on the topic of Student Reading
People shave with colloids, put colloids in their hair and on their sandwiches, and then have a cold colloid for desert. You may have topped your hot chocolate with a colloid or put a colloid in your cereal this morning. It seems that the world is full of colloids. But what are they?
As you know, the states of matter commonly found on Earth are solid, liquid and gas. It seems like most of the substances, materials, and objects around us can pretty easily be placed into one of these categories. But there are a surprising number of common substances that are not so easy to state their state. They seem to be somewhere in between. Many of these substances tend to be food like Jello, whipped cream, or ice cream. They are a little different from the normal solid, liquid, or gas because they are combinations of different states. Scientists call these kinds of weird substances colloids.
Colloids are made of tiny particles of solid, drops of liquid, or bubbles of gas that are evenly distributed throughout a liquid. They are not dissolved in the liquid but are small enough and intermingled enough with the liquid that they stay thoroughly mixed and do not settle to the bottom or float to the top. The word colloid is made up of coll and oid. Coll comes from a Greek word for glue and oid means similar or like. So colloid means glue-like. Colloids tend to be thick like glue because they have particles mixed in them that make them thicker than water or other solutions like salt water or vinegar.
Milk is a pretty thin colloid with tiny globules of fat thoroughly mixed throughout water. Normally fats and water don’t mix but these little blobs of fat have milk proteins surrounding them that help them mix with the water. Their tiny size also helps them stay mixed up.
Mayonnaise and hair gel are also colloids. Just be sure that you do not confuse the two because you probably don’t want to use mayonnaise as hair gel. Mayonnaise has tiny globules of oil mixed in vinegar or lemon juice, which are both mostly water. The oil and water would normally not mix but egg yolk is also added to the mixture. The egg yolk has a substance in it called lecithin. One end of the lecithin molecule attaches to oil and the other end to water. This helps the tiny oil droplets stay mixed in the liquid to create the thick stuff that is mayonnaise.
Hair gel is made from molecules called polymers mixed throughout water. The polymers intertwine and attach to one another forming a network that traps the water and creates a loose gel. The special polymers used in hair gel are designed to form a film over the hair. When water evaporates, the film gets stiffer and holds the hair in place.
Jello is a kind of strange substance which is also a colloid. Jello is made from water with flavorings, sweetener, and gelatin mixed in. Gelatin is made from a protein called collagen which is the main protein in cartilage, the flexible material that forms your outer ear and nose.
When Jello is added to hot water, the long collagen molecules separate from each other and mix throughout the water. But when this mixture is cooled, the collagen molecules link up with each other in a different way, forming a 3-dimentional network. Water molecules get trapped in the network and help give Jello its more wiggly characteristics.
Whipped cream and shaving cream are similar colloids. In both, tiny air bubbles are thoroughly mixed throughout liquid soap or liquid cream. The whipped cream, and the shaving cream for that matter, will support a cherry on top but that doesn’t make them a solid. Although they are made from a liquid, they no longer pour like a liquid. And even though they are mostly gas, they don’t act like a gas at all. That’s the beauty of a colloid. The combination of states creates unique characteristics.
Some people might say that ice cream is the colloid champ. The world’s favorite desert has solid, liquid, and gas all thoroughly mixed into a liquid. If you looked at ice cream under a strong enough microscope, you would see very tiny ice crystals (solid), tiny pockets of air (gas), and tiny droplets of fat (liquid) all thoroughly mixed throughout a sweet creamy liquid.
I scream, you scream, we all scream for cold triple-state colloid!