Formation of nanoparticle rings on heterogeneous soft surfaces

摘要

Many soft materials, such as block copolymers and micelles, are characterized by a tunable organization that can be exploited for formation of nanostructures. In this work, drying patterns, formed when nanoparticle solutions are spin coated on ultrathin films of the block copolymer poly[styrene-b-ethylenepropylene] (PS-PEP), are investigated as a function of the film's organization. Prior to particle deposition, thermal annealing was used to adjust the polymer film organization between a layer of PS-PEP micelles (no annealing) and a bilayer with a uniform PEP 'polymer brush' layer on top of an underlying layer of PS (extensive annealing). For intermediately annealed films, ring-shaped drying patterns consisting of as few as 5 or as many as 30 nanoparticles are observed. The nanorings are poly disperse with a diameter between 15 and 50 nm, and cover macroscopic surface areas of the film. It is suggested that these rings form as a consequence of inhomogeneous drying of particle solutions due to heterogeneities in the film structure, as deposition of nanoparticles on extensively annealed, uniform films did not produce rings.