Interfaces Against Pollution 2014Colloidal models. A bit of history
Introduction
Colloid science is an old discipline, older than polymer science, atom theory, quantum mechanics, biochemistry, electrolyte solution theory and environmental science, and, for that matter, older than its offsprings nanoscience and soft matter science. The oldest illustrations of systems that we nowadays recognize as “colloidal” date back to half the 19th century: the names of Selmi (1845), Baudrimont (1846), Graham (1861), Nägeli (1858), Van Bemmelen (1877) and many others are connected to this early history. As these investigators might have been different, they had one item in common, namely their interest into the existence of a state of matter that was dispersed on the nano- to microscale. Nowadays we would say: between molecular and macroscopic level, but at that time the notion of molecules was not yet fully established, let alone any insight into their sizes. The materials studied in these investigations ranged from inorganic (sulfur, Prussian blue, silver chloride, etc.) to biological (agar, starches, proteins, etc.). This variety of systems is typical: the state of matter was and remains the binding principle rather than the specific properties of the model systems. Historically, various terms for such systems were suggested, such as pseudosolutions, demulsions, and micelles. The term “colloid” was coined by Graham. It stems from the Greek κoλλα, meaning glue, but most colloids do not have this property. With time the meaning of terms may have changed, but for science that does not matter as long as everybody agrees. As an example, the word “atom” comes from the Greek ατoμoς meaning indivisible, but nowadays everybody speaks with impunity of nuclear fission.
Over the almost two centuries since its inception, colloid science has matured together with physical sciences in general and so did the interaction between these disciplines, with mutual benefit. Often colloids have provided model systems to test physical laws, but in turn, physics and chemistry have provided colloid science with excellent tools and measuring techniques. For example, nowadays well-defined colloids act as models for the understanding of liquid matter and statistical thermodynamics have been essential in understanding the behavior of dissolved and adsorbed polymers. By definition, models are abstractions from reality, helping to understand parts of this reality. The better the model, the more it has to offer with respect to generalization to real systems.
It is not surprising that this intertwining between disciplines also was a main element in the conference “Interfaces Against Pollution” held in Leeuwarden, the Netherlands in June 2014, for which the present paper was written. Many contributions to this interdisciplinary meeting reflected the area of tension between pure and applied colloid and interface science, in particular that between the desire to abate environmental problems as fast as possible against the limitations imposed by generic laws, like those of basic thermodynamics. Against this background the present paper was written, presenting an anthology of people, phenomena, lines of thought, developing insights and perspectives, partly based on personal reminiscences.
Section snippets
Determination of Avogadro’s number by Perrin
The Frenchman Jean Baptiste Perrin (1870–1942) was a very original scientist. Like many other Nobel laureates and other really outstanding scientists he also was very versatile. His expert oeuvre included a variety of topics, such as colloid stability, diffusion, foams, nuclear reactions, and the interpretation of electro-osmosis. He was the discoverer of the so-called black holes in soap films, to which we shall return in Section 5.
For the present purpose we shall focus on his determination of
Early double layer models
The very idea that at solid–liquid interfaces spontaneously electric double layers can be formed stems to a large extent from the observation of the various electrokinetic phenomena. In the beginning of the 20th century this knowledge was already a century old. It was also known that by application of an external electric potential difference across some interfaces a double layer could be created. The Lippmann capillary electrometer was a typical example. For purely electrostatic reasons charge
Silver iodide, the lucky strike model of the Dutch school
Out of the many model colloids probed during the first part of the 20th century the silver iodide system was exemplary because many insights were gained with observations for this system and many generalization were made. In many respects AgI is an excellent model system. It is chemically inert, and stable hydrophobic sols and electrodes can be made of it. Let us summarize some achievements.
Soap films as models, Debye and the pope
In the 1960s thin liquid films became an additional popular model for colloid stability studies. Obviously, their spectacular colors and the changes therein immediately fascinate the researcher. But they are also promising models for colloid interaction studies, which was not immediately recognized. By the way of introduction we include Fig. 2, taken from the book by Weselowski [16]. The picture to the right shows how the uninitiated onlooker will recall its phenomenology: a flurry of patches
Reunion in Portmeirion and the polywater hoax
Portmeirion is a remote, little picturesque site in Wales, UK. The place is easy to miss, notwithstanding numerous street signs. Nevertheless, it deserves to be mentioned in the series of conferences on surface and colloid science because it acted as the cradle for a number of developments in the European theater. In 1968 Geoff Parfitt organized there the First Euchem Conference on Chemistry at Interfaces. His aim was to emulate the style of the American Gordon conferences, an intention that
Analyses without a model. Thermodynamics. Salt exclusion
Thermodynamic analyses are the very opposite of model interpretations, because they start from generally valid physical laws, needing no assumptions beyond the two assets that it is impossible to construct a perpetual motion of the first or second kind. Tinkering with these principles is impossible. On the other hand, thermodynamics enables us sometimes to evaluate physical quantities that are difficult to measure directly. The most well-known illustration is using Maxwell relationships, or
Conclusions
The purpose of this anthology was to review some developments in the interplay between models and interpretations in that part of colloid science that may be of direct, or indirect interest to Interfaces Against Pollution. No attempt has been made to arrive at a complete account, and the choice was a matter of taste. For example the vast recent development in utilizing well-defined colloidal systems as models for the phase behavior of liquid matter, a broad field of research on its own, was not
References (25)
- D. Weselowski, The Oxide–Water System (Plenary Talk IAP 2014, also Publication in Special Issue of...
- et al.
J. Colloid Interface Sci.
(1967) - J. Perrin, Les atomes, Paris,...
- For Detailed References and Elaborations, see J. Lyklema, Electric double layers, in: Fundamentals of Interface and...
- H. Freundlich, Kapillarchemie, Eine Darstellung der Chemie der Kolloide und verwandter Gebiete. 4th Auflage,...
Reinhold
(1939)Chem. Rev.
(1947)- E.J.W. Verwey, PhD Thesis, State Univ of Utrecht,...
- et al.
J. Electroanal. Chem.
(1947)
Kolloid Beih.
Kolloid Beih.
Rocz. Chem.
Cited by (11)
Electrophoresis of a Single Rigid Particle
2019, Interface Science and TechnologyCitation Excerpt :The ions that can penetrate into the Stern layer and have some surface reaction there are called the specific ions, or the potential-determining ions [44]. It may also be called the charge-determining ions [66–68], as the total amount of surface charges is changed by the reaction. The dehydrated specific ions may also conduct physical adsorption there in the Stern layer due to the strong affinity with the particle surface [6].
What are the microscopic events of colloidal membrane fouling?
2018, Journal of Membrane ScienceCitation Excerpt :Further, looking into the mechanism on a nanoscopic level interfacial interactions between membrane and foulant play a decisive role. These surface interactions are often described by the DLVO theory, which is named after Derjaguin and Landau and Verwey and Overbeek [15–17]. According to the DLVO theory the surface interactions result from van-der-Waals and electrostatic double layer interactions.
Calcium chloride adsorption at liquid-liquid interfaces: A molecular dynamics simulation study
2017, Colloids and Surfaces A: Physicochemical and Engineering AspectsCitation Excerpt :The presence of salts can change the mutual solubility through a structural change of the bulk solutions, and also can affect the electrical behavior of the interface [14–18]. The experimental [19–21] and theoretical [22–24] studies show a complicated behavior of the salts at the hydrophilic-hydrophobic interfaces. The conventional experimental methods, e.g. tensiometry, cannot be used to explain the salt impact at the molecular level [25,26].
Local reaction environment in electrocatalysis
2024, Chemical Society ReviewsOxide- and Silicate-Water Interfaces and Their Roles in Technology and the Environment
2023, Chemical Reviews