Browsing by Author "Callegari, Agnese"

Now showing 1 - 11 of 11

Open Access
Active matter alters the growth dynamics of coffee rings
(OSA, 2018) Callegari, Agnese; Andaç, Tuğba; Weigmann, Pascal; Velu, Sabareesh K. P.; Pinçe, Erçağ; Volpe, G.; Volpe, Giovanni
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.
Open Access
Clustering of Janus particles in an optical potential driven by hydrodynamic fluxes
(Digital Library, 2021-08-01) Callegari, Agnese; Mousavi, S. Masoumeh; Kasianiuk, Iryna; Kasyanyuk, Denis; Velu, Sabareesh K. P.; Biancofiore, Luca; Volpe, Giovanni
Self-organisation is driven by the interactions between the individual components of a system mediated by the environment, and is one of the most important strategies used by many biological systems to develop complex and functional structures. Furthermore, biologically-inspired self-organisation offers opportunities to develop the next generation of materials and devices for electronics, photonics and nanotechnology. In this work, we demonstrate experimentally that a system of Janus particles (silica microspheres half-coated with gold) aggregates into clusters in the presence of a Gaussian optical potential and disaggregates when the optical potential is switched off. We show that the underlying mechanism is the existence of a hydrodynamic flow induced by a temperature gradient generated by the light absorption at the metallic patches on the Janus particles. We also perform simulations, which agree well with the experiments and whose results permit us to clarify the underlying mechanism. The possibility of hydrodynamic-flux-induced reversible clustering may have applications in the fields of drug delivery, cargo transport, bioremediation and biopatterning.
Open Access
Clustering of Janus particles in an optical potential driven by hydrodynamic fluxes
(Royal Society of Chemistry, 2019-06) Mousavi, S. Masoumeh; Kasianiuk, Iryna; Kasyanyuk, Denis; Velu, Sabareesh K. P.; Callegari, Agnese; Biancofiore, Luca; Volpe, Giovanni
Self-organisation is driven by the interactions between the individual components of a system mediated by the environment, and is one of the most important strategies used by many biological systems to develop complex and functional structures. Furthermore, biologically-inspired self-organisation offers opportunities to develop the next generation of materials and devices for electronics, photonics and nanotechnology. In this work, we demonstrate experimentally that a system of Janus particles (silica microspheres half-coated with gold) aggregates into clusters in the presence of a Gaussian optical potential and disaggregates when the optical potential is switched off. We show that the underlying mechanism is the existence of a hydrodynamic flow induced by a temperature gradient generated by the light absorption at the metallic patches on the Janus particles. We also perform simulations, which agree well with the experiments and whose results permit us to clarify the underlying mechanism. The possibility of hydrodynamic-flux-induced reversible clustering may have applications in the fields of drug delivery, cargo transport, bioremediation and biopatterning.
Open Access
Controlling active brownian particles in complex settings
(OSA, 2017) Velu, Sabareesh K. P.; Pinçe, Erçağ; Callegari, Agnese; Elahi, Parviz; Gigan, S.; Volpe, Giovanni; Volpe, G.
We show active Brownian particles (passive Brownian particles in a bacterial bath) switches between two long-term behaviors, i.e. gathering and dispersal of individuals, in response to the statistical properties of the underlying optical potential.
Open Access
Controlling the dynamics of colloidal particles by critical Casimir forces
(Royal Society of Chemistry, 2019-01) Magazzu, A.; Callegari, Agnese; Staforelli, J. P.; Gambassi, A.; Dietrich, S.; Volpe, Giovanni
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.
Open Access
Erratum: controlling the dynamics of colloidal particles by critical Casimir forces (Soft Matter (2019) 15 (2152-2162) DOI: 10.1039/C8SM01376D)
(Royal Society of Chemistry, 2020) Magazzu, A.; Callegari, Agnese; Staforelli, J. P.; Gambassi, A.; Dietrich, S.; Volpe, Giovanni
Correction for ‘Controlling the dynamics of colloidal particles by critical Casimir forces’ by Alessandro Magazzù et al., Soft Matter, 2019, 15, 2152–2162, DOI: 10.1039/C8SM01376D. The authors regret an error in the grant number for one of the authors in the Acknowledgements section. The Acknowledgements section should read as follows: This work was partially supported by the ERC Starting Grant ComplexSwimmers (grant no. 677511) and by Vetenskapsrådet (grant no. 2016-03523). A. C. acknowledges partial financial support from TUBITAK (grant no. 116F111). J. P. S. acknowledges partial financial support from FONDECYT (grant no. 1171013). The Royal Society of Chemistry apologises for these errors and any consequent inconvenience to authors and readers.
Open Access
Experimental investigation of critical Casimir forces in binary liquid mixtures by blinking optical tweezers
(OSA, 2017) Magazzu, Alessandro; Schmidt, F.; Callegari, Agnese; Gambassi, A.; Dietrich, S.; Volpe, Giovanni
We investigate, for the first time and by blinking optical tweezers, the effects of critical Casimir forces (CCFs) on the free dynamics of a pair of spherical colloidal particles, immersed in binary liquid mixtures upon approaching their critical points.
Open Access
Microscopic engine powered by critical demixing
(American Physical Society, 2018) Schmidt, F.; Magazzù, A.; Callegari, Agnese; Biancofiore, Luca; Cichos, F.; Volpe, G.
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 subcritical 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.
Open Access
Microscopic engine powered by critical demixing
(OSA, 2017) Schmidt, F.; Magazzu, Alessandro; Callegari, Agnese; Biancofiore, Luca; Cichos, F.; Volpe, Giovanni
We propose a new type of engine that is powered by the local, reversible demixing of a critical binary liquid. A microscopic particle is optically trapped and performs revolutions due to the emergence of diffusiophoresis.
Open Access
Nonadditivity of critical Casimir forces
(OSA, 2017) Callegari, Agnese; Paladugu, Sathyanarayana; Tuna, Yazgan; Barth, Lukas; Dietrich, S.; Gambassi, A.; Volpe, Giovanni
We provide the first experimental evidence of nonadditivity for critical Casimir forces: the force that two colloidal particles exert together on a third one differs from the sum of the forces they exert separately.
Open Access
Ordering of binary colloidal crystals by random potentials
(Royal Society of Chemistry, 2020) Nunes, A. S.; Velu, Sabareesh K. P.; Kasianiuk, Iryna; Kasyanyuk, Denis; Callegari, Agnese; Volpe, G.; Telo da Gama, M. M.; Volpe, Giovanni; Araujo, N. A. M.
Structural defects are ubiquitous in condensed matter, and not always a nuisance. For example, they underlie phenomena such as Anderson localization and hyperuniformity, and they are now being exploited to engineer novel materials. Here, we show experimentally that the density of structural defects in a 2D binary colloidal crystal can be engineered with a random potential. We generate the random potential using an optical speckle pattern, whose induced forces act strongly on one species of particles (strong particles) and weakly on the other (weak particles). Thus, the strong particles are more attracted to the randomly distributed local minima of the optical potential, leaving a trail of defects in the crystalline structure of the colloidal crystal. While, as expected, the crystalline ordering initially decreases with an increasing fraction of strong particles, the crystalline order is surprisingly recovered for sufficiently large fractions. We confirm our experimental results with particle-based simulations, which permit us to elucidate how this non-monotonic behavior results from the competition between the particle-potential and particle–particle interactions.