Supercooled Liquids and Glasses

Glasses are materials that are much more common in our daily life than one might naively expect. Apart from the obvious (inorganic) glasses, such as wine glasses, bottles and windows, we also have the organic (often polymeric) glasses, such as most plastic materials (bags, coatings, etc.). In the last few years also metallic glasses have come to our daily (St. Andrews) life since they are used, apart from many other applications, in the head of golf clubs. In view of this widespread use of these materials it might be a bit surprising to learn that glasses are not very well understood from a microscopic point of view and that even today very basic questions such as “What is the difference between a liquid and a glass?” cannot be answered in a satisfactory way. In the present lecture notes we will discuss some of the typical properties of supercooled liquids and glasses and theoretical approaches that have been used to describe them. Since unfortunately it is not possible to review here all the experiments on glasses and theoretical models to explain them we will discuss here only some of the most basic issues and refer the reader who wants to learn more about this subject to other review articles and textbooks [1]. In the following section we will review some of the basic phenomena that are found in supercooled liquids and glasses. Subsequently we will discuss the theoretical approaches to describe the dynamics of these systems, notably the so-called mode-coupling theory of the glass transition. This will be followed by the presentation of results of computer simulations to check to what extend this theory is reliable. These results are concerned with the equilibrium dynamics. If the temperature of the supercooled liquid is decreased below a certain value, the system is no longer able to equilibrate on the time scale of the experiments, i.e. it undergoes a glass transition. Despite the low temperatures the system still shows a very interesting dynamics the nature of which is today still quite unclear. Therefore we will present in the final part of these lecture notes a brief discussion of this dynamics and its implication for the (potential) connection of structural glasses with spin glasses.