Production and characterization of nanoparticles of defined shape and size

The focus of the research work in the Colloid Chemistry Group is on the formation and stabilization of nanoparticles of defined shape and size in different solvents and template phases using polyelectrolytes.

Gold nanoparticle formation in aqueous solution

Polycations [31, 37], polyanions [28] and polyampholytes [34] can be used as reducing and stabilizing agents in the production of gold nanoparticles of defined shape and size. The resulting gold nanoparticles are electrosterically stabilized and can be adjusted to particle sizes smaller than 4 nm by using sugar-modified polyethyleneimines (PEI) [44].

Gold nanoparticle formation in ionic liquids

In analogy to the aqueous system, gold nanoparticle formation can also be carried out in ionic liquids in the presence of PEI [45]. The resulting gold nanoparticles with an average particle size between 5 and 7 nm can be redispersed in chloroform and incorporated into electrodes via a covalent bond formation [45].

Microemulsions

Water-in-oil microemulsion droplets can be used as a nanoreactor for particle formation. As already mentioned under point II, polyelectrolytes can be introduced into the water droplets without macroscopically phase separation. The polyelectrolyte-modified microemulsions can be used as a template phase directly for the nanoparticle formation [18,27,29,31,34-36,38-42]. The polyelectrolytes can be used as reducing agents in the formation of gold nanoparticles [31,34,38] or as stabilizing agents in CdS [30,40,42], BaSO₄ [18,27,29,39,41], magnetite [35] and zinc sulfide production [36]. The polyelectrolytes are of particular importance in the redispersion of the nanoparticles after the complete removal of the solvents and prevent aggregation of the individual nanoparticles.

Vesicle phases

Gold nanoparticle formation can also take place directly on the surface of mixed phospholipid vesicles, in which triangles and rods are formed besides spherical gold particles [33]. In the presence of sugar-modified PEI, rods and triangles are formed, which is ascribed to the polycation [43]. The formation of nanoparticles directly in the bilayer phase, on the other hand, leads to an increased formation of rods [32]. The latest work (DFG project KO 1387 / 14-1) shows that in the presence of polyampholytes (PalPhBisCarb) the amount of nanotriangles can be optimized and their separation is successful [46].

TEM image of anisotropic gold nanoparticles prepared in the presence of PalPhBisCarb

Hydrogels

Polyelectrolyte-modified nanoparticles can also be introduced into hydrogels or formed directly in the hydrogel [47].

Cooperation

• Prof. M. Gradzielski (TU Berlin)
• Dr. D. Appelhans (Leibniz Institut, Dresden)
• Prof. S. Kudaibergenov (Kazakh National Technical University, Almaty)

Selected Publications: