Wettability of the morphologically and compositionally varied surfaces prepared from blends of well ordered comb-like polymer and polystyrene

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Abstract

Phase-separated surfaces of blends of polystyrene (PS) and well ordered comb-like polymer, poly[(oxy(decylsulfonylmethyl)ethylene)] (CH3-10SE), were prepared by spin casting polymer mixtures. Various surface morphologies, such as holes, islands, connected islands and pillars, were prepared by changing the blend compositions. Due to the influence of the CH3-10SE domain with a well ordered molecular conformation, a very low energy surface (≈22 mN/m) was created, which is close to the value of the pure polymer (≈20 mN/m), even when the blends contained only 20 wt.% of the pure polymer. Furthermore, by selective etching the PS domain in the blend surfaces, the advancing contact angles of water and n-hexadecane were highly increased from 113.5° and 43.2° for the pure CH3-10SE surface to 133.3° and 67.2° for the CH3-10SE structural surfaces with holes prepared using the solvent etching method, respectively. The result of the water advancing contact angles measured on the samples immersed in water over 20 days showed that the film stability of CH3-10SE could be improved considerably by even adding small amounts of PS.

Graphical abstract

Morphologically and compositionally varied surfaces were prepared from the blends of a well ordered comb-like polymer and polystyrene and their surface properties were systematically studied.

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Research highlights

► A very low energy surface (≈22 mN/m) was created when the blends (CH3-10SE/PS) contained only 20 wt.% of CH3-10SE. ► The blend surfaces showed the better film stability than that of pure CH3-10SE and PS. ► The advancing contact angles of water and n-hexadecane were highly increased from 113.5° and 43.2° for CH3-10SE surface to 133.3° and 67.2° for the surface with holes prepared by removing the PS domains on the blend surface, respectively.

Introduction

Thin polymer films have been modified to obtain surfaces with properties to satisfy the requirements for a range of applications [1], [2], [3], [4], [5]. Among the many methods for modifying the surface properties, polymer blending is considered one of the simplest methods for obtaining the desirable surface characteristics by controlling the surface morphology and wettability [6], [7], [8], [9], [10], [11], [12], [13], [14], [15] and commercially available polystyrene (PS) and poly(methyl methacrylate) (PMMA) have been studied extensively as blending components [16], [17], [18], [19], [20], [21], [22], [23]. Polymer surfaces with extremely low surface energies are used widely in electric and biomedical applications [24], [25], [26]. Therefore, there have been many attempts to use fluoropolymers and silicon polymers with very low energy values as one of the blends component. However, there are limitations in wider applications due to their poor processibility, low compatibility with other polymers and relatively high cost [27], [28], [29], [30], [31].

Comb-like poly(oxyethylene)s with alkyl sulfonylmethyl side chains have been studied extensively due to their unique barrier property and liquid crystalline behavior [32], [33], [34]. The polymer films spin-coated on a glass or a silicon wafer have double layered lamellar structures in which the ordered layers are parallel to the substrate surface and their side chains are almost perpendicularly oriented to the surface [35], [36], [37], [38]. As a result, these polymers exhibit very low surface energies in the 21–23 mN/m range [38], which is close to those of the silicone polymer, such as poly(dimethylsiloxane) (PDMS), and a fluoropolymer, such as poly(tetrafluoroethylene) (PTFE). This study examined the potential of the comb-like polymer, CH3-10SE (Fig. 1), as the modifying component to tune the surface properties, such as morphology and wettability, of a blended surface. Furthermore, the wetting properties of CH3-10SE structural surfaces prepared from CH3-10SE/PS blends using a simple solvent etching method were demonstrated.

Section snippets

Materials

Poly[oxy(decylsulfonylmethyl)ethylene] (CH3-10SE) was synthesized using the previously reported procedure [32], [33]. Two types polystyrenes (PS) with different molecular weights, PS280k (Mw = 280,000) and PS45k (Mw = 45,000), were purchased from Aldrich. Diiodomethane (99%, Aldrich) (MI), and n-hexadecane (99.9%, TCI) were used as received.

Film preparation

Silicon wafers were cleaned in a piranha solution (70 vol.% H2SO4 and 30 vol.% H2O2) for 2 h followed by rinsing with distilled water and drying under a nitrogen

Results and discussion

CH3-10SE is a side chain crystalline polymer with both glass transition (Tg) and melting transition (Tm) temperatures, whereas PS is an amorphous polymer with only Tg, as shown from their second DSC heating curves in Fig. S1 of Supplementary material [43]. In addition, the surface energy of CH3-10SE (≈20 mN/m) is much lower than that of PS (≈42 mN/m), as reported previously, due to the well ordered structures of alkyl side chains of CH3-10SE oriented perpendicular to the surface [35], [36], [37],

Summary

CH3-10SE/PS blends show various surface morphologies, such as holes, islands, connected islands and pillars, by varying the blend composition owing to the immiscibility between the polymers. It was found that the surface energies of the blends were affected mainly by CH3-10SE with lower surface energy. The surface energies of the blends were close to that of pure CH3-10SE, even when the CH3-10SE content in the blends was only 20 wt.%. CH3-10SE structural surfaces with inversed forms of the blend

Acknowledgments

This research was a part of the project titled “Development of new restoration technology for marine environment” funded by the Ministry of Land, Transport and Maritime Affairs, Korea. This research was also supported by a grant from Construction Technology Innovation Program (CTIP) funded by Ministry of Land, Transportation and Maritime Affairs (MLTM) of Korean government and Korea Science and Engineering Foundation (KOSEF) Grant funded by the Korean government (MEST) (Grant Code:

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