Liquid gold nanoparticles

Photodissociation of Diiodoethane Hydrodynamics of Laser-Heated Liquids Gold Nanoparticles in Water... 

However, the main research result from those years was the discovery of the room-temperature single-electron phenomenon. In the 1990s, STM experiments on liquid crystal had shown a very weak staircase (Nejoh 1991) only one year later, the clear observations of the coulomb blockade and the coulomb staircase were demonstrated on gold nanoparticles (Shonenberger et al. 1992a) and the role of system symmetry on the appearance of these two phenomena was outlined (Shonenberger et al. 1992b). 

The preparation and study of metal nanoparticles constitutes an important area of current research. Such materials display fascinating chemical and physical properties due to their size [62, 63]. In order to prevent aggregation, metal nanoparticles are often synthesized in the presence of ligands, functionalized polymers and surfactants. In this regard, much effort has focused on the properties of nanoparticles dispersed into LCs. In contrast, the number of nanoparticles reported that display liquid crystal behavior themselves is low. Most of them are based on alkanethiolate stabilized gold nanoparticles. 

Figure 8.29 Compounds used to prepare liquid crystal mixtures containing gold nanoparticles.

Mixtures of a nematic liquid crystal (LC or LC ) with small quantities of gold nanoparticles coated with alkylthiolates (<5 wt%) including an alkylthiolate functionalized with a chiral group have been studied (Figure 8.29) [72]. All mixtures show nematic mesophases with transition temperatures and phase stability very similar to those oftheliquid crystal precursors LC or LC. The introduction ofachiral center into the mixtures (mixtures of Au ) produce chiral nematic mesophases. A similar result is obtained in mixtures of Au and LC doped with the chiral dopant (s)-Naproxen. 

Lyotropic liquid crystalline nanoparticles have also been described. Concentrated solutions of gold nanorods in water in the presence of a surfactant (cetyltrimethyl-ammonium bromide) display a nematic mesophase stable up to 200 °C [74[. The N mesophase was identified by optical microscopy by their typical nematic droplets texture. 

Kanayama, N., Tsutsumi, O., Kanazawa, A. and Ikeda, T. (2001) Distinct thermodynamic behaviour of a mesomorphic gold nanoparticle covered with a liquid-crystalline compound. Chemical Communications, (24), 2640-2641. 

Bmst M, Walker M, Bethell D, Shiffrin DJ, Whyman R (1994) Synthesis of thiol-derivatised gold nanoparticles in a two-phase liquid-liquid system. J Chem Soc Chem Commun 801-802... 

M. Bnist, M. Walker, D. Bethell, D. J. Schiffrin, and R. Whyman Synthesis of thiol-derivatized gold nanoparticles in a 2-phase liquid-liquid system, J. Chem. Soc., Chem. Commun. 801-802 (1994). 

Many reports are available where the cationic surfactant CTAB has been used to prepare gold nanoparticles [127-129]. Giustini et al. [130] have characterized the quaternary w/o micro emulsion of CTAB/n-pentanol/ n-hexane/water. Some salient features of CTAB/co-surfactant/alkane/water system are (1) formation of nearly spherical droplets in the L2 region (a liquid isotropic phase formed by disconnected aqueous domains dispersed in a continuous organic bulk) stabilized by a surfactant/co-surfactant interfacial film. (2) With an increase in water content, L2 is followed up to the water solubilization failure, without any transition to bicontinuous structure, and (3) at low Wo, the droplet radius is smaller than R° (spontaneous radius of curvature of the interfacial film) but when the droplet radius tends to become larger than R° (i.e., increasing Wo), the microemulsion phase separates into a Winsor II system. 

Guo, S., Shi, R, Gu, Y., Yang, J., Deng, Y., Size-controllable synthesis of gold nanoparticles via carbonylation and reduction of hydrochloroauric acid with CO and H2O in ionic liquids, Chem. Lett., 34,830-831,2005. 

Most of the work dealing either with the assembly of metal nanoparticles or with metal nanoparticles as additives in liquid crystals has been carried out using nanoparticles with gold cores. Such gold nanoparticles display unusual and unique size-dependent chemical and physical properties their surface can be passivated in... 

Yoshida et al. recently disclosed an alternative method that allowed them to produce stable suspensions of gold nanoparticles (1-2 nm in diameter) in nematic liquid crystals [315]. They used a simple sputter deposition process, which allowed them to prepare thin liquid crystal films of well-dispersed gold nanoparticles in both 5CB and E47 (available from Merck) with a nanoparticle size depending on the used nematic liquid crystal. Unfortunately, the authors did not provide any details on whether the nanoparticles were capped with a ligand or bare, non-coated particles, which makes it difficult to assess and compare the reported thermal as well as electro-optic data. However, very similar effects were found as a result of nanoparticle doping, including lower nematic-to-isotropic phase transition temperatures compared to the used pure nematics as well as 10% lower threshold voltages at nanoparticle concentrations below 1 wt% [315]. 

Our group pursued another approach of combining the properties of nanoparticles with chiral nematic liquid crystal phases. The idea was to decorate gold nanoparticles with chiral molecules known to be strong inducers of chiral nematic phases. To realize the idea, we prepared a series of alkylthiol-capped gold nanoparticles, either pure monolayer or mixed monolayer, with all or about every second of the alkylthiols end-functionalized with (5)-naproxen (e.g., 6 in Fig. 11) [349]. 

In comparison to nematic liquid crystals, examples of smectic liquid crystals doped with quasi-spherical nanoparticles became more elusive over the last few years. This is surprising especially considering recent work by Smalyukh et al., who found that nanoscale dispersion (based on /V-vinyl-2-pyrrolidone-capped gold nanoparticles with 14 nm diameter) in a thermotropic smectic liquid crystal (8CB) are potentially much more stable than dispersions of nanoparticles in nematics [367]. 

Cseh and Mehl at last showed that quasi-spherical gold nanoparticles are capable of forming genuine liquid crystalline phases. The approach they used was to decorate gold nanoparticles (1.6-2 nm in diameter) with a mixed monolayer of... 

Preliminary investigations of the liquid crystal phase behavior of these gold nanoparticles initially revealed an enantiotropic nematic phase (based on polarized light optical microscopy and thermal analysis) as well as some pattern formation of the gold nanoparticles in TEM experiments [540, 541],... 

Fig. 19 Gold nanoparticles 13 and 14 capped with a mixed monolayer of hexanethiol (13) or dedecanethiol (14) and a lateral substituted nematic liquid crystal thiol attached in a side-on fashion (thiol ratio 1 1) [540, 541]...

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