Kung-Chin Chang

Nanocasting Technique to Prepare Lotus-leaf-like Superhydrophobic Electroactive Polyimide as Advanced Anticorrosive Coatings

Nanocasting technique was used to obtain a biomimetic superhydrophobic electroactive polyimide (SEPI) surface structure from a natural Xanthosoma sagittifolium leaf. An electroactive polyimide (EPI) was first synthesized through thermal imidization. An impression of the superhydrophobic Xanthosoma sagittifolium leaf was then nanocasted onto the surface of the EPI so that the resulting EPI was superhydrophobic and would prevent corrosion. Polydimethylsiloxane (PDMS) was then used as a negative template to transfer the impression of the superhydrophobic surface of the biomimetic EPI onto a cold-rolled steel (CRS) electrode. The superhydrophobic electroactive material could be used as advanced coatings that protect metals against corrosion. The morphology of the surface of the as-synthesized SEPI coating was investigated using scanning electron microscopy (SEM). The surface showed numerous micromastoids, each decorated with many nanowrinkles. The water contact angle (CA) for the SEPI coating was 155°, which was significantly larger than that for the EPI coating (i.e., CA = 87°). The significant increase in the contact angle indicated that the biomimetic morphology effectively repelled water. Potentiodynamic and electrochemical impedance spectroscopic measurements indicated that the SEPI coating offered better protection against corrosion than the EPI coating did.

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).

3D-bioprinting approach to fabricate superhydrophobic epoxy/organophilic clay as an advanced anticorrosive coating with the synergistic effect of superhydrophobicity and gas barrier properties†

Correction for ‘3D-bioprinting approach to fabricate superhydrophobic epoxy/organophilic clay as an advanced anticorrosive coating with the synergistic effect of superhydrophobicity and gas barrier properties’ by Chi-Hao Chang et al., J. Mater. Chem. A, 2013, 1, 13869–13877.

Self-Assembly Behavior of Amphiphilic Poly(amidoamine) Dendrimers with a Shell of Aniline Pentamer

A series of amphiphilic poly(amidoamine) dendrimers (PAMAM, G2-G5) composed of a hydrophilic core and a hydrophobic shell of aniline pentamer (AP) were synthesized and characterized. The modified dendrimers self-assembled to vesicular aggregates in water with the critical aggregation concentration (CAC) decreased in the order of G2 > G3 > G4 > G5. It was found that the modified dendrimers self-organized into spherical aggregates with a bilayer vesicular structures and that the dendrimers in higher generation have more order structure, which may be attributed to the crystallization induced by the compacted effect of AP segments. In addition, larger spherical vesicles were observed under acidic and alkaline conditions, as compared with sizes of aggregates in neutral medium. At low pH, the tertiary amine groups of PAMAM-AP were transformed to ammonium salts; the polarons were formed from AP units by doping with strong acids, thereby leading to the stability of vesicular aggregates being better than that in double distilled water. Nevertheless, in high pH environment, the deprotonation of PAMAM-AP caused the enhancement of π-π interactions, resulting in generation of twins or multilayered vesicles.

In situ gelation of PEG-PLGA-PEG hydrogels containing high loading of hydroxyapatite: in vitro and in vivo characteristics

Thermosensitive hydrogels are renowned carriers that are used to deliver a variety of drugs with the aim of combating diseases. In this study, the injectability of thermosensitive hydrogels comprised of poly(ethylene glycol)-poly(lactic acid-co-glycolic acid)-poly(ethylene glycol) (PEG-PLGA-PEG, PELGE) and hydroxyapatite (HA) were examined for their ability to deliver bone morphological protein 2 (BMP-2). The physicochemical characteristics of PELGE, HA, and PELGE/HA hydrogel composites were investigated by (1)H NMR, GPC, FTIR, XRD, SEM, and TEM. The rheological properties, injectability, in vitro degradation, and in vivo biocompatibility were investigated. The hydrogel with a weight ratio of 4:6 of polymer to HA was found to be resistant to auto-catalyzed degradation of acidic monomers (LA, GA) for a period of 70 days owing to the presence of alkaline HA. Injectability was quantitatively determined by the ejected weight of the hydrogel composite at room temperature and was a close match to the weight amount predetermined by the syringe pump. The results not only revealed that the PELGE/HA hydrogel composite presented a minor tissue response in the subcutis of ICR mice at eight weeks, but they also indicated an acceptable tolerance of the hydrogel composite in animals. Thus, PELGE/HA hydrogel composite is expected to be a promising injectable orthopedic substitute because of its desirable thermosensitivity and injectability.

Advanced Anticorrosive Coatings Prepared from Polymer-Clay Nanocomposite Materials

Corrosion control is an important subject of increasing interest to the modern metallic finishing industry. Surface modification of metallic substrates by organic or polymeric coatings is an essential approach for enhancing surface properties such as wear, oxidation, and corrosion. Various conventional techniques are utilized to depositing the desired materials onto the metallic substrate to achieve surface modifications with better protection for the substrate. Organic or polymeric coatings on metallic substrates provide an effective barrier between the metal and its environment and/or inhibit corrosion through the presence of chemicals. Chromium-containing compounds (CC) have generally been used as effective anticorrosive coatings in the past decades. However, due to the environmental and health concerns, CCs may need to be replaced by alternative materials that would not pose biological and ecological hazards. Thus, research has focused on the development of novel polymeric coating materials that contain effective anticorrosive agents. During the early stage of corrosion protection engineering, various neat organic or polymeric coatings were developed. These coatings generally function as a physical barrier against aggressive species such as O2 and H+ that cause decomposition. Examples of representative polymers are include epoxy resins [MacQueen & Granata, 1996; Dang et al., 2002], polyurethanes [Moijca et al., 2001], and polyesters [Malshe & Sangaj, 2006; Deflorian et al., 1996]. Moreover, conjugated polymers such as polyaniline [Wessling & Posdorfer, 1999; Tan & Blackwood, 2003], polypyrrole [Iroh & Su, 2000, Krstajic et al., 1997], and polythiophene [Kousik et al., 2001], have also been employed as advanced anticorrosive coatings due to their redox catalytic properties, forming metal oxide passivation layers on metallic substrates. Conversely, not all neat polymeric coatings are permanently impenetrable because small defects in the coatings can lead to gateways that allow corrosive species to attack the metallic substrate; thus, localized corrosion can occur. As a second line of defense against corrosion, various nanoscale inorganic additives have been incorporated into various polymer matrices to generate a series of organic–inorganic hybrid anticorrosive coatings. Recently, montmorrillonite (MMT)–layered silicate (clay) has attracted intensive research interest for the preparation of polymer–clay nanocomposites (PCNs) because its lamellar elements display high in–plane strength, stiffness, and high aspect ratios. Typically, the chemical structures of MMT consist of two fused silica tetrahedral sheets that sandwich an

Preparation and thermal properties of UV-curable polyacrylate–gold nanocomposite foams

In this study, we prepare UV-curable polyacrylate–gold nanocomposites (PGNs) for the first time and analyze their thermal properties. The microemulsion architectures of these PGNs contain gold nanoparticles (GNPs) whose surface is modified with carboxyl groups; furthermore, 2-hydroxyethyl methacrylate (HEMA) and methyl methacrylate (MMA) monomers are first chemisorbed onto the surface of the GNPs and then photopolymerized to form a shell. The effects of the dispersion characteristics of GNPs in a PGN matrix were analyzed by transmission electron microscopy (TEM). PGN foams (FPGNs) can be obtained by subjecting the as-prepared bulk PGN materials to physical batch foaming processes, where nitrogen is used as a blowing agent. The cellular structures of the prepared FPGNs were investigated by scanning electron microscopy (SEM). FPGNs containing 15 nm GNPs (herein, denoted by FPGN-15) were found to exhibit a smaller cell size and a higher cell density than FPGNs containing 25 nm GNPs (herein, denoted by FPGN-25). FPGN materials exhibit an apparent increase in thermal stability (including decomposition temperature (Td)) as well as a decrease in the thermal transport properties (including thermal conductivity (k) and thermal diffusivity (α)) as compared to their corresponding bulk PGN materials. Moreover, results of the measurements of the compression modulus showed that the mechanical strength of FPGN-15 and FPGN-25 increased by 72% and 57%, respectively, as compared to that of neat polyacrylate foam.

Electroactive Polymer-Based Anticorrosive Coatings

Abstract Use of electroactive polymer (EAP) coatings for corrosion protection has been discussed for many years. Quite a number of possible protection mechanisms are proposed, of which the possible passivation of the metal through the high potential of redox EAP such as polyaniline is maybe the most frequently stated. However, introducing the conjugated oligoaniline into the EAP backbones for using anticorrosive coatings are rarely discussed. This chapter focuses on the introduction to the anticorrosive properties of EAP-based coatings. The polymer coatings include EAP, electroactive polymer nanocomposites, and electroactive polymer with hydrophobic/superhydrophobic surfaces. The synthesis and mechanism for metal corrosion of the EAP-based coatings are also be discussed.

Synthesis and Characterization of Novel Self-assembly and Ph-Sensitive Anticancer Drug Carriers: (PAMAM-AP)-Modified PEG Loading with DOX

A self-assembly and pH-sensitive drug release system that is based on aniline pentamer (AP) as a shell conjugated to polyethylene glycol (PEG)-modified dendrimers (PAMAM) with doxorubicin (DOX) (DOX-PEG-PAMAM-AP) has been constructed and characterized. First of all, the higher generations (G = 5) are demonstrated to self-assemble into bilayer vesicles owing to the strong tendency of the AP to form PAMAM-AP G5. Subsequently, PAMAM-AP G5 modified hydrophilic and biocompatibility segment PEG synthesis of PEG-PAMAM-AP G5. Finally, load with the anticancer drug (DOX) to synthesis DOX-PEG-PAMAM-AP G5. The use of amphiphilic characteristics form these aggregations as new drug carrier to explore the ability to cytotoxicity of human breast cancer cells, and compare the drug release efficiency.