Preparation Of Ordered Monolayers Of Polymer Grafted Nanoparticles: Impact Of Architecture, Concentration, And Substrate Surface Energy

Rapid fabrication of large area, ordered assemblies of polymer grafted (hairy) nanoparticles (PGNs) will enable additive manufacturing of novel membrane, electronic, and photonic elements. Herein, we discuss the relationship between select processing conditions, substrate surface energy, and canopy architecture on the hierarchical structure of sub- to monolayer PGN assemblies. Varying concentrations (10, 20, and 70 nM) of polystyrene (PS) grafted (sigma similar to 1 chain/nm(2)) gold nanoparticles (AuNP, r(0) = 9 nm) were flow coated onto surface-modified silicon wafers (gamma(s) similar to 20 mN/m, hydrophobic to 80 mN/m, hydrophilic). The profile of an isolated gold-polystyrene (PS) PGN depends on substrate-canopy interface energy. At low substrate-PS interface energy (20 mN/m), the PS canopy spreads to maximize contact with the surface, whereas at high substrate-PS interface energy (80 mN/m), the chains minimize contact area resulting in a more compact, thicker PGN corona. This behavior is translated up to monolayer assemblies, where rougher, less-ordered assemblies with smaller AuNP-surface separation form on substrates with low interface energy. These films are also thinner with greater Au volume fraction, indicating that the segment density within the PS canopy depends on substrate surface energy. The impact of these processing parameters on PGN film formation parallels classic colloidal deposition even though the PS concentration is within the Landau-Levich regime for film formation from linear chains. The factors influencing local morphology, however, resemble those that affect polymer thin films. Using this understanding, we demonstrate fabrication within seconds of large area monolayer films with close-packed order.