Linker-free grafting of fluorinated polymeric cross-linked network bilayers for durable reduction of ice adhesion

Abstract

Thin films of bilayer poly(divinyl benzene) p(DVB)/poly(perfluorodecylacrylate) (p-PFDA) are synthesized via iCVD on steel and silicon substrates. Nanomechanical measurements reveal that the elastic modulus and hardness of the films are enhanced through the bilayer structure and that the adhesion of the films to the substrate is improved via in situ grafting mechanism. The strength of ice adhesion to the treated surfaces is reduced more than six-fold when the substrates are coated with these bilayer polymer networks. 9 Icing can decrease efficiency in power production, result in mechanical and/or electrical failure, impact monitoring and control, and generate safety hazards.2,3,5,7 Active deicing methods that are employed to melt and break previously formed ice layers necessitate increased design complexity, may have detrimental environmental consequences, and require substantial power input for operation.10,11 Passive methods have recently been employed to protect exposed surfaces using icephobic coatings with characteristics designed to retard the formation of ice and facilitate the removal of ice deposits.3,9,12-22 Such coatings have been developed using solgel systems containing uorinated compounds and low surface energy rubbers, 20 lubricant-impregnated textured surfaces, 4 via hydrothermal reaction method, 23 low-pressure plasma polymerization, 24 and phase-separation methods. 7 However, a need remains for deposition methods that produce durable and mechanically-robust coatings over the large areas with enhanced adhesion to textured/rough surfaces that are commonly encountered in real world applications.In the present work, we have designed and synthesized for the rst time a mechanically-robust bilayer consisting of a thick and dense polymer base layer that is highly cross-linked and then capped with a covalently-attached thin icephobic uorine-rich top layer. We believe that the presence of a highly cross-linked polymer layer underneath a very thin u-oropolymer cap acts as a steric barrier resisting local surface reorganization, forcing the uorinated groups to remain on the surface even under wet conditions (Fig. S1, ESI †). In addition, the mechanical properties (for example the elastic modulus and hardness) of these customized bilayer polymer networks can be signicantly enhanced. Conceptual insightsIce formation and accumulation on surfaces can result in severe problems for solar photovoltaics, offshore oil platforms, wind turbines, and aircra. Practical adoption of icephobic surfaces requires mechanical robustness and stability under the harsh real-world environments. Here we design an icephobic surface using a bilayer strategy, optimizing the base layer for mechanical properties, while the top layer provides the desired high receding water contact angle (WCA). Both layers are formed sequentially by initiated chemical vapor deposition (iCVD) in the same reaction chamber. The iCVD polymerization of divinyl benzene (DVB) yields a cross-linked hydrocarbon base layer which is capped with an ultrathi...

Designing Durable Vapor‐Deposited Surfaces for Reduced Hydrate Adhesion

“…On the other hand, a relatively thicker layer of pPFDA (~ 40 nm) grafted to underlying pDVB was found to provide full coverage of the bilayer film Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) were performed on the bilayer polymer and confirmed successful deposition of both pPFDA and pDVB components through the presence of bands corresponding to carbonyl, carbon-fluorine bonds, and phenyl groups in the FTIR spectra. [15] …”

“…In addition, the linker-free grafted bilayer films did not delaminate during nanoscratch tests performed at 5 mN normal loads. [15] Finally, the strength of ice adhesion was reduced by more than six-fold when substrates were coated with these bilayer films as a result of the low surface energy and smoothness of the iCVD coatings.…”

“…The indenter-microscope calibration was performed using a copper seconds were applied throughout the indentation measurements. [15] This ensured appropriate deformation of the polymer networks during loading/unloading cycles and enabled a linear fit to the load-penetration curves during unloading. The Poisson's ratio for all of the polymers was assumed to be the same and equal to 0.5.…”

“…We recently developed bilayer polymers which are covalently bonded to substrates using an in-situ grafting mechanism. [15] Such bilayer polymers were shown to exhibit enhanced mechanical properties (e.g., elastic modulus and hardness) when compared to other coatings developed using traditional iCVD polymerization, which potentially makes them suitable for industrial applications such as flow assurance strategies by coating inside oil and gas pipelines. Other types of vapor deposition methods have been commercialized for coating the inside of pipes used in the oil and gas industry [16] and it is anticipated that similar process strategies would be successful for iCVD.…”

“…[15] The bilayer polymers consisted of a thick, mechanicallyrobust and dense polymer base layer, poly-divinyl benzene (pDVB), that is highly crosslinked and then capped with a covalently-attached thin fluorine-containing top layer, poly(perfluorodecylacrylate) (p-PFDA). A linker-free grafting in which covalent chemical bonds form across the substrate-polymer interface was developed to enhance the interfacial adhesion of the bilayer iCVD polymers to the underlying substrates.…”