Synthesis of Free-Standing Quasi-Two-Dimensional Polymers

This paper describes a synthesis of free-standing, 10−15-nm-thick polymer films of well-defined lateral size and shape. The three key elements of this procedure are (1) formation by microcontact printing (μCP) of a patterned, self-assembled monolayer (SAM) with hydrophobic regions (alkane-terminated) and adsorption-resistant regions (oligo(ethylene oxide)-terminated); (2) initiation of spatially selective growth of films of poly(electrolyte) multilayers by adsorption on the hydrophobic regions of the patterned SAM; and (3) dry transfer of these films to a water-soluble sacrificial backing, from which the films can be released into solution. This technique exploits the hydrophobic effect as an interaction that can be switched off when it is not needed: during the growth of the films in aqueous buffer, the hydrophobic effect anchors the polymers to the surface; once these films have been dried after synthesis, they are bound to the substrate only by van der Waals interactions and can be transferred nondestructively to a sacrificial backing. The growth and final state of the films were characterized using surface plasmon resonance (SPR), polarized infrared external reflectance spectroscopy (PIERS), ellipsometry, fluorescence microscopy, and atomic force microscopy (AFM).