Nanostructured Films of Amphiphilic Fluorinated Block Copolymers for Fouling Release Application

Abstract

New amphiphilic block copolymers S nSz m consisting of blocks with varied degrees of polymerization, n and m, of polystyrene, S, and polystyrene carrying an amphiphilic polyoxyethylene-polytetrafluoroethylene chain side-group, Sz, were prepared by controlled atom transfer radical polymerization (ATRP). The block copolymers, either alone or in a blend with commercial SEBS (10 wt% SEBS), were spin-coated in thinner films (200-400 nm) on glass and spray-coated in thicker films ( approximately 500 nm) on a SEBS underlayer (150-200 microm). Angle-resolved X-ray photoelectron spectroscopy (XPS) measurements proved that at any photoemission angle, varphi, the atomic ratio F/C was larger than that expected from the known stoichiometry. Consistent with the enrichment of the outer film surface (3-10 nm) in F content, the measured contact angles, theta, with water (theta w > or = 107 degrees ) and n-hexadecane (theta h > or = 64 degrees ) pointed to the simultaneous hydrophobic and lipophobic character of the films. The film surface tension gamma S calculated from the theta values was in the range 13-15 mN/m. However, the XPS measurements on the "wet" films after immersion in water demonstrated that the film surface underwent reconstruction owing to its amphiphilic nature, thereby giving rise to a more chemically heterogeneous structure. The atomic force microscopy (AFM) images (tapping mode/AC mode) revealed well-defined morphological features of the nanostructured films. Depending on the chemical composition of the block copolymers, spherical (ca. 20 nm diameter) and lying cylindrical (24-29 nm periodicity) nanodomains of the S discrete phase were segregated from the Sz continuous matrix (root-mean-square, rms, roughness approximately 1 nm). After immersion in water, the underwater AFM patterns evidenced a transformation to a mixed surface structure, in which the nanoscale heterogeneity and topography (rms = 1-6 nm) were increased. The coatings were subjected to laboratory bioassays to explore their intrinsic ability to resist the settlement and reduce the adhesion strength of two marine algae, viz., the macroalga (seaweed) Ulva linza and the unicellular diatom Navicula perminuta. The amphiphilic nature of the copolymer coatings resulted in distinctly different performances against these two organisms. Ulva adhered less strongly to the coatings richer in the amphiphilic polystyrene component, percentage removal being maximal at intermediate weight contents. In contrast, Navicula cells adhered less strongly to coatings with a lower weight percentage of the amphiphilic side chains. The results are discussed in terms of the changes in surface structure caused by immersion and the effects such changes may have on the adhesion of the test organisms.

Amphiphilic block copolymer/poly(dimethylsiloxane) (PDMS) blends and nanocomposites for improved fouling-release

“…Fluorosilicones showed excellent release of the green seaweed, Ulva, and barnacles compared to the control silicone (Marabotti et al 2009), although the release of diatoms was not improved (unpublished data). In the last few years, a widely researched strategy to improve the FR properties of polymers consists of combining hydrophobic, low surface energy fluorinated moieties with hydrophilic poly(ethylene glycol) (PEG) segments in the same coating (Gudipati et al 2005;Krishnan et al 2008;Martinelli et al 2008;Grozea and Walker 2009;Park et al 2010). PEG is well known for its resistance to protein adsorption and cell adhesion (Mrksich and Whitesides 1997;Walton et al 1997;Li et al 2005).…”

Functional Nanomaterials For Energy And Sustainability

“…Systematic studies on conventional coatings support the conclusion that microorganisms adhere weakly to mechanically weak surfaces (and vice versa), but those coatings tend to be peeled off quickly and need to be reapplied frequently [21]. Nanoscale sculpturing at the vessel surface is a promising strategy to create non-toxic fouling release coatings [22,23]. The approach aims to create surfaces with complex topological patterns so that attached microorganisms cannot get a firm grasp and are easily removed, for example by getting the vessel to speeding.…”

Designing nanostructured block copolymer surfaces to control protein adhesion

“…Furthermore, because these block copolymer systems are relatively unexplored, it was important to characterize their morphology. The characterization of the block copolymer surface morphology has been performed by atomic force microscopy (AFM) [99][100][101][102]. AFM is commonly used to characterize block copolymer morphology and to confirm that the synthesized block copolymer phase-separated into nanodomains.…”