Introduction
Anti-bubbles (fig. 1) are small spherical fluid formations that consist of a pocket of liquid surrounded by a film of air surrounded by a volume of liquid (Hughes and Hughes, 1932; Strong and Connet,1974; Tufaile et al, 2003).
Figure 1: Photograph of anti-bubbless created in the laboratory (left) compared to a schematic diagram of the structure of an antibubble (right).
Although the existence of antibubbles has been known since the 1800’s, little scientific work on their formation and properties has been conducted (Strong and Connett, 1974; Dorbolo et al, 2003). Anti-bubbles form from water droplets or globules, which, because of the presence of surfactant molecules or the presence of electrical charge, are separated from the surface of the medium by a small layer of air. As globules are poured onto the surface of the medium, they are driven beneath the surface of the medium by inertia, yet kept separate from the medium by a thin surrounding film of air (Figure 2).
Figure 2: A globule is poured from a beaker onto the surface of a medium (1) and driven down to form an anti-bubble (2).
Aspects of the formation and properties of anti-bubbles have been recently reported in amateur science forums on the Internet for those interested in creating them for educational demonstrations or personal amusement (Beatty, 1997; Nadovich, 1999; Fritz, 2003). Fritz (2003) and Beatty (1997) report that the formation of anti-bubbles is greatly affected by the electrical potential between the falling globule and the accepting medium.
The goal of this research was to quantify the effect that electric charge may have on the formation of anti-bubbles. It was hypothesized that if an electric charge is applied to a system where anti-bubbles are forming, then anti-bubble formation will be reduced or inhibited.
Materials and Methods
A tank measuring 19 cm x 19 cm x 20 cm was constructed by hand from 6mm plate glass and silicone aquarium sealer and placed in a 1 gallon Pyrex baking pan. One face of the tank was 1 cm lower than the other three to allow for an overflow into the Pyrex pan where solution was returned to the tank by an aquarium pump connected to an automotive fuel filter (fig. 3).
Figure 3. Water flow within anti-bubble tank. The red line denotes the flow of water through the filtration system.
This cycle constantly filtered the water in the tank during all trials, assuring that there would be a minimum of particle contamination to interfere with the procedure.
The medium used during this procedure was a tap water-dish soap (Liquid Joy) solution with a volume fraction of 0.1%. Soap was added to the solution as a surfactant to create an environment where anti-bubble formation was more likely to occur.
Anti-bubbles were created during each trial by using a 50 mL beaker to collect approximately 40 mL of soap solution medium from the tank and pouring drops of the solution back onto the surface of the medium in the tank from a height of approximately 1 cm using the pour spout on the 50 mL beaker. When water in the beaker was exhausted, the beaker was refilled and this process was continued until the time period of the trial had elapsed.
The effect of charge on the formation of anti-bubbles was tested using four different electrical circuit options: open, grounded, capacitor, and 6V battery connected to the system via a four-way switch. The switch was incorporated into the system through a bare copper wire in the tank’s medium and a copper foil rim on the 50 ml beaker used to pour the medium during anti-bubble formation. During each trial, the switch was engaged on only one setting chosen at random (Figure 4).
The first setting on the switch was the control setting, which left the circuit open and therefore the beaker was not attached to the circuit. The second setting was the first experimental setting, which placed a six-volt battery in the circuit between the beaker and the tank. The third setting on the switch was the second experimental setting, which placed a 15-ųF capacitor between the beaker and the tank. This setting was used to determine if a capacitor was able to store and thus remove any static charge from the system. The fourth setting on the switch was the third experimental set, which grounded the beaker by attaching it to a water pipe. This setting was used based on the same logic behind the capacitor, except with the earth absorbing any electrical charge.
During each one-minute trial, there were three assistants aiding the experimenter. The first aid recorded the time with a stop watch and randomly engaged the switch by selecting a slip of paper with a number on it, each number corresponding to a setting on the switch. The switch itself was blocked from view and the setting was not revealed during the trial so that experimenter bias would be minimized. The other two aids counted the number of anti-bubbles created from the time the first aid signaled the experimenter to start until the one-minute trial was over. Each trial consisted of the experimenter constantly pouring globules onto the surface of the medium for the duration of the trial, stopping occasionally to refill the beaker. The experimenter wore rubber gloves during all trials. Only trials where the aids concurred on one set number of anti-bubbles were accepted.
Results.
Of the 46 trials performed, 11 were control sets (open), 12 were experimental set 1 (battery), 12 were experimental set 2 (capacitor), and 11 were experimental set 3 (grounded).
In the control (open) trials, a mean of approximately 47 anti-bubbles were produced per trial. In the first experimental set (battery), a mean of 4 anti-bubbles were produced per trial. In the second experimental set, a mean of 52 anti-bubbles were produced per trial and in the third experimental set, the mean number of anti-bubbles created was 42. A one-way ANOVA test of the data revealed that the mean number of anti-bubbles in the first experimental set (battery) differed significantly from the other sets allowing for rejection of the null hypothesis that the number of anti-bubbles created with the battery circuit was equal to the others (p < 0.01). All other comparisons showed now significant difference between means (table 1).
Table 1: Number of antibubbles created under each experimental condition.
Control(Open Switch) / Experimental 1
(Battery engaged) /
Experimental 2
(Capacitor Engaged)
/ Experimental 3(Beaker Grounded
43 / 6 / 44 / 57
55 / 4 / 40 / 28
77 / 3 / 20 / 27
50 / 4 / 49 / 34
55 / 5 / 44 / 60
30 / 2 / 50 / 47
29 / 4 / 62 / 57
60 / 4 / 82 / 6
30 / 4 / 44 / 34
38 / 6 / 42 / 52
46 / 2 / 70 / 56
4 / 74
Mean / 46.6 / 4 / 51.8 / 41.6
ANOVA / p> 0.01 / p < 0.01 / p> 0.01 / p> 0.01
Discussion and Conclusions
In amateur websites, electric charge was reported to influence anti-bubble formation and was presumed to result from triboelectric processes either between the experimenter and the surroundings or between the falling globule and the air (Beatty, 1997; Fritz 2003). Preparatory equipment tests for the experiments conducted here also suggest that static electric charge may inhibit anti-bubble formation since certain individuals would be unable to produce anti-bubbles at one point in time, only to return and find that they suddenly were endowed with the ability to produce them (Pajonk, 2004). Such results are consistent with an individual occasionally obtaining or discharging static electricity while moving around a classroom, although further studies would be needed to confirm this.
In the case of the experiments conducted here, an electrical potential was created using a direct current source and did not result from the triboelectric processes commonly associated with static electricity. Exactly how this inhibitory effect is achieved was not determined during the experiment, but it may involve an alteration of the surface tension of the medium, globule or both since decreased surface tension is reported as an important factor for the formation of anti-bubbles (Strong and Connett, 1974; Dorbolo et al, 2003). Surface tension is caused by the adhesion of water molecules resulting from the electrical dipoles possessed by the water molecules themselves (Zumdahl, 2003), so it is conceivable that the addition of electrical charge might alter this process. Finally, the decreased number of anti-bubbles produced during the 6V battery trials may have been the result of the anti-bubbles themselves acting as capacitors and storing an electric charge obtained from the battery. This idea is supported by Dorbolo et al (2003) who stated that falling globules had the ability to act as capacitors by absorbing charge from triboelectric processes and that this electrical potential difference destabilized the air film surrounding a forming anti-bubble.
The ability to actively inhibit the formation of anti-bubbles may have several applications. The surface tension of blood is lower than that of water or saline solution, and many hemodialysis and heart-lung machines employ components that require blood to fall through air as droplets on a surface (Esitashvili, 2002). It is possible that such systems might allow anti-bubbles to form in fluids that can be found in close proximity to the human bloodstream. The effects of anti-bubbles on the human body are currently unknown, but from the effects of a bubble in the bloodstream, it can be assumed that they would not be positive. Although anti-bubbles are not long-lived (approximately 2 min.), when they are destroyed, a conventional air bubble is formed (Dorbolo et al 2003), and bubbles in the human blood stream are known to have negative effects (Book, DATE). If the results of this study can be applied to medical and biomedical fluids, any possible threat of anti-bubbles to the human body might be eliminated by disrupting the formation of anti-bubbles where they are undesirable.
Future research on anti-bubbles holds many possibilities. Based on the reasoning discussed previously, it would be practical to repeat this procedure in a solution similar to human blood or to determine if hemodialysis and heart-lung machines are even capable of creating anti-bubbles. It may also be useful to test the current ultrasonic bubble detection devices employed by such machines to determine their ability to detect anti-bubbles or how bubble detectors/fluid volume calibration devices in other systems might interpret the small volume fraction of air that they contain.
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