In October 2017 the international colloid and interface community had lost two scientists of high professional authority and prominent representatives of European Colloid and Interface Science: Dotchi Exerowa and Dimo Platikanov. Both had actively promoted the microscopic thin liquid films as an advanced methodology to investigate surface forces and related phenomena in the physics and chemistry of interfaces. Throughout the years their studies mostly were running in parallel, with each of them having specific scientific contributions. They had also jointly made valuable experimental and theoretical accomplishments enhancing the knowledge about the properties and interactions in foams, emulsions and related applications.
The name of Dotchi Exerowa is firmly linked with one of the most successful research instrumentation in the field of surface forces: the microinterferometric setup for the formation and investigation of thin liquid films. Microscopic foam film was also proposed as an in vitro model for the study of the alveolar interface and the estimation for the stability of the alveoli. Based on this model a new clinical method for early diagnostics of lung maturity of neonates was proposed (Exerowa Black Film method). A particular progress was achieved in studying the properties and the stability of foam and emulsion systems. A basic accomplishment was the outline of the role of the foam film type (common thin, common black or bilayer) for the syneresis and lifetime of foams. In the recent years a new version of the microinterferometric technique was initiated, with a specific option for electrochemical investigations of thin liquid films. The technique is now applied for the investigation of emulsion films, stabilized by polymeric and natural surfactants. These films are of crucial importance for understanding the properties of emulsions, which are used in oil, pharmaceutical, cosmetic and food industries.
Dimo Platikanov had comprehensively investigated three-phase contact and wetting phenomena. An original experimental cell was constructed for the formation of microscopic circular wetting liquid films on solid surface and the microinterferometric technique of Scheludko-Exerowa had been modified accordingly. The shape of the three phase contact gas/liquid film/meniscus/solid surface had been studied in detail; the equilibrium profile of the transition zone between a wetting film and the bulk liquid had been experimentally obtained and data for the “contact thickness” had been calculated. The new methods allowed the determination of film tension and line tension of Newton black films (NBFs). Another important trend was the determination of gas permeability through foam films.
In the recent two decades they had authored together a number of essential review publications and chapters in encyclopedic books edited by: Hans Lyklema (“Fundamentals of Interface and Colloid Science”, Elsevier, 2005); Johan Sjöblom (“Emulsions and Emulsion Stability”, CRC Taylor & Francis, 2005); Tharwat Tadros (“Emulsion Science and Technology”, Wiley-VCH, 2009); Victor Starov (“Nanoscience: Colloidal and Interfacial Aspects”, CRC Press, Taylor & Francis, 2010); Hiroyuki Ohshima and Kimiko Makino (“Colloid and Interface Science in Pharmaceutical Research and Development”, Elsevier, 2014); Hiroyuki Ohshima (“Encyclopedia of Biocolloid and Biointerface Science”, John Wiley & Sons, Inc., Hoboken, 2016). In 2009 the book “Highlights in Colloid Science” (Wiley-VCH), was published with them being Editors. They are co-editors of the latest book “Foam Films and Foams: Fundamentals and Application”, CRC Press, to appear in 2018. In the last decade they had also been Editors for the topic “Thin Liquid Films and Foams” in the Elsevier journal “Current Opinion in Colloid and Interface Science”.
Through their research activities Dotchi Exerowa and Dimo Platikanov had developed numerous collaborations with leading scientists and research laboratories in the field of physical chemistry of interfaces and colloids and were closely engaged in the development and the organizational advance of the international colloid and interface scientific community. Each of them had been elected twice as Member of the IACIS Council; Platikanov was also President of IACIS (2000 – 2003) and later was elected as Lifelong Member of the Standing Committee and of the IACIS Council. He had been Member of the Standing Committee of the European Chemistry at Interfaces Conferences (ECIC). Since 2004 he had been Member of the Physical and Biophysical Chemistry Division Committee of IUPAC. In 1997 they both co-chaired the 9th International Conference on Surface and Colloid Chemistry in Sofia, organized under the aegis of International Association of Colloid and Interface Scientists (IACIS); in 2013 they were members of the Scientific Committee of the 27th ECIS Conference in Sofia.
The long scientific careers of Dotchi Exerowa and Dimo Platikanov and their personal union resulted in mutual inspiration and research collaboration that produced important scientific results in the field of surface forces, thin liquid films, foams and emulsions. Throughout the years they had succeeded in attracting many gifted young people and they established two strong research teams: Exerowa in Department of Interfaces and Colloids (Institute of Physical Chemistry, BAS) and Platikanov in Department of Physical Chemistry (Sofia University). Dotchi Exerowa and Dimo Platikanov will be remembered by their colleagues, friends, collaborators and former students with their deep passion for science, the wide horizon of the research interests and the keen intuition to address challenging problems. The legacy of their scientific results, teaching and applied activities constitutes a notable contribution to the productive development of the European Colloid and Interface Science.
Department of Interfaces and Colloids
IPC-BAS, Sofia, Bulgaria