Fast Imaging Technique to Study Drop Impact Dynamics of Non-Newtonian Fluids

The overall goal of the following experiment is to study the impact dynamics of non-Newtonian droplets of liquid metals and dense granular suspensions using a fast imaging technique. This is achieved by setting up a fast camera facility to visualize the instantaneous dynamics when droplets hit a surface. As a second step, perform a series of impact experiments of liquid metals to provide information about how the oxidation induced surface elasticity affects the spreading radius.

Next, perform impact experiments with dense suspensions to investigate their splashing onset and spreading dynamics. Results are obtained that show different fluid parameters, such as effective surface tension, viscosity impact velocity and suspended particle diameter together govern the impacts dynamics of non-Newtonian droplets. This method can help answer key questions in the field of dense suspensions, such as when the behavior of a system can be described by its global properties or when individual particles have to be taken into account.

Though this measured can provide insight into the impact dynamics of complex fluid. It can also be applied to the observation of other processes that include fast dynamics, such as the formation of fracture states, solid pinch off of drop liquid drops, and the fast particle movement in granule systems Begin by preparing the imaging setup. One component is a vertical track capable of supporting a syringe pump mount, the syringe pump so it can be moved to different heights to alter the test fluid free fall height.

Next to the track is a frame that supports a clean glass plate that serves as a horizontal impact plane. Make sure the surface of the plate is leveled horizontally. Position an inclined reflective mirror beneath the glass surface to visualize the drop impact from below.

Next, attach opaque white paper above the glass plate to reflect light, to aid bottom viewing to image liquid metal impact. Place a transparent paper diffuser opposite the viewing direction to aid side view imaging. Then place a light source in the region behind the diffuser.

Turn on the light sources to uniformly illuminate the impact region. Now level a camera with an appropriate lens on a tripod so that it can image the surface. Connect to the camera to a computer used for control and display.

Begin sample preparation with gallium indium utic that has been stored in a sealed container At room temperature, use a pipette to extract three milliliters from the container. Obtain an acrylic plate and extrude the gallium indium UTA onto it. Wait 30 minutes for the sample to be fully oxidized in air.

A thin layer of oxidized skin will completely cover the sample surface. Take proper precautions for working with hydrochloric acid and prepare a 200 milliliter acid bath in a TER vessel. The concentration of the bath is an experimental parameter.

Put the sample in the acid bath with the sample in the bath. Employ a TER to shear it at 60 revolutions per second for 10 minutes. Once the acid pre washes done, remove the bath from the ReMeter.

Use a plastic two milliliter syringe with a one to two millimeter steel nozzle tip to recover the sample extract 1.5 milliliters of gallium indium actic from the bath. The sample is now ready for use and experiments. Mount the syringe on the syringe pump sample preparation for dense suspensions.

Experiments begins with a commercial syringe cut off its end to use it as a cylindrical tube for dispensing the suspension To fill the syringe. First, obtain a container of water. Place the end of the syringe in the water, pull the piston back to fill it, making sure there is no air bubble.

Next, hold the syringe with the open end up. Put spherical zirconium dioxide or glass beads into the syringe until it is full, allowing the water to spill out. Use a razor blade to remove extra wedded particles from the top to keep that end flat.

Flip the syringe and mount it on the pump surface. Tension will prevent the particles from falling out. Before recording videos, take steps to adjust the imaging and lighting systems and calibrate the spatial resolution.

First, start the syringe pump to push out the fluid at a rate of 20 milliliters per hour. Wait for the fluid here, a dense suspension to detach from the syringe and fall to make a test impact on the glass surface. Once the impact has occurred, turn off the syringe pump.

Then adjust the camera position and orientation until the splat is shown on the monitor. Next, set the reproduction ratio of the image to one to one and modify the working distance so the image is in the focal plane with the camera set to a frame. Greater than 6, 000 frames per second vary the aperture size, exposure, time, and lighting angle to obtain the best quality image.

Once the camera settings are found, place a ruler in the field of view on the monitor. Use the ruler to calculate the spatial resolution by counting the number of pixels that fit across one centimeter. Make sure there is no difference in resolution between horizontal and vertical directions.

After calibrating the imaging system, restart the syringe pump at 20 milliliters per hour. At the same time, ready the camera controlling software to monitor the impact process Before recording data. Practice watching carefully as the drop starts to form to allow manual triggering of the camera at the moment the drop detach from the nozzle.

After data is recorded, edit the video to the portion containing the impact and save it as an image sequence for analysis. The fast imaging technique has been used to study the impact of gallium indium actic with different oxide. Skin strength determined by acid.

Pre-wash shown here are frames showing the spreading of three different preparations as they impact a glass surface. Each drop fell from the same nozzle height and hit with a speed of approximately one meter per second. The initial drop diameter was 6.25 millimeters with no pre-wash.

An oxide skin prevents the fluid from relaxing the surface energy resulting in a nons spherical shape during the falling stage, washing the samples and acid reduces the oxide and weakens the skin effect. At strong enough acid concentrations. No difference is observed between the gallium, indium and ordinary fluids.

The data allows demonstration of the transition from the capillary regime to the viscous regime. The data collapses to a single curve when the ratio of the initial to final radius pm divided by the Reynolds number to the one fifth power is plotted against the ratio of an effective Weber number and the Reynolds number to the four fifths power splash onset in dense suspension has been studied in the regime where viscous dissipation is negligible compared to inertial effects. This is the splashing phase diagram for different particle densities and radio whose product is along the horizontal axis.

The vertical axis is the particle Weber number defined in the manuscript. The red circles indicate that a splash was always found. The inset shows a typical splash image.

Blue dots correspond to no splash found. The second inset is an example of a nons splash image. Cases where both splash and no splash were found are indicated by green squares.

The experiment was repeated 10 times for each point. The results are consistent with a critical Weber number of about 14 plus or minus two. While attempting this procedure, it's important to practice making your samples and to determine the packing fraction frequently so that you're confident that you can make your samples consistently.

This will ensure that your experimental results Will be reproducible after its development. This technique paved the way for researchers in the field of complex fluids to explore the impact dynamics of varied liquid systems.