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Engineering shape: the novel geometries of colloidal self-assembly
Sacanna, Stefano,Pine, David J.,Yi, Gi-Ra The Royal Society of Chemistry 2013 Soft matter Vol.9 No.34
<P>This article investigates the role of shape in colloidal self-assembly and argues for the importance of a tight synergy between particle design and assembly strategies. To this end, we review synthetic methodologies developed to impart colloidal building blocks with anisotropic shapes and self-assembly mechanisms that exploit geometry to direct and control the particles' organization. This paper, which deliberately focuses on micron-scale colloids, is divided into two main sections. Firstly, we discuss the impact of shape on particles' interactions and how this has been exploited to develop heuristic rules for the creation of self-assembling architectures. Secondly, we examine state-of-the-art advances in colloidal synthesis with a clear emphasis on design rules and bulk methods, which are aimed at producing shape-anisotropic particles.</P> <P>Graphic Abstract</P><P>This Review examines the role of shape in particles' interactions and how this has been exploited to develop heuristic rules for the creation of self-assembling architectures. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c3sm50500f'> </P>
Light-activated self-propelled colloids
Palacci, J.,Sacanna, S.,Kim, S.-H.,Yi, G.-R.,Pine, D. J.,Chaikin, P. M. Royal Society 2014 Philosophical transactions. Series A, Mathematical Vol.372 No.2029
<P>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-Fe<SUB>2</SUB>O<SUB>3</SUB> and TiO<SUB>2</SUB>), 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.</P>