The objective of this lab is to investigate the properties of a pair of colloids that you will make yourself. A secondary objective is to enjoy doing some science. The Oobleck is named for a 1949 Dr. Suess story called Bartholemew and the Oobleck.
Some materials do not conform neatly to the designations for solids, liquids, and gases. For example, a colloid is a material that consists of one substance suspended within another. The suspended material is comprised of particles so small that they don’t sink to the bottom of the second substance. Yet they are too large to be considered to be a homogeneous solution. Colloidal particles range in size from 1 nm to 1 µm and usually are made up of more than one molecule stuck together. Mixtures involving only homogeneously mixed single molecules are called solutions; every part of the mixture has an equal amount of each component of the mixture.
Colloids display properties unlike those of their separate components. Some examples of colloids include smoke (a solid suspended in a gas), fog (a liquid suspended in a gas), meringue (a gas suspended in a liquid), protoplasm, homogenized milk, synthetic rubber, and mayonnaise. The Oobleck is an example of a colloid of starch and water.
Long chains of molecules formed from repeated units are called polymers. The repeating units are called monomers. Polymers have very different chemical and physical properties when compared to the monomers that make them up. PVC pipes are made by polymerizing vinyl chloride, a small molecule that is highly toxic, flammable and carcinogenic. And yet, the pipes made by stringing these molecules together are solid, durable, and chemically unreactive. Nylon is a fiber useful for making things from high quality clothing to parachutes. It is made by creating a polymer of two foul-smelling liquids (hexamethylene diamine and sebacoyl chloride for one version). The molecules in the starting liquids are perfectly useless for making bike shorts or evening gowns but when these small molecules are strung together they make a startlingly useful material.
Starch molecules are long chains of simple sugar molecules. Starch is a naturally occurring polymer made by many living organisms and it is used as cellular food storage since the sugar monomers it is made of can be broken off the long chain and used for energy. By making the sugars form a long chain the cell can reduce osmotic pressure, which would otherwise swell the cell to the bursting point. In water the long starch chains assume a globular shape. The globular starch molecules can become entangled when the they are suspended in water. This entanglement leads to the odd properties of the Oobleck. Technically, the Oobleck is a colloid made up of a polymer suspended in water.
The Glurch is based on an artificial polymer. White glue is a polymer of a chemical called vinyl alcohol. The polymer is called polyvinyl alcohol. The long chains of polyvinyl alcohol can flow around and over each other, albeit slowly. Think of it like a bowl of spaghetti noodles with oil on them. You can stir the noodles around but they do tend to cling together. When you add borax solution to the polymer it causes what is called cross-linking. This makes it harder for the long chains to flow past each other. The stickiness which slows their movement is caused by hydrogen bonds: chemical bonds that have a certain strength but which are easily broken and reformed elsewhere.
You will be investigating the properties of these two strange substances. The properties you should investigate are viscidity (stickiness), resiliency (elasticity), and fluidity (ability to flow). You will be asked to come up with your own tests for these properties. Some suggestions will be given.
Don’t eat any of the materials.
Write some well-thought-out answers to the following questions. Please write a full paragraph for the first two and the last two questions. Use complete sentences for all questions. Please write as legibly as possible! Use a separate piece of paper for your answers and remember to rephrase the question as part of your answer.