Toluene, gold colloid stabilization

Application of amphiphilic block copolymers for nanoparticle formation has been developed by several research groups. R. Schrock et al. prepared nanoparticles in segregated block copolymers in the sohd state [39] A. Eisenberg et al. used ionomer block copolymers and prepared semiconductor particles (PdS, CdS) [40] M. Moller et al. studied gold colloidals in thin films of block copolymers [41]. M. Antonietti et al. studied noble metal nanoparticle stabilized in block copolymer micelles for the purpose of catalysis [36]. Initial studies were focused on the use of poly(styrene)-folock-poly(4-vinylpyridine) (PS-b-P4VP) copolymers prepared by anionic polymerization and its application for noble metal colloid formation and stabilization in solvents such as toluene, THF or cyclohexane (Fig. 6.4) [42]. 

Stabilization of Gold Colloids in Toluene by Block Copofymers of Pofystyrene and Pofy(ethylene oxide)... 

ROESCHER MOLLER Stabilization of Gold Colloids in Toluene... 

One hundred milliliters of a 0.001% solution of tetrachloroauric (III) acid (or silver nitrate) in distilled water ia treated with several drops of 1% sodium carbonate 10-hydrate and heated to boiling in a flask. Every 30 seconds one drop of a fresh 1% tannin solution (XJ.S.P.) is added with agitation. When a deep red gold color has formed (or yellow-brown to red-brown for the silver) the colloidal solution is cooled and stabilized by the addition of a few milliliters of chloroform or toluene. 

Although polyethyleneoxide is a bad stabilizer for colloidal noble metals, it appeared possible to prepare rather stable colloidal gold solutions in toluene with polystyrene/polyethyleneoxide block copolymers by reduction of LiAuCU. When polymer/salt complexes were allowed to approach their equilibrium during longer times, a more homogeneous distribution of gold salt in the micelles resulted in more narrow particle size distributions. 

The freeze fracture method has been used to study the structure of colloidal particles in water-oil mixtures stabilized by polymer emulsifiers. Microemulsions consisting of water, toluene and graft copolymer composed of a polystyrene backbone and a poly(ethylene oxide) graft were deposited onto a small gold plate, quenched in liquid nitrogen in equilibrium with its own solid phase [436]. Replicas of the fractured surfaces were washed with tetrahydrofuran, which showed the micellar structure of the copolymers. A similar method was used for the preparation of polystyrene polymer latexes for TEM study of the size distribution [437]. In this case, the frozen droplet was microtomed, with a cold knife at -100 to -120°C, etched for up to 90 s and then a platinum-carbon replica was prepared. Etching was found to be unnecessary and a potential cause of error. The remaining latex was dissolved away before examination of the replica. Such replicas can reveal the size distribution and structure of the latex particles. 

Colloidal solutions of gold in different solvents have been one of the most intensively studied and well-understood systems. Polar solvents such as acetone, dimethylformamide, tetrahydrofuran... and nonpolar solvents such as toluene, hexane, cyclohexane, decane... were broadly used as reaction media or solvent-madiated media. Acetone, as a polar solvent, solvates the metal atoms and clusters during the warmup stage [23]. In this way steric stabilization is achieved and some metal colloids can be stable for months. This behavior is the main motivation for choosing polar solvent as an initial solvent or co-stabilizer. Generally, the additional stabilizing agent such as alkylamine, alkylthiol, or alkylalcohol is mostly needed for the stabilization of final metal fluid. As reported [24, 25], two types of stabilization are characteristic for these systems ... 

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