Solution and Surface Composition Gradients via Microfluidic Confinement: Fabrication of a Statistical‐Copolymer‐Brush Composition Gradient

Abstract

A stable solution composition gradient is generated inside a microchannel by varying the relative flow rates of two solutions that differ in composition. This solution gradient is used to synthesize a surface‐grafted statistical‐copolymer‐brush composition gradient via surface‐initiated atom transfer radical polymerization (ATRP; see schematic). Near‐edge absorption fine structure spectroscopy confirms the continuous transition of surface composition from one end of the substrate to the other.

Formation of Hierarchically Structured Thin Films

“…[16][17][18][19][20][21][22][23] A range of strategies has been reported to prepare brushes with lateral chemical and topographical inhomogeneities, ranging from using initiator density gradients, [24][25][26] to creating mixed brushes by micro-and nanocontact printing. [27][28][29] However, most of these studies are limited to single step contact printing using a single initiator concentration.…”

Spatiotemporally Controlled Formation of Two‐Component Counterpropagating Lateral Graft Density Gradients of Mixed Polymer Brushes on Planar Au Surfaces

“…[7,8] A number of techniques to generate gradients on various substrates have been reported, including diffusion-controlled vapor deposition, [1] cross diffusion, [9,10] corona discharge, [11,12] photoimmobilization, [13,14] electrochemical-potential gradients, [5,[15][16][17] the use of microfluidic devices, [18,19] and, more recently, surface-initiated polymerization through atom-transfer radical polymerization (ATRP). [7,8,[20][21][22][23][24][25][26] ATRP is of special interest because of its versatility, robustness, controllability, the living nature of the polymerization, [27][28][29][30] and as a facile route to surface-grafted polymers, which are attractive because they can be used to tailor surface properties such as wettability, biocompatibility, adhesion, adsorption, corrosion resistance, and friction. Therefore, extensive research has been dedicated to understanding the behavior of tethered polymer chains at interfaces.…”

Gradient and Microfluidic Library Approaches to Polymer Interfaces

“…Composition data from a PnBMA-s-PDMAEMA statistical copolymer library, collected via near edge X-ray absorption fine structure (NEXAFS) spectroscopy, can be seen in Fig. 11c [60]. This achievement is exciting since it represents a way of producing surface chemistry libraries that exhibit both the reliability and enhanced coverage of covalently bound polymer brushes, and the potential for creating chemical gradients that exhibit the extensive chemical and architectural functionality available from advanced polymerization routes.…”

“…10b, a more sophisticated statistical copolymer gradient library can also be fabricated through the μ-SIP method [60]. The key to this library is a microfluidic mixer, positioned between two monomer solution feeds and the microchannel.…”