(54a) John Quinn:  Master Weaver of a Remarkable Professional Tapestry

Professor John A. Quinn first came to prominence in chemical engineering circles for his fundamental research on mass transfer and interfacial phenomena. His work featured experiments thoughtfully conceived to permit accurate determination and rigorous analysis of interphase mass transfer rates at freshly created interfaces â?? an achievement made possible by his design of apparatus that brought immiscible fluids together in well-defined geometries at unprecedentedly short phase contact times. These experiments enabled the intrinsic mass transfer resistance of the interface itself to be explored, thus providing John with the opportunity to test the prevailing assumption that solutes diffusing from one immiscible phase into another would always experience equilibrium across the infinitely thin gas/liquid and liquid/liquid interfaces separating them.

While in the process of elucidating the role of the interface in mass transport, John Quinn and his students would initially be plagued by -- and then later intrigued with -- the thin films of surface-active materials that invariably concentrated at phase boundaries. Exploration of these insoluble monolayers revealed that their influence frequently extended well beyond the immediate vicinity of the interface; under some circumstances these interfacial films promoted convective instabilities while at other times they exerted a stabilizing effect on the bulk phases on either side of them.

Given his preoccupation with these thin films or interfacial â??membranesâ? that spontaneously accumulated at phase boundaries, it was inevitable that John Quinnâ??s attention would turn to synthetic membranes, inasmuch as these afforded controllable properties (e.g., porosities and thicknesses) that made them compelling platforms for fundamental transport studies. Track-etched mica membranes provided particularly fertile ground for the investigation of various steric, hydrodynamic, and electrodynamic effects key to the transport of solutes and colloids through submicron pores. Out of this work would come a much-improved theoretical description of sterically hindered diffusion, as well as critical insights on filtration and adsorption in finely porous media. Synthetic membrane composites also informed studies in his group of gas permeation across the skin.

 By virtue of his fundamental mass transfer work and his keen observations of transport across thin films, John Quinn was well-positioned to witness and participate in the birth and subsequent growth of a membrane separation industry initially focused on simple polymer films. But Johnâ??s vision extended far beyond the capabilities of those conventional synthetic membranes to what might be possible if engineers were to mimic elements of the structure and function of vastly more powerful biological membranes. For instance, John noted that cell membranes achieved unparalleled selectivity by exploiting reversible reactions between permeants and membrane-localized carriers, and he was fascinated by the ability of membrane-bound biomolecules to deftly orchestrate key biochemical reactions. He responded by materially advancing the theory of carrier-mediated or facilitated transport and by inspiring the development of enzyme membrane bioreactors capable of chiral separations important to the pharmaceutical industry.

More significantly, John Quinnâ??s enthusiasm for the intellectual interface between biology and engineering â?? and his influence on the direction that his department at Penn and his chosen field of chemical engineering would take -- amply justify his recognition as a pioneer in the then-emerging field of biomolecular engineering. John and his students would go on to explore several phenomena mediated by biomolecule-rich cell membranes, including, for instance, the attachment of cells to surfaces, the motility of cells on those surfaces, and the directed transport of motile bacteria.

This presentation traces the logic and serendipity that underlie the evolution of John Quinnâ??s varied research interests, identifying the threads that tie together the body of his work into a coherent whole â?? a truly remarkable â??professional tapestryâ?. It documents the considerable impact that his scientific and technical contributions have had on our profession â?? and it provides an occasion to honor the thoughtful guidance and warm friendship that John so generously offered to so many, his students and colleagues alike.