About bubbles

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overview

… soap bubbles are physical examples of the complex mathematical problem of minimal surface …

… they will assume the shape of least surface area possible containing a given volume …

… a true minimal surface is more properly illustrated by a soap film, which has equal pressure on inside as outside, hence is a surface with zero mean curvature …

… a soap bubble is a closed soap film: due to the difference in outside and inside pressure, it is a surface of constant mean curvature …

… while it has been known since 1884 that a spherical soap bubble is the least-area way of enclosing a given volume of air (a theorem of h schwarz) …

… it was not until 2000 that it was proven that two merged soap bubbles provide the optimum way of enclosing two given volumes of air of different size with the least surface area …

… this has been dubbed the double bubble conjecture …

… due to these qualities soap bubbles films have been used with practical problem solving application …

… structural engineer frei otto used soap bubble films to determine the geometry of a sheet of least surface area that spreads between several points …

… and translated this geometry into revolutionary tensile roof structures eg west german pavilion at expo 67 in montreal …

merging

… soap bubbles can easily merge …

… when two bubbles merge, they adopt a shape which makes the sum of their surface areas as small as possible …

… compatible with the volume of air each bubble encloses …

… if the bubbles are of equal size, their common wall is flat …

… if they aren't the same size, their common wall bulges into the larger bubble …

… since the smaller one has a higher internal pressure than the larger one, as predicted by the young–laplace equation …

… at a point where three or more bubbles meet, they sort themselves out so that only three bubble walls meet along a line …

… since the surface tension is the same in each of the three surfaces, the three angles between them must be equal to 120° …

… only four bubble walls can meet at a point, with the lines where triplets of bubble walls meet separated by cos−1(−1/3) ≈ 109. 47° …

… all these rules, known as plateau's laws, determine how a foam is built from bubbles …

stability

… the longevity of a soap bubble is limited by the ease of rupture of the very thin layer of water which constitutes its surface, namely a micrometer-thick soap film …

… it is thus sensitive to :

  1. ‘’’drainage’’’ within the soap film: water falls down due to gravity …

… this can be slowed down by increasing the water viscosity, for instance by adding glycerol …

… still, there is an ultimate height limit, which is the capillary length, very high for soap bubbles: around 13 feet (4 meters) …

… in principle, there is no limit in the length it can reach …

  1. ‘’’evaporation’’’: this can be slowed down by blowing bubbles in a wet atmosphere, or by adding some sugar to the water …

  2. ‘’’dirt and fat’’’: when the bubble touches the ground, a wall, or our skin, it usually ruptures the soap film …

… this can be prevented by wetting these surfaces with water …

antibubble

… an antibubble is a droplet of liquid surrounded by a thin film of gas, as opposed to a gas bubble, which is a sphere of gas surrounded by a liquid …

… antibubbles are formed when liquid drops or flows turbulently into the same or another liquid …

… they can either skim across the surface of a liquid such as water, in which case they are also called water globules …

… or they can be completely submerged into the liquid to which they are directed …

air bubbles compared to antibubbles

… comparison of three different types of bubbles: normal bubbles on the surface, antibubbles on the surface, and submerged air bubbles within an antibubble …

… the behavior of antibubbles differs from that of air bubbles in three primary ways, and provides a ready means of identification …

  1. antibubbles are held in place by surface tension, and move rapidly across the surface of the water …

… they can also be seen to ricochet off other objects in the water (such as air bubbles) and off the sides of a container in a manner similar to that of billiard balls …

  1. under ordinary circumstances, antibubbles are short-lived …

… an air bubble with a soap skin may last several minutes …

… antibubbles often have lifetimes of a few seconds or less …

… however, if the electrical potential between the inner and outer fluid is equalized, antibubbles can last as long as, or longer than, air bubbles …

… recently, antibubbles with a lifetime of at least tens of hours were produced by adsorbing colloidal particles at the air-water interfaces of the antibubble …

  1. antibubbles refract light in a different manner than air bubbles …

… because they are water droplets, light entering them is refracted back toward its source in the same manner as rainbows are produced …

… because of this refraction, antibubbles have a bright appearance

potential uses for antibubbles

… if antibubbles can be stabilized they can be used to form a long lasting froth — antifoam …

… possible uses for antifoam are as a lubricant or using the thin passageways permeating antifoam as a filter for air or other gasses …

… replacing the air in antibubble shells with another liquid could be used for a drug delivery system by creating a shell of liquid-polymer around a drug …

… hardening the polymer with ultraviolet light would create a drug filled capsule

antibubble and vibration

… the lifetime of surface antibubbles can be prolonged indefinitely by making the water under them vibrate …

[source Wikipedia: bubbles]