Jui-Ming Yeh

Preparation and properties of poly(vinyl alcohol)–clay nanocomposite materials

Abstract A series of polymer–clay nanocomposite (PCN) materials that consist of poly(vinyl alcohol) (PVA) and layered montmorillonite (MMT) clay are prepared by effectively dispersing the inorganic nanolayers of MMT clay in organic PVA matrix via an in situ free radical polymerization with AIBN as initiator. Organic vinyl acetate monomers are first intercalated into the interlayer regions of organophilic clay hosts and followed by a one-step free radical polymerization. The prepared poly(vinyl acetate)–clay (PVAc–clay) solution are then saponified via direct-hydrolysis with NaOH solution to form PVA–clay nanocomposite materials. The as-synthesized PCN materials are typically characterized by Fourier-Transformation infrared (FTIR) spectroscopy, wide-angle X-ray diffraction and transmission electron microscopy. The molecular weights of poly(vinyl alcohol) (PVA) extracted from polymer-clay nanocomposite (PCN) materials and bulk PVA are determined by gel permeation chromatography (GPC) analysis with THF as eluant. The viscosity property of PCN materials with different feeding amount of MMT clay is studied by an ubbelohode capillary viscometer. The morphological image of as-synthesized materials is studied by scanning electron microscopy (SEM) and optical polarizing microscope (OPM). Effects of the material composition on the thermal stability, mechanical strength, optical clarity of PVA along with a series of PCN materials, in the form of fine powder and free-standing film, are also studied by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), dynamic mechanical analyzer (DMA) and UV–visible transmission spectra, respectively.

Polyaniline as corrosion protection coatings on cold rolled steel

A series of electrochemical measurements, including corrosion potential, corrosion current, Tafels constants and polarization resistance, have been made on polyaniline-coated cold rolled steel specimens under various conditions. Both the base and acid-doped forms of polyaniline were studied. The base form of polyaniline was found to offer good corrosion protection. This phenomenon may not originate merely from the barrier effect of the coatings, because nonconjugated polymers such as polystyrene and epoxy did not show the same electrochemical behaviour.

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.

Comparing micellar electrokinetic chromatography and microemulsion electrokinetic chromatography for the analysis of preservatives in pharmaceutical and cosmetic products

In this study, separation and determination of nine preservatives ranging from hydrophilic to hydrophobic properties, which are commonly used as additives in various pharmaceutical and cosmetic products, by micellar electrokinetic chromatograpy (MEKC) and microemulsion electrokinetic chromatography (MEEKC) were compared. The effect of temperature, buffer pH, and concentration of surfactant on separation were examined. In MEKC, the separation resolution of preservatives improved markedly by changing the sodium dodecyl sulfate concentration. Temperature and pH of running buffers were used mainly to shorten the magnitude of separation time. However, in order to detect all preservatives in a single run in a MEEKC system, a microemulsion of higher pH was needed. The separation resolution was improved dramatically by changing temperature, and a higher concentration of SDS was necessary for maintaining a stable microemulsion solution, therefore the separation of the nine preservatives in MEEKC took longer than in MEKC. An optimum MEKC method for separation of the nine preservatives was obtained within 9.0 min with a running buffer of pH 9.0 containing 20 mM SDS at 25 degrees C. A separation with baseline resolution was also obtained within 16 min using a microemulsion of pH 9.5 which composed of SDS, 1-butanol, and octane, and a shorter capillary column at 34 degrees C. Finally, the developed MEKC and MEEKC methods determined successfully preservatives in various cosmetic and pharmaceutical products.

Induction of cytotoxicity and apoptosis in mouse blastocysts by silver nanoparticles

Silver nanoparticles (nanoAg) are antibacterial materials widely used in various products and medical supplies. In this report, we examined the cytotoxic effects of nanoAg on mouse embryos at the blastocyst stage, subsequent embryonic attachment and outgrowth in vitro, and in vivo implantation by embryo transfer. Blastocysts treated with 50 microM nanoAg exhibited significantly increased apoptosis and a corresponding decrease in total cell number. Importantly, the implantation success rate of blastocysts pretreated with nanoAg was lower than that of their control counterparts. Moreover, in vitro treatment with 50 microM nanoAg was associated with increased resorption of post-implantation embryos and decreased fetal weight. Our results collectively indicate that in vitro exposure to nanoAg induces apoptosis and retards early post-implantation development after transfer to host mice. However, nanoAg-stimulated embryonic cytotoxicity appeared lower than that induced by the Ag+ ion. The results collectively show that nanoAg has the potential to induce embryo cytotoxicity. Further studies are required to establish effective protection strategies against the cytotoxic effects of these nanoparticles.

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.

Novel triphenylamine-containing ambipolar polyimides with pendant anthraquinone moiety for polymeric memory device, electrochromic and gas separation applications

Novel electron-donating triphenylamine (TPA)-containing electroactive functional polyimides with electron-withdrawing pendant anthraquinone moiety were designed and prepared for memory devices, electrochromic and gas separation applications. These high-performance polymers exhibited two conductivity states and could be swept negatively with a high ON/OFF current ratio of 109. The ON state of OAQ-6FPI polyimide remained around 8 min after removing the applied voltage, while the AQ-6FPI polyimide quickly returned to the OFF state during the backward sweep in a dual sweep process, implying that devices based on OAQ-6FPI and AQ-6FPI reveal static random access memory (SRAM) and dynamic random access memory (DRAM) behaviors resulting from the isolated donor–acceptor (D–A) and non-isolated D–A structures, respectively. Meanwhile, the polymer films exhibited electrochromic characteristics with a color change from neutral colorless or pale yellowish to blue and green at applied potentials, ranging from 0.00 to 1.40 V. Furthermore, the presence of a bulky and carbonyl-containing anthraquinone unit could enhance effectively CO2 permeability coefficients (PCO2) and permeability selectivity (PCO2/PCH4) for these polyimide membranes in the range of 21.6–69.9 and 28.8–31.7, respectively, and permeability increased with higher efficiency by directly attaching the bulky group to the backbone than incorporating via a spacer.

Reaction mechanism and synergistic anticorrosion property of reactive blends of maleimide-containing benzoxazine and amine-capped aniline trimer

This work studies the reaction mechanism and properties of reactive blends possessing a maleimide-containing benzoxazine compound (MI-Bz) and an amine-capped aniline trimer (ACAT). For the blends of MI-Bz and ACAT undergoing thermally induced reactions, the quinoid reaction of ACAT occurs first at about 96 °C, and the Michael addition reaction between the amine groups of ACAT and the maleimide group of MI-Bz follows at higher temperatures. The amine group of ACAT catalyzes the ring-opening reaction of benzoxazine groups of MI-Bz. The active species in the ring-opening reaction of benzoxazine groups are reactive toward the amine groups of ACAT. These two reactions build up the covalent bonding between ACAT and MI-Bz compounds. The thermally cured MI-Bz/ACAT mixtures (CR-MI-Bz/ACAT) demonstrate good thermal stability, high flame retardancy, and a synergistic effect on their respective anticorrosion properties. The water resistance (from MI-Bz) and the electroactivity (from ACAT) of the CR-MI-Bz/ACAT materials contribute to their high anticorrosion efficiencies. The sample possessing 33 wt% ACAT shows a protection efficiency of 98% and a corrosion rate of 4.8 μm per year for a cold-rolled steel substrate, which is about one order of magnitude lower than that recorded with the neat ACAT sample.