Alessandro Magazzù – Soft Matter Lab

Presentation by Alessandro Magazzù at the OSA Biophotonics Congress, Tucson, 16 Apr 2019

Dynamics of optically trapped particles tuned by critical Casimir forces and torques

Alessandro Magazzù, Agnese Callegari, Juan Pablo Staforelli, Andrea Gambassi, Siegfried Dietrich & Giovanni Volpe.
OSA Biophotonics Congress, Tucson (AZ), USA 16 April 2019

Fluctuations have always played a crucial role in physics, especially when spatially confined by objects. Density fluctuations of the composition of a binary critical mixture emerge when its temperature is in proximity of the critical point. If these fluctuations are confined between two objects (e.g., two colloids, or a colloid and a planar surface), they give rise to Critical Casimir forces (CCFs). Although, these forces were predicted theoretically in 1978 in analogy to quantum-electrodynamical (QED) Casimir Forces they have never aroused a lot of attentions. They have always been considered mostly like a curiosity, until recently. Thanks to the development of nano-technology, CCFs seem to have establish their role in nano-science. They have been measured only recently, proving their relevance at nanoscale.

Session: Enhancing Techniques
14:00 –16:00, Tuesday, April 16, 2019
Chair: Frank Cichos; University Leipzig, Germany

Controlling Colloidal Dynamics by Critical Casimir Forces published in Soft Matter

Controlling the dynamics of colloidal particles by critical Casimir forces
(Back cover article)
Alessandro Magazzù, Agnese Callegari, Juan Pablo Staforelli, Andrea Gambassi, Siegfried Dietrich & Giovanni Volpe
Soft Matter 15(10), 2152—2162 (2019)
doi: 10.1039/C8SM01376D
arXiv: 1806.11403

Critical Casimir forces can play an important role for applications in nano-science and nano-technology, owing to their piconewton strength, nanometric action range, fine tunability as a function of temperature, and exquisite dependence on the surface properties of the involved objects. Here, we investigate the effects of critical Casimir forces on the free dynamics of a pair of colloidal particles dispersed in the bulk of a near-critical binary liquid solvent, using blinking optical tweezers. In particular, we measure the time evolution of the distance between the two colloids to determine their relative diffusion and drift velocity. Furthermore, we show how critical Casimir forces change the dynamic properties of this two-colloid system by studying the temperature dependence of the distribution of the so-called first-passage time, i.e., of the time necessary for the particles to reach for the first time a certain separation, starting from an initially assigned one. These data are in good agreement with theoretical results obtained from Monte Carlo simulations and Langevin dynamics.

Alessandro Magazzù awarded Best Presentation Prize at Soft Matter Days 2018

Alessandro Magazzù has been awarded a best oral contribution “Soft Matter poster price” during the conference Italian Soft Matter Days 2018, held in Padua, Italy on September 13-14, 2018. The prize has been given by Emanuela Zaccarelli, editorial board members of the Soft Matter journal. This prize mainly consists in an invitation to submit a manuscript without the pre-screening by the Editors. It also includes a “poster prize” and a personal yearly subscription to the journal.

Review on Optical Tweezers published in J. Quant. Spectrosc. Rad. Transf.

Optical tweezers and their applications
Paolo Polimeno, Alessandro Magazzù, Maria Antonia Iata, Francesco Patti, Rosalba Saija, Cristian Degli Esposti Boschi, Maria Grazia Donato, Pietro G. Gucciardi, Philip H. Jones, Giovanni Volpe & Onofrio M. Maragò
Journal of Quantitative Spectroscopy and Radiative Transfer 218(October 2018), 131—150 (2018)
DOI: 10.1016/j.jqsrt.2018.07.013

Optical tweezers, tools based on strongly focused light, enable optical trapping, manipulation, and characterisation of a wide range of microscopic and nanoscopic materials. In the limiting cases of spherical particles either much smaller or much larger than the trapping wavelength, the force in optical tweezers separates into a conservative gradient force, which is proportional to the light intensity gradient and responsible for trapping, and a non-conservative scattering force, which is proportional to the light intensity and is generally detrimental for trapping, but fundamental for optical manipulation and laser cooling. For non-spherical particles or at intermediate (meso)scales, the situation is more complex and this traditional identification of gradient and scattering force is more elusive. Moreover, shape and composition can have dramatic consequences for optically trapped particle dynamics. Here, after an introduction to the theory and practice of optical forces with a focus on the role of shape and composition, we give an overview of some recent applications to biology, nanotechnology, spectroscopy, stochastic thermodynamics, critical Casimir forces, and active matter.

Talk by A. Magazzù at Italian Soft Days 2018, Padua, 13-14 Sept 2018

Microscopic engine powered by critical demixing
Alessandro Magazzù, Falko Schmidt, Agnese Callegari, Luca Biancofiore, Frank Cichos & Giovanni Volpe
Italian Soft Days 2018, Padua, Italy
13-14 September 2018

We propose a new type of engine powered by the local, reversible demixing of a critical binary liquid. In particular, we show that a light absorbing, optically trapped particle, performs revolutions around the trapping beam producing work.
This behavior results from an equilibrium between optical forces and diffusiophoresis induced by a local demixing of the critical mixture. This new kind of engine can be controlled by the optical power supplied, the temperature of the environment and the criticality of the system.

Reference: Schmidt et al. Microscopic Engine Powered by Critical Demixing, Phys. Rev. Lett. 120, 068004 (2018)

Microscopic Critical Engine featured in Phys.Org

Our recent article Microscopic engine powered by critical remixing
by Falko Schmidt, Alessandro Magazzù, Agnese Callegari, Luca Biancofiore, Frank Cichos & Giovanni Volpe, published in Physical Review Letters 120(6), 068004 (2018) has been featured in “Tiny engine powered by demixing fluid” Phys.Org (February 12, 2018)

Microscopic Critical Engine featured in Optics & Photonics News

Our recent article Microscopic engine powered by critical remixing
by Falko Schmidt, Alessandro Magazzù, Agnese Callegari, Luca Biancofiore, Frank Cichos & Giovanni Volpe, published in Physical Review Letters 120(6), 068004 (2018) has been featured in “Laser + Critical Liquid = Micro-Engine”, Optics & Photonics News (February 12, 2018)

Optics & Photonics News (OPN) is The Optical Society’s monthly news magazine. It provides in-depth coverage of recent developments in the field of optics and offers busy professionals the tools they need to succeed in the optics industry, as well as informative pieces on a variety of topics such as science and society, education, technology and business. OPN strives to make the various facets of this diverse field accessible to researchers, engineers, businesspeople and students. Contributors include scientists and journalists who specialize in the field of optics.

Microscopic Critical Engine featured in APS Physics

Our recent article Microscopic engine powered by critical remixing
by Falko Schmidt, Alessandro Magazzù, Agnese Callegari, Luca Biancofiore, Frank Cichos & Giovanni Volpe, published in Physical Review Letters 120(6), 068004 (2018) has been featured in “Focus: A Tiny Engine Powered by Light and Liquid Physics”, Physics 11, 16 (February 9, 2018)

Physics provides daily online-only news and commentary about a selection of papers from the APS journals collection. It is aimed at the reader who wants to keep up with highlights of physics research with explanations that don’t rely on complex technical detail.

The category Physics: focus stories features only a few number of articles each week selected among the set of articles published on all the APS journals.
Research articles that have an interdisciplinary character are usually selected, and their explanations are geared toward students and non-experts. Features are written by a journalist for an audience with a general interest in physics.

Microscopic Critical Engine published in Phys. Rev. Lett.

Microscopic engine powered by critical demixing
Falko Schmidt, Alessandro Magazzù, Agnese Callegari, Luca Biancofiore, Frank Cichos & Giovanni Volpe
Physical Review Letters 120(6), 068004 (2018)
DOI: 10.1103/PhysRevLett.120.068004
arXiv: 1705.03317

We experimentally demonstrate a microscopic engine powered by the local reversible demixing of a critical mixture. We show that, when an absorbing microsphere is optically trapped by a focused laser beam in a sub-critical mixture, it is set into rotation around the optical axis of the beam because of the emergence of diffusiophoretic propulsion. This behavior can be controlled by adjusting the optical power, the temperature, and the criticality of the mixture.

Featured in :
“Focus: A Tiny Engine Powered by Light and Liquid Physics”, Physics 11, 16 (February 9, 2018)
“Laser + Critical Liquid = Micro-Engine”, Optics & Photonics News (February 12, 2018)
“Tiny engine powered by demixing fluid” Phys.Org (February 12, 2018)
“Расслаивание растворителя закрутило микрочастицы вокруг лазерного пучка”, N+1: научные статьи, новости, открытия (February 12, 2018)
“Tiny engine powered by remixing fluid”, Brinkwire (February 16, 2018)

Alessandro Magazzù joins the Soft Matter Lab

Alessandro Magazzù from the University of Messina, Italy, joined the Soft Matter Lab on 1 July 2015 as a postdoctoral researcher.

His PhD thesis, “Optical trapping and thermal dynamics of Silicon nanowire”, deals with experimental work on various aspects of optical trapping and manipulation of non-spherical object and, in particular, nanowires.

At the Soft Matter Lab, he will work on a project related to the study of critical Casimir forces.