Supporting Information
Absorbance (a.u.)
3.0
2.5
2.0
1.5
1.0
0.5
0.0
0.0
=287 nm
0.2
0.4
0.6
0.8
Concentration (mM)
1.0
Figure S1 Calibration curve for KAuCl4 derived from UV–vis spectra.
The Au content in PDMS is determined by the concentration of Au precursor that gets fully
consumed on reaction with PDMS by UV–vis spectroscopy. The concentration of KAuCl4
solution is estimated from the calibration curve shown above.
(a)
(b)
Figure S2 The optical photograph of Au-PDMS nanocomposite (a) without ethanol wash and
(b) with ethanol wash observed after 3 days.
-1-
The washing of AuPDMS composite with ethanol is an important step for the stable gel
formation. The AuPDMS has unreacted small oligomers present, which on aging cures the
nanocomposite by slow crosslinking (see figure S2a). Instead, when the nanocomposite is
rinsed with ethanol after synthesis, the oligomeric units get washed out resulting in a stable
gel formation, which do not undergo any aging with time as seen in figure S2b.
Figure S3 Rheometer (MCR 301-WESP) used for the study of AuPDMS composite gel.
-2-
Figure S4 Estimation of AuNPs loading in PDMS matrix with respect to KAuCl4 consumed.
The amount of precursor consumed in the reaction was estimated by the difference in the
KAuCl4 peak intensity at 287 nm. As seen from the figure below, KAuCl4 is completely
reduced to Au nanoparticles without any leftover precursor upto 1 mM, beyond which there is
unconsumed KAuCl4 leftover after the reaction. Thus, 1 mM solution was used in subsequent
experiments involving temperature variation.
(a)
(b)
200 nm
200 nm
Figure S5 (a) STEM and (b) SEM image of AuPDMS nanocomposite with 0.38 wt% Au
prepared at room temperature.
The STEM and SEM images show Au nanoparticles dispersed in the PDMS matrix. The Au
nanoparticle size ranges from 10 to 50 nm. The polymer matrix is dissolved in toluene to
extract the nanoparticles for imaging.
-3-
-4-