The Preparation of Electrohydrodynamic Bridges from Polar Dielectric Liquids

The overall goal of this procedure is to create and study electro hydrodynamic liquid bridges between two containers filled with pure polar liquid. This is accomplished by first placing two beakers on insulating platforms, bringing them close and filling them with a pure polar liquid. The second step is to submerge pure platinum electrodes into each of the beakers.

Next, a DC voltage of about 15 kilovolts is applied between the electrodes, which creates a liquid bridge between the beakers. The final step is to separate the beakers by a few centimeters to create a free hanging liquid connection. Ultimately, these experiments show these liquid bridges have a well-defined operational stability, possess complex flow patterns, and emit thermal radiation based on high speed, visible and infrared video recording.

The implications of this technique extend to environmental science, process technology and microbiology because electric fields of the same magnitude are commonly found in nature and can be employed in the manufacturer of advanced materials. Though this method can provide insight into water, physics, chemistry, and biology, it can be applied to other systems as well. Alcohols, DMO acetone, glycerol any liquid with a strong permanent dipole moment and a low conductivity.

Prepare for setting up the experiment by wearing disposable powder free gloves to prevent contamination of the apparatus. Then check that any surfaces that will be in contact with the liquid under the study are clean. This video will focus on a horizontal bridge system composed of two adjustable height platforms on a level non conducting surface.

The two platforms should be the same height with one platform fixed in place. The other platform is mounted on a motorized linear stage that can travel at least 25 millimeters horizontally. An insulating acrylic sheet is fixed to the top of each platform so that it overhangs it at least 10 millimeters on all sides.

The sheets are thick enough to prevent breakdown at the planned maximum voltage. Now prepare the electrical apparatus. Start with a properly connected high voltage power supply with its output disabled.

Obtain a high voltage wire and a ground wire each with an alligator clip soldered to one end. Connect one wire to each of the high voltage and ground terminals of the power supply, keeping the alligator clips free. Next construct supports for the electrodes over each platform.

For each support clamp a rigid insulating rod to a ring stand so the rod extends horizontally over a platform. Place the high voltage wire over the support for the fixed platform. Secure the wire on the support so that the alligator clip is suspended above the platform.

Secure the ground wire on the other support so that its alligator clip is suspended over the moving platform. Next, attach a platinum electrode of greater than 99%purity to the ground wire alligator clip. Connect an identical platinum electrode to the high voltage wire.

The next step is to introduce the liquid here, deionized water. This experiment uses two 60 milliliter crystallizing dishes to hold the liquid. Fill each vessel to within one to five millimeters of the rim, about 67 grams of water before proceeding.

Use a conductivity meter to be certain that the conductivity is less than one microsiemens per centimeter. When ready, place one vessel on each of the insulating platforms. Arrange them such that they physically contact each other in one location in this case at the spouts.

Next, adjust the platform heights so that the liquid will only contact the platinum electrodes and not the alligator clips or wires. Then position the platinum electrodes in the liquid filled vessels so that they are a minimum of 15 millimeters from the contact position where the bridge will form if desired. Wet a pipette tip in the fluid and use it to wet the spouts as an aid to bridge ignition.

Before applying power to the experiment, check its electrical safety. Also, be certain that all surfaces are dry and that there is no liquid on the insulation platforms. With the power supply output still disabled, configure it for the experiment.

Set the current limit so as to provide no more than five to six milliamps of current. Also, make sure the power supply is set to provide zero volts. Then enable the output of the power supply and slowly to increase the voltage limit at a rate of about 250 volts per second.

Monitor the vessels and observe when bridge ignition occurs. The voltage at which this takes place is the approximate ignition threshold. Confirm bridge ignition by observing a steady stream of liquid flowing between the two vessels.

This high speed video of a similar experiment provides an example of bridge ignition and the establishment of a steady flow. Now, depending on the liquid, increase the voltage to 10 to 15 kilovolts and the current to about 1000 milliamps to tune the bridge for extension. When this is done, use the translational stage to move the vessel connected with the ground terminal.

Translate the vessel so that the bridge is extended one millimeter per kilovolt of applied voltage up to 25 millimeters over 30 to 60 seconds. Further tuning can be done if required. Bridge extension is demonstrated in this video clip of a comparable experiment.

A stable bridge can last for many hours to extinguish the bridge, disable the output of the high voltage power supply, and wait several seconds for the capacitors to discharge. Pick up a dead stick and approach the system. Use the dead stick to short the electrode holders.

Once this has been done, it is safe to handle any previously energized parts plotted. Here are the current voltage relationship for liquid water horizontal bridges. These bridges were obtained with 0, 5, 10, and 15 millimeter gaps as the voltage was ramped from zero.

A region of stability is bounded by a lower threshold below which no liquid bridge will form, and an upper threshold above which bridges are unstable. The insets labeled one through four show the rupture of a 15 millimeter bridge beyond the upper threshold. Most bridges with extension of five millimeters or more have a total power dissipation between 10 and 20 watts.

In this thermographic video, a horizontal water bridge is ignited in a system with an initial separation of zero millimeters. Once the bridge is established, current flow leads to swelling to a diameter of several millimeters. When the bridge is extended, the diameter undergoes low frequency fluctuations.

Visible surface waves provide evidence of high frequency oscillations in the system. When power is no longer provided to the system, the bridge reduces its diameter. Eventually, instabilities disrupt the bridge and form a string of droplets that migrate in the electric field After its development.

This technique paved the way for researchers in the field of water technology to explore how electromagnetic fields affect water quality. The bridge is a lab in its own right and opens new possibilities not previously available. After watching this video, you should have a good understanding of how to create a horizontal floating liquid bridge and thus a new liquid state to experiment with as described in the manuscript, these bridges can also be created vertically.