Introduction and Historical Evolution – Nano- and Microtechnology from A – Z: From Nanosystems to Colloids and Interfaces

Introduction and Historical Evolution

Dispersions of one phase in another, such as glues and dyes, have been known to, and used by humans since circa 3000 to 2800 BC. However, systematic studies of dispersions as a classification of material did not occur until the late 1700s and early 1800s. In the late 1700s, Pierre Macquer studied the dispersions of finely divided gold particles in liquids, such as the gold tinctures of alchemy and medicine [1]. In the early 1800s, Thomas Graham studied the diffusion, osmotic pressure, and dialysis properties of a number of substances, including a variety of solutes dissolved in water (see References [2–4]). He noticed that some substances diffused quite quickly through parchment paper and animal membranes and formed crystals when dried. Other substances diffused only very slowly, if at all, through the parchment or membranes and apparently did not form crystals when dried. Graham proposed that the former group of substances, which included simple salts, be termed crystalloids, and that the latter group, which included albumen and gums, be termed colloids. Although colloidal dispersions had certainly been studied long before this time, and the alchemists frequently worked with body fluids, which are colloidal dispersions, Graham is generally regarded as having founded the discipline of colloid science.

The test of crystal formation later turned out to be too restrictive, the distinction of crystalloids versus colloids was dropped, and the noun colloid was eventually replaced by the adjective colloidal, indicating a particular state of dispersed matter: matter for which at least one dimension falls within a specific range of distance values. The second property that distinguishes all colloidal dispersions is the extremely large area of the interface between the two phases compared with the mass of the dispersed phase. Table 3 illustrates the wide range of dispersions concerned. It follows that any chemical and physical phenomena that depend on the existence of an interface become very prominent in colloidal dispersions. Interface science thus underlies colloid science.1 In 1917, Wolfgang Ostwald, another founder of colloid science, wrote:

It is simply a fact that colloids constitute the most universal and the commonest of all the things we know. We need only to look at the sky, at the earth, or at ourselves to discover colloids or substances closely allied to them. We begin the day with a colloid practice – that of washing – and we may end it with one in a drink of colloid coffee or tea [5].

Now, more than 300 years since Graham's time, a vast lexicon is associated with the study of colloid and interface chemistry because, in addition to the growth of the fundamental science itself, we recognize a great diversity of occurrences and properties of colloids and interfaces in industry and indeed in everyday life. The field has also become more generally referred to as colloid and interface science (not just chemistry) because so many other scientific disciplines become involved in the study and treatment of colloidal systems, and of course, each discipline has brought elements of its own special language. The most recent additions are the fields of nanoscience and nanotechnology.

In 1959, physicist Richard Feynman gave the first known lecture on nanotechnology (without using that term) at the annual meeting of the American Physical Society [6], in which he proposed the idea that atomic manipulation could be used to build structures. The term nanotechnology itself was coined in 1974 by Norio Taniguchi, to describe processes at the nanometre scale.2 Significant interest, and work in, the areas of nanoscience and nanotechnology grew particularly rapidly following the publication of the book Engines of Creation by Eric Drexler in 1986 [7]. An illustration of the new way of thinking that is represented by nanotechnology has been given by B.C. Crandall:

We are distinct from all previous generations in that we have seen our atoms –with scanning tunneling and atomic force microscopes. But more than simply admiring their regular beauty, we have begun to build minute structures. Each atom is a single brick; their electrons are the mortar. Atoms, the ultimate in material modularity, provide the stuff of this new technology [8].

Over the next two decades interest in nanoscience and nanotechnology grew exponentially, leading to a plethora of new terms. The “nano” regime (0.1–100 nm), by definition, overlaps heavily with the size range of colloid and interface science and technology (1–1000 nm). As a result, some of the literature now distinguishes between nanoscience and nanotechnology, and microscience and microtechnology, the latter referring to the 0.1–100 μm regime (the microscale). There has been an explosion of terms with the “nano” prefix3 [9] and the number of possible “nano” terms is virtually unlimited, especially when material types are included (Table 4 provides an illustrative listing and Table 2 shows the prefix nano in relation to other decimal prefixes in science and technology). For example, there are a wide range of types of nanorods, nanotubes, nanowires, nanobelts, and nanoribbons in nanoscale electronic circuit elements alone. Accordingly, some choices have had to be made regarding how many “nano” terms to include in this book.

Although some nanodispersions are simply colloidal dispersions under a new name, many other aspects of nanotechnology are genuinely new and distinct, such as transitive nanomaterials like carbon nanotubes and quantum dots. Quantum dots are an example of transitive nanoscale materials whose dimensions approach characteristic quantum wave function excitations, contributing quantum properties in addition to those contributed by chemical composition and structure. It has been suggested that the term nanotechnology be used to refer to the study of the nanoscale regime, and the term molecular nanotechnology to refer to the “nano approach,” by which is meant the precise, controlled assembly of structures up from the molecular scale that are well organized. This is in contrast to the classical “top down” approach of making things by cutting, bending, and otherwise shaping structures from large starting pieces. In the dispersions area, an analogy would be the use of colloidal ink dispersions in robocasting to build near-nanometre-scale three-dimensional structures, as opposed to the formation of materials by subdividing bulk phases and then kinetically stabilizing their dispersions using emulsifiers and stabilizers.

Finally, as it becomes possible to more fully investigate the subatomic scale regime, new terms are also emerging in pico-, femto-, and atto-science and technology (such as Hollow Atom and Attoreactor). Tables 1, 2, and 5 provide some comparisons among the length scales in micro-, nano-, pico-, femto-, and atto-science and technology.

This book provides brief explanations for the most important terms that may be encountered in a study of the fundamental principles, experimental investigations, and industrial applications of nano-, colloid and interface-, and microscience. Even this coverage represents only a personal selection of the terms that could have been included were there no constraints on the size of the book.

I have tried to include as many important terms as possible, and cross-references for the more important synonyms and abbreviations are also included. The difficulty of keeping abreast of the colloid and interface science vocabulary, in particular, has been worsened by the tendency for the language itself to change as the science has evolved since the 1800s, just as the meaning of the word colloid has changed. Many older terms that are either no longer in common use, or worse, that now have completely new meanings, are included as an aid to the reader of the older colloid and interface science literature and as a guide to the several meanings that many terms can have. As emerging fields, the meanings of terms in nanoscience and nanotechnology are still somewhat in flux, although some standardization is beginning to occur.

Some basic knowledge of underlying fields such as physical chemistry, geology, and chemical engineering is assumed. Many of the important named colloids and phenomena (such as Pickering emulsions), equations, and constants are included, although again this selection represents only some of the terms that could have been included. I have also included a selection of brief biographical introductions to more than 120 scientists and engineers whose names are associated with famous named phenomena, equations, and laws in nano- and microscience and technology, and colloid and interface science (Table 27). Students first become aware of the people who have laid the foundation for a scientific discipline as they encounter these eponyms. By adopting the “students' view” of famous names in the field, it will be seen that in some cases the scientists are very famous, and biographies are readily found. In other cases, the scientists are not as well known. For those interested in this feature specifically, I have included an index of famous names in nano-, colloid and interface-, and microscience for easy searching (Table 27).

Specific literature citations are given when the sources for further information are particularly useful, unique, or difficult to find. For terms drawn from fundamental colloid and interface science, much reliance was placed on the recommendations of IUPAC (e.g., References [10, 11]. Numerous other sources have been particularly helpful in colloid and interface science (textbook references [12, 17]) and its subdisciplines and related, specialized fields (References [18–33]). I recommend these sources as starting points for further information. Similarly, for terms emerging in nanoscience and nanotechnology, much reliance was placed on the recommendations of ASTM Committee E56 on Nanotechnology [34] and the British Standards Institution Vocabulary on Nanoparticles [35]. Other helpful sources include [36–41]. Some richly illustrated descriptions of objects at the nanoscale are provided by Frankel and Whitesides [42]. For the famous names entries, I have drawn on a number of general references [43–48] and have also included numerous specific references for those interested in additional information. Finally, Table 28 provides a summary of common units and symbols in colloid and interface science, much of which crosses over into nanoscience.