Smectic‐Layer Alignments of Surface‐Modified Gold Nanoparticles in the Nanocomposite Induced by a Hydrogen‐Bonded Bent‐Core Liquid Crystalline Host under Electric Fields

Abstract

There has been great interest recently in the fabrication of highly ordered metal nanoparticle (NP) assemblies. Large scale periodical arrangements of NPs are fascinating systems for the development of nanostructural materials exhibiting new electronic, magnetic, optical, and photonic properties. Many examples of the application of templates have appeared for the generation of ordered assemblies of NPs, by using, for example, surfacemodified polymers, self-assembled monolayers, lipid films, and DNA. In addition, the self-organization behavior of gold NPs surface-modified with rod-like, bent-core, and discotic liquid crystal (LC) surfactants has been reported. Moreover, several strategies have been proposed to template arrays of NPs by using block copolymer systems, in which the spatial arrangements are directed through self-assembly of the block copolymers. LC materials possessing a variety of mesomorphic structures can be aligned in a straightforward manner through the application of electric fields, magnetic fields, and polymer networks. The self-organization of LC molecules is determined by the characteristic arrangements of the mesophasic types, including the nematic, cholesteric, smectic, and columnar phases. Herein, we describe the synthesis of the novel hydrogenbonded bent-core LC host VPy-SiA (bearing a flexible carbosilane chain) and the gold nanocomposite (VPy-SiA/ AuNPs-S) by adding 5 wt% the surface-modified gold NPs (AuNPs-S) to the self-assembled LC host (VPy-SiA; Scheme 1). We developed a novel in situ technique for alignment of the nanocomposite VIPy-SiA/AuNPs-S under (DC/AC) electric fields, and examined the orientation behavior of the smectic layer structures using two-dimensional X-ray diffraction patterns and frozen transmission electron microscopy (FTEM). To the best of our knowledge, no previous reports have described the ordered layer arrangements of NPs in a nanocomposite—induced by compatibility of the NPs in the phase of the LC hosts—that could then be further aligned under electric fields. [a] W.-H. Chen, Y.-T. Chang, Prof. H.-C. Lin Department of Materials Science and Engineering National Chiao Tung University, Hsinchu 300 (Taiwan) Fax: (+8863)5724727 E-mail : linhc@cc.nctu.edu.tw [b] J.-J. Lee, W.-T. Chuang National Synchrotron Radiation Research Center Hsinchu, 30076 (Taiwan) Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem.201102607. Scheme 1. Chemical structures of the hydrogen-bonded bent-core LC host VPy-SiA (containing the hydrogen bond acceptor VPy and the hydrogen bond donor SiA) and the surface-modified gold NPs AuNPs-S presenting the covalently bonded bent-core surfactant S.