EventProf. Lucio Isa

New Directions for Active Colloids: Swimming at Oil-Water Interfaces and Position-Dependent Rotational Diffusivity

As research on artificial microswimmers continues to fascinate a broad community of scientists, new directions emerge by extending the scope of their application and by introducing new ways to control active motion. In this talk, I will first demonstrate how by confining Janus particles at oil-water interfaces, we can reveal new propulsion schemes. In particular, I will show how asymmetric temperature gradients enable propulsion via Marangoni stresses. These are extremely efficient propulsion schemes, leading to speeds up to cm/s for micron-sized colloids upon moderate heating (order 1-10K temperature increase). A careful balance between thermal and chemical Marangoni effects enables us to control particle velocity over four orders of magnitude. I will then describe the case of active magnetic particles with external feedback. By applying randomly oriented magnetic fields, we can effectively impose rotational diffusivities decoupled from the bath temperature. This, combined with real-time tracking of the particle position, makes it possible to realize landscapes of spatially varying rotational diffusion with dramatic consequences on particle dynamics. By comparing experiments with numerical simulations, we show that interesting anomalous diffusion and particle localization emerge [1]. Both parts indicate new ways in which we can control the active motion of artificial microswimmers, taking us one step closer to realizing the vision of active materials.

Lucio-abs

Figure1. Left: Schematic of the feedback loop to impose position-dependent rotational diffusivity to active magnetic colloids. Right: example of an active trajectory over a checkerboard pattern of alternating regions of high and low rotational diffusivity

About The Speaker

LucioIsa

Lucio Isa is the ETH Zurich Associate Professor of Soft Materials and Interfaces.

Lucio Isa was born in Milan (Italy) in 1979. He obtained a Masters degree (110/110 cum laude) in Nuclear Engineering from the Polytecnico di Milano (Italy) in 2004 and a PhD in Soft Matter Physics at the University of Edinburgh (UK) in 2008. After a short postdoctoral spell in Edinburgh, he moved to the Materials Department of ETH Zurich at the end of 2008 to work in the Laboratory for Surface Science and Technology, first as a Marie-​Curie Fellow and then as a Swiss National Science Foundation (SNSF) Ambizione Fellow. In 2012 he was awarded a SNSF travel grant as visiting fellow at the Chemical Engineering Department of the University of California, Santa Barbara, USA. In September 2013 Lucio Isa became SNSF Assistant Professor, heading the Laboratory for Interfaces, Soft matter and Assembly in the Department of Materials at ETH Zurich. In April 2019, he was promoted to Associate Professor of Soft Materials and Interfaces.

Lucio Isa is a co-​founder of Swiss Soft Days, an initiative aimed at creating a national network of scientists working in Soft Matter in Switzerland.

He lives in Zurich with his partner and two children.