Chien-Hua Hsu

UV-curable nanocasting technique to prepare bio-mimetic super-hydrophobic non-fluorinated polymeric surfaces for advanced anticorrosive coatings

In this study, a UV-curing nanocasting technique was first used to develop advanced anticorrosive coatings with bio-mimetic Xanthosoma sagittifolium leaf-like, non-fluorinated, super-hydrophobic polymeric surfaces. First of all, a transparent soft template with negative patterns of Xanthosoma sagittifolium leaf was fabricated by thermally curing the PDMS pre-polymer in molds at 60 °C for 4 h, followed by detaching the PDMS template from the surface of the natural leaf. Epoxy-acrylate coatings with biomimetic structures were prepared by performing the UV-radiation process after casting UV-curable precursor with photo-initiator onto a cold-rolled steel (CRS) electrode using the PDMS template. Subsequently, the UV-radiation process was carried out by using a light source with an intensity of 100 mW cm2 with an exposing wavelength of 365 nm. The surface morphology of as-synthesized epoxy-acrylate coatings obtained from this UV-curing nanocasting technique was found to have lots of micro-scaled mastoids, each decorated with many nano-scaled wrinkles and was investigated systematically by scanning electron microscopy (SEM) and atomic force microscopy (AFM). It should be noted that the water contact angle (CA) of coating with bio-mimetic natural leaf surface was 153°, which was found to significantly higher than that of the corresponding polymer with a smooth surface (i.e., CA = 81°). The significant increase of the contact angle indicated that this bio-mimetic morphology exhibited effectively water-repelling properties, implying that it may be a potential candidate as advanced anticorrosive coating materials, which can be identified by series of electrochemical corrosion measurements. For example, it should be noted that the corrosion potential (Ecorr) and corrosion current (Icorr), respectively, was found to shift from Ecorr = −730 mV and Icorr = 5.44 μA cm−2 of coating with smooth surface (SS) to Ecorr = −394 mV and Icorr = 2.30 μA cm−2 of coating with biomimetic super-hydrophobic surface (SPS).

Synergistic effects of hydrophobicity and gas barrier properties on the anticorrosion property of PMMA nanocomposite coatings embedded with graphene nanosheets

In this paper, the surface of a PMMA/graphene nanocomposite (PGN) with biomimetic hydrophobic structures was first prepared by the nanocasting technique and applied in corrosion protection coatings. First of all, a transparent soft template with negative patterns of a Xanthosoma sagittifolium leaf can be fabricated by thermal curing of the polydimethylsiloxane (PDMS) pre-polymer in molds at 60 °C for 4 h, followed by detaching the PDMS template from the surface of the natural leaf. Subsequently, PGN with a hydrophobic surface (HPGN) of the biomimetic natural leaf was fabricated, using PDMS as the negative template, through casting onto a cold rolled steel (CRS) electrode. The surface morphology of as-synthesized hydrophobic PMMA (HP) and PGN coatings was found to show lots of micro-scaled mastoids, each decorated with many nano-scaled wrinkles, which were investigated systematically by scanning electron microscopy (SEM). The contact angle (CA) of a water droplet on the sample surface can be increased from ∼80° for the PMMA surface to ∼150° for HP and HPGN and the sliding angle (SA) decreased from ∼60° to 5°. The morphological studies of the dispersion capability of graphene nanosheets (GNSs) in the polymer matrix can be carried out by observation under a transmission electron microscope (TEM). It should be noted that HPGN coating was found to reveal an advanced corrosion protection effect on the CRS electrode as compared to that of neat PMMA and HP coatings based on a series of electrochemical corrosion measurements in a 3.5 wt% NaCl electrolyte. The enhancement of corrosion protection of HPGN coatings on the CRS electrode could be interpreted by the following two possible reasons: (1) the hydrophobicity repelled the moisture and further reduced the water/corrosive media adsorption on the epoxy surface, preventing the underlying metals from corrosion attack, as evidenced by contact angle (wettability) measurements. (2) The well-dispersed GNSs embedded in the HPGN matrix could hinder corrosion due to their relatively higher aspect ratio than clay platelets, which further effectively enhance the oxygen barrier property of HPGN, as evidenced using a gas permeability analyzer (GPA).

Synergistic effect of electroactivity and hydrophobicity on the anticorrosion property of room-temperature-cured epoxy coatings with multi-scale structures mimicking the surface of Xanthosoma sagittifolium leaf†

A novel method is introduced to fabricate an electroactive epoxy (EE) coating with structured hydrophobic surfaces using an environmentally friendly process for anticorrosion application. First of all, the electroactive amine-capped aniline trimer (ACAT) was used as a curing agent to cure the epoxy resin and additionally provided electroactivity to the cured epoxy resin. The EE coating was cured at room temperature without using any solvent. The increased amount of the ACAT component in the EE coating not only accelerated the curing process but also promoted the thermal stability and anticorrosion performance. Subsequently, the multi-scale papilla-like structures on the surface of the Xanthosoma sagittifolium leaf were successfully replicated on the surface of the EE coating using PDMS as a negative template, as evidenced by the SEM investigation. The resulting hydrophobic electroactive epoxy (HEE) coating with the replicated nanostructured surface showed a hydrophobic characteristic with a water contact angle close to 120°. The developed HEE coating exhibited superior anticorrosion performance in electrochemical corrosion tests as its corrosion rate is better than that of the bare steel substrate by a factor of 450. The significantly improved corrosion protection is attributed to, besides the steel substrate isolated by the coating, the synergistic effect of electroactivity and hydrophobicity from the HEE coatings with the multi-scale structures mimicking the surface of the Xanthosoma sagittifolium leaf.