Nanoparticle Gradient Materials by Centrifugation.

Nanoparticle gradient materials are a unique class of functional materials. They combine the specific properties of nanoparticles with macroscopic materials. A continuous spatial gradient of the nanoparticle concentration leads to diverse physical property profiles. Therefore, these materials have a remarkable potential for applications in optics, electronics, and sensors. A novel approach for the defined and controlled synthesis of this material class is the fabrication in ultracentrifugal fields. The formation of a nanoparticle gradient by sedimentation in a gelatin solution is monitored online with optical systems inside an analytical ultracentrifuge. As soon as the desired nanoparticle concentration gradient is generated, the material is solidified by gelation and the desired gradient is fixed in the material. Application of the established theory of analytical ultracentrifugation allows simulations of the sedimentation process of the nanoparticles in advance. Thus, desired nanoparticle gradient materials can also be tailor-made and fabricated on a preparative scale. This is demonstrated for the example of spherical gold nanoparticles of different sizes, gold nanorods, mixtures thereof, and spherical superparamagnetic iron oxide nanoparticles.