Abstract
Robust control over the position, orientation and self-assembly of nonspherical colloids facilitate the creation of new materials with complex architecture that are important from technological and fundamental perspectives. We study orientation, elastic interaction and co-assembly of surface functionalized silica nano-rods in thin films of nematic liquid crystal. With homeotropic boundary condition, the nano-rods are predominantly oriented perpendicular to the nematic director which is different than the mostly parallel orientation of the micro-rods. The percentage of perpendicular nano-rods are significantly larger than the parallel nano-rods. The perpendicular nano-rods create very weak elastic deformation and exhibit unusual, out-of-plane, attractive interaction. On the other hand, the nano-rods oriented parallel to the director create strong elastic deformation and shows anisotropic, in-plane, dipolar interaction. In both orientations, the induced defects reside in the nano-rods. With the help of a dynamic laser tweezers and using nano-rods as building blocks we demonstrate colloidal analogues of linear polymer chains, ribbons and two-dimensional binary crystals.
Highlights
Achieving colloidal analogues of atoms, molecules and chemical elements has been challenging in colloidal science
We focus on the spontaneous orientation, elastic interaction and directed co-assembly with micro-rods and microspheres in a nematic liquid crystal
We find that the silica nano-rods are predominantly oriented orthogonal to the nematic director and exhibit out-of-plane attractive interaction
Summary
Achieving colloidal analogues of atoms, molecules and chemical elements has been challenging in colloidal science In this field, significant advances have been made in variety of systems such as janus magnetic rods, DNA coated patchy colloids, co-assembly of soft patchy nanoparticles, paramagnetic colloids, photocatalic colloids etc[1,2,3,4,5,6,7,8,9]. Ours is the first experiment among several nematic colloidal systems, showing spontaneous out-of-plane interaction giving rise to vertical assembly of silica nano-rods in a liquid crystal. Such studies have important bearing on the efforts in making three-dimensional, periodic nematic colloidal systems, in which the orientational direction of the nano-rods is orthogonal to the nematic director
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