Agnese Callegari – Page 5 – Soft Matter Lab

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.

Funding:

H2020 European Research Council (ERC) Starting Grant ComplexSwimmers (677511).

Active Matter Influence on Coffee Rings published in Soft Matter

Active Matter Alters the Growth Dynamics of Coffee Rings
(Back cover article)
Tuğba Andaç, Pascal Weigmann, Sabareesh K. P. Velu, Erçağ Pinçe, Agnese Callegari, Giorgio Volpe, Giovanni Volpe & Agnese Callegari
Soft Matter 15(7), 1488—1496 (2019)
doi: 10.1039/C8SM01350K
arXiv: 1803.02619

How particles are deposited at the edge of evaporating droplets, i.e. the coffee ring effect, plays a crucial role in phenomena as diverse as thin-film deposition, self-assembly, and biofilm formation. Recently, microorganisms have been shown to passively exploit and alter these deposition dynamics to increase their survival chances under harshening conditions. Here, we show that, as the droplet evaporation rate slows down, bacterial mobility starts playing a major role in determining the growth dynamics of the edge of drying droplets. Such motility-induced dynamics can influence several biophysical phenomena, from the formation of biofilms to the spreading of pathogens in humid environments and on surfaces subject to periodic drying. Analogous dynamics in other active matter systems can be exploited for technological applications in printing, coating, and self-assembly, where the standard coffee-ring effect is often a nuisance.

Talk by A. Callegari at LAOP, Lima, 14 Nov 2018

Active Matter Alters the Growth Dynamics of Coffee Rings
Agnese Callegari, Tugba Andaç, Pascal Weigmann, Sabareesh K. Velu, Erçag Pince, Giorgio Volpe & Giovanni Volpe
LAOP – Latin America Optics & Photonics Congress, Lima, Peru
12-15 November 2018

Abstract: We show that bacterial mobility starts playing a major role in determining the growth dynamics of the edge of drying droplets, as the droplet evaporation rate slows down.

Tutorial by G. Volpe and A. Callegari on Optical Tweezers at LAOP, Lima, 12 Nov 2018

Optical Trapping and Optical Manipulation
Giovanni Volpe & Agnese Callegari
Tutorial at LAOP – Latin America Optics & Photonics Congress, Lima, Peru
12-15 November 2018

Description: This course will review the theoretical underpinnings of optical trapping and optical manipulation; a review of recent applications; and provide a hands-on tutorial on the use of computational methods to simulate optical trapping and the motion of optically trapped particles.

Time: 09:00 – 13:00
Location: INICTEL-UNI, Lima, Peru

Link: https://www.osa.org/en-us/meetings/topical_meetings/osa_latin_america_optics_photonics_conference/program/short_courses_and_tutorials_on_monday_12_november/

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.

Poster by A. Callegari at Flowing Matter 2018, Lisbon, 5-9 Feb 2018

Casimir forces investigated by blinking optical tweezers
Agnese Callegari
Flowing Matter 2018, Lisbon, Portugal
5-9 February 2018

https://sites.google.com/view/flowing-matter-2018/home

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)

Nonadditivity of Critical Casimir Forces published in Nature Commun.

Nonadditivity of critical Casimir forces
Paladugu Sathyanarayana, Agnese Callegari, Yazgan Tuna, Lukas Barth, Siegfried Dietrich, Andrea Gambassi & Giovanni Volpe
Nature Communications 7, 11403 (2016)
DOI: 10.1038/ncomms11403
arXiv: 1511.02613

In soft condensed matter physics, effective interactions often emerge due to the spatial confinement of fluctuating fields. For instance, microscopic particles dissolved in a binary liquid mixture are subject to critical Casimir forces whenever their surfaces confine the thermal fluctuations of the order parameter of the solvent close to its critical demixing point. These forces are theoretically predicted to be nonadditive on the scale set by the bulk correlation length of the fluctuations. Here we provide direct experimental evidence of this fact by reporting the measurement of the associated many-body forces. We consider three colloidal particles in optical traps and observe that the critical Casimir force exerted on one of them by the other two differs from the sum of the forces they exert separately. This three-body effect depends sensitively on the distance from the critical point and on the chemical functionalisation of the colloid surfaces.

Featured in:
“2+1 is not always 3: In the microworld unity is not always strength”, Phys.org
“Wenn 2 plus 1 nicht 3 ergibt”, Scinexx
“Физики доказали существование эффекта множества тел”, Gazeta.ru
“2+1 is not always 3”, Health Medicinet
“Nei colloidi 2 +1 non è uguale a 3”, Le Scienze
“Nei colloidi 2 +1 non è uguale a 3”, All News 24
“Wenn 2 plus 1 nicht 3 ergibt”, Scinexx
“2+1 ist nicht immer 3 – In der Mikro-Welt macht Einigkeit nicht immer”, idw – Informationsdienst Wissenschaft