Immobilization of Water Drops on Hydrophobic Surfaces by Contact Line Pinning at Nonlithographically Generated Polymer Microfiber Rings

Abstract

metal-organic framework (MOF) microstructures. [9] The most common and viable strategy to immobilize water drops is the use of hydrophobic-hydrophilic micropatterns-the water drops are located on hydrophilic areas bordered by hydrophobic areas. Such chemically patterned substrates are typically produced by top-down lithographic methods including photolithography and microcontact printing. [1,[10][11][12] Immobilization of water drops on hydrophobic surfaces has commonly been realized only by means of 3D topographic patterns, such as geometric poly(dimethylsiloxane) (PDMS) obstacles, [2] hydrophobic Si pillars, [13] and superhydrophobic black silicon indentations generated by photolithography and deep reactive ion etching. [14] It is highly attractive to immobilize water drops on hydrophobic surfaces that are typically inert, repulsive to adsorbates and characterized by antifouling behavior. For example, flexible lab-on-chip configurations, in which water drops are immobilized on hydrophobic rather than on hydrophilic surfaces, could be employed to trap nonadherent cells. However, water drops on hydrophobic surfaces show nonsticking behavior and roll off. [15] Arresting water drops on hydrophobic surfaces has thus remained challenging. Here, we present a nonlithographic approach for the creation of polymeric barriers that efficiently immobilize water drops on highly hydrophobic perfluorinated surfaces. We dropped a solution of asymmetric polystyrene-block-poly(2-vinylpyridine) (PS-b-P2VP) (Figure 1) with P2VP as the minority component onto hydrophobically modified macroporous silicon (mSi) [16,17] (Figure S1, Supporting Information) and subjected the obtained circular PS-b-P2VP films to selective-swelling induced pore formation. [18,19] Subsequent mechanical detachment of the circular PS-b-P2VP films yielded rings of ruptured PS-b-P2VP fibers located in the mSi macropores within annular areas having diameters of a few mm and a width of ≈0.2 mm (Figure 2). While water drops deposited onto hydrophobically modified mSi without PSb-P2VP fiber rings roll off, the PS-b-P2VP fiber rings immobilized water drops having volumes up to 50 µL even when the hydrophobically modified mSi was turned into a vertical orientation ( Figures 5 and 6; Movies S1 and S2, Supporting Information).Water drops used as reaction compartments are commonly immobilized on hydrophilic areas bordered by hydrophobic areas. For many applications, such as the trapping of nonadherent cells, it is desirable to exploit the inertness and the antifouling behavior of hydrophobic surfaces as well as their repulsive behavior toward adsorbates in lab-on-chip configurations. However, the immobilization of water drops on hydrophobic surfaces has remained challenging. A nonlithographic approach is reported to arrest water drops on hydrophobically modified macroporous silicon (mSi) with perfluorinated surface. Contact line pinning at rings of polystyrene-blockpoly(2-vinylpyridine) (PS-b-P2VP) fibers protruding from the mSi macropores immobilizes water drops when th...

Phenolic Resin Dual-Use Stamps for Capillary Stamping and Decal Transfer Printing

“…It was stressed that solid elastomeric PDMS is far from being optimal for decal transfer since it is a low-modulus material that is considerably stretched prior to rupture . As an alternative, decal stamping with spongy nanoporous block copolymer stamps has recently been studied. , However, the obtained PDMS and block copolymer microstructures are difficult to modify, as required to introduce further application-specific functionalities. By contrast, micropatterns of materials characterized by high densities of functional groups, like phenolic resins, enable further functionalization of the deposited patterns.…”