Chemical combination among metals has been studied for a long time. In the early days, chemists had much difficulty in understanding how metals could combine at all among themselves, often in several different proportions, since this often seemed to be at variance with elementary notions of valency. Indeed, in the last century a distinction was proposed between daltonides and berthollides, the former being compounds with simple ratios of the numbers of constituent atoms… consistent with Dalton's atomic theory!… the latter, called after a skeptical French chemist, being the name reserved for compounds with a wide composition range which scarcely seemed explicable on any reasonable atomic model. A few nostalgic souls still employ these distinctions.

An early classic on the subject was a book published by two Italian chemists in 1918. British metallurgist C.H. Desch also wrote a monograph on intermetallic compounds in 1914 (the year when the name “physical metallurgy” was first proposed, and the chemical bias of metallurgy shifted toward a physical one), and he declared that “attempts to form a theory of the constitution of intermetallic compounds… have been comparatively unsuccessful.” When he returned to the subject 20 years later, he felt much more cheerful about the state of the theory because in the meantime Hume-Rothery had introduced the concepts of atomic size factor, electron/atom ratio, and electronegativity (a concept also associated with the name of Linus Pauling) into the discussion of intermetallic phases, or compounds. Today, a battery of sophisticated physical concepts is used to make sense of both binary and multielement intermetallic compounds and they are no longer regarded as chemical anomalies.

The two feature articles in this issue present numerous contrasts, but both reflect the vitality of research in polymer science today. David Tirrell and co-authors paint a picture of how the techniques of molecular biology may be applied to the synthesis of novel “proteinlike” polymers with control over molecular weight, composition, and stereoregularity that is unprecedented in the realm of traditional polymer chemistry. Wolfgang Knoll turns his attention to ultrathin polymer films with thicknesses comparable to molecular chain dimensions and demonstrates how evanescent wave optical methods may be used to provide spectroscopic as well as imaging information on the characterization of these “restricted geometry” systems.

Both authors address the issue of supermolecular structure, whether approached from the synthetic or physical chemical viewpoints. Tirrell describes a series of target polymers, expressed by genetically engineered microorganisms, which may provide a fundamental understanding and control over chain folding, a critical morphological feature governing solid-state behavior of synthetic polymers. Knoll analyzes the fundamentals of evanescent wave optical methods for interrogating the molecular organization in polymer films that have considerable potential in electronic or photonic applications.

My fellow authors and I have assembled a series of articles on using rheology to understand the structure and processing of a wide range of materials. We approach this task by presenting an introduction to the concepts of rheology and some illustrative applications, followed by a description of linear vis-coelasticity and a description of the rheological behavior of elastic fluids. These concepts and related tools are then used to describe molten polymers, colloidal suspensions, latex systems, electrorheological fluids, and gels. In each of these areas, we show how rheology provides insights into the structure of materials and the type of information required to process them. We also show that the rheological approach spans macroscopic and microscopic domains. These aspects of rheology are of value to materials scientists and engineers. We hope these examples will clarify the relevance of rheology to materials.

If we are successful in this presentation, you will obtain a flavor of the process of rheological studies. While reading through these articles, look for the interplay of the concepts of molecular or domain structures and the flow and deformation of the bulk materials. These articles may even inspire you to examine the role that rheology may play in your own studies.

In this issue of the MRS Bulletin we present five papers that involve point defect phenomena in a wide variety of materials—metals, conducting ceramic oxides, semiconductors, amorphous alloys, and high Tc superconducting oxides. The unifying theme of this issue is point defects—zero-dimensional defects. Even for the high Tc oxides, where planar defects are discussed, it is the ordering of oxygen/vacancy chains that ultimately gives rise to twins in the famous YBa2Cu3O7.δ (1:2:3) oxide superconductor.

Hillard Huntington, professor emeritus of physics at Rensselaer Polytechnic Institute, is an early and important pioneer in the study of point defects in metals. A theorist, he has also performed many experiments over the years; for example, he performed key early experiments on electromigration effects. Huntington's article presents a historical review of the research on vacancies and self-interstitial atoms in metals during the period that stretches from the mid-1930s to the mid-1960s. He played a crucial role in this field as a result of his seminal theoretical calculations, with Fred Seitz in 1942, on the enthalpies of formation and migration of vacancies or self-interstitial atoms in pure copper. Huntington's and Seitz's calculations indicated that diffusion occurs predominantly by a monovacancy mechanism since the enthalpy of formation of a self-interstitial atom, the [100] split form, also called the dumbbell form, is too large to be compatible with the activation enthalpy for self-diffusion in copper. It is now well established that the latter is given by the sum of the enthalpy of formation and the enthalpy of migration of a monovacancy in many face-centered-cubic (fcc), body-centered-cubic (bec), and hexagonal-close-packed (hcp) metals.

A renaissance in research and development of solid lubricants has taken place during the past 10 years. This renaissance has been driven by the needs of advanced technological applications, for which liquid lubricants alone have become either ineffective or undesirable. Increasing the efficiency of jet and automobile engines, which entails engine operation at significantly higher temperatures, and increasing the longevity of space vehicles have been central technology drivers.

In the past 10 years, many new solid lubricants have been developed to address these needs for higher temperature operation and longer life. Their development, for the most part, has taken advantage of what is known concerning their mechanism of action. Although this mechanistic knowledge is incomplete, particularly at high temperatures, significant advances in material performance have been made. In addition, new methods of applying solid lubricant coatings, namely plasma and ion-beam-assisted vacuum deposition methods, have recently come into their own and produced improved materials.

This article will highlight developments in the 1980s which produced new solid lubricants and the advanced technologies which these materials will enable.

Several reviews of solid lubricants survey the area in more detail than is possible here. For overview purposes, this article will briefly describe the classes of materials used as solid lubricants, their mechanism of action, and areas of application.