Chemistry Reference
In-Depth Information
Figure 6.1 General schematic representation of polymer-mediated assembly of nanoparti-
cles: (a) functionalization of nanoparticles through place-exchange method, (b) incorporation
of complementary functional group to polymers, and (c) self-assembly of nanoparticles
through electrostatic or hydrogen bonding interactions.
In general, electrostatic interaction provides a straightforward method for assembling
nanoparticles but with limited control of the resulting structure because of kinetic
trapping in the assembly process. Hydrogen bonding interactions in self-assembly
processes tend to be easier to modulate, giving rise to the formation of morphologi-
cally controlled and highly well-ordered structures that are attributable to their
thermodynamically driven equilibrium nature (Beijer et al. 1998; Prins et al. 2001;
Lehn, 2002; Sivakova and Rowan, 2005; Xu et al. 2005).
6.2. DESIGN OF NANOPARTICLES AND POLYMERS
Effective functionalization of nanoparticle surfaces and complementary polymers is a
prerequisite for realization of polymer-mediated nanoparticle assembly. The metal or
semiconductor nanoparticles can be easily functionalized through a two-step process.
Nanoparticles are synthesized by photo- or chemical-reduction of metal salt in the
presence of capping agents (Brust et al. 1994, 1995). The desired functionality can
be attached to the particle at this stage or introduced on the nanoparticle surface by
place exchange with the appropriate functional ligand (Templeton et al. 1998,
2000). The self-assembled organic monolayer of nanoparticles not only passivates
the surface to prevent particle agglomeration but also modulates the solubility
(Hostetler et al. 1999; Shenhar and Rotello 2003; Drechsler et al. 2004). The
ability to fine-tune the solubility of the nanoparticles allows them to be characterized
by standard solution-phase techniques, such as nuclear magnetic resonance, infrared,
and ultraviolet (UV) visible spectroscopy.
Awell-controlled polymerization method in terms of polymer length, polydispersity,
and spatial distribution of functional groups is crucial for effective nanoparticle
assembly (Chiefari et al. 1998; Bielawski and Grubbs 2000; Coessens et al. 2001;
