Recent progress in gold nanoparticles (Au NPs) material science leads to the development of new composites with novel electronic and photonic properties. During the last decade, great attention has been given to the synthesis and physical properties of Au NPs with an alkanethiolate-monolayer. Recent development regarding Au NPs synthesis with different mesogenic capping groups has enlarged the research field on functionalized Au NPsý [1]. The Au plasmon resonance (PR) is widely used as chemical probe since it is influenced by the NPs size, organic shell, and matrix such as liquid crystal (LC). Controllable spectral shift of the Au PR can in fact be achieved by electrically changing the anisotropic refractive index of the LC medium ý[2]. Our objective is to tune the Au NPs optical properties using LC capping agents and matrix. The Brust-Schiffrin ý[3] and place exchange ý[4] reactions were used to synthesize 2-5 nm diameters Au NPs with mono- and mix mono-layers made of thiocholesterol, thioalkoxycyanobiphenyl (SHnOCB – n = 8, 12) and/or alkyl thiol (CnSH – n = 6, 10). The NPs were dispersed in cholesteryl oleyl carbonate or octylcyanobiphenyl (8CB) LCs. The characterization of the materials was done with Nuclear Magnetic Resonance, Transmission Electron Microscopy, Thermogravimetric Analysis, IR spectroscopy, and UV-visible spectroscopy. The NPs effect on the LCs is rationalised using Differential Scanning Calorimetry and Wide Angle X-ray Scattering given that the self-assembly structure depends on the NP organic shell and its interaction with the LC. Little change if any was observed in the LC properties of the composites when compared to the bulk system and dispersions with larger particles displayed a red shifts in the surface PR indicating particle-particle interaction.
References
[1]T. Hegmann, H. Qi and V.M. Marx J. Inorg. Organomet. Polym. & Mater, 17, 483 (2007).
[2]S. Park and D. Stroud PRL, 94, 217401 (2005).
[3]M. Brust, M. Walker, D. Bethell, D.J. Schiffrin and R. Whyman J. Chem. Soc., Chem. Commun., 801 (1994).
[4]D.I. Gittins and F. Caruso Angew. Chem., Int. Ed., 40, 3001 (2001).