Image courtesy of Nicholas Abbott and Juan de Pablo
Left: Fluorescent image of two polystyrene particles positioned at the north and south poles of a liquid crystal droplet. Right: Simulation of particle adsorption; region of disorder within droplets coincides exactly with the particle positions at the poles.
For the first time, the ability of liquid crystals to control the organization of particles at the surfaces of micrometer-sized droplets has been demonstrated. This is similar to how specific features on membrane surfaces control the orientation of fatty molecules (lipids) or proteins within a cell.
A new micro-assembly approach using liquid crystals, materials used in electronic displays and found in living systems, demonstrates that predictable positioning of small particles on a surface is feasible. This approach could provide a new route to form ordered, functional assemblies with the precise organization required to optimize energy harvesting and transfer in electronic and optical applications.
For the first time, the ability of liquid crystals to control the organization of particles on a spherical surface has been demonstrated. Conceptually, this approach mimics how specific features on membrane surfaces control the organization of lipids or proteins within a cell. Liquid crystals are comprised of elongated molecules that adopt a uniform orientation in a liquid phase and the surface-mediated electrical manipulation of this orientation is the key operating factor in modern display technologies. Now, researchers at the University of Chicago and the University of Wisconsin-Madison have demonstrated the predictable positioning of small particles on a liquid crystal surface based solely on the orientation of the liquid crystal molecules. Using a powerful combination of theory, computer simulations and experimental observations, they have shown that liquid crystals encapsulated in spherical droplets can control the assembly of small particles located at their surfaces, much like how the polarized structural organization of a component of a living cell, the Golgi complex, influences protein orientation. When droplets were comprised of a simple liquid, the particles on the surface adopted a random distribution. In contrast, when the droplets were comprised of liquid crystal, the surface molecules adopted ordered structures or nanophases containing one or two points or nodes at which fluorescent polystyrene particles were anchored. The attraction between the particles and these anchoring sites was particle-size dependent: The smallest particles roamed in the interior of the droplet whereas larger particles remained anchored at these sites until the liquid crystalline organization was disrupted by heating of the droplet. Interestingly, larger particles placed on the droplet surface away from these anchoring sites quickly migrated across the surface to them. If this assembly process can be extended to higher surface coverages of particles, such liquid crystalline nanophases could have important implications for design and assembly of functional three-dimensional structures with high fidelity.
Juan de Pablo
University of Chicago & Argonne National Laboratory
University of Wisconsin-Madison
DOE Office of Science, Basic Energy Sciences program. One participant (J.K.W.) was partially supported by a National Human Genome Research Institute Research utilized computing resources at Argonne National Laboratory, the University of Chicago, and the UW-Madison (supported by the NSF and DOE).
J.Whitmer, X. Wang, D. Miller, F. Mondiot, N.L. Abbott, and J.J. de Pablo, “Nematic-Field-Driven Positioning of Particles in Liquid Crystal Droplets,” Physical Review Letters, 111, 227801, 2013); [DOI: http://dx.doi.org/10.1103/PhysRevLett.111.227801]
University, DOE Laboratory
Collaborations, Non-DOE Interagency Collaboration