Surface morphologies and wetting properties of layer-by-layer assembled films of polyelectrolytes with bimodal molecular
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pISSN: 0256-1115 eISSN: 1975-7220
INVITED REVIEW PAPER
INVITED REVIEW PAPER
Surface morphologies and wetting properties of layer-by-layer assembled films of polyelectrolytes with bimodal molecular weight distribution Choonghyun Sung†, Subin Choi, and Jinkyeong Kim Polymeric Materials Engineering Major, Dong-eui University, 176 Eomgwang-ro, Busanjin-gu, Busan 47340, Korea (Received 31 January 2020 • Revised 7 March 2020 • Accepted 16 March 2020) AbstractLayer-by-layer (LbL) assembly has been rigorously applied to the construction of superhydrophobic surfaces. Typically, this involves generating a hierarchical porous structure which is then coated with a low surface energy compound. In this study, a porous LbL film was constructed from poly(allylamine hydrochloride) (PAH)/poly(acrylic acid) (PAA) using a PAA solution with a bimodal molecular weight distribution. This solution was prepared by mixing two PAA solutions with different average molecular weights (100,000 and 15,000 g/mol). The mixing ratio was adjusted for fine control of the porous structure, which was induced by acid treatment at pH 2.0-2.4. Generally, surface pore structure was weakened as the 15,000 g/mol PAA ratio increased. However, the surface roughness decreased or increased as the 15,000 g/mol PAA ratio increased depending on the acid treatment pH and time. The porous LbL films were coated with fluorinated silane to make them hydrophobic. When the acid condition was pH 2.4 for 5 min, the water contact angle decreased significantly from 132o to minimum of 105o as the amount of 15,000 g/mol PAA increased. However, at pH 2.0 for 5 min, the water contact angle decreased smaller from 148o to 139o as the amount of 15,000 g/mol PAA increased. Keywords: Layer-by-layer, Porous, Superhydrophobic, Molecular Weight, Multilayer
molecular level. Furthermore, LbL assembly is suitable for an aqueous based processing and it is a conformal coating method that can be used to coat any shape of substrate. Superhydrophobic surface has been fabricated by constructing hierarchical surface which is then coated with a low surface energy compound. The majority of research has concentrated on preparing proper hierarchical structure, and fluorinated or alkyl silanes are typically used for low surface energy compounds. Several approaches have been used to fabricate superhydrophobic coatings using LbL assembly technique. The most popular method incorporates nanoparticles in the LbL film for hierarchical structure. Silica, graphene, carbon nanotube, metal oxide, and wax nanoparticles or nanomaterials have been used extensively. LbL films of polymer/ nanoparticle and nanoparticle-only have been reported. Shiratori et al. prepared nanoparticle-only superhydrophobic surface via calcination of polylectrolyte/nanoparticle LbL film [22]. Guo et al. produced electrically conductive superhydrophobic fabric by coating PET fiber with LbL film made from carbon nanotube and polyelectrolyte which was then coated with polydimethylsiloxane [23]. In addition, a transparent superwetting LbL
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