Joel A. Cohen (1940–2023), Professor Emeritus of Biomedical Sciences at the University of the Pacific, passed away on June 14 after a long illness. Cohen’s research focused on the biophysics of bilayer lipid membranes and related physical phenomena, with particular interest in colloidal crystals.
Cohen grew up in Swampscott, MA, the son of Ruth Krentzman Cohen and Morris Cohen, renowned Professor of Physical Metallurgy at the Massachusetts Institute of Technology. He graduated with a BA in Physics from Harvard University in 1962, then moved to the University of Illinois for graduate work in physics for his PhD with a dissertation in solid-state physics. When he took a postdoc at the University of Pennsylvania in solid-state physics, it seemed he would follow in his father’s footsteps, but Cohen found his true academic love in biophysics in a second postdoc at the University of the Pacific, where he stayed for almost all of his career.
His research focused on membranes, and he loved both the work and his collaborations with many wonderful colleagues, including the late Adrian Parsegian, Daniel Ou-Yang, Rudi Podgornik, Per Hansen, Paul Chaikin, Nejat Düzgüneş, Steven Wei, and many others. One important result, which he published with Podgornik, Hansen, and Parsegian, was that a simple, one-parameter scaling equation of state describes osmotic pressures for very different polymers (PEG and PAMS) in solution, in line with de Gennes’s scaling concepts. Much of Cohen’s research to study properties of lipid vesicles involved their suspension in deionized water to form colloidal crystals. Toward the end of his career, he was delighted by a surprising, counter-intuitive result: adding charge to liposomes beyond a relatively low threshold leads to weaker electrostatic interactions. He worked with colleagues Ou-Yang, Wei, and others on this phenomenon, showing it experimentally and developing theory to explain it.
Cohen served on the faculty of the University of the Pacific’s School of Dentistry from 1975 to 2014. He was recognized for his teaching, including courses in physiology and pharmacology, being selected for awards by his students as well as by his colleagues. He retired from his professorship in 2014 to focus more fully on his research, which he continued as an Adjunct Professor of Physics at the University of Massachusetts, Amherst, for as long as his health permitted.
After retirement, he returned to his childhood home in Swampscott, and he spent his final years there in the care of his devoted and loving wife, Sara Larsson Cohen. He will be remembered for the two great passions of his life, Sara and physics, for his playful spirit, the twinkle in his eye, and his enduring disrespect for time. Donations in Joel’s memory can be made to the Union of Concerned Scientists (www.ucsusa.org).