Experiments on the Colloidal State of Matter

What is a Colloid?

• Many people who have heard of colloids think of them as mixtures of solids and liquids. However, this view is not quite complete. Colloids are actually systems created by two different types of matter, usually of different states. In these systems, one type of matter is suspended in another. For example, regions of warm air carrying tiny particles of ash create a common colloid called smoke. When the food industry processes oils and milk into mayonnaise, they are creating a colloid of two different types of liquid.

Liquid/Soild Colloid Experiments

• To explore the colloidal systems made between liquids and solids, there are many experiments you can perform. If you want to study the features and properties of ready-made systems, you can use toothpaste, gelatin or silly putty and put them through various trials, such as determining if they can be compressed, or how much weight they can support without measurable deformation. You can also readily form water and corn starch into a colloid. An interesting experiment with your corn starch creation is to place it upon a plate resting atop a loud speaker and watch how it dances and deforms as you change the sound source.

Gas/Solid Colloid Experiments

• The most common gas/solid colloid is smoke. Experimenting with various combustion products reveals much about this type of colloidal system. If you compare the properties of cigarette smoke to that from burned wood, wax or hydrocarbons the differences and similarities reveal much. Often, you can pour cooled smoke like a liquid into containers and weigh it in a precision balance. Exposing the various types of smoke to a spray of mist or filtering it through coffee filters reveals much about the solid particles that reside within it.

Gas/Liquid Colloids

• The most commonly observed gas/liquid colloid is a system called foam. You can find foams for experimentation in common beverages such as on the frothy head of a glass of root beer or the top of a latte. You can also create foams by whipping heavy cream or mixing water with soap. Since foams form in liquid, they are great for surface tension experiments. You can try adding various concentrations of soaps or salts to the liquid to see how they either hinder or promote the production of foam, or monitor foams under different heat levels to see how that affects their cohesion.