**2.4.5 Viscosity**

The role viscosity is in the stabilization of the jet and diameter of the jet produced. In high viscous liquid, the jet is stable for larger portion of the length but also produces the thicker diameter. This is due to charge mobility, which is reduced significantly in high viscosity liquid, and causes decrease in conductivity.

#### **2.4.6 Surface tension**

The formation of the jet occurs when the electrical forces overcomes the surface tension on the apex of the meniscus. The required applied voltage will be increased with increase in surface tension of the liquid.

#### **2.5 Operating envelop**

In order to perform the patterning of any liquid containing nanoparticles, the operating parameters of flow rate corresponding to applied voltage for stable cone-jet has to be

Electrohydrodynamic Inkjet – Micro Pattern Fabrication for Printed Electronics Applications 553

(a)

(b) Fig. 6. (a) Schematic of lab developed system and (b) Photograph of the electrohydrodynamic

Electrohydrodynamic printing can be divided in two different categories, depending on the ejection of liquid from the nozzle, continuous and drop-on-demand. The experiment setup

For continuous printing, ink containing copper nanoparticles is used. Initial patterning is performed by using metallic capillary of internal diameter of 210µm and outer diameter of

inkjet system used for patterning

for both the modes is same.

**4. Electrohydrodynamic printing** 

**4.1 Continuous electrohydrodynamic printing** 

determined. Starting with high flow rate formation of stable cone-jet is determined by applying different voltages. Then for each flow-rate, the range of applied voltage is investigated at which the stable cone-jet is observed. This creates an operating envelop of certain liquid in electric field and voltage domain. Based on the operating envelop, behavior of the jetting is observed and parameters for patterning are determined. Operating envelop along with different modes of electrohydrodynamic jetting of the liquid containing Copper nanoparticles is shown in figure 5.

Fig. 5. Operating envelop (stable con-jet region) along with different electrohydrodynamic jetting mode of ink containing copper nanoparticles, using metallic capillary of inner diameter 410µm, external diameter 720µm and capillary to ground distance is 2mm.

#### **3. Patterning setup**

For direct patterning through electrohydrodynamic printing, lab developed system was used. The equipment used for patterning is consistent of high voltage power supply, function generator, 5 channel voltage distributor, syringe-pump for ink supply, X-Y stage with motor controller, substrate holder, high-speed camera and nozzle holder with Z-axis controller, which are connected to National Instruments PXI-1042Q hardware system. Which is controlled through lab made software based on LabView. Positive potential is applied to the nozzle head while ground is applied to the conductive plate. The substrate is place on the top of metallic ground plate. The schematic of experiment setup along with the actual system is shown in Figure 6.

determined. Starting with high flow rate formation of stable cone-jet is determined by applying different voltages. Then for each flow-rate, the range of applied voltage is investigated at which the stable cone-jet is observed. This creates an operating envelop of certain liquid in electric field and voltage domain. Based on the operating envelop, behavior of the jetting is observed and parameters for patterning are determined. Operating envelop along with different modes of electrohydrodynamic jetting of the liquid containing Copper

Fig. 5. Operating envelop (stable con-jet region) along with different electrohydrodynamic jetting mode of ink containing copper nanoparticles, using metallic capillary of inner diameter 410µm, external diameter 720µm and capillary to ground distance is 2mm.

For direct patterning through electrohydrodynamic printing, lab developed system was used. The equipment used for patterning is consistent of high voltage power supply, function generator, 5 channel voltage distributor, syringe-pump for ink supply, X-Y stage with motor controller, substrate holder, high-speed camera and nozzle holder with Z-axis controller, which are connected to National Instruments PXI-1042Q hardware system. Which is controlled through lab made software based on LabView. Positive potential is applied to the nozzle head while ground is applied to the conductive plate. The substrate is place on the top of metallic ground plate. The schematic of experiment setup along with the

nanoparticles is shown in figure 5.

**3. Patterning setup** 

actual system is shown in Figure 6.

Fig. 6. (a) Schematic of lab developed system and (b) Photograph of the electrohydrodynamic inkjet system used for patterning
