New Frontiers in Colloid Science
A Celebration of the Career of Brian Vincent
By Simon Biggs, Terence Cosgrove, Peter Dowding
The Royal Society of Chemistry
Copyright © 2008 The Royal Society of Chemistry
All rights reserved.
ISBN: 978-0-85404-113-8
Contents
Chapter 1 A Journey Through Colloid Science Brian Vincent,
Chapter 2 Synthesis of Poly(N-isopropylacrylamide) Microgel Particles Containing Gold Nanoshell Cores with Potential for Triggered De-swelling Paul Luckham, Carlo Strazza, Pierre Bussierre, Paulo Nassari and Neil Patel,
Chapter 3 Polymer Chemistry, Hypervelocity Physics and the Cassini Space Mission Steven P. Armes,
Chapter 4 From Novel Monodisperse “Silicone Oil”/Water Emulsions to Drug Delivery Clive A. Prestidge,
Chapter 5 Polymers and Surfactants at Interfaces: Colloidal Lego for Nanotechnology Simon Biggs,
Chapter 6 Polymer Depletion: Recent Progress for Polymer/Colloid Phase Diagrams Gerard Fleer,
Chapter 7 Nanobubbles, Dissolved Gas, Boundary Layers and Related Mysterious Effects in Colloid Stability John Ralston,
Chapter 8 Heteroflocculation Studies of Colloidal Poly(N-isopropyl-acrylamide) Microgels with Polystyrene Latex Particles: Effect of Particle Size, Temperature and Surface Charge Martin J. Snowden, Louise H. Gracia and Hani Nur,
Chapter 9 Surface Modification, Encapsulation and Coating: A Career Built on Graft David Fairhurst,
Subject Index, 194,
CHAPTER 1
A Journey Through Colloid Science
Brian Vincent
SCHOOL OF CHEMISTRY, UNIVERSITY OF BRISTOL, BRISTOL BS8 1TS, UK
1.1 Early Days
Colloid science was not part of the chemistry curriculum at Bristol University during my undergraduate years (1961–4). However, interfacial science was very strongly established at Bristol, both in teaching and research. The Leverhulme Chair in Physical Chemistry had been established in Bristol in 1919, in part to keep J.W. McBain (a Canadian) from being tempted back to North America. McBain had been appointed as a lecturer in chemistry in the old University College of Bristol in 1906, three years before the University of Bristol received its charter and four years before the first, purpose-built university chemistry building in Woodland Road was completed. McBain rapidly established his name internationally for his work on the association of soap molecules in solution; hence the approach to Lord Leverhulme, who had built his soap factory (and Port Sunlight village for his workers) in Cheshire. Eventually, in 1927, McBain did succumb to a position in the USA, at Stanford University. In his place, W.E. Garner (an expert in solid-state chemistry and heterogeneous catalysis) was appointed to the Leverhulme Chair, and he was followed in turn by Douglas Everett in 1954. Douglas’s primary early interests were in gas adsorption (especially the role of porosity) and in adsorption from solution.
I joined Douglas’s very large research group in the academic year 1963–4 to carry out my final year undergraduate research project, although my project was supervised on a day-to-day basis by Alan Leadbetter (as was that of a contemporary chemistry student and good friend to this day, Terry Blake). My project was concerned with determining the surface tension, at low temperatures, of liquid ethane and nitrous oxide for some porosity studies Douglas was doing at that time. It required the building of a high-vacuum rig, for distilling the two liquids into a differential capillary rise cell. This was a challenging task for an undergraduate, but I received splendid help from a young trainee glassblower at that time, one Jim Goodwin, who, much later, after having obtained his PhD, transferred to the academic staff at Bristol and subsequently became an internationally renowned rheologist! Despite only obtaining reliable results pretty close to the end of my allocated project time, that work did result in my first scientific publication. In addition to Terry Blake, there were several others doing their undergraduate projects in physical chemistry at the same time, and with whom I have remained in contact over the years: John Comyn who became a professor in polymer science at De Montfort University, David Billett who worked at Tioxide before becoming a school teacher, Julian Waters who went to ICI Paints and Barry Ingram who had a long career with Proctor and Gamble.
During my final undergraduate year, in early 1964, a new lecturer was appointed in physical chemistry. He initially set up his equipment in our laboratory, where he also located his desk and his cohort of young researchers from Cambridge he had brought with him. That was Ron Ottewill, who subsequently went on to become the fourth Leverhulme Professor of Physical Chemistry, succeeding Douglas in 1982. Ron brought with him to Bristol expertise in colloid science. Douglas had hired him primarily to set up, along with Dr Aitken Couper, a new postgraduate, one-year master of science course in surface chemistry and colloids, by advanced study and research. Despite having applied to do a postgraduate teacher-training course, I was “informed”, as was Dave Billett, by Douglas Everett that we were to be “guinea pig” students on that very first MSc course in 1964–5 (the course was to last for more than 30 years!). There were six of us in total in that first year. The first two academic terms (twenty weeks) were spent doing lectures and “set experiments” (although most of these had to be set up as we went along!). The summer was spent doing a four-month research project, and I was allotted to work in Ron Ottewill’s group. That was where and when my introduction to the world of colloid science began, and I followed this up working with Ron for my PhD (1965–8).
At the time of his move to Bristol, Ron had already established himself as a leading international expert in the field of polymer latices prepared by emulsion polymerisation. My PhD project was concerned with studying the properties of polystyrene latex particles in alcohol–water media. The work fell in two parts. The first part was concerned with determining the composite adsorption isotherms of a series of alcohol (methanol to n-butanol)–water mixtures onto polystyrene particles, together with contact angle (sessile drop) studies of these same liquid mixtures onto thin polystyrene films, prepared by dissolving the latex particles in methylethylketone and evaporating a liquid film of the resulting solution on a glass slide placed in an oven. That work was followed up by me later with a theoretical analysis of the data, which led to a value for the surface tension of polystyrene (55 [+ or -] 3 mN m-1), and which was published as a conference proceedings. However, in hindsight, a much longer-term research interest was to develop from the second part of my PhD project. This was concerned with the coagulation (and corresponding electrophoretic mobility) studies of polystyrene latex particles (with surface carboxylic acid groups) in alcohol–water mixtures. We showed that the critical coagulation concentration (c.c.c.) for Ba(ClO4) 2 passed through a maximum with increasing concentration for each of the lower alcohols, from methanol to n-butanol. This was mirrored by corresponding maxima in the (negative) electrophoretic mobility of the particles and also in the relative adsorption of the alcohol molecules concerned on the particles. The explanation offered was that, at low concentrations of each alcohol species, the specific adsorption of the Ba2+ ions on the COO- groups on the particles was reduced by the adsorption of the alcohol molecules, raising the Stern potential, but that at higher alcohol concentrations the subsequent decrease in electrophoretic mobility, and hence the c.c.c. value, was due to a decrease in the ionisation of the COOH groups (to COO-) as the dielectric constant of the medium was reduced.
After my PhD studies were finished, I was fortunate to be awarded a Royal Society fellowship for one year, and, on the advice of Ron Ottewill, went to work with a young (relatively!) professor in Wageningen University in the Netherlands: Hans Lyklema. I was Hans’ second postdoc, Tharwat Tadros being the first. There I was introduced to the world of silver iodide (AgI) dispersions. Such dispersions had been a hot topic of research in both Utrecht (Hans’ alma mater) and Wageningen, as they seemed to be excellent model particles, whose charge was controlled by the pAg of the dispersion medium, rather than the pH, as in most other aqueous colloidal systems. AgI is a known ice-nucleator (in seeding clouds to induce rainfall, for example), so it was of interest to study AgI dispersions as the temperature was reduced towards 0 °C. The potentiometric titration data and c.c.c. values, in the presence of a series of alkali metal nitrate salts, suggested that there is indeed an increase in “water structure” at the AgI/water interface as the temperature approaches 0 °C, at least in the region of the zero point of charge of the AgI particles. Measurements on the effect of adding n-butanol to aqueous AgI dispersions were also carried out, in a follow-up to my PhD work. Again, a maximum in the c.c.c. for 1 : 1 electrolytes was found with increasing n-butanol concentration, with the evidence again pointing towards an initial displacement of specifically adsorbed counter-ions from the Stern layer by the preferentially adsorbed n-butanol molecules. That part of the work was carried out in collaboration with a young student, who later became a professor and world expert on proteins at interfaces: Willem Norde.
My year in Wageningen (1968–9) laid the foundations for subsequent collaborations in later years, not only with the Wageningen group (in particular a PhD student of Hans at the time, Gerard Fleer), but also with Tharwat Tadros, whom I came to know very well during that year. In fact, after a year working in the TNO laboratories in Delft, both Tharwat and I joined ICI in 1969, Tharwat at the ICI Plant Protection Division laboratory at Jealotts Hill, near Bracknell (now the Syngenta laboratory), and myself some 10 or so miles away, at the ICI Paints Division laboratory at Slough. In fact initially our two young families each occupied an apartment in an ICI-owned block of apartments in Maidenhead. I stayed at ICI Paints for almost three years, and during that time was privileged to work with some great scientists (and great people!). The praises of industrially based scientists rarely get sung sufficiently, but I learned so much working in the Slough laboratory (principally with “Ossie” Osmond, Fred Waite, Derek Walbridge, Ron Lambourne and Andrew Doroszkowski). In particular, I was introduced to the synthesis, characterisation and stability of polymer particles in non-polar solvents, and the concept of steric stabilisation. Working in a major industrial laboratory at that time was not so different from working in an academic laboratory. The laboratories were often directed by academically minded persons, who encouraged one to work on longer-term, more fundamental projects (with some relevance, of course, to the company’s products!), and also to publish!
One project I worked on at ICI concerned extending Marjorie Vold’s earlier theoretical analysis for calculating the van der Waals interaction between colloidal particles carrying adsorbed or grafted polymer layers, having a segment density distribution. Another project I worked on, which was later to become a major research theme of mine in my early years at Bristol, was the question of why some solvent-based, supposedly gloss paints lose some of their gloss during drying, especially under poor drying conditions. It was known that this was associated with aggregation of the pigment particles within the drying film. To help unravel this problem we worked on some model aqueous systems, polystyrene particles carrying terminally grafted poly(ethylene oxide) chains (PS-g-PEO particles). These particles aggregated over a fixed concentration range of PEO + water mixtures. This general phenomenon, i.e. the aggregation of colloidal particles in the presence of non -adsorbing polymers, eventually became known as “depletion flocculation”. I shall return to this theme in Section 1.3.3. We also tried to understand why the (reversible) aggregation we observed with our aqueous PS–PEO particle dispersions, in the presence of free PEO chains, was more akin to a phase separation process than classical (irreversible) coagulation (see Section 1.3.2).
My position at ICI also involved an appointment as a part-time lecturer at Bristol University. In fact Don Napper had held a similar dual position (ICI + Bristol) before me, prior to returning to Sydney. By the early 1970s, the first major international oil crisis was upon us and we had experienced the three-day working week in the UK, imposed by the Government in response to power shortages brought about by the miners’ strike. This brought changes to industrial practice and, in particular, managers decided that research needed to be more “focused”; “academic”-style research from then on would be less and less tolerated in industrial R&D laboratories — world wide. So for me it was time to move on from ICI. Fortunately for me, Frank Stone moving to Bath University from Bristol created a vacancy in the physical chemistry staff. So I applied and was fortunate to be selected, and in 1972 I moved full time to Bristol, as a lecturer.
My research over the last 35 years at Bristol has evolved in many different directions. In many cases new research themes have been initiated by something discussed at a conference or by tackling some challenge proposed by a colleague in industry. Indeed, I would estimate that roughly half my research sponsorship over the years (which has supported about 90 PhD students and about 50 postdocs/visitors) has come from industry. I have always enjoyed the challenge of solving technological challenges, as well as opening up new basic, scientific directions. However, I have always insisted that any research that we did in collaboration with industry should be of a nature that would lead to eventual publication in the open literature. In order to describe the last 35 years’ research of my group at Bristol, I will from here on resort to research “themes”, rather than to continue to describe the work in chronological order.
1.2 Novel Colloidal Systems
1.2.1 Particle Synthesis
For maybe forty years after the Second World War, one could argue that colloidal physics was the most dominant and influential area of colloid science. Not only did an extensive literature develop around the theory of the physical properties of colloidal systems, mainly in the wake of the “DLVO” theory of the aggregation of colloidal particles, but there were considerable developments also in the various areas of physics which underpinned the new instrumentation available to experimental colloid scientists. However, during that period the actual systems available for study were rather limited: latex particles (especially PS latex), metal oxides (e.g. silica) and inorganic salts (e.g. AgI) were the prime candidates for most researchers in the field. Each system had its advantages and disadvantages. Studies of classical liquid–liquid dispersions (emulsions) were also limited in that polydispersity was a real problem, although the much more monodisperse microemulsions were being increasingly investigated. In the last twenty to thirty years, colloidal chemistry has made a strong comeback. We now have available a large array of particles which have well-defined size and shape, as well as structure, composition and physical properties; monodisperse liquid droplets are also now available. These developments have been stimulated, in part, by the challenges that have been thrown up by so-called “nanotechnology”.
I have always tried to maintain a strong synthetic aspect to my research at Bristol, and in the sections that follow I describe some of the main types of colloidal system on which we have worked. There have been a number of systems we have worked on where we have tried to understand, often in collaboration with industrial colleagues, the physical principles underlying the formation of specific types of colloidal particles. One example would be the work that Jenny Saunders did for Laporte Ltd in trying to control the properties of synthetic Laponite clay particles by systematically varying the ratios of chemicals used in the synthesis, and then studying the structure of the particles with small-angle X-ray scattering. Tim Muster, in collaboration with Rhodia, studied particle formation (and subsequent gel formation) on adding oligomeric phthalate-based polyesters to water. David Voisin, sponsored by Unilever, similarly studied particle (and gel) formation in mixtures of cationic polyelectrolytes and anionic surfactants.
Polymer latex particles, as discussed earlier, have proven to be a major class of model systems, widely studied in colloid science. Much of the earlier work on the synthesis of specific types of latex particles in my group will be described in later sections, e.g. “hairy” latex particles carrying terminally attached polymer chains (Section 1.2.2), electrically conducting latex particles (Section 1.2.3), very small (~ 10 nm) polystyrene particles (Section 1.2.4), very large (~ 100 µm) monodisperse, porous polystyrene particles (Section 1.2.5) and swellable latex particles (Section 1.2.7). However, we have returned very recently to a couple of “classical” themes in this area. In one project Ciaran Martin has been trying to advance our understanding, in collaboration with AGFP, of the mechanisms underlying the formation of polytetrafluoroethylene particles by dispersion polymerisation of the dissolved, gaseous monomer. In the second topic Aaron Olsen, from Newcastle University in Australia, has been synthesising amphoteric polystyrene particles, with a controlled iso-electric point, by using a mixed initiator system, and trying again to understand the mechanisms involved, following up some earlier studies by Ron Ottewill.
One fascinating area of particle formation in biosystems that I was closely involved with was undertaken by Alan Hemsley, a palaeontologist at Cardiff University. The pore walls of certain pollen and spore species exhibit iridescent colours (see Figure 1.1). This is due to the crystallisation of natural latex particles in the walls, subsequent to their formation in aqueous droplets which eventually evaporate. We tried to simulate the particle formation and subsequent crystallisation processes using synthetic materials.
(Continues…)Excerpted from New Frontiers in Colloid Science by Simon Biggs, Terence Cosgrove, Peter Dowding. Copyright © 2008 The Royal Society of Chemistry. Excerpted by permission of The Royal Society of Chemistry.
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