Laser-induced onset of electrospinning

We present a method to start electrospinning from a polymeric drop. This method uses a pulsed laser which is focused inside the drop close to the liquid surface. The pulse cavitates the liquid and produces a protrusion from the tip of the drop. The protrusion narrows by drainage and vertical stretching, thus concentrating the electric field and increasing the charge density until it overcomes the surface tension and produces the electrified jet. This approach can reduce the required value of applied electric field to half of its value required to start convectional electrospinning from a stationary drop.

Figure 1

(Color online) Schematic depicting the setup for laser-initiated electrospinning. Not drawn to scale.

Figure 2

The sequence of frames depicts the laser-initiation of the electrified jet, from a drop of $2\text{wt}\mathrm{\%}$ (PEO) solution. Frames are shown at $t=0.089$, 0.178, 0.444, 0.711, 1.11, 1.69, 2.36, 3.33, 4.22, 4.53, 4.78, 10.5, and 400 ms after the laser pulse visible in the first frame. The last frame shows the jet shape much later, at 0.4 s after the laser pulse. The applied electric field was 3000 V/cm. Scale bar is 1.0 mm.

Figure 3

(a) Close-up images of the onset of the microjet, from the same sequence as in Fig. 2. The frames are $44.4\mu \text{s}$ apart. Scale bar is 0.5 mm. (b) The increase in tip curvature vs time approaching the microjetting. The tip-curvature is normalized by the undisturbed drop curvature.

Figure 4

(a) Jetting for a laser spot very close to the surface of the drop $\left(<100\mu \text{m}\right)$. The first 5 frames are spaced by $44.4\mu \text{s}$ with the last frame $667\mu \text{s}$ after the laser pulse. The applied electric field was 3000 V/cm. (b) Jetting from a 10 mJ laser pulse. First 8 frames are spaced by $dt=20\mu \text{s}$, with the last one 2.4 ms later. Scale bars are 1 mm.