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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>
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>
Patchy Colloidal Clusters with Broken Symmetry
김유진,김재현,조인성,David J. Pine,Stefano Sacanna,이기라 한국고분자학회 2021 한국고분자학회 학술대회 연구논문 초록집 Vol.46 No.2
Colloidal clusters are prepared by assembling positively charged crosslinked polystyrene (PS) shell particles onto negatively charged liquid cores of swollen polymer particles. Shells at the interface of the liquid core are closely packed around the core due to interfacial wetting. By evaporating solvent, cores are solidified, and the clusters are cemented. Finally, by density gradient centrifugation, high-purity symmetric tetrahedral colloidal clusters are obtained. When silica-PS core-shell particles are swollen and served as the liquid cores, hybrid colloidal clusters are obtained. As each silica nanoparticle is relocated to the liquid core interface, broken symmetry as the silica nanoparticle is comparable in size with PS shell. The configuration of clusters is determined once shells around the liquid core is given, which depends on the size ratio of liquid core and shell. Since hybrid clusters are heavier than PS particles, they can be purified using centrifugation.