Nanocomposites
Based on “Take-Home Nanochemistry: Fabrication of Gold- or Silver- Containing Cling Film, Campbell, D. et al.
JChemEd, 89, pp.1312-15, 2012
This lab will go over three weeks. Experimental Part A will be done during the Ferrofluids lab,
Experimental Part B during the ZnO lab and Part C during the Gold Nanolayer lab.
The purpose of this laboratory experiment is to introduce aspects of nanocomposites using
a polymer matrix and developing gold nano-reinforcement in situ within the polymer. There
are essentially two ways to incorporate metal nanoparticles into a polymer matrix, in situ;
where the metal nanoparticles are formed in the matrix and ex situ; where metal
nanoparticles are added to the polymer. Both have advantages/disadvantages and will be
discussed in lectures later in the semester.
The matrix material, polydimethylsiloxane (PDMS) can be produced as a colourless,
transparent elastomer that is used for a variety of applications, such as encapsulation of
electronic components to protect them from moisture and dirt.
When the liquid kit components are mixed together (Fig 1) silicon−hydrogen bonds attached
to PDMS oligomers (species 2) oxidatively add to a platinum catalyst (possibly Karstedt’s
catalyst formed by the reaction of chloroplatinic acid, H2PtCl6, and
divinyltetramethyldisiloxane). The carbon-carbon double bonds, attached to short polymer
chains (Species 1), react with the silicon-hydrogen single bonds attached to other short
polymer chains (Species 2). Vinyl groups attached to PDMS oligomers (species 1) insert into
the platinum−hydride bond and then the alkyl and silyl groups reductively eliminate to
produce −Si−CH2−CH2−Si− cross-links within the PDMS.
After the cross-linking is essentially complete, however, some of the leftover
silicon−hydrogen bonds can still reduce some metal-containing ions, such as
tetrachloroaurate- (III), tetrachloropalladate(II), tetrachloroplatinate(II), and silver(I), that
are carried into the elastomer by organic solvents. The metallic particles produced by this
reduction reaction are embedded within the polymer matrix, which restricts particle
aggregation. The PDMS is transparent to visible light wavelengths, so the colours of the
nanoparticles can be examined both by the eye and by visible light spectroscopy.
Fig. 1. Hydrosilylation Cross-Linking Reaction of PDMS
