Inorganic Nanocrystals with Dendrimer Templates: Mesoscopic Model System and Route to New Nanocomposites
- PDF / 2,935,845 Bytes
- 12 Pages / 612 x 792 pts (letter) Page_size
- 64 Downloads / 171 Views
Inorganic Nanocrystals with Dendrimer Templates: Mesoscopic Model System and Route to New Nanocomposites Franziska Gröhn1, Barry J. Bauer, Eric J. Amis Polymers Division, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA. 1 recent address: Max Planck Institute for Polymers, Ackermannweg 10, D-55128 Mainz, Germany.
ABSTRACT We investigate nanostructures that are formed when dendrimers act as hosts. Poly(amidoamine) (PAMAM) dendrimers can be used as templates for inorganic nanocrystals, both in aqueous solution1-3 and in a polymeric matrix.4 SANS, SAXS and TEM are used to characterize the resulting hybrid structures. Different inorganic colloids like noble metal and cadmium sulfide colloids are studied.1,2 With increasing dendrimer generation, we observe a transition from low molecular colloid stabilizing to an effective polymer templating in terms of a “host-guest nanoscale synthesis”. For these higher generation dendrimers, inorganic colloids are formed inside single dendrimer molecules and the size of the nanocrystal can precisely be controlled by the dendrimer generation (“fixed loading law”). Hydrophobically modified dendrimers in organic solvent represent a further, different kind of host system that we have investigated using scattering methods.5
I.
INTRODUCTION
Quantum-size effects cause inorganic particles of nanometer size to have unique optical, electrical and magnetic properties that characteristically depend on their size and shape, and can lead to a wide variety of practical applications. On the other hand, organic compounds and polymers in particular, often have advantageous mechanical properties, can self-assemble into ordered structures and in addition can be functionalized via chemical modification. Therefore it is expected that the combination of both, inorganic and organic matter, in hybrid structures with characteristic length scales of nanometers can provide special materials with promising property combinations. While such organic-inorganic hybrid nanostructures can be found in natural materials quite often, e.g. in sea shells or bone, the synthetic design of hybrid nanostructures has only recently come into focus. Polymer nanotemplating is one approach to synthesize organic-inorganic hybrid nanostructures: An inorganic crystal is nucleated within a polymeric matrix that in addition to general factors as free energy of the crystal formation and surface tension influences the growth of the inorganic colloid.6,7 In order to take advantage of such approaches, it is necessary to understand the formation of hybrid structures. Dendrimers, organic molecules with a well defined size of (1 to 15) nm are known to be able to act as host for smaller guest molecules, as was first shown by Meijer with the Y1.2.1
encapsulation of the organic dye molecule Bengal rose into poly(propyleneimine) (PPI) dendrimers modified with amino acids.8 Our interest is in dendrimers as a mesoscopic model system for nanotemplating, covering the range from typical organic low molecular-mass m
Data Loading...
