Fiber diameter is usually the first property researchers try to control, because it influences pore size, surface area, mechanical behavior and — ultimately — performance. Electrospinning offers many levers. The challenge is that they interact, so it helps to understand the typical direction of each effect before designing experiments.
Solution parameters
1. Polymer concentration and viscosity
This is generally the strongest lever. Higher concentration means more chain entanglement and higher viscosity, which resists stretching of the jet and produces thicker fibers. Too low a concentration and the jet breaks up into beads or droplets.
2. Molecular weight
At the same concentration, a higher-molecular-weight polymer entangles more easily. This makes bead-free fibers achievable at lower concentration, and typically shifts diameter upward.
3. Conductivity
A more conductive solution carries more charge, so the jet experiences stronger stretching forces. Adding a small amount of salt is a common way to obtain thinner and more uniform fibers.
Process parameters
4. Flow rate
Feeding more solution per unit time generally gives thicker fibers, and at high flow rates the solvent may not fully evaporate before reaching the collector. Lower flow rates are usually preferred, provided the Taylor cone stays stable.
5. Applied voltage
The effect of voltage is less straightforward. Higher voltage increases the stretching force, but it also pulls more solution from the needle. Depending on the system, diameter can decrease, stay similar or even increase. The most reliable guide is cone stability: aim for a steady cone, not the maximum voltage.
6. Tip-to-collector distance
A longer distance gives the jet more flight time to stretch and dry, which often reduces diameter and prevents fibers fusing together. Too long a distance, however, weakens the field and can destabilise the jet.
Ambient parameters
7. Humidity and temperature
Relative humidity affects solvent evaporation and can create surface pores on fibers. Temperature lowers viscosity and speeds evaporation. Neither is a convenient control knob, but both must be recorded — they are a frequent cause of results that cannot be reproduced.
| Increase in… | Typical effect on diameter |
|---|---|
| Concentration / viscosity | Larger |
| Molecular weight | Larger (and fewer beads) |
| Conductivity | Smaller |
| Flow rate | Larger |
| Voltage | System-dependent |
| Tip-to-collector distance | Often smaller |
Fix your solution first, then explore flow rate and voltage around a stable operating point. Measure at least 100 fibers per sample from SEM images and report the mean and standard deviation.
