The hydrodynamic size of polymer stabilized nanocrystals

Abstract

For many emerging applications, nanocrystals are surface functionalized with polymers to control self-assembly, prevent aggregation, and promote incorporation into polymer matrices and biological systems. The hydrodynamic diameter of these nanoparticle–polymer complexes is a critical factor for many applications, and predicting this size is complicated by the fact that the structure of the grafted polymer at a nanocrystalline interface is not generally established. In this work we evaluate using size-exclusion chromatography the overall hydrodynamic diameter of nanocrystals (Au, CdSe, d<5 nm) surface coated with polystyrene of varying molecular weight. The polymer is tethered to the nanoparticles via a terminal thiol to provide strong attachment. Our data show that at full coverage the polymer assumes a brush conformation and is 44% longer than the unbound polymer in solution. The brush conformation is confirmed by comparison with models used to describe polymer brushes at flat interfaces. From this work, we suggest an empirical formula which predicts the hydrodynamic diameter of polymer coated nanoparticles based on the size of the nanoparticle core and the size of the randomly coiled unbound polymer in solution.

Back to Basics: Exploiting the Innate Physico‐chemical Characteristics of Nanomaterials for Biomedical Applications

“…In addition to the NP's intrinsic properties, agglomeration depends also on the composition of the dispersing medium, and thus measurements of hydrodynamic diameters should always be performed in the biological medium in which they are studied ( Figure ). For the determination of hydrodynamic diameters (of single NPs in case of no agglomeration, and of the agglomerate size in case of agglomeration) many different methods exist, though all need to be interpreted differently, as they are based on different detection principles. Dynamic light scattering (DLS) is probably the most frequently used technique for determining hydrodynamic diameters, as commercial machines are easily available in many laboratories.…”

Size-exclusion chromatography of metal nanoparticles and quantum dots

“…There, it was demonstrated that SEC of CdS QDs stabilized with alkanethiols, in THF containing 1 mmol L −1 Cd(ClO 4 ) 2 + 1 mmol L −1 dodecanethiol, is feasible. Later studies by Wilcoxon and Provencio [37], Wang et al [39], and Kruger et al [36,38] have shown how SEC reveals various characteristics and size-dependent properties of CdSe and CdSe/ZnS core/shell nanocrystals, as described below.…”

“…[36,38] were able to employ SEC with toluene containing 0.1 mol L −1 trioctylphosphine for the hydrodynamic size determination of polystyrene- and alkythiol-coated CdSe nanocrystals. Polystyrene standards were used for size calibration of the SEC column.…”

“…The successful SEC separation of alkylthiol-coated CdSe nanocystals, however, required complete capping for both Cd and Se atoms to eliminate particle-column interactions. An additional aim of this study was to investigate the change in the length of polystyrene chains when attached to CdSe versus unbound [36]. It was found that polystyrene linked to a metal core at full coverage (full coverage was defined by the maximum NP size measured by SEC) assumes a brush conformation and is 44 % longer than is the unbound polymer in solution.…”

Determining the core, corona, and total size of CdSeS/ZnS quantum dots by SEC/QELS and TEM

“…One explanation for this difference in organic layer thickness between the two QDs examined could, possibly, be due to a difference in “grafting density” of octadecylamine, with a lower density in QD 510 than in QD 620. High packing density is known to restrict the movement of polymer chains, leading to more extended conformation than when the packing density is lower [20, 21]. It should be noted, however, that both these values for the size of the alkyl layer appear to be quite reasonable.…”