Effect of Polymer Chain Length on the Superlattice Assembly of Functionalized Gold Nanoparticles

Abstract

We report on the assembly of gold nanoparticle (AuNPs) superlattices at the liquid/vapor interface and in the bulk of their suspensions. Interparticle distances in the assemblies are achieved on multiple length scales by varying chain lengths of surface grafted AuNPs by polyethylene glycol (PEG) with molecular weights in the range 2000−40,000 Da. Crystal structures and lattice constants in both 2D and 3D assemblies are determined by synchrotron-based surface-sensitive and small-angle X-ray scattering. Assuming knowledge of grafting density, we show that experimentally determined interparticle distances are adequately modeled by spherical brushes close to the θ point (Flory−Huggins parameter, χ ≈ 1 2 ) for 2D superlattices at a liquid interface and a nonsolvent (χ = ∞) for the 3D dry superlattices.

Binary Superlattices of Gold Nanoparticles in Two Dimensions

“…Single-component PEG-functionalized AuNPs in suspensions can assemble into 2D hexagonal superlattices at the vapor/suspension interface. The assembly and crystallization depend on a number of factors, such as the type of salt in the suspensions (e.g., K 2 CO 3 or NaCl), its concentration, Au core size, and PEG chain length. ,,, Long-range ordered 2D PEG-AuNPs assemblies at aqueous surfaces are manifested by Bragg-reflections in GISAXS patterns. Figure a shows GISAXS 2D patterns for single component PEG-AuNP suspensions and binary mixture suspension containing PEG5k-AuNP5 and PEG2k-AuNP10 in the presence of K 2 CO 3 .…”

“…Thiolated polyethylene glycol (mPEG) of various molecular weights (MW) was obtained from Creative PEGWorks. AuNPs were functionalized with mPEG through a ligand exchange method . Approximately 15 nM PEG-functionalized AuNPs (PEG-AuNPs) were obtained and confirmed by the dynamic light scattering (DLS) and UV–visible spectroscopy (see Figure S1).…”

“…AuNPs were functionalized with mPEG through a ligand exchange method. 37 Approximately 15 nM PEGfunctionalized AuNPs (PEG-AuNPs) were obtained and confirmed by the dynamic light scattering (DLS) and UV− visible spectroscopy (see Figure S1). Thermogravimetric analysis (TGA) was used to determine the grafting density of PEG-AuNPs (see Figure S2).…”

“…The assembly and crystallization depend on a number of factors, such as the type of salt in the suspensions (e.g., K 2 CO 3 or NaCl), its concentration, Au core size, and PEG chain length. 25,26,36,37 Long-range ordered 2D PEG-AuNPs assemblies at aqueous surfaces are manifested by Bragg-reflections in GISAXS patterns. Figure 1a S5).…”

Examination of Oil Structural Motifs and Temperature in Promoting Reversible Self-Assembly of Gold Nanoparticle Langmuir Films

“…Designing and forming nanoparticle films with defined spacing, order, and orientation will enable a large number of nanoparticle-based technologies. , Self-assembly is an essential strategy used to synthesize 2D and 3D nanoscale structures and is mediated by interactions such as van der Waals and electrostatic forces. , The self-assembly of the nanoparticles into larger structures is primarily determined by the size and shape of the nanoparticle core . The effects of solvent and temperature on nanoparticle ligand shells can also significantly impact nanoparticle interactions in solution and morphology in 2D films. − Many studies have shown increased control over nanoparticle self-assembly by modifying nanoparticle surface chemistry, , applying external stimuli (e.g., light or magnetic fields), − and/or incorporating additives (e.g., polymers or salts) ,− to drive the self-assembly process. However, much remains to be understood regarding nanoparticle mixing interactions.…”