SCI Members' News

Colloid and Surface Chemistry Group

Getting to grips with 'heads' and 'tails' in surfactants

Interfaces, whether they be solid-solid, solid-liquid, solid-gas, liquid-liquid, or liquid-gas are everywhere in nature. They are of increasing scientific importance as material is divided up into ever smaller pieces in the name of ‘nanotechnology’. However, mankind has always modified these interfaces. For example, to make them non-stick for mould release or non-fouling, or slippery, in the case of lubricants; to make stable dispersions of solid in liquid in the pharmaceutical industry; to make stable emulsions of oil in water in paints and food; to make fine sprays in aerosols and inkjet printers; to clean hard surfaces as detergents; and to make uniform films of liquids and solids.

To facilitate this, a wide variety of molecules are employed that are interfacially active. These go under a wide variety of names including surface modifiers, surface active agents (also known as surfactants), detergents, emulsifiers and dispersants. Such interfacially active molecules are typically designed for two-phase system, for example solid-liquid or liquid-gas, with one part of their structure showing an affinity for the first phase of interest and the other part of their structure showing an affinity for the second phase or, in the very least, a much lower affinity for the first phase. As such they are said to be amphiphilic in structure. Not surprisingly, a certain amount of design is required in the selection of such molecules for each system of interest.

Designer molecules for interfacial activity is the chosen theme for this year’s Rideal lecture, to be held at SCI’s international headquarters in Belgrave Square, London, UK on 24 April. Rideal lecturers are selected on the basis of a distinguished and sustained contribution to colloid and interface science. The 2007 lecturer, Alan Pitt, is a leading scientist and inventor in Kodak’s Research Laboratory who has developed a deep understanding of structure-property relationships of surfactants and dispersants and their effects on formulations and in applications. The molecular structures he has designed include: one, two or three ‘tails’; one or two ‘heads’; sugar and flouro components; and, more recently, oligomeric moieties. Recent studies have involved investigating the properties of homologous series, leading to an understanding of the sometimes delicate balance of competing interactions in these multi-functional molecules.

The lecture will describe surfactant design for control of static and dynamic surface tension as applied to, for example, multi-layer coating. The second part will focus on a novel range of oligomeric-based surfactants which enable easy incorporation of a wide range of ‘chemistry’ (enabling tunable specificity at low cost) with applications including, for example, the dispersion of inorganic particles. It will become clear that not only the detailed structure of the ‘head’ and ‘tail’ components is important but also that the balance between these component parts plays a crucial part in controlling the performance of the surfactants.

The lecture will be preceded by a half-day symposium, sponsored by Kodak, featuring many of the leading UK experts in surfactant science:

• Robert Thomas, Oxford University: From surfactant molecular architecture to interfacial behaviour;
• Colin Bain, Durham University: The overflowing cylinder – sixty years on;
• Paul Fletcher, Hull University: Unusual surfactants; Julian Eastoe, Bristol University Surfactants for supercritical CO₂; and
• Peter Griffiths, Cardiff University Connecting the nano and macro scale.

Andrew Howe
Colloid and Surface Chemistry Technical Interest Group