article published yes Jérémie A Palacci author 8fb92548-2b22-11eb-b7c1-a3f0d08d7c7d0000-0002-7253-9465 S. Sacanna author S.-H. Kim author G.-R. Yi author D. J. Pine author P. M. Chaikin author Light-activated self-propelled colloids are synthesized and their active motion is studied using optical microscopy. We propose a versatile route using different photoactive materials, and demonstrate a multiwavelength activation and propulsion. Thanks to the photoelectrochemical properties of two semiconductor materials (α-Fe2O3 and TiO2), a light with an energy higher than the bandgap triggers the reaction of decomposition of hydrogen peroxide and produces a chemical cloud around the particle. It induces a phoretic attraction with neighbouring colloids as well as an osmotic self-propulsion of the particle on the substrate. We use these mechanisms to form colloidal cargos as well as self-propelled particles where the light-activated component is embedded into a dielectric sphere. The particles are self-propelled along a direction otherwise randomized by thermal fluctuations, and exhibit a persistent random walk. For sufficient surface density, the particles spontaneously form ‘living crystals’ which are mobile, break apart and reform. Steering the particle with an external magnetic field, we show that the formation of the dense phase results from the collisions heads-on of the particles. This effect is intrinsically non-equilibrium and a novel principle of organization for systems without detailed balance. Engineering families of particles self-propelled by different wavelength demonstrate a good understanding of both the physics and the chemistry behind the system and points to a general route for designing new families of self-propelled particles. The Royal Society2014 eng General EngineeringGeneral Physics and AstronomyGeneral Mathematics 1364-503X 1471-2962 1410.7278 2533238310.1098/rsta.2013.0372 3722029 yes Palacci, Jérémie A, S. Sacanna, S.-H. Kim, G.-R. Yi, D. J. Pine, and P. M. Chaikin. “Light-Activated Self-Propelled Colloids.” <i>Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences</i>. The Royal Society, 2014. <a href="https://doi.org/10.1098/rsta.2013.0372">https://doi.org/10.1098/rsta.2013.0372</a>. Palacci, J. A., Sacanna, S., Kim, S.-H., Yi, G.-R., Pine, D. J., &#38; Chaikin, P. M. (2014). Light-activated self-propelled colloids. <i>Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences</i>. The Royal Society. <a href="https://doi.org/10.1098/rsta.2013.0372">https://doi.org/10.1098/rsta.2013.0372</a> Palacci, Jérémie A., et al. “Light-Activated Self-Propelled Colloids.” <i>Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences</i>, vol. 372, no. 2029, 20130372, The Royal Society, 2014, doi:<a href="https://doi.org/10.1098/rsta.2013.0372">10.1098/rsta.2013.0372</a>. J.A. Palacci, S. Sacanna, S.-H. Kim, G.-R. Yi, D.J. Pine, P.M. Chaikin, Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 372 (2014). J. A. Palacci, S. Sacanna, S.-H. Kim, G.-R. Yi, D. J. Pine, and P. M. Chaikin, “Light-activated self-propelled colloids,” <i>Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences</i>, vol. 372, no. 2029. The Royal Society, 2014. Palacci JA, Sacanna S, Kim S-H, Yi G-R, Pine DJ, Chaikin PM. 2014. Light-activated self-propelled colloids. Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences. 372(2029), 20130372. Palacci JA, Sacanna S, Kim S-H, Yi G-R, Pine DJ, Chaikin PM. Light-activated self-propelled colloids. <i>Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences</i>. 2014;372(2029). doi:<a href="https://doi.org/10.1098/rsta.2013.0372">10.1098/rsta.2013.0372</a> 91662021-02-18T14:31:11Z2021-02-22T10:44:16Z