Browsing by Subject "Janus particles"

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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
Janus particles in a Gaussian optical potential: a comparative experimental study
(2020-07) Bilgin, Muhammed
It has been shown recently that gold coated silica Janus particles can cluster when subject to a smooth optical ﬁeld due to the presence of an attractive interaction of hydrodynamic nature (1). Such an interaction comes from the simultaneous presence of various factors: the thermophoretic ﬂow around the Janus particle itself by the temperature gradient due to the partial absorption of the optical intensity on the gold cap of the particle, the presence of a boundary near the particle, the particular orientation (cap down) due to the gravity and the distinctive property of silica particles in water to move from colder to hotter regions. The model presented in the article suggests that there are various possibilities for driving the behaviour of the system: if the material constituting the particle had opposite thermophoretic features (particle moving from hotter to colder regions) then the sign of the hydrodynamic interaction would be reversed and we wouldn’t observe any tendence to form clusters. In this study we investigate the two cases stated above: we compared the behaviour of gold coated silica Janus particles with the behaviour of gold coated polystyrene Janus particles under the eﬀect of a Gaussian optical potential, for two diﬀerent kind of boundaries (glass slide, polymer slide). We ﬁnd that in the case of polymer slide there is evidence of a repulsive hydrodynamic interaction among gold coated polystyrene Janus particles, which is less pronounced for gold coated silica Janus particles. Moreover, the interplay of optical forces and repulsive hydrodynamic interaction is such that, in case of a mixed solution with Janus colloids and normal colloids, we obtain a relatively fast separation of the two species, that might ﬁnd applications for particles sorting. Though relatively simple in the experimental realisation, this study shows how varied can be the interplay of diﬀerent eﬀects of diﬀerent nature, i.e., due to external ﬁelds (optical, thermophoretic, hydrodynamic forces related to the beam itself) and due to the self-generated ﬁeld (thermophoretic, hydrodynamic interaction due to the absorption by the gold cap). Understanding and engineering the experimental conditions might lead to realise systems where one can switch from clustering to sorting, opening possibilities for the realisation of reconﬁgurable colloidal structures, that might be interesting for cargo deliveries, or the realisation of micro-rotors.
Open Access
Modeling of electro-kinetic motion of Janus droplet
(ASME, 2017) Öner, S. Doğan; Çetin, Barbaros
Electro-kinetic manipulation Janus particles and droplets has attracted attention in recent years due to their potential application in microfluidics. Due to the presence of two different zone on the surface of particles with different charge distribution, the motion of the Janus particles are quite different than the that of regular particles. Therefore; the fundamental understanding of this motion is the key element for the further development of the microfluidic systems with Janus particles. In present study, electro-kinetic motion of Janus droplets inside a micro-channel is modeled using boundary element formulation. 2D formulation is verified against the reported experimental data in the literature. Results show that the 2D boundary element formulation is successful for the prediction of the electrophoretic velocity of the Janus droplets. The current formulation has a potential to model non-spherical particles and to study particle-particle and particle-wall interactions.
Open Access
Optically driven janus microengine with full orbital motion control
(American Chemical Society, 2023-09-20) Bronte Ciriza, D.; Callegari, A.; Donato, M. G.; Çiçek, Berk; Magazzù, A.; Kasianiuk, Iryna; Kasyanyuk, Denis; Schmidt, F.; Foti, A.; Gucciardi, P. G.; Volpe, G.; Lanza, M.; Biancofiore, Luca; Maragò, O. M.
Microengines have shown promise for a variety of applications in nanotechnology, microfluidics, and nanomedicine, including targeted drug delivery, microscale pumping, and environmental remediation. However, achieving precise control over their dynamics remains a significant challenge. In this study, we introduce a microengine that exploits both optical and thermal effects to achieve a high degree of controllability. We find that in the presence of a strongly focused light beam, a gold-silica Janus particle becomes confined at the stationary point where the optical and thermal forces balance. By using circularly polarized light, we can transfer angular momentum to the particle, breaking the symmetry between the two forces and resulting in a tangential force that drives directed orbital motion. We can simultaneously control the velocity and direction of rotation of the particle changing the ellipticity of the incoming light beam while tuning the radius of the orbit with laser power. Our experimental results are validated using a geometrical optics phenomenological model that considers the optical force, the absorption of optical power, and the resulting heating of the particle. The demonstrated enhanced flexibility in the control of microengines opens up new possibilities for their utilization in a wide range of applications, including microscale transport, sensing, and actuation.