Enzo Ferroni (1921-2007): the History of an Eclectic Chemist

. Enzo Ferroni (Florence, 25 March 1921 – 9 April 2007) was an Italian chemist, full professor in physical chemistry at the University of Florence, where he served as Rector from 1976 to 1979, a renowned international scientist who initiated a new branch of chemistry, that applied to cultural heritage conservation. The history of his scientific and academic life offers a particular interest in a half-century cross-section of the history of chemistry in Italy and the entire world. In particular, Ferroni developed the colloids, surface


INTRODUCTION
From the vantage point of the second fifth of the 21 st century we have the possibility to look at the history of science of the second half of the 20 th century with the eyes of the science historian, considering that all the discoveries made after the end of the Second World War until the beginning of the new century can be considered as sufficiently sedimented to re-evaluate them in a historical perspective. 1 The advance of science and technology in every field during such period was tremendous, and the people devoted to its progress have exponentially increased. Every discipline underwent an extraordinary multiplication of specialisations; simultaneously, science and technology had the need to be increasingly more multi-and inter-disciplinary. Moreover, science and technology started to create bridges towards human and social sciences in a sort of total globalisation of knowledge. In this frame, many scientists in every part of the world substantially increased their cooperation and research groups in different countries developed the various topics of each discipline, creating centres of excellence able to attract young scholars interested in the progress of science and technology. In this context, Italy was a noteworthy case since it emerged from twenty years of darkness characterised by the totalitarian fascist regime with all the consequences for the freedom of research and teaching.
Since the present paper aims to report and discuss the work of the academic chemist Enzo Ferroni (Florence, 1921(Florence, -2007, it seemed worthwhile to frame the scenario where he carried out most of his scientific activity, that is, the University of Florence. After the end of the Second World War, chemistry in Italy presented six main branches: analytical, industrial, inorganic, organic, pharmaceutical, and physical; inside each of these broad sub-disciplines, there were some specialisations within which, during the following decades, some important centres of excellence developed. At the University of Florence, inorganic chemistry took the path of coordination chemistry thanks to work initiated by Luigi Sacconi (Santa Croce sull'Arno, 1911 -Florence, 1992). 18 As far as organic chemistry is concerned, the path set by Angelo Angeli (Tarcento, 1864 -Florence, 1931) 8,19 and Adolfo Quilico (Milan, 1902(Milan, -1982 8,19 who moved to the Politecnico di Milan in 1943, was followed by Giovanni Speroni (Florence, 1910(Florence, -1984. 8,19 Analytical chemistry was led by the already mentioned Giovanni Canneri. In contrast, pharmaceutical chemistry had two key scientists, Sergio Berlingozzi (Montevarchi, 1890 -Fiesole, 1957) and Mario Torquato Passerini (Casellina e Torri, now Scandicci, 1891 -Florence, 1962). 8,19 Industrial chemistry started to develop precisely in the period subject of the present study thanks to the work of Franco Piacenti (Florence, 1927(Florence, -2002. 20 The chair of physical chemistry, the discipline that Enzo Ferroni selected for his chemistry master's degree thesis, was held by Giorgio Piccardi (Florence, 1895 -Riccione, 1972), a significant Italian scientist, though for some aspects quite controversial. 21 Enzo Ferroni defended his chemistry master's thesis (from now on, it will be used for this title the verb to graduate) in 1945 magnum cum laude, under the supervision of Giorgio Piccardi. The title of his work was "Recent advances and opinions on chemical kinetics" . 23 Starting from this first research, Enzo Ferroni began a long academic career that allowed him to open many new research fields in physical chemistry that the time will reveal being characterised by the strong impact on the history of chemistry.
This paper aims to reconstruct the milestones of the academic life of this scientist, individuating the five topics which demonstrate the remarkable visionary capacity of this man to open new horizons in his field of research, creating research paths that nowadays appear normal and foregone but that at the time of Ferroni's work were completely uncharted and for which it was impossible to foresee the success they would have. By initially looking at his pioneering studies on colloids, surfaces, and interfaces, the present study is devoted to following how Ferroni sensed the importance of the nascent resonance spectroscopies and surface diffraction techniques, the fruitful relationship between chemistry and cultural heritage conservation, the new frontiers in soft matter, and the strategic role played by applied chemistry, technology, and industry. Finally, the study aims to show that some of the most current topics in chemistry, such as supramolecular chemistry, self-assembly, nanoscopic world, nanomaterial chemistry, scientific diagnostics in cultural heritage conservation, and soft matter, were already outlined in the studies and research Enzo Ferroni designed and carried out.

THE BEGINNING: COLLOIDS, SURFACES, AND INTERFACES
Ferroni started his research activity at the beginning of the second half of the 20 th century: indeed, his first two articles 23,24 clearly showed the direction he wanted to pursue, i.e., physical chemistry of colloids, surfaces, and interfaces. One of these systems' most peculiar physical properties is surface tension, which became the first topic on which Ferroni focused his attention and desire to deepen his knowledge. Ferroni intuitively knew that the works by three Nobel laureates in the chemistry of the last decades, namely, Richard A. Zsigmondy (1925), Theodor Svedberg (1926), and Irving Langmuir (1932) 2 could be fundamental milestones and the basis for a new branch of physical chemistry in Italy. In particular, he read with great curiosity and interest Langmuir's papers,  from which the crucial and peculiar role of the solid-liquid, solid-gas, solid-vacuum, and liquid-gas interfaces emerged, indicating that surface chemistry was fundamental in determining the physicochemical mechanisms of a vast multitude of phenomena.
At the beginning of his research career, Ferroni was attracted by the liquid-gas interface. His attention was focused on measuring the surface tension of many liquid systems in static or dynamic conditions. [54][55][56][57][58] These first studies were also the result of the interaction with the group of Raymond Defay (Anderlecht, 1897-Brussels, 1987 59 and Ilya Prigogine (Moscow, 1917-Brussels, 2003 60 at the Université Libre de Bruxelles with whom Ferroni had collaborations, even spending time at their laboratories in Brussels. Indeed, during these years, Ferroni's scientific activity converged with the studies of these two great scientists, as proved by the subject of some of their publications 61-66 focused on surface tensions of many different liquid systems. Moreover, the proof of these relationships is given by correspondence dated some years later, also denoting a friendship, from which we report, in Figures 1 and 2, two letters (from Raymond Defay to Ferroni and from Ferroni to Maria Prokopowicz Prigogine, the second wife of Ilya Prigogine) coming from Ferroni's Archive. 67,68 The research on the liquid-gas (air) interface was immediately extended to the bulk of the liquid that contained surfactants to investigate critical micellar concentration, 69,70 polymerisation, 71,72 electrophoresis, 73 aggregation phenomena, 74,75 and equilibrium constants and complex formation. 76,77 Following the path traced by Langmuir, Ferroni continued his pioneering work for building a school of colloids, interfaces, and surfaces in Italy, extending his studies to monomolecular films at the liquid-gas interfaces but also starting to explore solid-gas and solid-solid interfaces. His attention was concentrated on polymorphisms at the interface, 78-81 mono-and multilayers of organic substances, 82,83 adsorption onto solid surfaces, 84 solid → gas reactions, 85 and epitaxy. 86 Ferroni's intense work resulted in a remarkable scientific impact in the physical chemistry of condensed phases following the research lines of two great schools, that of Irving Langmuir at General Electric Company Laboratories, Schenectady, USA, and of Raymond Defay and Ilya Prigogine at the Université Libre de Bruxelles, and allowed him to gain the chair -full professor in physical chemistry -at the University of Cagliari in 1961 presenting 85 scientific publications, 88 including three articles on the Journal of Physical Chemistry, 76 the Journal of the American Chemical Society, 84 and Nature. 79 In 1965, he succeeded in gaining the same chair at the University of Florence, Faculty of Mathematical, Physical, and Natural Sciences, where he remained until his retirement in 1996, becoming Emeritus the subsequent year. During the years spent at the University of Florence, he was Director of the Institute of Physical Chemistry (1965 -1968), Dean of the Faculty of Mathematical, Physical, and Natural Sciences (1968 -1971), Rector (1976Rector ( -1979, and Head of the Chemistry Department (1983 -1985). 89   He had already constituted the first seed during 1950-1961, writing some papers with Gabrielli and directing his pupil Guarini to investigate solid interfaces. Still, on his return to Florence at the end of 1965, he had his second great visionary idea, partly generated by a fortuitous case (vide infra), sowing the seed for a novel approach to the physical chemistry of large interface systems by exploiting the unique potentialities of the nascent resonance spectroscopies and surface diffraction instrumental techniques. Indeed, Ferroni had already perceived the importance of the spectroscopic approach when he published two papers with Marzocchi 100, 101 studying halogen-amine interactions by infrared spectroscopy, but he had not yet in mind, immediately after the graduation of Tiezzi and Rovida, what topics could represent some new research lines in the field of colloids and surfaces. The fortuitous case originated the research line dealing with Nuclear Magnetic Resonance (NMR) and Electron Paramagnetic and Spin Resonance (EPR/ESR) spectroscopies, while the second idea was associated with the subject of surface diffraction techniques. Tiezzi and Rovida, after graduating in chemistry in 1963, became Ferroni's assistants at the University of Cagliari where they remained until 1965 -Tiezzi -and 1966 -Rovida -, and participated with him in the 20 th International IUPAC Congress in Chemistry held in Moscow on 12 -18 July 1965. Figure 3 shows Ferroni and Tiezzi at the Congress discussing with the Russian chemist and physicist Boris Vladimorovič Derjagin (1902 -1994), one of the world's most prominent scientists in the field of colloids and surfaces. But Ferroni was also always eager to hire promising young researchers besides his pupils and consequently, when back to Florence, selected Leo Burlamacchi (Viareggio, 1933), a 1960 graduate from the University of Pisa, to work as a pioneer in the field of EPR/ESR. Indeed, Burlamacchi, as a graduate worked some years in the industry, and in 1965 he attended the laboratories at the National Council of Research, Institute on Microwaves in Florence, founded and directed by the distinguished physicist Nello Carrara (Florence, 1900(Florence, -1993. 102 In these laboratories, two instruments were built for EPR/ESR and NMR measurements. Still, nobody used them since no chemists -the principal users of such apparatuses for physicochemical characterisation -were present there at that time. Therefore, Burlamacchi had been involved in scientific investigations using these two emerging techniques. Ferroni, consulted by Director Carrara, immediately found a fellowship for Burlamacchi, entrusting him with opening new research frontiers. He suggested creating a couple of young researchers -Burlamacchi and his pupil Tiezzi -to introduce EPR/ESR and NMR techniques to the Florence research group on colloids and surfaces. The first papers [103][104][105][106][107] showed that exploring these new frontiers of physicochemical research was possible. It is worth recalling that Tiezzi taught at the University of Cagliari 102  , further refining his skills in the field of magnetic resonance spectroscopies. In particular, Tiezzi started to explore the possibility of using resonance spectroscopies in biology and medicine. 102,108 Tiezzi would always be deeply grateful to Ferroni, stating several times that he considered Ferroni his mentor since the academic year 1957-1958 when he attended his lectures on Fundamentals of Chemistry 2 nd course at the University of Florence. 102 When Tiezzi returned to Florence, he was ready to carry out fundamental research using ESR/EPR and NMR spectroscopies collaborating with Burlamacchi and, from 1967, with the young Martini (see above). [109][110][111][112][113][114] After the Florence flood, in 1967, Ferroni obtained funds to buy the EPR/ESR instrument from Varian that was placed at the Institute of Physical Chemistry of the University of Florence in the city centre, via Gino Capponi, 7-9. Tiezzi would become a full professor in physical chemistry at the University of Siena in 1979 and one of the most distinguished scientists in the world developing, the first in Italy, the concept of sustainability together with other scientists from across the globe. Burlamacchi became a full professor in 1980 at the same University of Cagliari that twenty years before had welcomed Ferroni.
This research line was pursued for many years with the contribution of other people, among which the already mentioned Baglioni, Maurizio Romanelli (Florence, 1943) and Maria Francesca Ottaviani (Florence, 1951; later Sandra Ristori (Florence, 1960) also joined the team. The research was developed in collaboration with Larry Kevan (1938 -2002) at the Chemistry Department of the University of Houston. Many papers were published over several years, finally extending their scope to large interface systems, as it was in Ferroni's mind.  It is worth mentioning that Ferroni appeared only a few times as co-author of these studies of which he was a staunch supporter: we recognise in this behaviour both a commendable generosity and a habit of mind diametrically opposed to what one might imagine in the common sense of the university barony, and intellectual honesty, since Ferroni was aware that he had no skills in resonance techniques when he suggested to Burlamacchi to start his adventure with EPR/ESR and to Tiezzi with NMR. The fortuitous case allowed Ferroni to meet Nello Carrara and Leo Burlamacchi and to create the conditions for the subsequent development of resonance techniques in the Florence colloids and surfaces group headed by Ferroni.
The second route associated with his visionary idea to apply new instrumental techniques to colloids and surfaces studies dealt with surface diffraction techniques. Ferroni set the goal to understand atomic and molecular mechanisms at the basis of gas adsorptions on well-characterised surfaces, namely {hkl} metal monocrystal faces. To realise this objective Ferroni encouraged his pupil Rovida to spend some months in Paris at Trillat's Laboratories (vide infra) to ascertain whether the technique of Reflection of High Energy Electron Diffraction (RHEED) under grazing incidence was able to reach the goal or not. Rovida's trials did not produce reliable results. Indeed, Ferroni was fascinated by the concept of understanding atomic and molecular mechanisms at the basis of gas adsorptions onto solid surfaces. When he was back at the University of Florence, Ferroni had the opportunity to read a brochure illustrating that, thanks to the ultra-high-vacuum instrumentation supplied by Varian Associates, it had become possible to build instrumentations able to collect reproducible and well-interpretable Low Energy Electron Diffraction (LEED) patterns. Ferroni was impressed by the brochure's content, which illustrated this innovative technique's impressive power to study all the phenomena at the solid-vacuum interface, especially to deepen the gas adsorption mechanisms onto well-characterised solid surfaces, namely well-defined crystallographic faces. The future Nobel Prize in chemistry (2007) Gerhard Ertl (Stuttgart, 1936) was involved in these studies, and two years later he published a ground-breaking article that opened vast horizons for surface science studies. 140 Ferroni grasped the opportunity and gave Rovida the brochure asking his opinion about the new LEED instrumentation. The answer was positive and a new and fascinating challenge started. Ferroni obtained funds to order the LEED apparatus, which arrived in the autumn of 1966. Still, it had to remain at the customs offices for several months due to the Florence flood (vide infra) that had damaged the Institute of Physical Chemistry of the University. Finally, during the spring of 1967, the LEED instrument arrived, was installed, and in a short time, the first two articles on surface studies by LEED from the University of Florence Institute of Physical Chemistry were published. 141,142 Once again, the path was open thanks to a scientist who constantly desired to see farther, to guide his pupils, but simultaneously leave them free to unleash their talents and abilities without undue pressure or need for complacency and flattery towards him. In the following years, the group that welcomed Ermanno Zanazzi, Marco Torrini, Ugo Bardi and Andrea Atrei gradually came to be headed by Rovida and published many important papers, 143 160 Ferroni had been back in Florence for just a year and he was immediately involved with all his other colleagues in rescuing damaged instrumentations, books, documents, chemicals, laboratory glassware from the Chemistry Institutes (see Figure 4) in the centre of the city where the Arno's water reached ca. 1 m of height. After the emergency of the first few days, it appeared clear that the damage to the works of art was vast, especially for the wall paintings that could not be removed. Ferroni understood that a scientific approach was essential to help in solving the myriad of problems that conservators and cultural heritage officials encountered. During those frantic days Ferroni was able to invent two different methodologies and simultaneously inaugurate a new epoch for conservation and restoration, the scientific approach and the continued and constant integration between art history, conservation, science and specifically chemistry. 161 The first dramatic emergency came from the rapid deterioration of the fresco L'ultima cena (The last supper) by Taddeo Gaddi (ca. 1300 -1366) in the Refectory of Santa Croce Basilica. After the waters receded the consequent salt efflorescence due to nitrates was rapidly causing the colour to fall off the wall. This masterpiece was literally vanishing before the anxious eyes of the experts. The only solution was to urgently detach the fresco from the wall and transfer it onto another suitable support. Unfortunately, the detachment was made impossible due to the very high nitrates concentration into the water impregnating the porous structure of the wall. This high ionic force inhibited the sol → gel transition of the animal glue solutions used to impregnate both the paint surface and the canvases onto which, after the gelation of the animal glue, the painting layers would have had adhered allowing the detachment of a few microns of pictorial mortar. The situation was desperate; each day that went by, the coloured powder was found at the feet of the fresco. Ferroni remembered some of his studies 96,162 where he had demonstrated that tributyl-phosphate (TBP), an organic compound almost insoluble in water (only 6 g/L at 20 °C) 163 and with very low surface tension (27.79 mN/m at 20 °C), 163 forms monomolecular films onto nitrates water solution with an average molecular area depending on the cations, due to the formation of the different complexes at the water-air interface. He thought that wetting the wall surface with TBP would lead to monomolecular films spread onto the aqueous nitrate solution layers, which adhered to the solid particles of both the mortar and the pigments, besides filling the wall pores. In a way, he prefigured that in this manner, the whole exposed surface of the first layers of the wall would become highly hydrophobic due to TBP, forming a sort of impermeable film that would prevent the migration of the ions coming from the nitrates into the animal glue solution, which therefore would be able to gel and allow the subsequent detachment. 164,165 The various experts were very sceptical about this hypothesis, and Ferroni replied as Isaac Newton: "hypotheses non fingo, please try!" The trial was carried out by the restorer Dino Dini on a small portion of a less famous fresco by Jacopo Ligozzi (ca. 1547 -1627) and the result was astonishing: the glue set, and the small portion could be easily detached. The whole fresco by Gaddi was then subjected to the same treatment, detached, and repositioned in the same place onto appropriate support. It is still there in good health: it was an actual rescue rather than a restoration or conservation intervention. Without this most significant and brilliant idea by the chemist Ferroni, we would not be able to admire this wonderful work of art now.
The second critical question about wall painting damage was the worsening of the degradation by a process called sulphatisation. 166 The transformation of the binding CaCO3, formed by the setting of lime, into gypsum (CaSO4 . 2H2O) resulted in a severe deterioration of the painted surface with formation of white patinas, crusts, powdering, and other dangerous pathologies that compromised both the reading and the stability of the pictorial surface: it was evident that the flood had visibly accelerated this phenomenon. Again, Ferroni activated his brilliant and eclectic mind and proposed to re-convert gypsum into CaCO3 by using ammonium carbonate followed by a barium hydroxide treatment. To ascertain whether this chemical approach was effective in recovering a readable and compact painting surface, Ferroni remembered both his time at the CNRS Laboratoire de Diffraction des Rayons X at Bellevue in France and the correspondence 167 with its Director Jean Jacques Trillat (Paris, 1899 -Versailles, 1987). Trillat was a very distinguished scientist with expertise in colloids and interfaces. In 1956 he authored a fundamental book 168 and precursor of the studies that would be developed in Italy by Ferroni, such as those on molecular layers of fatty substances on metals. 169 Reflecting on these memories, Ferroni and co-workers measured the reconversion of gypsum to CaCO3 using ammonium carbonate and subsequent barium hydroxide treatment by X-Rays Diffraction (XRD) using an apparatus invented by Trillat and reconstructed at the Institute of Physical Chemistry of the University of Florence. 170 The results were extremely encouraging since the XRD patterns were in agreement with a total reconversion (see Figure 5). The successive application on the wall painting San Domenico in adorazione del crocifisso (St. Dominic in adoration of the crucifix) by Beato Angelico (ca. 1395 -1455) at the San Marco Convent in Florence showed excellent results, not only in terms of reconversion but also in firmly consolidating the painting surface and the thin layers of mortar (intonaco) underneath. 171 During the subsequent years and up to the present day, this technique became the legacy of wall painting conservators worldwide. It was named the Ferroni-Dini method after the chemist inventor and the conservator who devised and applied the procedure. 172-178 Figure 5. Enzo Ferroni close to a flow chart recorder during the collection of XRD to ascertain the mechanism of the frescoes' sulphatisation and the reconversion to calcium carbonate thanks to the treatment with ammonium carbonate followed by barium hydroxide, the so-called Ferroni-Dini method.
Ferroni's passion for connecting science and art continued throughout his life, and several other studies testified to the outstanding contribution this chemist made to the world of cultural heritage conservation: autogenous lime-based grouts [179][180][181] and oil-in-water microemulsions [182][183][184][185] used for the conservation of wall paintings by Masaccio (1401 -1428) in the Brancacci Chapel 164,165,[186][187][188] in Florence, the role of the deliquescent salts 189,190 for the deterioration of the wall paintings of La leggenda della vera croce (The legend of the true cross) by Piero della Francesca (ca. 1412 -1492) in the San Francesco Basilica in Arezzo, 191 the chemical stability of some pigments 192 or solvents 193 used for cleaning pictorial surfaces, until his last intuition about a possible role of nanoscience and nanotechnology [194][195][196][197][198][199] for a revolutionary approach to conservation and restoration. Ferroni had been convinced ever since that the studies dealing with the physical chemistry of colloids and interfaces with potential applications for cultural heritage conservation had to be considered on par with traditional physicochemical papers. Towards the end of his long career, he received a prestigious award when the Journal named after the scientist that was Ferroni's inspiration, Irving Langmuir, decided to dedicate the cover of its 26 th issue of 1999, published on 1 December to a photo illustrating the damage done by salt efflorescence in wall paintings. The image was the damaged face of Christ in The last supper by Taddeo Gaddi, which Ferroni had rescued about thirty years before. The article 200 was penned, among others, by two of Ferroni's pupils, Piero Baglioni and the author of the present article. Subsequently, many renowned international journals accepted papers on the physical chemistry of colloids and interfaces devoted to bringing a contribution to the improvement of cultural heritage conservation and sometimes dedicating again their covers 201 : Enzo Ferroni's challenge was definitively won at the beginning of the 21 st century, as testified by various papers 201-208 that received critical reviews . 209-220

NEW FRONTIERS IN SOFT MATTER
As previously written, at the beginning of the 1990s, the physical chemistry of colloids and interfaces was well cultivated at the Department of Chemistry of the University of Florence into which, in 1983, the Institute of Physical Chemistry was merged. There were at least six sub-groups that germinated from the seeds sown by Ferroni: the teams of monolayers and Langmuir-Blodgett films (Gabrielli with her pupil Gabriella Caminati, Florence, 1960), surface diffraction techniques (Rovida), ESR/EPR (Martini), solid-state reactions and solid-gas interfaces (Guarini), scattering techniques (Baglioni), and electrified interfaces (Guidelli). Moreover, in almost all the Universities in Italy, there were scientists actively working on these topics and the discipline that forty years before was almost inexistent in Italy was in excellent health. During the second part of the 1970s and the entire 1980s, Ferroni pointed his attention to monomolecular films constituted of polymers. [221][222][223][224][225][226][227][228][229][230][231] This interest had been certainly inspired by his previous relationship with the Nobel laureate Giulio Natta 167 and by the Flory-Huggins theory 232-234 for polymer solutions. Indeed, one of the articles Ferroni published in these years directly involved Huggins 221 . The results of a study on the bidimensional state conformation of poly β-benzyl-L-aspartate were compared precisely with Huggins' theory.
Ferroni's interest in surface properties of polymers was also stimulated by reading the studies by de Gennes: the future Nobel laureate in physics (1991) considered the physical chemistry of polymers at the interface and their interactions with surfactants as one of the most advanced topics in the physics of the condensed phases. [235][236][237][238][239][240][241] The year after winning the Nobel Prize, de Gennes published a short survey on Science entitled Soft Matter: 242 a new era for physics, chemistry, and physical chemistry was born, and Ferroni would have been pleased to have preconised, some forty years before, that this branch of science had the characteristics to play a fundamental role. In his article, 242 de Gennes explained the peculiarities of this soft matter, often called complex fluids, and he introduced the two main characteristics: complexity and flexibility. He then investigated the various systems that can be considered as belonging to this fourth state of the matter: polymers, surfactants, monolayers, bilayers and multilayers, cell membranes, liquid crystals, micelles, vesicles, and liposomes. This opened a staggering multitude of theoretical and applicative studies in many fields, such as biology and medicine, materials science, technology, and electronics, among others.

APPLIED CHEMISTRY, TECHNOLOGY, AND INDUSTRY
The first mention in the Chemical Abstract of Enzo Ferroni as an author is relative to an Italian patent 243 deposited on 27 February 1948 aimed to formulate a thermosetting powder. The young researcher who had carried out a chemistry master's degree thesis on theoretical considerations of chemical kinetics, 22 immediately demonstrated to be interested in aspects dealing with applied chemistry, technology, and industry. Indeed, this feeling and approach would continue throughout his long career and life: Ferroni profoundly understood the deep meaning of IUPAC (International Union of Pure and Applied Chemistry), that, as its name implies, focused on the union of pure and applied chemistry.
Among the various aspects of his applied research, we selected four emblematic instances of his approach. First, we thought it significant to recall the ten years of correspondence between Ferroni and Natta from 1958 until 1968, as recently studied by Laura Colli. 167 The interaction between them was intense and found its significant moment just one year after the awarding of the Nobel Prize to Natta: they published a paper in cooperation that linked the two domains of study these scientists had carried out in the last years, that is polymers for Natta and surface adsorbed films for Ferroni. 244 The second significant contribution was generated by the extended partnership with the Italian entity SnamProgetti operating in the field of fuels and energy. Ferroni was convinced that the idea of SnamProgetti to build a coal pipeline, apparently, a utopian mirage, could actually be pursued since large interface systems as coal-water stable dispersions would be able to generate slurries with suitable fluidity to flow into the pipeline and simultaneously burn at the end of the pipeline without separating the coal from the water. Thanks to some ad hoc surfactants Ferroni and co-workers developed stable suspensions of fine powdery coal in water containing up to 70% coal by weight, which was above the threshold required to be burnt without eliminating water. 245,246 These suspensions are called slurries, and they were heavily investigated 247-249 discovering their viscosity behaviour as non-Newtonian fluids with memory. Ferroni had the idea to involve his friend and colleague, the mathematician Mario Primicerio (Rome, 1932), in the study: the mathematical analysis succeeded in calculating the exact length (security distance) of the pipeline between two contiguous pumping stations to avoid coal sedimentation and stoppage. 250,251 Another interesting connection with the industry to find applications of large interface systems has already been mentioned in section 4. dedicated to chemistry applied to cultural heritage conservation. Both autogenous lime-based grouts and oil-in-water microemulsions created during the conservation workshop of the Masaccio, Masolino, and Filippo Lippi wall paintings in the Brancacci Chapel were developed in cooperation with the national industry Syremont S.p.A. whose President at the time was a friend of Ferroni's, Paolo L. Parrini. [179][180][181][182][183][184] Finally, there was the long and fruitful cooperation with yet another industrial sector, Tecnotessile of Prato, founded in 1972 and still actively operating in the field of new technologies applied in the textile industry. Ferroni was designated as President of this Technology Centre right from its inception in 1972. In 1980 he was still collaborating with the textile industry district in Prato (see Figure 6). The cooperation was mainly dedicated to developing large interface systems able to improve textile production. Ferroni was convinced that soft matter could offer many fruitful opportunities to the textile industry, but at that time, the textile industry was not ready to develop strong synergies with academic research. And again, in this case as well, Ferroni could see ahead of him: at the beginning of the 21 st century, some papers from researchers of the CSGI were published, and Ferroni was lucky enough to see them. [252][253][254][255][256] The last of his ideas we will mention is that of UV radiation-absorbing fabrics using nanotechnology; it was again a brilliant idea, but Ferroni was not able to read the paper: it was published online on 30 October 2007, six and half months after the eclectic chemist had passed away. 257

CONCLUSIONS
The scientific activity of Enzo Ferroni, critically revisited and investigated in the present study, allowed us to individuate the main original, novel, and creative ideas developed by this scientist, who operated mainly in the second half of the last century. It showed how he succeeded in creating a new physicochemical school in Italy on colloids, interfaces, and surfaces, a field that the future would reveal particularly worthy of being thoroughly investigated until the end of the 20 th century when it became a sort of new state of the matter called "soft", after the studies by the 1991 Nobel laureate in physics Pierre-Gilles de Gennes.
Ferroni perceived this discipline's enormous potential, studying Irving Langmuir's work and deepening his knowledge and skills attending the laboratories led by Raymond Defay and Ilya Prigogine at the Université Libre de Bruxelles. His first visionary idea to develop a branch of physical chemistry, almost neglected in Italy until the end of the Second World War, was followed by his second extraordinary intuition of applying the new and budding resonance spectroscopies (NMR and EPR/ESR) to research, first in solution chemistry and successively to investigate large interface systems.
His eclecticism forcefully emerged in the aftermath of the Florence flood in 1966 when he understood that chemistry, and science and technology in general, could play a fundamental role first in solving the dramatic and urgent problems facing the damaged works of art and then inaugurating a new conception of conservation and restoration, with solid scientific bases and a continuous cross-exchange among different and complementary competencies to create what, in the following years, would become the field of scientific restoration and conservation of cultural heritage. All these merits were acknowledged in the obituary that appeared in The Independent. 258 The consecration of his visionary ideas and intuition arrived in 1991 when Pierre-Gilles de Gennes was awarded the Nobel Prize in physics for having discovered that the methods developed for studying ordinary phenomena in simple systems can be generalised to more complex states of matter, especially liquid crystals, and polymers, individuating soft matter as a peculiar form of matter in the condensed phase. Some new topics, such as supramolecular chemistry, soft matter, self-assembly, nanoscience and nanotechnology, nanoscopic phases, and so on, surely have their root in the colloids and surfaces that Ferroni selected as his main interest for his long academic career.
The paper also showed Ferroni's eclecticism, considering his vision of the relationship between fundamental or basic research and applied chemistry, technology, and connection with industry. Ferroni was always convinced that all aspects of research possessed equal dignity, and the proof of this vision was the close relationship that Ferroni had with the Nobel laureate in chemistry Giulio Natta and the numerous applied studies he carried out having as Partners important companies in the energy, fuels, and textiles sectors.
Thanks to his long and fruitful work, Ferroni received numerous awards, among which we recall: the Gold Medal by the Italian Ministry of the Public Education (1967) as meritorious for school, culture, and art for "his generous collaboration offered for the preservation and recovery of the artistic and cultural The amazing variety of interests and subsequent content of his numerous studies and papers leads to conclude that for Enzo Ferroni, two different statements -the first by Leonardo da Vinci 259 and the second by Primo Levi 260 -can be used to summarise his multifaceted personality. Leonardo stated, "study science first, and then follow the practice born from that science" ("studia prima la scienza, e poi seguita la pratica nata da essa scienza") 259 . Levi wrote about his the following, speaking about his own chemistry, and we suggest the same is applicable to Ferroni's: "[a] solitary chemistry, unarmed and on foot, at the measure of man, which with few exceptions has been mine: but it has also been the chemistry of the founders, who did not work in teams, but alone, surrounded by the indifference of their time, generally without profit, and who confronted matter without aids, with their brains and hands, reason and imagination" ("chimica solitaria, inerme e appiedata, a misura d'uomo, che con poche eccezioni è stata la mia: ma è stata anche la chimica dei fondatori, che non lavoravano in équipe ma soli, in mezzo all'indifferenza del loro tempo, per lo più senza guadagno, e affrontavano la materia senza aiuti, col cervello e con le mani, con la ragione e la fantasia"). 260 Ken Shulman, in his wonderful book on the Brancacci Chapel, 164 succeeded in masterfully condensing these two quotations in an exceptional sentence: "Ferroni preferred to work alone, ruminating in his office in the early morning, applying his genially elastic mind until arriving at a solution". 261

ACKNOWLEDGEMENTS
The author expresses his gratitude to Drs Annantonia Martorano, Andrea De Santis, and Fabio Silari of the University of Florence, Dr Eleonora Todde of the University of Cagliari for the kind collaboration in finding the documents in the various Archives; thanks are also due to Sonia Carla Torretta for the accurate and careful revision of the English language and to Lucia Cappelli, Librarian at The British Institute of Florence for the kind assistance. The author also wishes to express his deep gratitude to Gabriella Caminati, Maurizio Romanelli, Marco Fontani, Maria Francesca Ottaviani, and Giulietta Smulevich for the valuable discussions about stories associated with the life of Enzo Ferroni. Section 3. The advent of resonance spectroscopies and surface diffraction techniques benefited from the invaluable testimonies of Leo Burlamacchi and Gianfranco Rovida, to whom the author expresses his deep gratitude. The financial support of the Fondi d'Ateneo per la ricerca from the Department of Chemistry "Ugo Schiff" of the University of Florence is gratefully acknowledged.