Two-Step Self-Assembly and Lyotropic Liquid Crystal Behavior of TiO2Nanorods

Zhimin Ren,Kaiguang Mai,Guodong Qian,Zhiyu Wang,Chao Chen,Rong Hu

doi:10.1155/2012/180989

Abstract

Several self-assembly structures of anatase TiO2nanorods were obtained by a two-step assembly process, and these structures formed different lyotropic liquid crystal in solution. Primary self-assembly occurred in synthesis process and formed two structures, in the morphology of ribbon and honeycomb, respectively. Secondary-assembly took place when the products were placed at lower temperature, where unique structures were obtained as the relative amount of ribbon and honeycomb changed with the increase of TiO2concentration. These structures showed nematic, spherulites, and lamellar phases. The mechanism of the two-step self-assembly was clarified. The driving force of primary assembly is deduced to be anisotropic attractive force, for NRs can assemble at any concentrations, while gravity is the driving force of the secondary assembly. It is worth mentioning that this paper is the first report about spherulites composing of anatase TiO2nanorods. The spherulites obtained were negative or of tangential type, and its structure, growth process, and temperature influences were also investigated. The spherulites may have promising application in temperature microsensor.

Highlights

For more than a hundred years, the new liquid crystal materials have acquired increasing attraction of scientists who focus on practical application and physical principles
It is a major breakthrough when mineral crystals were first observed by Zocher [1] in 1925 and since many reports had focused on inorganic liquid crystal (LC) phase with nanometer-scale objects [2, 3]
The development of liquid crystal composing of different morphology nanoparticles has been explored, including nanosphere, nanorods, nanodisk, graphene, and nanotubes [10,11,12,13,14], among which the study of rod-shape lyotropic LC behavior is under the spotlight

Summary

Introduction

For more than a hundred years, the new liquid crystal materials have acquired increasing attraction of scientists who focus on practical application and physical principles. There are two basic approaches to the assembly of nanoscale rigid-rod, while the assembly of nanorods (NRs) is necessary for the formation of lyotropic liquid crystals. Some groups had obtained various alignment of anisotropic nanoparticles by self-assembly in liquid crystal, including nanowire [19] and nanorods [20, 21]. Zorn and coworkers had reported on switching behavior under an applied AC (Alternating Current) electric field of ZnO nanorods [22] In this respect the orientation of functional semiconducting nanoparticles is interesting for materials science [23, 24]. Our group has obtained several self-assembled TiO2 nanorods structures and tried to study the mechanism of the assembly process [28]. We attempted to clarify the main driving force of the two-step assembly process

Experimental Section

Result and Discussion

Conclusion