Ordered surface structures from PNIPAM-based loosely packed microgel particles

Abstract

On-surface self-assembly of several types of microgels prepared via the precipitation polymerization of (N-isopropylacrylamide) (NIPAM) with N,N′-methylenebisacrylamide (MBA), acrylic acid or acrylamide as comonomers is investigated with the aim to establish the main factors that govern the formation of periodic loosely packed (PLP) two-dimensional arrays. A core–shell structure is detected for all microgels, with the thickest shells being observed for the microgels containing acrylic acid or acrylamide. The main factor driving the formation of PLP arrays and determining the microgel separation is found to be the presence of large low-density shells around the highly cross-linked cores of the microgels. This key observation of our experiments has been explained by the developed theoretical model that proves to adequately describe the experimental findings. The size of microgel dry-state “footprints” can be reduced by making use of plasma-etching. The periodic microgel arrays are used as masks for the preparation of patterns of reactive silanes with controllable separation between the patterned features. Sputtering of gold onto the periodic microgel arrays followed by washing out the microgels in ultrasonic bath is proven to be an efficient way of preparing perforated gold films with PLP holes.