Lithography-Free Route to Hierarchical Structuring of High-χ Block Copolymers on a Gradient Patterned Surface.

Ha Cho,Ayoung Choe,Woon Park,Myunghwan Byun,Hyunhyub Ko

doi:10.3390/ma13020304

Abstract

A chemically defined patterned surface was created via a combined process of controlled evaporative self-assembly of concentric polymer stripes and the selective surface modification of polymer brush. The former process involved physical adsorption of poly (methyl methacrylate) (PMMA) segments into silicon oxide surface, thus forming ultrathin PMMA stripes, whereas the latter process was based on the brush treatment of silicon native oxide surface using a hydroxyl-terminated polystyrene (PS-OH). The resulting alternating PMMA- and PS-rich stripes provided energetically favorable regions for self-assembly of high polystyrene-block-polydimethylsiloxane (PS-b-PDMS) in a simple and facile manner, dispensing the need for conventional lithography techniques. Subsequently, deep reactive ion etching and oxygen plasma treatment enabled the transition of the PDMS blocks into oxidized groove-shaped nanostructures.

Highlights

The wedge-on-Si geometry was set in a homemade-sealed chamber to minimize the effect of air convection and to keep temperature (~25 ◦ C) constant during the whole process of controlled evaporative self-assembly (CESA)
The PMMA toluene solution with concentration of 0.5 mg mL−1 was trapped in a confined wedge-on-Si geometry and formed a capillary-held solution, allowing the maximum evaporation rate at the perimeter of drying microfluid as schematically illustrated in the upper left panel of Figure 1
The dimensional features of the of the resulting PMMA stripes can be readily controlled by tuning the height of the wedge lens resulting PMMA stripes can be readily controlled by tuning the height of the wedge lens

Summary

Introduction

Irreversible drying droplets comprising nonvolatile solutes (e.g., polymers, colloids, nanoparticles, proteins, DNA, etc.) and volatile solvents often produce irregular dissipative ring-shaped deposits (i.e., “coffee rings”), fingering instabilities, and polygonal patterns via kinetically trapped self-assemblies [1].The formation of these spatially organized structures is mainly driven by the duplicative pinning–depinning motions of the contact line, whereby the edge of the drying droplet and the solid surface alternate between sticking to each other (i.e., pinning) and sliding over each other (i.e., depinning) [1,2,3].The stochastic distribution of the formed structures is originally derived from the lack of control over the pinning–depinning locomotion and the presence of temperature-gradient-induced convection [1,2,3].a number of advanced research works have been spawned for achieving the control of drying dynamics essentially required for potential improvement to ink-jet printing [4], pathways to patterning surfaces [5], and techniques for disease detection [6]. Irreversible drying droplets comprising nonvolatile solutes (e.g., polymers, colloids, nanoparticles, proteins, DNA, etc.) and volatile solvents often produce irregular dissipative ring-shaped deposits (i.e., “coffee rings”), fingering instabilities, and polygonal patterns via kinetically trapped self-assemblies [1]. The formation of these spatially organized structures is mainly driven by the duplicative pinning–depinning motions of the contact line, whereby the edge of the drying droplet and the solid surface alternate between sticking to each other (i.e., pinning) and sliding over each other (i.e., depinning) [1,2,3].

Methods

Results

Conclusion