  Employing small angle X-ray scattering (SAXS), we explore the conditions
under which the assembly of gold nanoparticles (AuNPs) grafted with the
thermo-sensitive polymer Poly(N-isopropylacrylamide) (PNIPAM) emerges. We find
that short-range order assembly emerges by combining the addition of
electrolytes or poly-electrolytes with raising the temperature of the
suspensions above the lower-critical solution temperature (LCST) of PNIPAM. Our
results show that the longer the PNIPAM chain is, the better organization in
the assembled clusters. Interestingly, without added electrolytes, there is no
evidence of AuNP assembly as a function of temperature, although untethered
PNIPAM is known to undergo a coil-to-globule transition above its LCST. This
study demonstrates another approach to assembling potential thermo-sensitive
nanostructures for devices by leveraging the unique properties of PNIPAM.
