solution like 70% ethanol can help set things straight again. However, if you don't see much waste, I'd just try increasing the voltage drop between the two electrodes like Michal said. You can also try deionizing the construct on the collector if you think charge may be trapped on the surface. We use the football goal-shaped deionizers that you see by balances.
If you're worried your solution is separating, it's possible to get a stir bar into the syringe. Wrap a stir plate in aluminum foil and set it up as far back from the needle as you can while still getting stirring. It's not ideal, but it works surprisingly well in a pinch. Also good in case you ever need to spin particles with your polymer.
Exist many factors that could explain electrospraying instead of electrospinning. Some may be the concentration of the polymer or its molecular weight, solvents you use, etc. it all influences conductivity, surface tension, and viscosity. You must make several formulations to establish a regular beam and a deposition of homogeneous filaments. If the Taylor cone is formed you will have to play with the distance between the tip and the collector, and the flow. The voltage will depend on the formation and stability of the Taylor cone.
Ideas you can apply: -establish the right concentration. Maybe 20% is very high. -Try a mix of THF:DMF 3: 2 or 2: 3. -Change the tip size. -Use high molecular weight polymers.
I hope I've helped. Good luck!
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