Light propelled micro-machines yield important advantages. While most other propulsion mechanisms require some kind of fuel in the surrounding medium, light acts as an external energy source which enables high spatio-temporal control. In our novel approach the actuation emerges from refraction of light on micro-machines with an asymmetric shape and refractive index profiles. The artificial micro-machines are fabricated by femtosecond laser lithography by two-photon polymerization which enables high precision and flexibility. We demonstrate and compare the propulsion of light propelled particles with different geometries and refractive index gradients.
Among the existing realizations of microscopic motile devices, photonically propelled nano- and microparticles are particularly advantageous. Their features pave the way for applying them in large numbers, e.g., as constituents of novel active materials with exceptional properties. However, the recently proposed photonically propelled particles have so far been studied only partially on the single-particle level so that their interesting collective dynamics remains unexplored. This talk will address this issue by presenting methods that allow to proceed from the single-particle motion of motile particles to their collective dynamics. It will focus on analytical modeling and computer simulations as well as their application to photonically propelled nano- and microparticles. Furthermore, it will present results, including unexpected pattern formation and transport effects, obtained by these methods for system sizes and particle numbers that are not yet accessible by experiments.
Among the numerous propulsion mechanisms developed in the past to self-propelled nano- and micro particles, light-driven machines are most promising, since they enable a natural spatio-temporal control of the motion. We report a novel fuel-free propulsion mechanism induced by an external light stimulus. The actuation relies on refraction of light, while the net propulsion force emerges from an asymmetric particle shape and a symmetry-broken refractive index profile. Two-photon polymerization is employed for fabrication of the artificial machines, whose geometries and refractive index profiles are optimized with the help of numerical simulations. We demonstrate the directional movement of refractive light-propelled particles, and the increased performance of artificial refractive index machines.
Artificial active nano- and microparticles driven by light are of special interest since their propulsion can easily be controlled via the illumination. Recently, we have established a propulsion mechanism based on asymmetric light refraction caused by a refractive-index gradient. We will introduce into this new approach based on two-photon polymerization of the active particles, and demonstrate active propulsion under illumination as well as pattern formation in colloidal suspensions of these active particles controlled by light.
The promising idea of using self-propelled particles in fields such as microfabrication and environmental remediation has led to the appearance of a plethora of different approaches for their motion during the past years. [1] Among them, the combination of living swimmers and nanocontainer cargos is especially attractive [2]. However, the usual necessity of a fuel in the environment hinders their application in biological tissue and consequently, their bio-medical usage. Here, we propose a novel propulsion mechanism based solely on the refraction of light in the volume of micro-scale particles.
In order to understand these artificial swimmers, numerical simulations were undertaken to identify optimized geometries and refractive index distributions of particles. In particles with broken symmetry, a resultant directional photon momentum transfer is intiating a propulsion force, which in turn can be enhanced by the inclusion of a GRadient of refractive INdex (GRIN).
We demonstrate fabrication of such artificial swimmers by femtosecond laser lithography based on two photon polymerization (TPP). The versatility of TPP along with the well-suited fabrication polymer Ormocomp allow replicating any of the numerically suggested particles, especially those containing GRIN distributions. We demonstrate the directional motion of the fabricated artificial swimmers under collimated illumination, with the GRIN particles outperforming their homogeneous counterparts.
With this first proof-of-principle we pave the way for numerous applications this new generation of fuel-free, refraction-driven self propelled swimmers.
[1] M. Guix, S. M. Weiz, O. G. Schmidt, M. Medina‐Sánchez, Part. Part. Syst. Charact. 35, 1700382 (2015).
[2] Á. Barroso et al., Biomedical Microdevices 17, 26 (2015);A. Barroso et al., SPIE Newsroom (2015); doi:10.1117/2.1201507.006023
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