Categoriearchief: Verhalen

Camperplaats De galgenwaard

De Galgenwaard is een recreatiegebied aan de Linge, vlakbij Oosterwijk. Er is een grasveld, speeltoestellen, sanitair en je kan er zwemmen. Maar je kan er ook met een kampeerwagen staan. Dat hebben wij afgelopen weekeinde gedaan.

We waren daar om kennissen te bezoeken die aan de overkant van de Linge, in het stadje Heukelum, wonen. Het bijzondere is nu, dat er ook een veerpont is die van 1 april tot 1 oktober vaart. Daarmee konden ze vanuit Heukelum overkomen om de kampeerauto te bekijken.

Dat is toch wel een bijzondere manier om gasten te ontvangen. Later zijn we overigens mee terug gegaan. Het regende die zondag best wel veel. Maar bijzonder was het wel. En de nacht hebben wij uitermate rustig doorgebracht!

Process Nano-Technology

Appeared earlier in TG magazine 6 of 2003.

At first glance, the title may seem a contradictio in términis because for nano-technology the relevant length scale is the nanometer – one billionth of a meter or the length of a row of 10 hydrogen atoms laid side by side – whereas for process technology the relevant length scale is meters or beyond. It is exactly this discrepancy of more than nine orders of magnitude in length scales that allows the new direction in chemical process technology that will be discussed below: in essence another way of Nature Inspired Chemical Engineering (NICE), or even better, Nature Inspired Colloidal Systems (NICS), as a new direction for our Colloid Science group.


“It is a staggeringly small world that is below,” said the famous physicist Richard Feynman in his 1959 speech about nano-technology There’s Plenty of Room at the Bottom [1]. “In the year 2000, when they look back at this age, they will wonder why it was not until the year 1960 that anybody began seriously to move in this direction”. Indeed, 40 years after, nano-technologists have come quite far and it is not easy to cover all the contributions that have been made. Surely nano-tubes come to mind as well as molecular motors, but also improvements in sub-micron lithography fall within the realm of nano-technology. A specific definition of this new field is however not so easily given. A generic definition would involve a characteristic length scale of about one na­no­meter. Quite unlike their wont, physicists do not bother too much about a definition and name nano-technology whatever lets them (i) Get essentially every atom in the right place; (ii) Make almost any structure consistent with the laws of physics that one can specify in molecular detail; (iii) Have manufacturing costs not greatly exceeding the cost of the required raw material and energy. Two main concepts associated with nano-technology are positional assembly and self-replication. The first concept implies an interest in molecular robotics. i.e. robotic devices that are molecular both in their size and precision. Self-replication on the other hand is of course required to scale up the production of the materials.

Contemporary chemical processes are crude at the molecular level moving around atoms in bulk quantities. It is the Law of Large Numbers that governs them and our main control mechanisms involve bulk properties such as flow rates and temperature. Process technology indeed does look like a giant’s attempt to make an origami butterfly. But surely, this is not the whole story about chemical process technology. There are many processes that make use of colloidal systems such as emulsions and particulate dispersions. Examples are easily found in the food or paint industry. For the relevant characteristic length scale one usually takes the dimension of the particles that constitute colloidal systems. This yields length scales in the range from tenths of nanometers up to hundreds of micrometers.

Interfacial Engineering

Fig. 1:    Schematic representation of the principle of charge stabilization. The diffuse double layer around the colloidal particles consists of co-ions (closed) and counter-ions (open). Upon closer approach the bare charge of the particles becomes less screened.

Most, if not all, properties of the colloidal systems derive from the interface between the dispersed phase and the continuous phase. The essential task of the interface is to keep the two phases separated and is commonly known as colloidal stabilization; see e.g. [2,3]. There are basically two different methods to achieve colloidal stability. One method involves dissociated groups at the interface that render electrical charge to the interface and the particle as a whole. Since equally charged objects repel each other, this charge prevents particles from aggregating or coalescing. The counter ions and added salt ions will, however, accumulate close to the interface in what is called the diffuse double layer, see figure 1. They do so in such a way as to diminish the effect of the charge over larger distances; a phenomenon called screening. The associated DLVO-theory is due to Derjaguin, Landau, Verwey and Overbeek. The multitude of contributions to this subject by Dutch colloid scientists is reflected by the two last names mentioned in the acronym DLVO by which this theory is known. The Debye length measures the thickness of the electrical double layer that, depending on ionic strength, varies from several tenths of nanometers down to less than a nanometer. The other method is called steric stabilization and, despite its frequent use in industrial processes, much less is formally known on its mechanism of which the essence is depicted in figure 2. The adsorbed or chemically grafted polymer chains prevent close encounters of colloidal particles. A (too) simple argument for the repulsion lies in the gain of the free energy of mixing when the polymer chains of neighboring particles are overlapping. The thickness of an adsorbed or grafted polymer layer can be varied at will. Since its function is to shield the omnipresent Van der Waals attraction between the colloidal particles, a thickness of a few nanometers is sufficient.

Fig. 2 Schematic representation of the principle of steric stabilization. Upon closer approach the polymer chains would mix which is entropically unfavorable.

The characteristic size of the colloidal interface is in the nanometer regime. And there is quite some of it! In a system with the rather modest fill factor of 10% consisting of colloidal particles of a typical size of one micrometer there is about 300 m2 of interfacial area per liter. Interfacial Engineering, a word coined by Stokes and Evans [3] as an alternative to the rather old fashioned name of colloid and interface science, therefore certainly belongs to the nano-technologies!

A classical example where interfacial engineering plays a dominant role on an industrial scale is emulsion polymerization for the preparation of polymer particles (latex) by radical polymerization. The dispersed phase is initially formed by the monomers. A small amount of monomers, in equilibrium with the dispersed monomer, is dissolved in the continuous phase. The initiator, also in the continuous water phase, starts the polymerization by penetrating through the particle surfactant membranes. Some initiator may encounter monomer in the continuous phase and start polymerization there, but at some point the growing molecules become insoluble and form surfactant coated polymer particles themselves. Excess heat is easily removed through the continuous water phase. Depletion of monomer terminates the reactions. The process is fully controlled by the interface and by the surfactant molecules that constitute the interface. Moreover, even at quite significant volume fractions the viscosity if the dispersion is quite low which renders processing extremely simple. Modern developments include the use of spherical and bicontinuous micro emulsions for polymer and inorganic particle templating.

Controlled Release and Separation

A multitude of present day products, such as high quality paper or water borne paints, are made by sophisticated use of interfacial engineering. In all these products and processes the interface plays the simple role of separating two phases, albeit a given level of permeability to certain constituents is programmed. Recently, new functions have been introduced and one has made interfaces that are responsive to their environment in a predetermined manner. An example is the potion containing cod liver oil, which of old is fed to young children in winter to supplement their vitamin A and D intake. In wintertime there is less sunlight and hence the body production of these vitamins is low, for instance causing rachitis.  Few children are fond of this potion in its classical form. The present form is in fact an emulsion where the yellow oil is dispersed in an orange juice. Due to the interface, the badly tasting oil will not free in the mouth. Upon digestion, the interfacial membranes in the emulsion are destroyed and the cod liver oil can release the vitamin in the intestines.

Nowadays, many pharmaceuticals make use of this principle of controlled release. However, when controlled release is one way to govern a process, then controlled separation would be another. The exposure of an absorbent when exterior conditions are fitting is also a technique and it is already used as a means to catch poisonous molecules before these can permeate into the blood circulation.

Nano-structured Interfaces

Much more control would be attainable if it were possible to integrate more functions in the interfaces. Such nano-structured interfaces could respond to changes in their environment in a predetermined manner, much in the same way as the simple examples given above. More interestingly, these nano-devices could also be made to respond to external signals brought about by magnetic fields or light. Imagine for instance two solutions con­tai­ning strong reagents. Simply mixing them would yield incomplete reaction and uncontrolled heat production. These may become well mixed, without reacting, when one component is dispersed in impermeable colloidally sized capsules. At some stage in the process, where mixing is deemed sufficient, the permeability of the capsules is increased proportional to an external signal. The reaction will now run in a controlled manner under optimal conditions. This maybe sounds too fantastic, but one way to achieve this would be to make the capsules of a material that can be selectively modified by the action of microwaves or ultra­violet light.

Fig. 3 Synthesis of a nano-capsule by sequential adsorption of counter charged polyelectrolyte layers and subsequent removal of the core particle.

What is needed to turn this fantasy into reality is first of all methods to make nano-structured interfaces. Currently, there are quite some promising developments in that direction. One such development uses layer-by-layer deposition of alternately cationic and anionic polyelectrolyte layers on a core particle. The core particle can be a polymer particle itself, or a metal or inorganic particle, see fig. 3. The result is a multilayer core-shell particle with predetermined surface properties. In an extension of the technique, one removes the core particle after which the shell remains of which the permeability can be tuned by external means. Another development involves the adsorption of nano-sized particles onto the surface of a colloidal particle, see fig. 4. Under the right conditions, capillarity forces the nano-particles to fully cover the colloidal particle. Extensions of this technique involve the fusion of the nano-particles after which a core-shell particle with specific properties is created. Another extension is, just as with the polyelectrolyte coated particles, the removal of the core after which a so-called colloidosome is created. The size of the shell particles depends on the size of the initiating core particle. These above examples deal with so-called self-assembling systems but of course direct synthesis constitutes another possibility.

Fig. 4: Synthesis of nano-structured colloids by adsorption of anano-particle monolayer. Subsequent removal of the core particleleaves a capsule (top right), and fusion of the adsorbed monolayerresults in a coreshell particle (bottom right).

The way nano-structured interfaces are made already suggests methods to control them. The multilayer polyelectrolyte capsules can be controlled by pH or ionic strength whereas the colloidosomes are quite insensitive to these variables. Other methods to induce a particular response in nano-structured interfaces require the incorporation of, for instance, inorganic particles or more complicated structures. Some macromolecules such as present in biological cells could also introduce useful functions. In this sense, nano-structured interfaces are not new at all as Nature has designed its systems likewise.

Control of processes by means of nano-structured interfaces can be based on two complementary approaches: (i) extreme control, an internal stabilization by coupling rate phenomena to the environmental variables such as concentrations; and (ii) process control, by using the functions of the interfaces either as sensors, as actuators, or both. The dynamics of the system will be completely different from what is presently known. It will for instance not be possible to treat the system as a continuum and it will be necessary to find ways of including nano-devi­ces that are acting almost at the molecular level into a complete system description. It poses a serious challenge to process engineers to devise new models to perform process nano-control. Certainly, there is the potential of more powerful process control with the added degrees of freedom provided by the nano-structured interfaces.


Nano-structured interfaces also provide a new pathway to design and operate processes in a sustainable manner according to a philosophy of closed material cycles and maximum energy efficiency. At first glance, there is the disadvantage of introducing components into the product that were used to build the nano-structured interfaces. It might contaminate the product and it may even pose a hazard. In terms of mass, the amount of these materials is quite low and in many cases the end product often comes in dispersed form anyway. The cost involved in making the nano-structured interfaces should be recovered by the added value to the products.

However, the nano-structured interfaces can actually be used to advantage. Firstly, one may contain toxic or otherwise harmful reagents in impermeable capsules so as to transfer the material in a safe and efficient way towards the relevant process step. Secondly, one might conceive the possibility of capturing selectively some products in capsules so as to separate them efficiently from the environment. Essentially, once a process is properly designed, sustainability can be achieved at any level.

More fantasy

Once the way to make nano-structured is known, many more tasks may become feasible. Some of those derive back to controlled release and separation between continuous and dispersed phase. And there is no limit to the number of dispersed phases. It is easy to conceive multiphase systems where exchange between phases is controlled by internal or external means. But the interface can act as a scavenger itself. In order to achieve that, we can dress the interface with molecular entities, in essence nano-devices, that complex specific molecular species such as contaminations. Recently, new molecules have been designed that allow the control over complexation by means of light. In one conformation the molecule is able to complex a metal ion and in the other not. Transition between these two conformers is affected by light.

An interesting possibility is to design nano-structured interfaces in such a way that they could also be used to bring molecules in the right proximity to synthesize special molecules, so as to produce for instance straight alkanes from methane without producing syngas. This would require more accurate positioning of groups within the interface. With present day polymerisation methods that are used to make for instance block copolymers this might become reality as well. Extending this idea, nano-devices could act as catalysts themselves or allow the external control of the action of catalysts. And similarly nano-devices could be used to control the number of crystallization nucleation sites and maybe even crystal shape and maximum size comes to mind.


The ideas presented above, of which some are actively being researched, constitute a new challenge to chemical process technology. It is in fact a combination of old and new science because colloidal stability will remain an issue, in particular when interfaces are changing their function. The challenge to good old colloid science is to rejuvenate with the newly available nano-possibilities while treasuring its scientific standards with respect to colloidal stability.

Let’s now come back to what the physicists believed nano-technology would allow them to do and see whether the above discussed process nano-technology. The first issue was “Getting essentially every atom in the right place”. Surely this is an easier job with fluids than with the solid state, but nano-structured interfaces indeed can do just that. But chemists can go further, as it is within their capabilities to synthesize new molecules. The second issue was “Making almost any structure consistent with the laws of physics that one can specify in molecular detail”. The relevant physical laws are those of quantum mechanics. Even though in principle these laws are known, their predictive power in chemistry is rather limited. In actual fact, chemists often devise methods that seem to lure quantum chemistry. Finally, the third issue was “Have manufacturing costs not greatly exceeding the cost of the required raw material and energy”. As argued before, the cost involved in making and using nano-structured interfaces should at least balance with the added value of the resulting products. In addition, legislation may make the difference, as was the case for water borne paints. The necessity to produce a solvent-free product made manufacturers introduce dispersions of binder and pigment despite their intrinsically higher cost. In conclusion, there is no contradictio in términis.


  • Feynman RP, see
  • Frens G, Cahiers Fysische Chemie, Delft University Press 2001.
  • Stokes RJ and Evans DF, Fundamentals of Interfacial Engineering, Jossey-Bass 1996.


Voorwoord bij TG almanak 106 in 2006.

Beste TG’ers en belangstellenden,

Het is een indrukwekkende traditie, de “Almanak van het Technologisch Gezelschap”. Nummer 106 alweer. Gefeliciteerd daarmee.

Als we ervan uitgaan dat elk jaar een nieuwe almanak is verschenen, dan zou in 1901 de eerste almanak zijn uitgegeven. Dat is precies het jaar waarin Jacobus Henricus van ’t Hoff, als eerste, de Nobelprijs voor de scheikunde kreeg. Voordat het zover was heeft van ’t Hoff een behoorlijk moeilijke tijd gehad. Terwijl hij uit alle macht op zoek was naar een fatsoenlijke aanstelling publiceerde hij het pamflet waarin hij voorstelde om moleculen niet als 2-dimensio­nale maar als 3-dimensionale objecten te zien. Daarmee kon hij allerlei tot dan toe onverklaarbare feiten verklaren, zoals het verschil in optische activiteit van glucose en fructose. Het was een gewaagd stuk en het ontlokte de organisch chemicus Kolbe een cynisch essay getiteld “de tekenen der tijden II” dat in mei 1877 werd gepubliceerd. Daarin betichtte hij van ’t Hoff er van “Pegasus” beklommen te hebben voor een gewaagde tocht door het “chemische Parnassus” vanwaar het hem toescheen dat atomen gerangschikt zijn in ruimtelijke structuren. Kolbe was van mening dat wetenschappers zich tot de feiten moesten beperken en betoogde dat het niet alleen onwetenschappelijk maar ook schadelijk is voor wetenschappers om de fantasie de vrije loop te laten. Dat kwam hard aan!

Maar van ’t Hoff sloeg keihard terug met een flitsende inaugurele rede in 1878 waarin hij betoogde dat fantasie en wetenschap niet zonder elkaar kunnen. Bij elke wetenschappelijke handeling is er

  • de keuze van wat en wanneer waar te nemen;
  • de keuze om de experimentele onderzoeksomstandigheden te veranderen;
  • het uitvinden van nieuwe onderzoeksmethoden;
  • de herkenning van onverwachte patronen in waarnemingen;
  • het uitvinden van een hypothese om de waarnemingen te verklaren

Einstein verwoordde het veel krachtiger “Verbeelding is belangrijker dan Kennis”.

Voor technologen, uw gezelschap dus, is verbeelding minstens zo belangrijk als kennis: creativiteit noemen we dat nu. De PublicatCie die deze almanak heeft samengesteld had daar zeker niet te kort aan, u zult het zien als u er in bladert. Het thema wordt geïntroduceerd  als “iets dat aandacht trekt, met weerlicht en discolicht. Vanzelfsprekend moet bij deze presentatie ook de aandacht worden getrokken voor het thema; dat doen we zo …

Jacobus Hendrikus van ‘t Hoff

Eerder verschenen in TG-Magazine 17-1 van oktober 2013.

J.H. van ‘t Hoff door Marian Nugteren (201 3)

De “Procestechnologie” heeft J.H. van ‘t Hoff als icoon verkozen, maar waarom eigenlijk? Van ’t Hoff staat bekend als de eerste – en bovendien de eerste Nederlandse – Nobelprijswinnaar in de Chemie. Hij is het meest bekend voor zijn uitwerking van de consequenties van een drie-dimen-sionale structuur van moleculen. Zijn verdere werk betrof reactiekinetiek en colligatieve verschijnselen zoals de osmotische druk. Onderwerpen die weliswaar dichter bij de procestechnologie staan dan de moleculaire structuur, maar toch niet het hart ervan vormen. De “Procestechnologie” zelf noemt als belangrijkste feit dat van ’t Hoff in Delft heeft gestudeerd maar als dat de enige reden is dan is dat wel een erg gezochte.

Is de keuze dan niet terecht geweest? Niets is minder waar! Er is een hele goede reden waarom juist van ’t Hoff gekozen zou moeten worden. Van ’t Hoff kwam immers tot het voorstellen van een driedimensionale molecuulstructuur doordat hij er achter kwam dat moleculen met precies dezelfde atoomgetallen toch verschillende fysische eigenschappen hadden en op basis daarvan
gescheiden konden worden. Hij zelf werkte het voorbeeld van melkzuur uit, waarvan een links- en een rechtsdraaiende variant
bestaan. En scheiding, dat is de kern van de procestechnologie. Wat dat betreft is het uiterst toepasselijk dat wij Nederlanders spreken van scheikunde voor wat in andere landen als chemie wordt betiteld. De andere bijdragen van van ’t Hoff, aan de reactiekinetiek en de colligatieve verschijnselen, komen daarmee ook beter tot hun recht.

En er is nog meer! Nadat van ’t Hoff zijn voorstel had gepubliceerd werd dat door de zittende chemici veroordeeld als fantasie. De organisch chemicus Kolbe schreef “Er hat es bequemer erachtet, den Pegasus (offenbar der Thierartzneischule entlehnt) zu besteigen, und zu verkünden, wie ihm auf dem durch kühnen Flug erklommenen chemischen Parnas die Atomen im Weltenraume gelagert erschienen sind …”. Op al die aantijgingen heeft van ’t Hoff niet gereageerd. Allengs raakte zijn voorstel meer geaccepteerd en in 1878 aanvaardde hij het ambt van hoogleraar in Amsterdam. In de inaugurele rede die hij toen uitsprak reageerde hij voor de eerste keer op alle aantijgingen uit het verleden. De titel van de rede was “de verbeeldingskracht in de wetenschap” en daarin zette hij nauwkeurig uiteen welke belangrijke rol fantasie in de wetenschap speelt. Velen hebben, voor en na hem, aangegeven dat creativiteit in de wetenschap belangrijk is voor de ontwikkeling, maar van ’t Hoff
gaf heel nauwkeurig aan dat het om een samenspel tussen kennis en creativiteit gaat: pas als men het wezen van de bekende verschijnselen kent kan men deze verweven tot nieuwe combinaties met nog niet eerder gerealiseerde eigenschappen.

Creativiteit en technologie zijn ook sterk verweven. Als de gemeente Delft een nieuwe brug over de Schie wil hebben, dan kan zij natuurlijk wat foto’s op het internet bekijken en een geschikte uitkiezen. Bijvoorbeeld de Golden Gate Bridge in San Francisco.
Daarna kan men contact leggen met een aannemer om een op schaal gemaakt model te laten maken zodat die goed past over de Schie. Dat doen gemeentes als Delft toch liever niet, men wil een “eigen” brug en stapt dus naar een architect om een nieuwe – nog niet bestaande – brug te laten ontwerpen die vervolgens door een aannemer geconstrueerd kan worden. Zo ook in de procestechnologie. Als een bedrijf een proces wil veranderen, dan
liefst tot een proces dat nog niet eerder ergens gerealiseerd is en zo mogelijk veel efficiënter is dan alle bestaande processen. Dat is de manier om een voorsprong op andere bedrijven te verwerven die de
realisatie van zo’n proces rechtvaardigt! Dus, als de procestechnologen weer gevraagd wordt om een reden waarom
zij van ’t Hoff verkozen hebben tot hun patroon dan doen zij er goed aan zich eens te verdiepen in zijn werk.

• J.H. van ’t Hoff, Voorstel tot uitbreiding der tegenwoordig in de scheikunde gebruikte structuur-formules in de ruimte: benevens een daarmee samenhangende opmerking omtrent het verband tusschen optisch actief vermogen en chemische constitutie van organische verbindingen, Greven 1874.
• W.J. Hornix en S.H.W.M. Mannaerts, Van t Hoff and the emergence of Chemical Thermodynamics, IOS Press 2001.
• J.H. van ‘t Hoff, De verbeeldingskracht in de wetenschap. P.M. Bazendijk, Rotterdam 1878.

Gert Frens 1937 – 2013

Eerder verschenen in TG Magazine 16-3 in maart 2013.

Gert Frens

Afgelopen februari is onze oud-collega prof. dr. Gert Frens overleden aan de gevolgen van een nare ziekte. Op 16 maart 1988 aanvaardde prof. Frens het ambt van gewoon hoogleraar in de fysische chemie met het uitspreken van de rede Omgaan met het Onbekende. Hij was een markante man die er niet voor schuwde om wat weliswaar zorgvuldig geformuleerde maar niettemin uitdagende, uitspraken te doen om de uitgebluste discussie over een onderwerp open te breken. Dat heeft hem tot een aantal wetenschappelijke successen gebracht waar tot op de dag van vandaag aan gerefereerd wordt!

Ook studenten daagde hij op onnavolgbare wijze uit, waarbij hij het zich als zijn taak zag de eerste Nobelprijswinnaar in de Scheikunde, Jacobus Henricus van ‘t Hoff, tot voorbeeld te stellen wanneer het belang van de Verbeeldingskracht in de Wetenschap* aan de orde was. Graag wees hij hen op hun eigen verantwoordelijkheid bij “de keuze van de weg die hen verder zou voeren dan de horizon van de TU”. De laatste zinsnede is een variatie op zijn lijfspreuk die hij ook als titel gebruikte voor zijn uittreerede uitgesproken op 1 november 2002. Nu siert deze spreuk – zeer gepast – de rouwkaart.

Na zijn vertrek uit Delft heeft prof. Frens zich verdiept in de oorsprong van kabouterverhalen in zijn woonomgeving Brabant, een belangstelling die al was gewekt toen hij werkzaam was bij het Philips Natuurkundig Laboratorium. Steeds minder frequent werden zijn bezoeken aan de TU, waarbij hij het niet kon nalaten ons ervan te overtuigen niet de kortzichtigheid van het management te volgen maar onze eigen lijn voorbij de einder te trekken. Dat is nu helaas definitief afgelopen: hij ruste in vrede! Wij wensen zijn familie veel sterkte toe met het dragen van het gemis van deze bijzondere man.

*Inaugurele rede JH van ‘t Hoff bij het aanvaarding van het hoogleraarsambt aan de Universiteit van Amsterdam, 1878.

Faraday’s gold

Appeared earlier in TG Magazine 22-3 of April 2019.

Faraday’s laboratory in the Royal Institution

Michael Faraday (1751-1867) was fascinated by gold when he found out that ultrathin sheets kept their yellowness upon light reflection as for normal gold but looked green upon transmission. Moreover, when etching the sheets to clean them he found the cleaning liquid to turn ruby red. This urged him to perform an impressive series of experiments the results of which are summarized in his Bakerian lecture to the Royal Society in 1857 [1]. He argued that the ruby red light was due to the strongly wavelength dependent scattering of light that we nowadays know as the Faraday-Tyndall effect. The same effect is also responsible for the blue color of the sky.

My first exposure to colloidal gold – metallic gold particles of submicron size – was in the late 70’s when working as an electronics engineer in the pre-clinical cytology laboratory of the Leiden academic hospital. The gold particles were used for the detection of tropical infections such as schistosomiasis (also known as bilharzia) in what is known as the Enzyme-Linked Immuno-Sorbent Assay  (ELISA). My involvement [2] was the automated readout of trays with cups, one for each essay, in such a way that it could also be used in the lesser equipped laboratories in the tropic areas where the infections were frequently found. The gold particles, coated with a special protein, were responsible for the amplification of signal used for the detection of reaction product from the immune-reaction.

Later on, during my PhD-studies at the Lorentz Institute for Theoretical Physics, I learned more about the properties of submicron-sized metallic particles. Some of my colleagues studied the optical properties of gold nanoparticles when deposited, a bit like truncated spheres, on sapphire. This was done under the supervision of Jan Vlieger and Dick Bedeaux who later on summarized these and many more findings in their monograph on the Optical Properties of Surfaces [3]. The scattering of gold particles that Faraday observed is due to the fact that the surface plasmon resonance causes a sharp absorption peak for light in the visible regime. Other metal particles in that size range do that similarly but due to material properties of gold this happens to be exactly in the visible part of the spectrum. As it is an interfacial property, it critically depends on surface coverage as employed in the ELISA, on the precise shape of the particles as studied by my colleagues and on the close vicinity of a surface.

Although Faraday was smart enough to identify the ruby red color of the cleaning liquid being due to small dispersed gold particles, the willful synthesis of colloidal gold is far from trivial.  Yet, it was one of the  most challenging areas in alchemy to produce the Elixer of Life,  i.e. potable gold; it was searched for during many centuries. Because of gold’s sheer indestructibility, alchemists ascribed a great therapeutic value to Aurum Potabile (drinkable gold). Only in the late 19th century systematic synthesis routes became available through the work of – amongst others –the 1925 Chemistry Nobel Prize winner Richard Zsigmondy.

It was not before the work of our late TG-Member of Honour, professor Gert Frens that controlled nanoparticle synthesis became feasible. As a consequence most Chemical Engineering students that studied in Delft between 1988 and 2002 were exposed to this synthesis route under the guidance of Nico van Westen, the physical chemistry laboratory technician of those days. Frens’ Nature paper [4] on this topic is still heavily being cited and techniques like the one he proposed are used as of today. The reason for this is most probably not in the many samples of Aurum Potabile that are on offer today and sell at rates of the order of 10 euro per ml; it is supposed to heal all illnesses! Despite the high price, the turnover is relatively little. It is also not in the ELISA applications for tropical deceases and others pharmaceutical applications. It is the pregnancy test that is based on ELISA that makes most of the money!

Much later, we ourselves turned our interest in the synthesis of metal nanoparticles. In contrast to the many synthesis routes available, our aim was in making fine, uniformly sized nanoparticles at high yields. Conventional routes provide nanoparticles at relatively low concentration, because at higher concentrations the particles aggregate into larger structures yielding non-uniform particles. While preparing a manuscript [5] on our high yield synthesis of uniformly sized gold nanoparticles, a discussion on the stability time scale of colloidal dispersions developed in which it seemed appropriate to mention the world record in this: the more than 150 year stability of the gold sols prepared by Michael Faraday. For the manuscript at hand, a primary source was needed to refer to but whatever we could find; they were all – at best – secondary sources: information collected by others. One of the more explicit sources, the web site of a well-known, British manufacturer of colloid scientific equipment, mentions the Science Museum in London. Many other sites and documents do likewise.

After sending an electronic request to the conservator of the museum, the following answer was received “The situation is a little bit complex. Until 1999 we had a Faraday exhibit which displayed gold films deposited on watch glasses made by Faraday alongside a tall vessel containing colloidal gold prepared according to the Zsigmondy’s method which otherwise had nothing to do with Faraday.” The interesting consequence of this statement by the conservator of the Science Museum could be that there are quite a few false statements about and very likely even pictures of vessels not older than a few years instead of the 155 as claimed!

Faraday’s Gold

A further message from the conservator of the Science Museum revealed that some gold sols, of which pictures circulate the internet, could be from the Royal Institution (Ri), also in London. The confirmation came from the Curator of Collections who stated that “They are on permanent display within the Michael Faraday Museum area of the Ri, on the lower ground floor of the building, within the only section of Faraday’s original laboratory that still exists.” In addition, pictures were sent of which one accompanies this article and demonstrates the Tyndall effect that betrays colloidal dispersions. So, the gold sols made by Faraday are indeed in London but not in the often mentioned Science Museum but in the museum of the Royal Institution. We are happy to have spent some time finding out the truth about these gold sols and not to have merely repeated a false statement.


  • M. Faraday, Philos. Trans. R. Soc. London, 147 (1857) 145 – 181.
  • A.M. Deelder, G. Koper, R. de Water, et al., Automated measurement of immune galactosidase reactions with a fluorogenic substrate by the aperture defined microvolume measurement method and its potential application to Schistosoma mansoni immune diagnosis. J Immunol. Methods 36 (1980) 269-83.
  • D. Bedeaux and J. Vlieger, Optical Properties of Surfaces, Imperial College Press, London 2002.
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Consultancy role game

One reason for an organization to employ a consultant is because there is a problem for which it is deemed that specific expertise is needed. Let me state beforehand that this is a very strange situation. Who would know more about the organization than the people working there themselves? It is almost certain that all the required knowledge is in the organization but that there is some specific – that is to say at least one – aspect that prohibits the people from addressing the problem. This is a very common situation and the method that is described below aims to help resolve this.

It is for certain that inviting an expert to discuss the problem may help. Many times, explaining the problem to a person who has not been exposed to it before already allows the people to see the solution themselves. For that situation, one just needs a patient listener who tells you when something is not clear. The role game that we discuss here actually allows people to solve problems amongst oneselves. In all cases, the art is to find a flaw in the reasoning that so far has kept the organization from finding the solution. The game below is designed in such a way to avoid the situation where the consultant is caught in the same trap by following the same flaw in the reasoning.

When a group is formed, roles are to be assigned. In this game there are three different roles. One is the problem owner, the next is the discussion leader who monitors the process and who notes down important facts and the other group members are consultancy students. The latter term originates from the fact that this game has been done many times during courses that we taught in universities and companies.

In this game we discriminate five different stages: preparation, problem statement, problem evaluation, solution generation and conclusion.

During the preparation, the roles are distributed and the problem owner is instructed how to present the problem. This problem statement must involve the desired state or process and the methods and/or experiments done to achieve this – and failed so far. A chronological order is not necessary and may even be undesirable. The best situation is where the problem owner has the problem written down on a single sheet of paper. The problem owner is to read each line slowly so that the consultancy students may ponder each. He should be prepared to stop at every instant of time such as required by the consultancy students.

During this part of the game, the consultancy students should not ask questions other than to clarify the text itself. They should carefully and quietly listen to follow the factual information. After each line, they should try to think of what the next line from the problem owner should be within their understanding of what has been said so far. At each point where their idea differs from what the problem owner states, they should make a note of this discrepancy. The problem owner may be stopped at any time to allow for time to write something down. Again, there should not be a discussion yet.

When the problem owner has brought forward his statement, the problem evaluation stage is entered where consultancy students may ask questions to clarify particular aspects to make their idea and notes clear. Still, no discussion is to take place but the consultancy students may benefit from each other’s questions and the subsequent answers from the problem owner.

When all questions are handled, the solution generation stage is entered. This is the time where the consultancy students may discuss amongst themselves about the discrepancies that have been found. The discussion leader is to take care that all discrepancies are dealt with, even if these seem to be similar. The problem owner is not to participate in this discussion but may – when asked – provide additional factual information.

After some time, a conclusion is drawn from the solution generation discussions. It is very common that the time for discussions proves to be too short but that in itself is not a problem. There may be more than one line of reasoning that may lead to a solution. These should be noted down by the discussion leader for the problem owner.

The role game described above does not necessarily lead to a solution of the problem but may point at discrepancies between information provided by the problem owner and what appears to be logical from common knowledge. These should then be taken home by the problem owner to work out.