Bubble-ology

Author: Bob Fiero--borrowing from various sources.

What is so fascinating about bubbles? The precise spherical shape, the incredibly fragile nature of the microscopically thin soap film, the beautiful colors that swirl and shimmer, or most likely, a combination of all these phenomena? Why does a bubble form a sphere at all? Why not a cube, tetrahedron, or other geometrical figure? Let's look at the forces that mold bubbles.

Scientific Principles:

membranes
surface tension and hydrogen bonding
reflection and interference of light waves & prisms
gas pressure laws

Standards:

Forces

Unbalanced forces cause changes in velocity. As a basis for understanding this concept:
• Students know a force has both direction and magnitude.
• Students know when an object is subject to two or more forces at once, the result is the cumulative effect of all the forces.
• Students know when the forces on an object are balanced, the motion of the object does not change.
• Students know how to identify separately the two or more forces that are acting on a single static object, including gravity, elastic forces due to tension or compression in matter, and friction.
• Students know that when the forces on an object are unbalanced, the object will change its velocity (that is, it will speed up, slow down, or change direction).
• Students know the greater the mass of an object, the more force is needed to achieve the same rate of change in motion.
• Students know the role of gravity in forming and maintaining the shapes of planets, stars, and the solar system.
Waves
Waves have characteristic properties that do not depend on the type of wave. As a basis for understanding this concept:
• Students know waves carry energy from one place to another.
• Students know how to identify transverse and longitudinal waves in mechanical media, such as springs and ropes, and on the earth (seismic waves).
• Students know how to solve problems involving wavelength, frequency, and wave speed.
• Students know sound is a longitudinal wave whose speed depends on the properties of the medium in which it propagates.
• Students know radio waves, light, and X-rays are different wavelength bands in the spectrum of electromagnetic waves whose speed in a vacuum is approximately 3×108 m/s (186,000 miles/second).
• Students know how to identify the characteristic properties of waves: interference (beats), diffraction, refraction, Doppler effect, and polarization.

Gases and Their Properties

The kinetic molecular theory describes the motion of atoms and molecules and explains the properties of gases. As a basis for understanding this concept:

• Students know the random motion of molecules and their collisions with a surface create the observable pressure on that surface.
• Students know the random motion of molecules explains the diffusion of gases.
• Students know how to apply the gas laws to relations between the pressure, temperature, and volume of any amount of an ideal gas or any mixture of ideal gases.
• Students know the values and meanings of standard temperature and pressure (STP).
• Students know how to convert between the Celsius and Kelvin temperature scales.
• Students know there is no temperature lower than 0 Kelvin.
• Students know the kinetic theory of gases relates the absolute temperature of a gas to the average kinetic energy of its molecules or atoms.
• Students know how to solve problems by using the ideal gas law in the form PV = nRT.
• Students know how to apply Dalton's law of partial pressures to describe the composition of gases and Graham's law to predict diffusion of gases.

Chemical Bonds

Biological, chemical, and physical properties of matter result from the ability of atoms to form bonds from electrostatic forces between electrons and protons and between atoms and molecules. As a basis for understanding this concept:

• Students know atoms combine to form molecules by sharing electrons to form covalent or metallic bonds or by exchanging electrons to form ionic bonds.
• Students know chemical bonds between atoms in molecules such as H2 , CH4 , NH3 , H2 CCH2 , N2 , Cl2 , and many large biological molecules are covalent.
• Students know salt crystals, such as NaCl, are repeating patterns of positive and negative ions held together by electrostatic attraction.
• Students know the atoms and molecules in liquids move in a random pattern relative to one another because the intermolecular forces are too weak to hold the atoms or molecules in a solid form.
• Students know how to draw Lewis dot structures.
• * Students know how to predict the shape of simple molecules and their polarity from Lewis dot structures.
• * Students know how electronegativity and ionization energy relate to bond formation.
• * Students know how to identify solids and liquids held together by van der Waals forces or hydrogen bonding and relate these forces to volatility and boiling/ melting point temperatures.
Cell Biology

The fundamental life processes of plants and animals depend on a variety of chemical reactions that occur in specialized areas of the organism's cells. As a basis for understanding this concept:

• Students know cells are enclosed within semi permeable membranes that regulate their interaction with their surroundings.

Demonstration:

Paper Cone Bubble Blower (link to construction page)

Two important factors are involved in the process: the shape of the cone and the material used to make it. Also of great importance is the bubble soap mixture.

If you blow into a straw, a rush of air comes out the other end at high velocity. If you were trying to blow bubbles with a straw, you would probably burst them because of the violent rush of air. The cone shaped bubble blower reduces the velocity but not the volume of air moving through it. When the air reaches the end of the cone, it has reduced in speed and does not violently fill the bubble with turbulent air. When you blow bubbles with the standard plastic ring, your bubble solution must cling to the plastic surface and span the opening. When this bubble solution runs out, the bubble will separate from the ring or burst.

The size of the bubble is limited by the small amount of soap solution clinging to the ring. When you blow bubbles with the absorbent paper cone, you first submerge it into the bubble solution which absorbs a large quantity of the soap mixture.

This solution becomes a reservoir for blowing really large bubbles. When you start blowing the bubble, the solution is pulled out of the cone as needed by the growing bubble. The size of it is limited only by your skill, lung capacity and the quantity and quality of solution that is available in the cone. Evaporation is also a factor that shortens the life of the bubble. The bubble wall becomes thinner because of evaporation and eventually the bubble pops.  Here is a link to a related bubble game!

Procedure: How does it work? Techniques

After mixing up the bubble blowing solution, fill a custard cup or shallow dish with the solution. The first time you use the blowing cone, submerge it for 30 seconds in the liquid so that it absorbs enough of the solution (Fig.1).

After this you will only need to submerge it for a couple of seconds. When you retrieve the cone tilt is slightly and tap it on the side of the dish to remove the excess solution. Start blowing the bubble downward. You will notice that the bubble drips excess solution at the start.

As the bubble grows you will observe that it becomes more buoyant and you will be able to lift the blowing tube to a horizontal position (Fig. 2).

This is because the warm air from your lungs is filling the bubble making it weigh less.

When the bubble gets really large you will notice that it wants to rise as if it was a balloon filled with helium gas (Fig. 3).

This is because the bubble is now filled with a large volume of warm air, surrounded with cooler air. If you are outdoors it may even become uncontrollable. I recommend that if you want to blow really large bubbles, start indoors with the windows closed so that you can learn to control the bubble. Even the slightest draft will try to move a large bubble. It is more difficult to control large bubbles than small ones.

When the bubble is the size you want, you can separate it from the cone by rapidly flipping the cone up or down (Fig. 4).

Do not pull the cone straight away from the bubble as it will be more likely to burst.

Bubble Art:  try adding food coloring to bubbles and let them pop on paper.

Cubist bubbles
What is the natural shape of a bubbles? To find out, you need some detergent or soap, a piece of soft florist's wire, a pair of pliers, and a dish.

Use the wire to make a cube with one or two wire handles (a bit like a Cubic frying pan!). Sink this in the soap solution, pull it out, and check the shape of the bubble formed. If you pass the cube through a simple ring carrying a flat film of soap, you can produce interesting effects. Adding glycerine to soap solution makes the bubbles last longer.

Then try the shape on the right, and any other interesting shapes that occur to you, and see what sorts of bubbles form.

Materials:

Bubble Formulas (there are many recipes but here is a basic one):

Mix 59 mL (1/4 cup) liquid soap, 15 mL (1 tbl) glycerine, 1.89 L (8 cups) water. We like Joy® or Dawn® soap the best. You can also use store bought bubble solution and dilute it with water.  Other ingredients to consider is Linseed oil (linen - flax - flaxseed) and glycerin.

Or consider this one:

1. Combine 1/2 cup dishwashing detergent, 4 1/2 cups water, and 4 tablespoons of glycerin in a large container with a cover.
2. Mix well, then allow the mixture to rest, covered, until ready for use.
3. Pour bubble solution into a shallow container. Dip bubble wands -- such as cookie cutters, shaped pipe cleaners or wire -- into the solution and blow!

Tips:

1. Joy is usually the recommended brand of dishwashing liquid.
2. For best results, use distilled water.
3. As an alternative to glycerin, some recipes recommend using white corn syrup.

What You Need:

• 1/2 c. dishwashing liquid
• 4 1/2 c. water
• 4 T. glycerin
• large covered container
• bubble wands

Mix the ingredients very thoroughly.

A few tips
Bubble mix keeps well in an airtight container. It works better if it is at least two weeks old. I once used a single 20L batch in science shows for over a year and it kept getting better.

Hard water isn't very good for bubble mixture.

Vinegar can help clean it up.

Explanation: What does it teach?

A bubble, like a balloon, is a very thin skin surrounding a volume of air. The rubber skin of the balloon is elastic and stretches when inflated. If you let the mouthpiece of the balloon go free, the rubber skin squeezes the air out of the balloon and it deflates as it flies around the room. The same thing happens if you start blowing a bubble and then stop. The liquid skin of the bubble is stretchy, somewhat like a piece of thin rubber, and like a balloon it pushes the air out of the bubble, leaving a flat circle of soap in the bubble wand. Unlike a sheet of rubber that when unstretched loses all tension, a bubble always has its "stretch" no matter how small the surface becomes. If you blow a bubble and close the opening by flipping the wand over, the tension in the bubble skin tries to shrink the bubble into a shape with the smallest possible surface area for the volume of air it contains. That shape happens to be a sphere--the most energetically effective shape in the universe.

 Shape # of sides Volume Surface Area Tetrahedron 4 1 cubic inch 7.21 square inches Cube 6 1 cubic inch 6 square inches Octahedron 8 1 cubic inch 5.72 square inches Dodecahedron 12 1 cubic inch 5.32 square inches Icosahedron 20 1 cubic inch 5.15 square inches Sphere infinite 1 cubic inch 4.84 square inches

On the other hand a  liquid bubble can be a globule of one substance in another, usually gas in a liquid. Due to the Marangoni effect, bubbles may remain intact when they reach the surface of the immersive substance.

If you could see molecules of water and how they act, you would notice that each water molecule electrically attracts its neighbors. Each has two hydrogen atoms and one oxygen atom, H20. The extraordinary stickiness of water is due to the two hydrogen atoms, which are arranged on one side of the molecule and are attracted to the oxygen atoms of other nearby water molecules in a state known as "hydrogen bonding." (If the molecules of a liquid did not attract one another, then the constant thermal agitation of the molecules would cause the liquid to instantly boil or evaporate.

Hydrogen atoms have single electrons which tend to spend a lot of their time "inside" the water molecule, toward the oxygen atom, leaving their outsides naked, or positively charged. The oxygen atom has eight electrons, and often a majority of them are around on the side away from the hydrogen atoms, making this face of the atom negatively charged. Since opposite charges attract, it is no surprise that the hydrogen atoms of one water molecule like to point toward the oxygen atoms of other molecules. Of course in the liquid state, the molecules have too much energy to become locked into a fixed pattern; nevertheless, the numerous temporary "hydrogen bonds" between molecules make water an extraordinarly sticky fluid.

Within the water, at least a few molecules away from the surface, every molecule is engaged in a tug of war with its neighbors on every side. For every "up" pull there is a "down" pull, and for every "left" pull there is a "right" pull, and so on, so that any given molecule feels no net force at all. At the surface things are different. There is no up pull for every down pull, since of course there is no liquid above the surface; thus the surface molecules tend to be pulled back into the liquid. It takes work to pull a molecule up to the surface. If the surface is stretched - as when you blow up a bubble - it becomes larger in area, and more molecules are dragged from within the liquid to become part of this increased area. This "stretchy skin" effect is called surface tension. Surface tension plays an important role in the way liquids behave. If you fill a glass with water, you will be able to add water above the rim of the glass because of surface tension.

Have you ever tried to blow a bubble with pure water? It won't work. There is a common misconception that water does not have the necessary surface tension to maintain a bubble and that soap increases it, but in fact soap decreases the pull of surface tension - typically to about a third that of plain water. The surface tension in plain water is just too strong for bubbles to last for any length of time. One other problem with pure water bubbles is evaporation: the surface quickly becomes thin, causing them to pop.

 Soap molecules are composed of long chains of carbon and hydrogen atoms. At one end of the chain is a configuration of atoms which likes to be in water (hydrophilic). The other end shuns water (hydrophobic) but attaches easily to grease. In washing, the "greasy" end of the soap molecule attaches itself to the grease on your dirty plate, letting water seep in underneath. The particle of grease is pried loose and surrounded by soap molecules, to be carried off by a flood of water. Glycerin--C3H5(OH)3, which can be bought in drugstores--is often included as well. Bubbles eventually burst once the layer of water evaporates, but adding glycerin lengthens the life span of bubbles. Glycerin forms weak hydrogen bonds with water, delaying evaporation. Dry air or dry hands can still burst a bubble, however.

In a soap-and-water solution the hydrophobic (greasy) ends of the soap molecule do not want to be in the liquid at all. Those that find their way to the surface squeeze their way between the surface water molecules, pushing their hydrophobic ends out of the water. This separates the water molecules from each other. Since the surface tension forces become smaller as the distance between water molecules increases, the intervening soap molecules decrease the surface tension. If that over-filled cup of water mentioned earlier were lightly touched with a slightly soapy finger, the pile of water would immediately spill over the edge of the cup; the surface tension "skin" is no longer able to support the weight of the water because the soap molecules separated the water molecules, decreasing the attractive force between them.

Because the greasy end of the soap molecule sticks out from the surface of the bubble, the soap film is somewhat protected from evaporation (grease doesn't evaporate) which prolongs the life of the bubble substantially.  This is just the opposite of a cell membrane where the phospholipids (greasy hydrophobic ends) stick in away from the water solutions inside and outside of the cell. Bubbles like cell membranes demonstrate the self-sealing nature of membranes and how tears might be repaired. Have the students form an opening in the membrane by floating a circle of thread on the film, popping the inside of it and then gently removing it. The membrane should self-seal. This can also be used as a metaphor for membrane pores.

A closed container saturated with water vapor (as in the Exploratorium "Soap Film" exhibit) also slows evaporation and allows soap films to last even longer. I've blown soap bubbles on a watchglass glued to the bottom of a jar with a large mouth. Once I've sealed the jar the environment will support the bubble for quite a long time. My longest lasting bubble survived for three months! Eiffel Plasterer, a dear departed friend, farmer, educator, and bubble fanatic who lived in Huntington, Indiana blew a bubble that lasted for 341 days!

 When one bubble meets with another, the resulting union is always one of total sharing and compromise (Human beings could learn a lot from bubbles.) Since bubbles always try to minimize surface area two bubbles will merge to share a common wall. If the bubbles are the same size as the bubbles to the left, this wall will be flat. If the bubbles are different sized, the smaller bubble, which always has a higher internal pressure, will bulge into the larger bubble.

 Regardless of their relative sizes, the bubbles will meet the common wall at an angle of 120 degrees. This is easy to see in the bubble picture to the right. All three bubbles meet at the center at an angle of 120 degrees. Although the mathematics to prove this are beyond the scope of this article, the 120 degree rule always holds, even with complex bubble collections like a foam.

 If you take two sheets of clear glass or plastic separated by about one-half inch, soak them in soapy solution and then blow bubbles between the sheets, you will get many bubble walls. If you look closely, you will notice that all of the vertices where three bubble walls meet (and there are always three,) form 120 degree angles. If your bubbles are of uniform size, you will notice that the cells form hexagons and start to look much like the cells of a beehive. Bees, like bubbles, try to be as efficient as possible when making the comb. They want to use the minimum possible amount of wax to get the job done. Hexagonal cells are the ticket.
Do bubbles last longer in cold weather or hot weather? Why?
Bubbles last longer in cold weather because their lifetimes are limited by evaporation. The water and other liquids in a bubble gradually evaporate and the bubble eventually loses its stability and pops.

If you watch a soap bubble carefully, you'll see that its colors change with time. These colors are caused by interference effects in the light waves as they reflect from the soap film's outer and inner surfaces. The tiny distance separating those two surfaces gets smaller as the bubble loses molecules and that length change affects the bubble's colors.

At a lower temperature, the rate at which molecules leave a soap bubble decreases and the bubble lasts longer. High humidity should also help preserve the bubble because molecules can also return to the bubble from moist air. My favorite time to blow soap bubbles is on a bitter cold but calm winter day when the bubbles freeze solid and settle to the ground as intact spheres. They can then last for many minutes before they finally lose enough molecules to let them tear. They then collapse slowly and gracefully, like tents settling after you remove their support poles.

Video:

Discovery Channel's "Time Warp" episode featuring Keith Michael Johnson - Bubble Artist
There is rapidly growing interest in the production and control of bubbles in numerous disciplines. Suspensions of stable gas microbubbles play a vital role in the food, cosmetics and pharmaceutical industries, as well as in biotechnology, environmental engineering, and minerals and materials processing. In molecular biology, microbubbles are central to the mesoscale self-assembly of smart materials, microfabrication and DNA-driven assembly. Microbubbles have also shown great promise in therapeutic applications such as targeted drug delivery, gene therapy, thrombolysis and ultrasound surgery, and are the most effective type of contrast agent available for ultrasound radiography. Recent developments in processing, diagnostics and therapeutics have generated a greatly increased need for advanced preparation technologies that provide a high degree of control over microbubble characteristics.

Bubbles are seen in many places in everyday life, for example:

• As spontaneous nucleation of supersaturated carbon dioxide in soft drinks
• As water vapor in boiling water
• As air mixed into agitated water, such as below a waterfall
• As sea foam
• As given off in chemical reactions, e.g. baking soda + vinegar
• As a gas trapped in glass during its manufacture
Bubbles are an example of "thin films" which are thin material layers ranging from fractions of a nanometre (less than the width of an atom, or monolayer) to several micrometres in thickness. Electronic semiconductor devices and optical coatings are the main applications benefiting from thin film construction.

A familiar application of thin films is the household mirror which typically has a thin metal coating on the back of a sheet of glass to form a reflective interface. The process of silvering was once commonly used to produce mirrors. A very thin film coating (less than a nanometer) is used to produce two-way mirrors.

The performance of optical coatings (e.g. antireflective, or AR, coatings) are typically enhanced when the thin film coating consists of multiple layers having varying thicknesses and refractive indices. Similarly, a periodic structure of alternating thin films of different materials may collectively form a so-called superlattice which exploits the phenomenon of quantum confinement by restricting electronic phenomena to two-dimensions.

Work is being done with ferromagnetic thin films for use as computer memory. It is also being applied to pharmaceuticals, via thin film drug delivery. Thin-films are used to produce thin-film batteries.[1]

Ceramic thin films are in wide use. The relatively high hardness and inertness of ceramic materials make this type of thin coating of interest for protection of substrate materials against corrosion, oxidation and wear. In particular, the use of such coatings on cutting tools can extend the life of these items by several orders of magnitude.

Research is being done on a new class of thin film inorganic oxide materials, called amorphous heavy-metal cation multicomponent oxide, which could be used to make transparent transistors that are inexpensive, stable, and environmentally benign.[2]

References:

Wikipedia

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Robert Fiero,
Nov 29, 2009, 9:39 PM