In memoriam Vittorio Degiorgio (5 January 1939–17 January 2021)

Since its dawn, the signature feature of soft matter science has been the blending of the complementary skills of chemists and physicists. Vittorio Degiorgio, who died last January after a long illness, can surely be regarded as a pioneer and advocate of such a fructuous joint venture.

A nuclear engineer by training, Vittorio started working on laser physics at CISE, a research centre that was in some way the Italian counterpart of the famous Bell Labs in the US. He then moved to MIT where he was pivotal in the development of Dynamic Light Scattering (DLS) by working out with John Lastovka the statistical analysis of intensity correlation measurements.

DLS was actually the “gateway” to the investigation of complex fluids that, back in Italy as a professor in Pavia, Degiorgio pursued together with Mario Corti by studying interactions and phase transitions in micellar solutions.

A landmark event that testifies to the role played by Vittorio in the development of colloid and interface science was the Enrico Fermi School “Physics of Amphiphiles: Micelles, Vesicles, and Microemulsions” that he organized with Corti in July 1983, a seminal meeting that brought together the leading experts in surfactant science and whose proceedings have obtained hundreds of citations.

But Vittorio's heyday in the field of colloid science was surely the ’90s, when his research interests broadened to encompass soft matter systems ranging from model colloids to polymers, from liquid crystals to proteins. Working together with him throughout that period, I have had the chance to appreciate and admire his superb skill in scrutinizing the experimental evidence, dissecting arguments, and rejecting hasty conclusions.

At the turn of the millennium, when most of his pupils in soft matter physics were already pursuing an independent career, Vittorio reverted to his youthful passion, retaining well after his formal retirement in 2011 a strong activity in nonlinear optics and in the design of photonic devices. Yet, his curiosity about colloid and soft matter science never faded away: the last paper we coauthored in 2014 deals indeed with subtle aspects of light scattering from colloidal suspensions.

Besides a first-class scientist, Vittorio was a fair person and a man of principle, gifted with a great intellectual honesty and endowed with a vast literary culture as well. He was an outstanding teacher too, endowed with lucidity, rigor, and expositive clearness. Mindful of his terse style, however, I wish to refrain from turning this brief and rather personal memory into a eulogy. The work done by Degiorgio speaks for itself, and I guess that the best way he would like to be remembered in this journal is by a short annotated list summarizing his main achievements in soft matter science.

• Interparticle interactions from virial coefficient measurements:

M. Corti and V. Degiorgio, Quasi-elastic light scattering study of intermicellar interactions in aqueous sodium dodecyl sulfate solutions, J. Phys. Chem., 1981, 85, 711.

• Critical phenomena in micellar solutions:

M. Corti, C. Minero and V. Degiorgio, Cloud point transition in nonionic micellar solutions, J. Phys. Chem., 1984, 88, 309.

• Counterion condensation and charge renormalization in colloids:

S. Bucci, C. Fagotti, V. Degiorgio and R. Piazza, Small-Angle Neutron-Scattering Study of Ionic–Nonionic Mixed Micelles, Langmuir, 1991, 7, 824.

• First experimental determination of the equation of state of hard spheres:

R. Piazza, T. Bellini and V. Degiorgio, Equilibrium sedimentation profiles of screened charged colloids: A test of the hard-sphere equation of state, Phys. Rev. Lett., 1993,71, 4267.

• Depolarized dynamic light scattering from interacting particles:

V. Degiorgio, R. Piazza and R. B. Jones, Rotational diffusion in concentrated colloidal dispersions of hard spheres, Phys. Rev. E, 1995, 52, 2707.

• Proteins close to crystallization modelled as adhesive hard spheres:

R. Piazza, V. Peyre and V. Degiorgio, “Sticky hard spheres” model of proteins near crystallization: A test based on the osmotic compressibility of lysozyme solutions, Phys. Rev. E, 1998, 58, R2733.

• Quenched disorder in nematic liquid crystals:

T. Bellini, N. A. Clark, V. Degiorgio, F. Mantegazza and G. Natale, Light-scattering measurement of the nematic correlation length in a liquid crystal with quenched disorder, Phys. Rev. E, 1998, 57, 2996.

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