My Research Story

Some of my former scientific colleagues and friends might be interested to know how everything started and why we ended up where we were. For this reason, I decided to write this short story about my scientific background. Its highly personal and hardly complete. Here it is:

University of Berne and State University of Oregon at Corvallis (1978-1982)

I studied chemistry at the University of Berne, Switzerland. We had German-style chemistry education with lots of organic and inorganic synthesis, quantum mechanics, spectroscopy, thermodynamics, and electrochemistry. The latter subjects were taught by Eberhard Schmidt, and it was in his research group, where I did my diploma thesis (similar to a Masters thesis). My subject was electrochemical noise. The thesis was bit of a failure, but I realized that these effects were hardly measurable in equilibrium electrochemical cells, and that the fluctuation-dissipation theorem also applies to such cells. Finally, why should they represent an exception?

At the University of Berne, I met John Westall, who supervised a practical of mine. I was then able to visit him at Oregon State University, Corvallis, Oregon, US, where he started as assistant professor. There I wrote my first paper, which involved a study of multivalent ions in the electrical double layer [1].

John reinforced my intention to do my PhD in the US, and patiently explained to me that Oregon State University might not the right place to do it. First time in my life I was confronted with the idea that there are better or worse universities, which, in my endless naivety concerning science politics, did not occur to me yet. I applied to several US universities, Columbia University accepted me, and since Bruce Berne, the author of the well-known book on dynamic light scattering, was working there (and at the time of writing still is), I did not hesitate too long, and moved to New York City.

Columbia University (1982-1986)

Starting at Columbia was bit agitated, since by diploma was just considered being equivalent to a Bachelor degree, so I was dumped into ivy-league-style graduate courses, full of smart youngsters. I survived. I did my PhD with Bruce Berne, who was a serious, but sympathetic theory professor working in statistical mechanics. He welcomed me with the words "Oh, I do not work on light scattering any more, why don't you look into the Kramer's turnover." So I did my PhD on thermally activated barrier crossing. There was a great buzz around that topic back then. Soon after I started my PhD, the Kramers turnover was experimentally observed by Martin Quack and Jürgen Troe. Once I have demonstrated that their experimental data agreed with a stochastic dynamic model we were using [2], Bruce remarked: "How much more do you want to know?"

We were further looking into the Grote-Hynes theory, which extends Kramer's approach to friction with memory. Together with John Straub, we added some confusion to the topic with accurate simulation data [3]. John was also a PhD student back then with Bruce, and is now professor at Boston University. I was also applying the Grote-Hynes theory to colloidal aggregation, in order to explain the disagreement between experimental aggregation rates and predictions of the theory of Derjaguin, Landau, Verwey, and Overbeek (DLVO), but nothing came out of this. But the colloid bug has bitten me back then. Only then I realized that colloids might be an interesting research topic. In my chemistry courses at the University of Berne, this topic has been skipped. Even at Columbia, colloids were a mere wallflower, with the exception of Ponisseril Somasundaran in Chemical Engineering, who I met much later.

During my PhD work I got also to know Peter Hänggi, who then was at the University of Brooklyn, and through him Peter Talkner. Both were theoretical physicists working on activated barrier crossing. Soon after my PhD, we wrote a review article on this topic, by far the best cited article of mine [4]. Together with Peter Talkner, we were able to generalize the reactive flux method to other types of dynamic processes, which probably was my most original, but least cited work from my PhD [5].

University of Basel (1986-1989)

Having been bitten by the colloid bug and missing the Swiss-type of life, I decided to do my postdoc with Hans-Friedrich Eicke at University of Basel. Hans-Friedrich was then leading one of the few colloid research groups in Switzerland, and their focus were microemulsions. Microemulsions resemble emulsions, but they form spontaneously, and the droplets are much smaller. This topic was quite a hype then, since after the oil crisis, the hope was that microemulsions might be able to extract the last bits of oil from the fields.

Hans-Friedrich was working with Aerosol-OT (or AOT) surfactant, which forms nanometer-sized water droplets in alcanes. With Bikram Dasgupta, we studied the surprisingly high electrical conductivity of such oil-continuous microemulsions, and I was able to explain the data quantitatively by postulating that the water droplets become charged through thermal fluctuations [6]. This paper had a substantial impact, particularly, since, stupid me, I solved the problem only partially. Many people were then able to improve our calculations. Still, this work was my first truly original contribution to science.

During that time, I once joined the coffee table in Hans-Friedrich's group. Who was not sitting there, Pierre-Gilles de Gennes, the last person in our field awarded the Nobel prize, namely in 1991. After briefly explaining to Pierre-Gilles what I was working on, he summarized the relevant physics in two sentences on the spot. Then, I was impressed! It took me several months to figure all this out.

Probably my second original contribution to science was on optically matched microemulsions in collaboration with Jaro Ricka, who was working in applied physics at the University of Berne. First I tried to do dynamic light scattering on these systems in Basel, but I could not get any sensible data. Frustrated, I approached Jaro, as they had state-of-the-art light scattering instrumentation, the needed know-how, and they were starting in the (back then new) field soft matter. AOT microemulsions have a curious property, namely, when one adds water, which causes the droplets to swell, one passes an optical matching point. At this point the droplets become invisible, meaning that the refractive index of the droplets matches the one of the continuous oil phase. This aspect was already recognized by Martin Zulauf, who did his PhD thesis with Hans-Friedrich earlier. But Martin only described the phenomenon qualitatively, while with Jaro, we tackled the problem quantitatively. Everything worked like a charm, and we were even able to extract the surprisingly low polydispersity of the microemulsion droplets accurately [7].

Swiss Federal Institute of Technology (ETHZ, 1989-1998)

Since I was tired of Basel, I found a new job at the ETHZ. In Zürich, many things looked fantastic. Long-term contract, good salary, and possibility to do colloid research. Being now in an engineering school, there, colloids were an entirely respectable research field. On the other hand, I was part of the soil chemistry program, having no clue about soils. Hans Sticher, my new boss, told me to work on colloid facilitated transport of heavy metals, which sounded interesting. But in retrospect, I probably should have said, "Sorry, Hans, I rather stick to microemulsions." While these systems became totally uninteresting for oil recovery due to collapsing oil prize, they turned into the next big thing for the remediation of contaminated soils. Was that a great opportunity missed?

My first and probably the most original contribution from ETHZ, which was actually published in a real soil journal, was the investigation of particle size distributions of soil particles [8]. What was surprising to me that these distributions are extremely wide. Next time when you are outside, look more closely a bit of soil: You'll find stones, sand, and much finer silt and clay particles. Strangely enough, the size distributions follow power-laws, which often span many orders of magnitude. The respective exponent can be interpreted as a fractal dimension, and has a value such that the mass of the sample is dominated by the largest particles and the surface by the smallest ones. I found all this pretty intriguing, but to my surprise, the soil scientists got rather confused.

Then I started to do research on colloidal suspensions, and this time, there was not even a light scattering instrument available in the group. While looking for one, I met Peter Schurtenberger, who had a similar position to mine at the ETHZ, but in a different department. Peter was an expert on light scattering, and he kindly allowed us to use his instruments. We interacted well, and supervised several PhD students together, namely Thomas Gisler, Helmut Holthoff, and Sven Behrens. Peter always impressed me with his remarkable ability to attract excellent students, and these three were no exception. Thomas looked into structuring in salt-free systems, which lead to most pleasant contacts with Rudolf Klein from the University Konstanz [9]. The other two worked on particle aggregation. Helmut has shown that aggregation rates can be easily measured with dynamic light scattering [10], and in this way he established the currently best technique for these measurements. Sven has demonstrated how to use DLVO theory to interpret such measurements [11], and we started to learn about the mysteries of charge regulation [12]. Peter also had a home-build multi-angle light scattering instrument, which we were able to exploit for these studies successfully. This work was the ground-stone of all my future studies on particle aggregation.

Since I was told to do something more useful for soil chemistry, I worked on transport of chemicals in the subsurface. Such processes can be modeled in the lab with chromatographic columns. Then I learned about transport in porous media, chromatography, and non-linear fronts. I owe much of this to Michel Sardin and Daniel Schweich from the University of Nancy, two very knowledgeable and cultivated chemical engineers. At that point, I also encountered another excellent scientist, Willem van Riemsdijk, from the University of Wageningen. Together, we understood reactive transport of protons (acids and bases) in porous media [13]. This work was probably my only original contribution to chromatography.

When dealing with transport in porous media, one must understand adsorption (or binding) processes. My thought was that all binding processes must be governed by the same principles, be it binding to small molecules, polyelectrolytes, or interfaces. When I discussed this topic with Ger Koper, then at the University of Leiden, he remarked: "I just solved such a problem!" His remark prompted a wonderful, two-decade long collaboration with Ger, where we were studying site binding models involving protons. This framework, which is better known as Ising models in the physics community to describe magnets, points out the importance of site-site interactions. One indeed recovers binding to small molecules with all microspecies, to polyelectrolytes, where these interactions are short-ranged, and to interfaces, where these interactions are long-ranged and mean-field like [14]. While we tried [15], we did not manage to make these models useful to model binding processes involving different species.

This aspect was commonly treated in the environmental chemistry community with surface complexation and ion-exchange models. Motivated by this approach, an inspiring collaboration emerged again with John Westall, who visited the ETHZ, myself (Mr. B), and Mirek Cernik (Mr. C), who was a PhD student back then. We developed empirical binding models, which were based on distributions of fictitious binding sites, whose properties were calibrated with experimental data. We were quite successful with one-component systems [16], and we even realized that affinity distributions are related to zeroes of the binding polynomial. That was an intriguing, but perfectly useless observation, in my view. We were partially successful with two-component systems, which we were, surprisingly, able to represent by distributions of ion-exchange equilibria [17]. But we got stuck with three or more component systems. Classical surface complexation approach deals with such situations better.

Nevertheless, this question remains a grand challenge for me: Take any type of insoluble powder, perform a set of well-chosen adsorption experiments involving several species, and construct a sensible binding model from those data, preferably automatically. This model should be able to smoothly interpolate the experimental data, but hopefully also able to sensibly extrapolate to species not investigated in the lab. We did our best to solve this problem, but failed badly.

Many years after the initial proposal from Hans, we also found a realistic scenario of colloid facilitated transport [18]. With Daniel Grolimund, who had the rare ability to immediately pinpoint actual causes of observable phenomena, we learned how colloidal particles get mobilized from soils, if this material is first saturated with divalent cations, and then these ions are exchanged for monovalent cations. When these particles are contaminated in the first place, for example, with a heavy metal, this mobilization induces a colloid facilitated transport of this metal. While we have nicely demonstrated that this situation indeed occurs in laboratory columns, I am still unsure whether this scenario is relevant in the field.

Towards the end of my stay at ETHZ, I met a wonderful man, Milan Schwuger, who was then the director of the Institute of Applied Physical Chemistry at the Research Center in Jülich, Germany. Together with his team he developed microemulsions for remediation of sites contaminated with organic solvents, and in fact, successfully tested them in the field. How would have things developed, if I would have refused the initial proposal from Hans?

Clarkson University (1998-2001)

Since my ETHZ contract was coming to an end, I was again looking for a job. After many unsuccessful attempts, I found one at Clarkson University, Postdam, New York, US. Now I was working at an institution full of scientists working on colloids, some of them brilliant, including Janos Fendler and Egon Matijevic. There, I got distracted from environmental questions, and being a professor, I enjoyed my freedom and independence. Soon, however, I was caught up by reality. Especially in the US, a good professor costs nothing to the university, I spent much of my time writing grants, and surprisingly, I even got a few. One of those grants shaped quite a bit my future work, as I proposed to study heteroaggregation, meaning aggregation of different types of particles, with multi-angle light scattering. This idea was actually prompted by Egon and Sven. Multi-angle instruments became commercially available in the meantime, and my PhD student, Weili Yu, was able to use such an instrument to study heteroaggregation for the first time [19].

Motivated by an industrial research project with the BASF, Ludwigshafen, we started to exploit the role of polyelectrolytes on particle aggregation [20]. These questions seemed to fit well into our previous work on proton binding to polyelectrolytes, which we brought with Ger Koper to a nice degree of perfection [14,21]. During these times, we also started to collaborate with Bernard Spiess, University of Strasbourg. Bernard had a beautiful set of nuclear magnetic resonance titration curves on inositol phosphates, some of which we were able to interpret with success [21]. Bernard was amazed how easily our cluster approach, as we started to refer to the Ising model, was able to extract the important microstates, seemingly for any number of binding sites. But at the same time, Bernard's data illustrated pitilessly, how far away I still was from proper understanding of these processes. Worse, I was unable to substantially improve their understanding in the meantime.

University of Geneva (2001-2021)

The situation at Clarkson was not bad, but far from ideal, and I continued to look for alternatives. To my surprise, such an alternative popped up back in Switzerland, namely at the University of Geneva. The possibilities seemed endless, I was able to generate substantial amount of funding, and establish a sensible research group. Still back at Clarkson, after I summarized to Egon all the advantages of my new job at Geneva, he told me: "I agree, but you will be alone." Egon was right, as usual.

The start in Geneva was bumpy, clouded by controversies about lab space, personnel, and research topics. These difficulties have driven me even further away from environmental chemistry and forced me to overcome my remaining naivety about scientific politics. Its last bits and pieces were only wiped out, when I worked as research counselor at the Swiss National Science Foundation, but I was getting old by then.

Polyelectrolytes remained important in our research, since the collaboration with BASF continued for a while. Binding processes had an initial (and final) upsurge through my collague Claude Piguet from the University of Geneva, who was happy to learn about our cluster approach to interpret binding of lanthanide ions to his helicate ligands [22]. While I still was secretly hoping that this activity may finally lead to the resolution of my central question how to model binding of multiple species, that turned out not to be the case. Few years later, heavyhearted, I removed the titration instruments from our labs.

Initially, I was thinking that we would be able to run successfully research in many different directions, but soon I got again caught up by reality. Finally, three, mostly experimental topics crystallized out, namely, particle aggregation, surface sensitive techniques, and direct force measurements with the atomic force microscope.

Particle aggregation continued along the lines that we started at ETHZ and Clarkson. Thanks to Paolo Galletto, Wei Lin, Gregor Trefalt, and Tianchi Cao, we even got heteroaggregation processes under control [23,24]. These processes turned out to be really interesting in the presence of multivalent and other strongly adsorbing ions [24]. But the most notable contribution to aggregation processes originating from Geneva still probably was the seemingly trivial inverse Schulze-Hardy rule, which popped up when working with Istvan Szilagyi [25]. Gregor explained later to us that this rule is not as trivial as it may seem.

Surface sensitive techniques were initiated through another industrial collaboration, this time with Givaudan, Dübendorf. Our contact was Christian Quellet, of whom I had most enjoyable souvenirs from Basel. Together with Jürg Kleimann, and again with Ger Koper, this time at Delft University of Technology, we constructed our own optical reflectivity setup [26]. At a later stage, we also acquired a quartz crystal microbalance. These techniques were brought to perfection by Plinio Maroni and Maria Porus [27]. Some of this work was complemented with computer simulations by Christophe Labbez, University of Burgogne, Dijon, who helped to revive the pleasant contacts with Bo Jönsson [14].

Force measurements with the atomic force microscope were initiated in Geneva by Georg Papastavrou, who surprised me by being able to make all this work perfectly well, often under less than ideal conditions. He introduced the symmetrical sphere-sphere geometry [28] and we measured forces induced by individual polymer chains [29]. The sphere-sphere geometry turned out to be the key to our later, probably most original type of force measurements, especially thanks for Ionel Popa with latex particles [30], Valentina Valmacco with sintered silica particles [31], and Javier Montes Ruiz-Cabello in the asymmetric sphere-sphere geometry [32]. While we tried to find something interesting by pulling individual polymer chains, I found this type of research difficult and hardly rewarding.

We even managed to realize my long-time plan, namely measuring aggregation rates and forces involving the same type of particles [33]. While technically impressive, the results disillusioned me. My hope to finally explain the discrepancies between measured aggregation rates and DLVO predictions did not materialize. Thus, I am still unable to pinpoint the origin of these discrepancies, which are haunting me since my PhD.

On the other hand, I found the measurements of forces in systems containing multivalent ions most gratifying. Besides having accumulated the needed experimental know-how, we developed a versatile Poisson-Boltzmann (PB) code to interpret the essential contribution of double layer forces. The unique aspects of this code were that it could handle mixtures of ions, deal with asymmetric systems, and include charge regulation. We measured many force profiles in the presence of various ions, including multivalent ones, and compared these results with such PB calculations. What is amusing that I came back to a very similar topic as addressed in my very first paper with John [1]. The novel aspect was, however, that we were able to clarify two essential issues concerning double-layer forces, which still remain hardly appreciated in our community.

First issue is that PB theory remains accurate even in the presence of multivalent ions, provided one is sufficiently far away from the interface. In practice, however, sufficiently far often means just a few nanometers, which is in fact quite close. This view was already preached by generations of electrochemists over about a century, but recently, reservations were loudly voiced in the theoretical community, including by Bo Jönsson and Christophe Labbez. But I now definitely align with the electrochemists.

Second issue is that charge regulation is essential, and that the constant regulation model, as initially developed by Sven Behrens at ETHZ [12], represents a most convenient framework. Besides the commonly used diffuse layer potential (or diffuse layer charge density) to characterize an interface, this model adds a second characteristic of the surface, namely the regulation parameter (or the inner capacitance). Charge regulation turns out to be essential to understand forces in asymmetric systems. These effects become huge in the charged-neutral case, where one interface is charged, while the other one is neutral. In this case, charge regulation even determines whether the double-layer forces are attractive or repulsive [30]. In asymmetric systems, others have probably (wrongly) suspected a failure of DLVO theory, just for the simple reason, that charge regulation was not properly taken into account. But unfortunately, a more fundamental interpretation of the essential regulation parameter, which we routinely extract from the force profiles, remains elusive to me.

Towards the end of my scientific activities, we started to investigate structuring and interactions in concentrated polyelectrolyte solutions and nanoparticle suspensions. Besides the interesting oscillatory layering, Mohsen Moazzami Gudarzi discovered strongly non-exponential PB profiles, which originate from the exclusion of the polyelectrolyte (or nanoparticles) in the vicinity of the like-charged interface [34]. These findings again confirm that the old good electrochemists were right, as PB is almost perfect bit away from the surface. But the layering further away from the surface is not captured by PB theory. Are the reservations of the theorist related to those? At the time of writing, these investigations are still ongoing, and only the future will tell whether our studies were relevant or not.

My research group at the University of Geneva will be dissolved in 2021, since I will be reaching my retirement age. With that my scientific activities will terminate as well. As Milan Schwuger once aptly pointed out: "Mister Borkovec, there are also other things in life besides microemulsions."

Thanks and Apologies

My thanks go to the funding agencies, former coworkers, colleagues, and friendly reviewers. Very little would have been possible without them. I apologize to those numerous coworkers, whose name is not mentioned here. This omission does not mean that their work was unimportant, but that I was unable to put their contributions into proper context. I also wanted to avoid that this text, which already is excessive, becomes even longer. Further, most of the references remain hidden behind paywalls. While our generation already tried to solve this problem, we failed, definitely in our field, and I also apologize for that. But I can email these articles to you, if you ask me.

Michal Borkovec, April 7, 2021

References

[1] Borkovec M. and Westall J. C. (1983) Solution of the Poisson-Boltzmann equation for surface excesses of ions in the diffuse layer at the oxide-electrolyte interface, J. Electroanal. Chem., 150, 325-337, 10.1016/S0022-0728(83)80214-9.

[2] Borkovec M. and Berne B. J. (1985) Collisional model for diatomic recombination reaction, J. Phys. Chem., 89, 3994-3998, 10.1021/j100265a013.

[3] Straub J. E., Borkovec M., and Berne B. J. (1985) Shortcomings of current theories of non-Markovian activated rate processes, J. Chem. Phys., 83, 3172-3174, 10.1063/1.449172.

[4] Hänggi P., Talkner P., and Borkovec M. (1990) Reaction-rate theory: Fifty years after Kramers, Rev. Mod. Phys., 62, 251-341, 10.1103/RevModPhys.62.251.

[5] Borkovec M. and Talkner P. (1990) Generalized reactive flux method for numerical evaluation of rate constants, J. Chem. Phys., 92, 5307-5310, 10.1063/1.458535.

[6] Eicke H. F., Borkovec M., and Das Gupta B. (1989) Conductivity of a water-in-oil microemulsion: A quantitative charge fluctuation model, J. Phys. Chem., 93, 314-317, 10.1021/j100338a062.

[7] Ricka J., Borkovec M., and Hofmeier U. (1991) Coated droplet model of microemulsions: Optical matching and polydispersity, J. Chem. Phys. 94, 8503-8509, 10.1063/1.460083.

[8] Wu Q., Borkovec M., and Sticher H. (1993) On particle size distributions in soils, Soil Sci. Soc. Am. J., 57, 883-890, 10.2136/sssaj1993.03615995005700040001x.

[9] Gisler T., Schulz S. F., Borkovec M., Schurtenberger P., D'Aguano B., Klein R., and Sticher H. (1994) Understanding colloidal charge renormalization from surface chemistry: Experiment and theory, J. Chem. Phys., 101, 9924-9936, 10.1063/1.467894.

[10] Holthoff H., Egelhaaf S. U., Borkovec M., Schurtenberger P., and Sticher H. (1996) Coagulation rate measurements of colloidal particles by simultaneous static and dynamic light scattering, Langmuir, 12, 5541-5549, 10.1021/la960326e.

[11] Behrens H., Borkovec M., and Schurtenberger P. (1998) Aggregation in charge-stabilized colloidal suspensions revisited, Langmuir, 14, 1951-1954, 10.1021/la971237k.

[12] Behrens, S. H. and Borkovec M. (1999) Electric double layer interaction of ionizable surfaces: Charge regulation for arbitrary potentials, J. Chem. Phys. 111, 382-385, 10.1063/1.479280.

[13] Scheidegger A., Bürgisser C., Borkovec M., Sticher H., Meeussen H., and van Riemsdijk W. H. (1994) Convective transport of acids and bases in porous media, Water Resour. Res., 30, 2937-2944, 10.1029/94WR01785.

[14] Borkovec M., Jönsson B., and Koper G. J. M. (2001) Ionization processes and proton binding in polyprotic systems: Small molecules, proteins, interfaces and polyelectrolytes, in Surface and Colloid Science, 16, 99-339, Matijevic E. (ed.), Kluwer Academic / Plenum Press link.

[15] Koper G. J. M. and Borkovec M. (2001) Binding of metal ions to polyelectrolytes and their oligomeric counterparts: An application of a generalized Potts model, J. Phys. Chem. B, 105, 6666-6674, 10.1021/jp010320k.

[16] Borkovec M., Rusch U., Cernik M., Koper G. J. M., and Westall J. C. (1996) Affinity distributions and acid-base properties of homogeneous and heterogeneous sorbents: Exact results versus experimental data inversion, Colloids Surfaces A, 107, 285-296, 10.1016/0927-7757(95)03339-4.

[17] Cernik M., Borkovec M., and Westall J. C. (1996) Affinity distribution description of competitive ion binding to heterogeneous materials, Langmuir, 12, 6127-6137, 10.1021/la960008f.

[18] Grolimund D., Borkovec M., Barmettler K., and Sticher H. (1996) Colloid facilitated transport of strongly sorbing contaminants in natural porous media: A laboratory column study, Environ. Sci. Technol., 30, 3118-3123, 10.1021/es960246x.

[19] Yu W. L., Borkovec M. (2002) Distinguishing heteroaggregation from homoaggregation in mixed binary particle suspensions by multi-angle static and dynamic light scattering, J. Phys. Chem. B 106, 13106-13110, 10.1021/jp021792h.

[20] Bouyer F., Robben A., Yu W. L., Borkovec M. (2001) Aggregation of colloidal particles in the presence of oppositely charged polyelectrolytes: Effect of surface charge heterogeneities, Langmuir 17, 5225-5231, 10.1021/la010548z.

[21] Borkovec M., Koper G., Spiess B. (2014) Intrinsic view of ionization equilibria of polyprotic molecules, New J. Chem., 38, 5679-5685, 10.1039/C4NJ00655K (open access).

[22] Zeckert K., Hamacek J., Rivera J. P., Floquet S., Pinto A., Borkovec M., Piguet C. (2004) A simple thermodynamic model for rationalizing the formation of self-assembled multimetallic edifices: Application to triple-stranded helicates, J. Am. Chem. Soc. 126, 11589-11601, 10.1021/ja0483443.

[23] Lin W., Kobayashi M., Skarba M., Mu C., Galletto P., Borkovec M. (2006) Heteroaggregation in binary mixtures of oppositely charged colloidal particles, Langmuir, 22, 1038-1047, 10.1021/la0522808.

[24] Cao, T., Sugimoto, T., Szilagyi, I., Trefalt, G., Borkovec, M. (2017) Heteroaggregation of oppositely charged particles in the presence of multivalent ions, Phys. Chem. Chem. Phys., 19, 15160-15171, 10.1039/C7CP01955F.

[25] Cao T., Szilagyi I., Oncsik T., Borkovec M., Trefalt G. (2015) Aggregation of colloidal particles in the presence of multivalent coions: The inverse Schulze-Hardy rule, Langmuir, 31, 6610-6614, 10.1021/acs.langmuir.5b01649.

[26] Kleimann J., Lecoultre G., Papastavrou G., Jeanneret S., Galletto P., Koper G. J. M., Borkovec M. (2006) Deposition of nanosized latex particles onto silica and cellulose surfaces studied by optical reflectometry, J. Colloid Interf. Sci. 303, 460-471, 10.1016/j.jcis.2006.08.006.

[27] Porus M., Labbez C., Maroni P., Borkovec M. (2011) Adsorption of monovalent and divalent cations on planar water-silica interfaces studied by optical reflectivity and Monte Carlo simulations, J. Chem. Phys. 135, 064701, 10.1063/1.3622858.

[28] Rentsch S., Pericet-Camara R., Papastavrou G., Borkovec M. (2006) Probing the validity of the Derjaguin approximation for heterogeneous colloidal particles, Phys. Chem. Chem. Phys., 8, 2531-2538, 10.1039/b602145j.

[29] Papastavrou G., Kirwan L. J., Borkovec M. (2006) Decomposing bridging adhesion between polyelectrolyte layers into single molecule contributions, Langmuir, 22, 10880-10884, 10.1021/la062046x.

[30] Popa I., Sinha P., Finessi M., Maroni P., Borkovec M. (2010) Importance of charge regulation in attractive double-layer forces between dissimilar surfaces, Phys. Rev. Lett, 104, 228301, 10.1103/PhysRevLett.104.228301.

[31] Valmacco V., Elzbieciak-Wodka M., Besnard C., Maroni P., Trefalt G., Borkovec M. (2016) Dispersion forces acting between silica particles across water: Influence of nanoscale roughness, Nanoscale Horiz., 1, 325-330, 10.1039/C6NH00070C (open access).

[32] Montes Ruiz-Cabello F. J., Trefalt G., Maroni P., Borkovec M. (2014) Accurate predictions of forces in the presence of multivalent ions by Poisson-Boltzmann theory, Langmuir 30, 4551-4555, 10.1021/la500612a (open access).

[33] Sinha P., Szilagyi I., Montes Ruiz-Cabello F. J., Maroni P., Borkovec M. (2013) Attractive forces between charged colloidal particles induced by multivalent ions revealed by confronting aggregation and direct force measurements, J. Phys. Chem. Lett. 4, 648-652, 10.1021/jz4000609.

[34] Moazzami-Gudarzi M., Kremer T., Valmacco V., Maroni P., Borkovec M., Trefalt G. (2016) Interplay between depletion and double layer forces acting between charged particles in solutions of like-charged polyelectrolytes, Phys. Rev. Lett., 117, 088001, 10.1103/PhysRevLett.117.088001 (open access).


Below you find comments on this article.


April, 15, 2021, 12:51. Congratulations Mischa for this great lifetime achievement. I am very proud to be a part of this story. Greetings from Hungary, Istvan