Author: Charles Keely
Project: Get Wet
September 30th, 2018
For my first individual project, I conducted the classic “milk, food coloring, and dish soap” experiment, which is a simple, yet effective demonstration of the Marangoni effect. The “Get Wet” assignment was our first photography/video production and it also happened to be the first time that I had ever used a DSLR camera. At the time of the experiment, I was unfamiliar with many of the functionalities of video capture, including how to manually focus the camera. Despite my naivety, I was able to capture some interesting flow patterns with fairly decent focus. If one were to attempt the experiment themselves, I highly recommend using manual focus, as well as informing any participants about how to effectively stay outside of the frame. Although my friends Teli Stathopolous and Spencer Tyson were a great help while conducting the experiment, I did not properly inform them of a procedure that would completely take them out of the shot, so we had some minor issues with the shots.
The Marangoni effect displayed in this particular example is due to properties of surface tension between milk and dish soap. Dish soap has a lower surface tension than that of milk, and as dish soap is considered a surfactant, a substance which can modify the surface properties of a substance, it lowers the surface tension of the milk in the immediate area where it is dropped by dissolving the fat molecules of the milk (Buddies 2014). The surrounding milk, yet untouched by the dish soap, still has a higher surface tension than the soap. Because of this, the surrounding milk pulls on the low-surface-tension area of the milk/dish soap. This is why the dish soap spreads in all directions from the initial point of contact between the milk and dish soap.
The food coloring moves in the same direction as the milk which allows one to easily see the otherwise imperceptible movement of the milk. Since I conducted some experiments with multiple drops of soap hitting the milk at once, some abstractions occurred as the individual outward movements would collide, causing smaller versions of the greater Marangoni effect to appear all over the plate.
The video is composed of two separate experiments. Both experiments used the same materials: 2% milk, McCormick assorted food coloring, Dawn dish soap, and an 8 x 8 black plate. Both experiments were shot by a Nikon D3400 (which is a DSLR) with a Nikon 18-55 mm lens and an XIT telephoto lens add on. The shots were zoomed in at approximately 45 mm. The video was captured at 1080p at 60 fps.
In the first experiment, two drops of each color: red, yellow, green, and blue were dropped in the middle of the plate with milk. Then, a drop of dish soap was dropped on the area with the food coloring from about four inches above the plate from a q-tip. This resulted in a quite quick and abstract explosion of movement. This shot is the last shot shown in the video.
In the second experiment, two drops of yellow and red were placed near the bottom of the plate and two drops of blue and green were dropped near the top of the plate in parallel fashion. Then, two separate q-tips that were dunked in dish soap were plunged into the areas of the food coloring for about 10 seconds. This caused two separate Marangoni effects to occur and collide, causing several Marangoni flows to pop up in one great mixture.
In both videos, I sought to capture as much of the colors as I could, so I framed the video such that only the milk was visible. The lens was quite close to the object, around about a foot away. However, for the intro shot, I took a picture of the aftermath of the second experiment from above and animated the liquid area using a program called Fantamorph. The technique to create the animation is called the George Redhawk technique, and it takes advantage of the way that photo morphing programs work to create an infinite flow. The rest of the video was heavily edited in order to make the flow work with the music, both by using fast and slow motion as well as using purposeful cuts to take out any footage of mistakes that we made during the experiment.
The videos reveal the underlying complexity of the Marangoni effect, particularly in the collision experiment. I am quite pleased with how complex and abstract the flows ended up. However, I was slightly disappointed with the colors schemes that occurred during the experiments. If I were to repeat the experiment, I would experiment with making more visually pleasing color schemes because there was a lot of color clashing going on. Also, at the time of the video, I was unfamiliar with the manual focus which could have made the image far sharper had I known how to use it.
Science Buddies. “Surfactant Science: Make a Milk Rainbow.” Scientific American, 13 Mar. 2014, www.scientificamerican.com/article/surfactant-science-make-a-milk-rainbow/.