Chuh-Yung Chen

Preparation and properties of LDHs/epoxy nanocomposites

Abstract Layered double hydroxides (LDHs)/epoxy nanocomposites were prepared by mixing the amino laurate intercalated LDHs, EPON 828 resin, and Jeffamine D400 as a curing agent. The organo-modified LDHs with hydrophobic property easily disperse in epoxy resin, and the amino laurate intercalated LDHs with large gallery space allow the epoxy molecules and the curing agents to easily diffuse into the LDHs galleries at elevated temperature. After the thermal curing process, the exfoliated LDHs/epoxy nanocomposites were formed. X-ray diffraction was used to detect the formation process of the exfoliated LDHs/epoxy nanocomposites. TEM was used to observe the dispersed behavior of the LDHs nanolayers, and the LDHs nanolayers were exfoliated and well dispersed in these nanocomposites. Owing to the reaction between the amine groups of the intercalated amino laurate and epoxy groups, the adhesion between the LDHs nanolayers and epoxy molecules makes these LDHs/epoxy nanocomposites more compatible. Consequently, the tensile properties from tensile test and the mechanical properties from DMA were enhanced, and the Tg of these nanocomposites from DMA and TMA were increased. Coefficients of thermal expansion (CTEs, below and above Tg) of these nanocomposites from TMA decreased with the LDHs content. The thermal stability of these nanocomposites was enhanced by the well dispersed LDHs nanolayers.

Study on metal ion adsorption of bifunctional chelating/ion-exchange resins

Ion-exchange resin has been considered as a suitable material for the recovery of heavy metals in water treatment. The chelating group, iminodiacetic acid (-R-N(CH 2 COOH) 2 ), was introduced into the weak-acid type (-R-(COOH) - ) -n ) ion-exchange resin to obtain bifunctional ion-exchange resins. Chromic, cupric, cadmium and lead ions were employed for adsorption experiments in this study. In isothermal experiments, the order of heavy metal ion adsorption decreased with increasing diameter of the heavy metal ion when the chelating group content was less than half. On the contrary, the adsorbed amount of lead ion would be higher than that of cadmic ion as the quantity of chelating group content was more than half owing to the stability constant difference (K s [ Pb2+ ] = 10 17.5 > K s[Cd2+] = 10 5.71 in iminodiacetic acid). The adsorption efficiency of bifunctional ion-exchange resins, especially for lead ions, would increase with rising chelating group content (from 0.08 mmol/mmol COOH to 0.31 mmol/mmol COOH). Meanwhile, the working pH range for metal ion adsorption in bifunctional ion-exchange resings was extended from 2.5 down to 0.5. Addition of chelating groups to weak acid ion-exchange resins could increase the adsorption efficiency for metal ions owing to the increased free volume of polymer structure.

Efficient decolorization of azo dye Reactive Black B involving aromatic fragment degradation in buffered Co2+/PMS oxidative processes with a ppb level dosage of Co2+-catalyst

In order to generate powerful radicals as oxidizing species for the complete decolorization and degradation of azo dye Reactive Black B (RBB) at near neutral pH (pH 6), homogeneous activation of peroxymonosulfate (Oxone: PMS) by the trace Co2+-catalysts was explored. We not only took advantage of the high oxidation-reduction potential of produced hydroxyl and sulfite radicals but also an opportunity to oxidize RBB to less complex compounds with extremely low dosages, especially the ppb level of the Co2+-catalyst (stoichiometric ratio: [Co2+](0)/[RBB](0)=1.7 x 10(-6)-1.7 x 10(-5); [PMS](0)/[RBB](0)=8-32). Anion effects and pH effects were also carried out and discussed to simulate an actual application such as that of a textile waste stream. Both the degradations of RBB and its derivative aromatic fragments were illustrated successfully at UV-visable absorptions of 591 and 310 nm, respectively, and the possible relationships between them were also proposed and discussed, based on the experimental results. The RBB degradation in this Co2+/PMS oxidative process successfully formulated a pseudo-first-order kinetic model at an isothermal condition of 25 degrees C with or without different anions present. The initial rate and rate constant were calculated under different comparative conditions, and the results indicate that the activity of both RBB decolorization and its degradation are not obviously dependent on the PMS concentration, but rather are related to the Co2+ dosage.

Bipolar membrane prepared by grafting and plasma polymerization

Abstract Ce4+-initiated and plasma-induced grafting polymerization was used to prepare bipolar membranes. The former method used the membrane of copoly(2-hydroxylethylene-methacrylate (2-HEMA)/n-butylacrylate (BA)/glycidyl-methacrylate (GMA)) on the surfaces of which were grafted acrylic acid (AA: COO−) and 4-vinyl pyridine (4VP: NH+Cl−), to prepare the bipolar membrane. The latter method utilized the porous PVDF membrane as a substrate, onto one side of which AA (or sodium vinyl sulfonate, SVS) monomer was grafted, and onto the other of which, 4-vinyl pyridine (or N′,N-dimethyl amino ethyl acrylate, DMAEA) monomer was grafted. The contact angle of bipolar membranes dramatically decreased when the ionic polymer covered the surface of the membranes by plasma-grafting polymerization. Meanwhile, the swelling level of bipolar membranes was in the range of 25–50%. Furthermore, the cross-section SEM photographs of bipolar membranes further illustrated a sandwich structure that consisted of anionic polymer, cationic polymer and PVDF substrate. The limiting current increased with the diffusion coefficient and the concentration of electrolysis; however, the critical voltage was independent of the concentration and the kind of electrolysis. The 963 of AA–PVDF–DMAEA bipolar membrane exhibited the best ratio of dissociation rate constants (kd/kd0) of all membranes. Results concerning the efficiency of the current showed plasma-induced preparation of a bipolar membrane is better than Ce4+-initiated preparation.

The effect of end groups on the thermal degradation of poly(methyl methacrylate)

Abstract The thermal degradation of poly(methyl methacrylate) was studied using a system of thiols as initiators. Depolymerization is the dominant reaction in the thermal degradation of such polymers, according to thermal analysis. The degradation mechanism involves only main-chain scission. Three methods of degradation were applied to elucidate the thermal degradation behaviour. The activation energy for the degradation of PMMA-thiols is 170 kJ/mol, higher than that of PMMA-AIBN (60 kJ/mol), as measured by the Flynn method. According to Ozawas method, the activation energy is 210 kJ/mol higher than that of an AIBN-initiated polymer (148–151 kJ/mol). By Kissingers measurement method, this system has a frequency factor (∼10 10 ) five orders of magnitude higher than the ordinary PMMA (∼10 5 ). The observed results are explained as a “blocking effect”.

The gas transport properties of amine-containing polyurethane and poly(urethane-urea) membranes

Abstract A series of amine-containing polyurethanes and poly(urethane-urea)s based on 4,4′-diphenylmethane diisocyanate and either poly(ethylene glycol) of molecular weights 400 or 600 were prepared as gas separation membranes. The amine functional groups of N -methyldiethanolamine (MDEA) and/or tetraethylenepentamine (TEPA) were introduced into the hard segment as a chain extender. The gas transport data of He, H 2 , O 2 , N 2 , CH 4 and CO 2 in these polymer membranes were determined by using the Barrers high-vacuum technique and the time-lag method. The restriction of chain mobility has been shown by the formation of hydrogen bonding in the soft segment and hard-segment domains, resulting in the increase in the density, glass transition temperature of soft segments ( T gs ). The separation mechanism of various gas pairs used in industrial processes is also discussed. Effect of pressure on permeability of the gases above and below T gs was studied. It was found that the gas permeability increased or decreased with upstream pressure above T gs , and should be described by a modified free-volume model. On the other hand, the condensable CO 2 exhibits a minimum permeability at a certain upstream pressure below T gs . The permeability of He and H 2 were pressure independent above and below the T gs .

Construction of nanocrystalline film on nanowire array via swelling electrospun polyvinylpyrrolidone-hosted nanofibers for use in dye-sensitized solar cells

A 74% enrichment of the efficiency of ZnO nanowire (NW) dye-sensitized solar cells (DSSCs) is achieved by the addition of a novel light-scattering nanocrystalline film (nanofilm). The 100 nm thick nanofilm is derived from the polyvinylpyrrolidone-hosted SnO(2)/ZnO nanofibers electrospun on the top of ZnO NW arrays via methanol vapor treatment followed by high-temperature calcination. Structural characterizations show that the film is composed of SnO(2) and ZnO nanocrystals with a diameter of ∼10 nm. Short-circuit current, open-circuit voltage, and fill factor of the nanofilm/ZnO NW DSSCs are all superior to those of the ZnO NW DSSCs. The mechanism of photocurrent enhancement in the nanofilm/ZnO NW DSSCs has been investigated using optical modulation spectroscopy. Intensity modulation photocurrent spectroscopy (IMPS) measurements reveal that the dye-sensitized nanofilm does not contribute significant photocurrent in the nanofilm/ZnO NW DSSCs. The significant enhancement of the efficiency of the ZnO NW DSSCs is achieved by reflecting unabsorbed photons back into the NW anode using the novel light-scattering layer of nanofilm.

The effect of different lithium salts on conductivity of comb-like polymer electrolyte with chelating functional group

The behaviors of lithium ions in a comb-like polymer electrolyte with chelating functional group complexed with LiCF3SO3, LiBr and LiClO4 were characterized by differential scanning calorimeter (DSC), thermogravimetric analysis (TGA), Fourier transform infrared (FT-IR) spectroscopy, AC impedance, and 13C solid-state NMR measurement. The comb-like copolymer was synthesized from poly(ethylene glycol) methyl ether methacrylate (PEGMEM) and (2-methylacrylic acid 3-(bis-carboxymethylamino)-2-hydroxy-propyl ester) (GMA-IDA). FT-IR spectra reveal the interactions of Li+ ions with both the ether oxygen of the PEGMEM and the nitrogen atom of the GMA-IDA segments. FT-IR spectra also indicate an increasing anion–cation association consistent with increasing LiCF3SO3 concentrations. Moreover, the 13C solid-state NMR spectra for the carbons attached to the ether oxygen atoms exhibited significant line broadening and a slight upfield chemical shift when the dopant was added to the polymer. These findings indicate coordination between the Li cation and the ether oxygens in the PEG segment. Tg and Td of copolymers doped with salts clearly increase, as shown by DSC and TGA measurements. These results indicate the interactions of Li+ with both PEGMEM and GMA-IDA segments form transient cross-links inside the copolymers. The Vogel–Tamman–Fulcher (VTF)-like behavior of conductivity implies the coupling of the charge carriers with the segmental motion of the polymer chain in this study. The maximum conductivity of copolymers relates to the composition of the copolymers and the concentration of doping lithium ions. In summary, the GMA-IDA unit in the copolymer promotes the dissociation of the lithium salt, the mechanical strength and the conductivity of the polyelectrolyte.

Modification of multi-walled carbon nanotubes by plasma treatment and further use as templates for growth of CdS nanocrystals

In this study, we present a novel method for preparing multi-walled carbon nanotubes (MWCNTs) grafted with a poly(2-methacrylic acid 3-(bis-carboxymethylamino)-2-hydroxy-propyl ester) (GMA-IDA)-cadmium sulfide complex (CNTs-G-ICdS complex) through plasma-induced grafting polymerization. The characteristics of the MWCNTs after being grafted with the GMA-IDA polymer were monitored by a Fourier transform infrared (FT-IR) spectroscope. Scanning electronic microscopy (SEM) shows that the amount of GMA-IDA grafted onto the MWCNTs increases with the concentration of GMA-IDA monomer. The complex resulting from GMA-IDA polymer grafting onto the MWCNTs, CNTs-G-I (15%), shows excellent dispersion properties in aqueous solution and has high Zeta potential values over a wide range of pH values, from 2 to 12. Moreover, Raman spectroscopy was used to confirm the successful chemical modification of MWCNTs through the plasma treatment. The chelating groups, -N(CH(2)COO(-))(2) in the GMA-IDA polymer grafted on the surface of the CNTs-G-I, are the coordination sites for chelating cadmium ions, and are further used as nano-templates for the growth of CdS nanocrystals (quantum dots). Moreover, TEM microscopy reveals that the size of the CdS nanocrystals on the CNT surfaces increases with increasing S(2-) concentration. In addition, high resolution x-ray photoelectron (XPS) spectroscopy was used to characterize the functional groups on the surface of the MWCNTs after chemical modification by the plasma treatment and grafting with GMA-IDA polymer.

Stability constants of water-soluble and latex types of chelating polymers containing iminodiacetic acid with some transition-metal ions

Abstract Two polymeric chelating agents, water-soluble and latex types of poly(styrene-co-GMA–IDA), are formed by reacting styrene with a chelating vinyl monomer, GMA–IDA. Acid dissociation constants ( K a ) and stability constants ( K s ) of these chelating agents with Cu(II), Ni(II), Zn(II) and Co(II) are determined by potentiometric titration and UV–Vis spectrophotometer, respectively. The values of K a1 and K a2 for the latex type of poly(styrene-co-GMA–IDA) are smaller than those for solution types. Stability constants are ordered, latex types>solution types>GMA–IDA. Latexes are surfactant-free, nearly nano-particles and the mean size declines as the amount of metal ions increases, when the particles are complexed therewith. The stability constants of the latex–metal complexes exceed those of the corresponding GMA–IDA–metal complexes by a factor of 10 2 –10 3 , depending on the metal ions. These results are explained by the neighboring effect and high concentrations of GMA–IDA on latex’s particulate surface (cooperative effect).