Supplementary Information

Viscoelastic nature of Au nanoparticle–PDMS nanocomposite gels - Ritu Gupta et al

0.0 0.2 0.4 0.6 0.8 1.00.0

0.5

1.0

1.5

2.0

2.5

3.0

=287 nm

Concentration (mM)

Abs

orba

nce

(a.u

.)

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.

Figure S2 The optical photograph of Au-PDMS nanocomposite (a) without ethanol wash and (b)

with ethanol wash observed after 3 days.

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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.

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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.

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.

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