A more in depth look at the States of Matter
This column first appeared in October 2016, in the Ponca City News.
When taking any general science class, one of the questions that might be asked is: what are the states of matter? Matter is essentially the stuff that makes up our world. And, most would answer there are three: solid, liquid, and gas. And, you know these states when you see them. A solid is something that holds is shape and does not require a container. A liquid will take the shape of its container and has a definite interface, i.e. that demarcation from it and its surroundings. A gas doesn’t have an interface, it surrounds us (unless we are in a vacuum) and will take the shape of the container.
But science, it isn’t always that simple. In physics class, a common fourth state is described, a plasma. We are familiar with plasmas from neon gas lights. A plasma while similar to a gas behaves differently due to the interaction of the atoms. It is a collection of electrically charged particles that behave in a collective manner. In one sense, a plasma is a gas that has an interface and has distinct properties when interacting with electromagnetic fields.
But, now think about a couple of other common items and how you would classify them: gelatin and hard tack type candies. Are they a solid? In a simple sense, yes, but leave them out for a time, they easily change shape. So, are they just a very thick liquid? Asphalt might be another example. Or, Silly Putty? They aren’t really a solid, but they aren’t really liquid either. These materials might be classified as gels or glasses, depending on other characteristics.
Thus, defining states of matter, at least for physicists that are trying to understand physical phenomena, isn’t as straightforward as solid, liquid or gas. Physicists have to get down to the atomic scale and see how the individual atoms or molecules interact with each other in order to determine its “state.” And, we know from experience that materials change state depending on temperature and pressure. Water goes from a solid, ice, to liquid at its melting point. Similarly, water goes from a liquid to a gas at its boiling point. As the phases change, the individual atoms or molecules interact with each other differently. This is why looking at the actual atomic structure of the material is of interest.
Gels, glasses, and plasmas have very different properties. They interact with their environment differently based upon the configuration of the atoms. Let’s look at carbon as an example. Think of three different “solid” states of carbon: diamond, coal, and graphite. Diamond is one of the hardest materials we know, while graphite can be used as a lubricant. They are both carbon, but the physical properties associated with each state is very different.
It is these intermolecular interactions based on the specific configuration or phase that result produces effects that are observed. Examples of these effects include numerous solid state properties like superconductivity and the Hall effect. But, explaining these has always been troublesome. It is this search for an explanation of how the phases and phases changes proceed that produced this year’s Nobel Prize in Physics. The prize went to three physicists, David J. Thouless, F.Ducan M. Haldan, and J. Michael Kosterlitz. Each of them have been working in the area of topology, i.e. a branch of mathematics that looks at step-wise changes. And, have been looking at the interactions of materials in two-dimensions, or essentially looking at the surface or a thin layer of material in a theoretical sense. And, Haldan has even put the methodology towards looking at threads of material, one-dimension interactions.
By looking at the interactions of the individual particles theoretically and proceeding in a step-wise manner, these scientists examined how collective structures behaved as conditions like temperature changed. Kosterlitz and Thouless were looking at superconducting materials where the phase transitions occur close to absolute zero (-273 degrees Celsius). Haldan was looking at magnetic chains. And, ultimately have been able to explain some of the unusual observed behavior, like superconductivity.
Ultimately, our view of the world is based primarily on the level of detail that is needed. Most of the time, we just need to understand that the state of the material is a solid, liquid or gas. If we want different properties, we may have to adjust our view. And, ultimately we may have to adjust our scale from macroscopic to atomic in order to determine just what state the matter is in.