Dr. Patricia Elisabeth Cladis (1937 - 2017)
On July 3, 2017 the international liquid crystal community lost one of its pioneers, Patricia E. Cladis, who was also an Honored Member of the International Liquid Crystal Society (ILCS).
Clearly Pat's most outstanding piece of work, among her many creative and well known contributions to liquid crystal science, is the discovery of the reentrant nematic phase in 1975. Pat demonstrated that a nematic phase could occur in temperature both above as well as below a smectic A phase. Typically smectic phases are arising in thermotropic materials below nematic phases, because they were thought to be more ordered. The possibility for nematic phases to reenter was investigated in numerous compounds for several decades.
Among Pat's many other creative contributions we just mention a few. Already her first paper in liquid crystals in 1970 (with J. Rault and J.-P. Burger) was of pioneering character. Following a prediction by Francoise Brochard and Pierre-Gilles de Gennes, ferronematics were discovered experimentally. Only a few years ago, following advances in the controlled production of nanoparticles, truly ferromagnetic nematics have been synthesized. In 1972 Pat discovered experimentally (with Claudine Williams and one of us (PP)) and analyzed theoretically (with Maurice Kleman) the nonsingular character of S = +1 defects in nematics. The measurements of the elasticity in cholesteric Blue Phases as well as the discovery and crystallographic characterization of additional Blue Phases induced by an electric field were performed by Pat and the group of one of us (PP). Together with Harald Pleiner and one of us (HRB), Pat predicted the existence of interesting electric properties in banana-shaped (bent-core) fluid smectic phases -four years before they were found experimentally. At that time chiral molecules were thought to be necessary for nontrivial electric properties in liquid crystalline phases for well over a decade. To round-up our selection of Pat's pioneering contributions we mention her work with Yves Couder (Ecole Normale Superieure, Paris) and of us (HRB) on pattern formation in freely suspended smectic films, first (1985) for a rotating needle piercing the film leading to a mechanical torque and ten years later (1995) for rotating electric fields. These studies demonstrated the striking influence of topology on the spatio-temporal pattern observed.
Pat was contributing to the ILCS in a number of ways. Her major formal position was clearly to be the chair of the Honors and Awards Committee for eight years (1996 - 2004). Her efforts to encourage women to do research in physics led already early on to the award of the Kreeger Wolf Distinguished Visiting Professorship at Northwestern University in 1975.
Pat's outstanding contributions to the field of liquid crystals were recognized by numerous honors and awards including the election to Fellow of the American Physical Society, a Guggenheim Fellowship, a Research Prize of the Alexander von Humboldt-Foundation (Germany), an Invitation Fellowship of the JSPS (Japan Society for the Promotion of Science, Japan) and last, but not least, by the election as an Honored Member of the International Liquid Crystal Society.
Pat was an internationally well connected scientist collaborating for over four decades with colleagues from three different continents. Her superb hospitality was brought out by the many visitors she hosted in her house in Summit (New Jersey) together with her late husband George.
Helmut Brand (Bayreuth, Germany) and Pawel Pieranski (Orsay, France)