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Making Anti-bubbles Project

- William J. Beaty

What are "antibubbles"? They're skins of air that float around underwater and vanish when touched! Before you launch into the making of antibubbles, it helps to understand the different types of bubbles that exist.

The Three Types of Basic Bubbles

fig. 1 Pockets of air under water

fig. 2 Air trapped under a water film

fig. 3 Bubbles that float in the air

The Three Types of "Antibubbles"

Besides the above basic bubbles, there are three other kinds that are not as familiar: the "antibubbles." An antibubble is similar to a bubble, but the roles of the water and the air are reversed.

The First Type of Antibubble

• The first type is familiar: It is simply a drop of water falling through the air.
• It is the opposite of an underwater bubble: Rather than being a blob of air in the water, it is a blob of water in the air.

fig. 4 - Falling droplet of water



The Second Type of Antibubble—the "water globule"

• When a drop of water falls into water, we expect it to vanish, but sometimes it does not.
• If the water is very clean, then a thin skin of air will become trapped between the water droplet and the rest of the water.
• This object is sometimes called a water globule or floating drop.
• A water globule is the opposite of an air bubble on the surface of water: Rather than being a pocket of air with a thin skin of water separating it from the air, it is a blob of water with a thin skin of air separating it from the water.
• If you've sat in a car on a rainy day, you've probably seen water globules skittering across the hood.
• When raindrops splash on the car hood, the splashing droplets roll across the wet surface without melding into the rest of the water.

fig. 5 - "Water globule" on the surface



The Third Type of Antibubble—usually called simply the "antibubble"

This antibubble is a very thin skin of air that floats around under the water.

Antibubbles have many of the characteristics of soap bubbles:

• They float underwater weightlessly.
• They will only rise to the surface of the water very slowly.
• When poked, they will pop. Note: When a soap bubble pops, it leaves behind a tiny drop of water, but when an antibubble pops it leaves behind a tiny normal bubble.
• Antibubbles also display rainbow colors. Note: Normal soap bubbles have rings of color at the top of the bubble where the soap film is thinnest, while antibubbles have their colors at the bottom.

fig. 6 - "Antibubble" floats underwater

BLOW YOUR OWN UNDERWATER ANTIBUBBLES

Antibubbles don't form easily, and they usually pop quickly, so most people have never seen them. However, it is possible to create them yourself with a little practice.

Materials

• kitchen sink (or continuous access to sink at Science Fair)
• large, clean jar
• Elmer's (tm) glue bottle, emptied and cleaned
• dishwashing detergent

Procedure

Clean Your Water Surface

The key to creating antibubbles is to create a very clean water surface. The tiniest bit of surface dirt will prevent antibubbles from forming, or will make them quickly pop. To create a clean surface:

• Allow a container of water to continuously overflow. Note: The overflow causes the surface of the water to stretch and be pulled sideways, and any dirt on the water's surface will be skimmed off.
• Fill your large jar, place it in the sink, and adjust the faucet to allow a continuous stream of water to pour in and overflow the jar.

fig. 7 - Constant overflow cleans water surface



Begin by Making "water globules"

To become familiar with how antibubbles behave, first try making some "water globules:"

• Add some soap to the jar of water and stir well.
• Fill your glue bottle with soapy water from the jar.
• Spray some droplets up from below the jar, so the droplets land on the surface of the water.
• If you can build up lots of globules, you'll see them bounce off each other, or "pop" and join the rest of the water.
• Sometimes the droplets join together into larger and larger ones.

fig. 8 - Squirt some "globules" onto the water



Science Fun with Water Globules

You can demonstrate that electrostatic forces disrupt the thin film of air:

• Comb your hair to give the comb an electric charge imbalance.
• Spray some globules on the surface of the water.
• Wave the charged comb near the water globules—they will abruptly vanish! They all "pop" and rejoin the water.

What happened?

• The electrified comb caused the water in each globule to split into areas of positive and negative charge.
• This imbalanced charge attracts the water below the globule, and the globule crashes into the water below.

Note: On a dry day, your body can become electrified from walking on the floor, which can disrupt antibubbles and globules just as the charged comb does. If your globules and antibubbles refuse to form, try touching the metal faucet to remove any charge imbalance from yourself.

Make Real Antibubbles!

• Place the tip of your water-filled squirt bottle very near the water's surface.
• Give it a gentle puff and create a single water globule.
• Immediately give a longer squeeze. This will send a jet of water through the globule and down into the jar.
• If your squeeze is gentle and brief, the water jet will take the air layer along, and a long silvery "worm" will extend into the water. This "worm" is water that is coated with air.
• Do this several times, and sometimes the worm will break up into antibubbles of different sizes.
• To prove that this is no ordinary bubble, poke it with a pencil or fork. It will instantly vanish.

fig. 9 Make a globule

fig. 10 Squirt through the globule

fig. 11 Watch for antibubbles!

Helpful Hints

Be patient and practice!

• Your first underwater antibubbles will probably be small, under 1/8" across.
• With practice it is possible to blow larger antibubbles of 1/4" and occasionally even up to 1/2".

To extend the life of your antibubbles:

• Put the bottle tip in the water and squirt at them to drive them deeper into the jar. Vibration is supposed to extend their lifetimes, so squirting them with underwater jets may keep them "alive" longer.
• Temperature difference is also said to lengthen their lifetimes. Try filling your glue bottle with hot water, while putting cold water in your overflowing jar.

Other Things to Try

Observe Your Antibubbles' Color Rings

Antibubbles display rings of color, but these colors appear at the bottom of the bubbles rather than at the top. Try observing the rings:

• Look closely at your antibubbles under bright light, and you'll see that each one has "soap film colors" which in this case we should call "air film colors."
• The colors of soap films (and of oil on water) are caused by light reflections from a very thin, transparent layer.
• Light reflects from the front of the thin layer and from the back.
• If the layer is almost as thin as light waves, the certain colors of light waves from the two reflections cancel out, producing a "subtractive rainbow" with cyan/magenta/yellow instead of red/green/blue.
• In a normal bubble, the thin water layer creates the colors.
• In an antibubble, the colors are created by the thin layer of air.

Color Your Antibubbles

To fill your antibubbles with color:

• Put some food coloring in your squirt bottle.
• Try this with a few friends, each with a different color in their squirt bottle, and you can all keep track of your own antibubbles in the same jar.

Make an Oil/Alcohol Bottle

You can demonstrate all the various bubbles (antibubbles, bubbles, globules, antibubbles inside bubbles, anti-foams, etc.) with this oil/alcohol bottle.

• Clean out a small jar and fill it halfway with salad oil.
• Fill the remainder of the jar with rubbing alcohol. Note: Try to fill it perfectly, right up to the top, so no air is trapped.
• Screw on the cap, then slosh it gently to create waves, or a bit harder to create all sorts of bubbles-within-bubbles. Note: Don't shake it hard, or it will take hours for the misty mixture to settle out.

Used with permission of William Beaty.

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Making Anti-bubbles Project