In Memoriam: Jan Mewis (1938-2025)

Jan Mewis was born on April 22, 1938 in Borgerhout, near Antwerp. He studied Chemical Engineering at the Katholieke Universiteit Leuven in Belgium, where he received his master degree in 1961. While he worked at the IVP Laboratory, the research institute of the Belgian paint and printing ink industry, he obtained his PhD at the KU Leuven in 1967 with a thesis on “Tack of Printing Inks”. In 1969 he returned to KU Leuven as a fulltime faculty member, where over the years he taught a wide range of courses, ranging from Rheology, Plastics Technology and Transport Phenomena to Safety of Chemical Plants and Hazardous Materials. He was chairman of the Chemical Engineering Department from 1989 to 1995 and again from 1999 until 2002 and coordinator of the Safety Engineering Programme from 1982 to 1987. In 1971-72 he spent a year at the University at Delaware with a NATO fellowship, working with professor A.B. Metzner. He was twice a visiting professor at the same university (1981 and 2004) and at Princeton University in 1982. He spent shorter visits at various universities in the US and Australia.

The research activities of Jan Mewis can be situated in the general area of rheology and processing of complex fluids. He authored or co-authored over 200 publications and gave hundreds of lectures and seminars all over the world on this topic. He is best known for his, often cited, work in three specific areas. In the area of suspension rheology he published with A.B Metzner the now classical paper on extensional flow of fibre suspensions as well as a series of papers establishing the rheology of sterically stabilized suspensions. Later he contributed substantially to the present understanding of the rheology of liquid crystalline polymers and that of immiscible polymer blends. In all these cases his approach was to link the rheology to the underlying flow-induced changes in microstructure. He successfully applied a wide range of rheological procedures for probing the microstructure during flow. This was supplemented very early by adding other techniques for in-situ, time-resolved structural analyses during flow. These included various scattering techniques, especially rheo-optics, as well as dielectric techniques. His trademark has been to develop and use an experimental methodology that produces theoretically meaningful results, thus bridging the gap between fundamental aspects of rheology and industrial applications. Jan Mewis is also known for his contributions to the controversial topic of thixotropy.

Over the years, Jan Mewis and his team were able to expand the Laboratory of Applied Rheology in Leuven, now known as the SMaRT laboratory (Soft Matter, Rheology and Technology) to one of the best equipped rheo-physical laboratories worldwide. Jan supervised numerous PhD theses and postdocs, and many of his former students have risen to prominent positions in academia and industry, making him the scientific father and grandfather of many rheologists worldwide.

For his various contributions to the field of rheology, both in breadth and in depth, Jan Mewis received the Gold Medal of the British Society of Rheology in March 2005 and the Society of Rheology’s Bingham Medal in October 2005.

Jan Mewis was quite active in the rheological community. He was a co-founder and former president of the Belgian Group of Rheology, was chairman of the International Committee on Rheology (1992-96) after he co-chaired with Marcel Crochet (UCLouvain) the 11^th International Congress on Rheology in Brussels in 1992 and until 2025 he was a member of the Executive Committee of the European Society of Rheology. Since October 2003 he was professor-emeritus but still active in research and consulting, always available to students to share his knowledge. His scientific activity can also be exemplified by the book on Colloidal Suspension Rheology (Cambridge University Press, 2011) he has published together with Prof. Wagner (University of Delaware).

Jan Mewis was very willing to collaborate with others but he only accepted to be a co-author of a paper if he felt he contributed significantly to the work. Several times he took off his name of joint papers because he felt that this condition was not fully satisfied. These norms and moral integrity (some would call it “old school”) is something that deserves respect.

On a personal note, Jan and his wife Ria (who passed away in 2023) were well known and liked within the academic world at Leuven and also to the rheology community as a whole. They travelled a lot together and were universally known as kind, warm and charming people. Although it is fair to say that Jan has dedicated much of his life to rheology, he was also much interested in culture and history, always eager to discover new places. Jan Mewis will be sorely missed by all who knew him for his wisdom, knowledge, tranquillity and friendship.