Template directed assembly of dynamic micellar nanoparticles

Abstract

The ability to pattern functional nanoparticle arrays in multiple dimensions will enable future devices which exhibit functions that cannot be realized using unstructured nanoparticle arrays. Here we demonstrate the unique assembly properties of dynamic micellar nanoparticles by combining a top down lithographic nanopatterning technique with a solution-based bottom up self-assembly. The templates for the directed self-assembly of the micelles consisted of arrays of cylindrical recess features fabricated by nanoimprint lithography. Silica was coated on this patterned substrate and subsequently selectively functionalized with a positively charged molecular monolayer (N-(3-Trimethoxysilylpropyl) diethylenetriamine) to regulate the micelle-surface interactions. The self-assembled block co-polymer polystyrene-b-poly(4-vinyl pyridine) (PS480k–PVP145k) micelles were approximately 325nm in diameter in aqueous solutions (pH = 2.5) and 50nm in diameter in the dry state. The average number of micelles assembled per feature increased from less than 1 to 12 with increasing feature diameter in the range of 200nm–1μm. Using a 2D model for maximum packing of circles in circular host features, the effective sphere size of the micelles during assembly was calculated to be 250nm in diameter. Thus, the micelles exhibited three characteristic sizes during assembly, 325nm in bulk solution, 250nm during assembly, and 50nm in the dry state. This dramatic variation in nanoparticle volume during the assembly process offers unique opportunities for forming nanometre scale, multidimensional arrays not accessible using hard sphere building blocks.