Tunable and Reversible Aggregation of Poly(ethylene oxide-st-propylene oxide) Grafted Gold Nanoparticles

Abstract

Two amino-terminated amphiphilic copolymers, M600 and M1000, with different ethylene oxide to propylene oxide EO/PO ratios, 1/9 and 19/3, respectively, were coupled by thioctic acid, which allows an excellent affinity with gold surface. Then, amphiphilic thermally responsive gold nanoparticles (AuNPs) were prepared either by ligands exchange on precursor gold nanoparticles or by direct reduction of gold source in presence of stabilizing copolymers. The as-obtained AuNPs are monodisperse with a size varying from 2 to 17 nm depending on the synthesis used. The main parameters controlling the AuNPs assemblies were identified: the ethylene oxide to propylene oxide ratio in the polymer corona, the ionic strength of the solution, and the curvature of AuNPs. An interesting result is the possibility to tune the aggregation temperature from 8 to 15 degrees C of AuNPs coated by the same polymer only by changing the curvature of the AuNPs from 17 to 2 nm. This temperature change versus the curvature of the nanoparticle is ascribed to the decrease in hydration volume per hydrophilic group in the corona due to the change of the polymer chain conformation with changing the particle size. Moreover, one unique aggregation temperature between 12 and 60 degrees C can be also obtained by mixing copolymers with different EO/PO ratios. Then, the corona, constituted by a mixture of polymers, behaves as a corona composed by an average statistic copolymer with the intermediate composition.

In-depth analysis of switchable glycerol based polymeric coatings for cell sheet engineering

“…The measurements indicate that immobilization of the copolymer chains on a surface renders the switching temperature independent of the overall polymer concentration, unlike the free copolymers in solution. It is therefore suggested that the switching temperature depends only on the local polymer concentration which is associated with the grafting density [39]. Upon surface grafting, the conformational freedom of the polymer chains is restricted causing a decrease of the hydration and therefore a decrease of the switching temperature.…”

“…Durand-Gasselin et al [39] reported that the switching temperature of poly(ethylene oxide)-stat-(propylene oxide) grafted gold nanoparticles decreases with decreasing curvature of the nanoparticle cores, i.e., with increasing size of the nanoparticles. The authors concluded that a decreasing curvature at a constant grafting density causes a compression of the polymer chains, leading to a decrease of the switching temperature.…”

Entropy‐Driven Reversible Agglomeration of Crown Ether Capped Gold Nanoparticles

“…Nanoparticles that assemble upon cooling have been developed by functionalising with polymers that have upper critical solution temperatures (UCSTs), such as poly( N ‐acryloylglycinamide) and poly( N , N ′‐dimethyl‐(methacrylamido propyl) ammonium propanesulfonate) . On the other hand nanoparticles that assemble upon heating are typically functionalised with polymers with lower critical solution temperatures (LCSTs), such as poly( N ‐isopropylacrylamide), better known as pNIPAm, and oligo(ethylene glycol) terminated polymers such as poly(ethylene oxide‐st‐propylene oxide) . Nanoparticles with thermoresponsive behaviour can prove useful to a wide range of applications such as cellular internalisation, controlled drug release, catalysis and colorimetric sensors .…”

Surface ligands in synthesis, modification, assembly and biomedical applications of nanoparticles

“…Polymeric ligands that are rationally designed to respond to various stimuli can be enabled to selectively shrink or swell, thus a reversible mechanism of assembly/disassembly can essentially be programmed into these structures in response to external temperature [64] or pH [65][66][67]. By example, polymeric ligands with carboxylate groups possess the capacity to intermolecularly hydrogenbond with each other, however this only occurs at low pH where the H-bond donating species exists.…”