Thermally Reversible Aggregation of Gold Nanoparticles in Polymer Nanocomposites through Hydrogen Bonding

Abstract

The ability to tune the state of dispersion or aggregation of nanoparticles within polymer-based nanocomposites, through variations in the chemical and physical interactions with the polymer matrix, is desirable for the design of materials with switchable properties. In this study, we introduce a simple and effective means of reversibly controlling the association state of nanoparticles based on the thermal sensitivity of hydrogen bonds between the nanoparticle ligands and the matrix. Strong hydrogen bonding interactions provide excellent dispersion of gold nanoparticles functionalized with poly(styrene-r-2-vinylpyridine) [P(S-r-2VP)] ligands in a poly(styrene-r-4-vinyl phenol) [P(S-r-4VPh)] matrix. However, annealing at higher temperatures diminishes the strength of these hydrogen bonds, driving the nanoparticles to aggregate. This behavior is largely reversible upon annealing at reduced temperature with redispersion occurring on a time-scale of ~30 min for samples annealed 50 °C above the glass transition temperature of the matrix. Using ultraviolet-visible absorption spectroscopy (UV-vis) and transmission electron microscopy (TEM), we have established the reversibility of aggregation and redispersion through multiple cycles of heating and cooling.

Wetting–Dewetting and Dispersion–Aggregation Transitions Are Distinct for Polymer Grafted Nanoparticles in Chemically Dissimilar Polymer Matrix

“…[33][34][35][36][37] Using highlycontrolled synthesis and characterization techniques, a few experiments have also shown that particle dispersion and aggregation is tuned by enthalpic interactions between grafted and matrix chains. [37][38][39][40] Especially in the case where there are attractive enthalpic interactions between the graft and matrix chains, the mixture is driven to a dispersed phase even with grafts that are shorter than matrix chains, a case where chemically identical systems would exhibit dewetting and particle aggregation. 38 This ability to disperse particles due to graft-matrix miscibility allows for higher filler loadings than athermal chemically identical graft-matrix composites.…”

“…38 Choosing graft-matrix polymers with specific H-bonding also enables thermoreversibility to particle dispersion-aggregation. 40 In the above studies, the wetting-dewetting transition and dispersion-aggregation transition have been assumed to occur simultaneously, and are treated synonymously. 10,12,20,22,[24][25][26][41][42][43][44] .…”

Dynamically self-assembled silver nanoparticles as a thermally tunable metamaterial

“…However, in none of these systems were optical properties of the assemblies investigated. Another strategy for achieving DSA of NPs into dense arrays is using polymer nanocomposites [48][49][50] . Unfortunately, this strategy suffers from the complexity of achieving initial dispersion of NPs, low NP loadings 51 and usually collective interactions of NPs were not examined.…”

“…Unfortunately, this strategy suffers from the complexity of achieving initial dispersion of NPs, low NP loadings 51 and usually collective interactions of NPs were not examined. Only lately, chiral plasmonic DNA nanostructures with switchable circular dichroism 52 , and switchable dispersion of Au NPs with reversible tunability of the aggregate optical characteristic were obtained 50 . Plasmonic band shifting by 5 nm was observed in the latter report after thermal annealing of the material for tens of minutes.…”

Enhanced Glassy State Mechanical Properties of Polymer Nanocomposites via Supramolecular Interactions

“…17,18 Excellent NP dispersion was achieved presumably due to the existence of multiple hydrogen bonds between the NPs and the polymer matrix, a concept that has been used in previous works. For example, Heo et al 19 used gold NPs grafted with 2.8 kg.mol -1 (noted K in the future use) P(S-r-2VP) chains (grafting density of 1.7 chains/nm 2 ) in a 24.4 K P(S-r-4VPh) matrix. While the H-bonding between the OH group on the vinyl phenol moieties groups in the matrix and the nitrogen of the ligand grafted on the NPs ensures good miscibility, the consequences of this improved miscibility on mechanical properties has not been investigated.…”