Thermal Aggregation Properties of Nanoparticles Modified
with Temperature Sensitive Copolymers
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Abstract
In this paper, we describe the use
of a temperature responsive polymer to reversibly assemble gold nanoparticles
of various sizes. Temperature responsive, low critical solution temperature
(LCST) pNIPAAm-<i>co</i>-pAAm polymers, with transition
temperatures (<i>T</i><sub>C</sub>) of 51 and 65 °C,
were synthesized with a thiol modification, and grafted to the surface
of 11 and 51 nm gold nanoparticles (AuNPs). The thermal-responsive
behavior of the polymer allowed for the reversible aggregation of
the nanoparticles, where at <i>T</i> < <i>T</i><sub>C</sub> the polymers were hydrophilic and extended between particles.
In contrast, at <i>T</i> > <i>T</i><sub>C</sub>, the polymer shell undergoes a hydrophilic to hydrophobic phase
transition and collapses, decreasing interparticle distances between
particles, allowing aggregation to occur. The AuNP morphology and
polymer conjugation were probed by TEM, FTIR, and <sup>1</sup>H NMR.
The thermal response was probed by UV–vis and DLS. The structure
of the assembled aggregates at <i>T</i> > <i>T</i><sub>C</sub> was studied via in situ small-angle X-ray scattering,
which revealed interparticle distances defined by polymer conformation
