Polystyrene/graphene composite electrode fabricated by in situ polymerization for capillary electrophoretic determination of bioactive constituents in Herba Houttuyniae

A novel graphene/polystyrene composite electrode was developed for the enhanced amperometric detection of CE in this work. The composite electrode was fabricated on the basis of the in situ polymerization of a mixture of graphene and prepolymerized styrene in the bore of a piece of fused‐silica capillary under heat. SEM, XRD, and FTIR offered insights into the nature of the composite. The results indicated that graphenes were well dispersed and embedded throughout the PS matrix to form an interconnected conducting network. The performance of this unique graphene‐based detector has been demonstrated by separating and detecting rutin, isoquercitrin, quercitrin, and chlorogenic acid in Herba Houttuyniae (a traditional Chinese medicine) in combination with CE. The prepared graphene‐based CE detector offered significantly lower detection potential, yielded enhanced signal‐to‐noise characteristics, and exhibited high resistance to surface fouling and enhanced stability. It showed long‐term stability and reproducibility with a relative standard deviation of 3.1% for the peak current (n=15).     

Graphene/poly(ethylene‐co‐vinyl acetate) composite electrode fabricated by melt compounding for capillary electrophoretic determination of flavones in Cacumen platycladi

In this report, a graphene/poly(ethylene‐co‐vinyl acetate) composite electrode was fabricated by melt compounding for the amperometric detection of capillary electrophoresis. The composite electrode was fabricated by packing a mixture of graphene and melted poly(ethylene‐co‐vinyl acetate) in a piece of fused silica capillary under heat. The structure of the composite was investigated by scanning electron microscopy and Fourier transform infrared spectroscopy. The results indicated that graphene sheets were well dispersed in the composite to form an interconnected conducting network. The performance of this unique graphene‐based detector has been demonstrated by separating and detecting rutin, quercitrin, kaempferol, and quercetin in Cacumen platycladi in combination with capillary electrophoresis. The four flavones have been well separated within 9 min in a 50‐cm‐long capillary at a separation voltage of 12 kV using a 50 mM sodium borate buffer (pH 9.2). The graphene‐based detector offered significantly lower operating potentials, substantially enhanced signal‐to‐noise characteristics, lower expense of operation, high resistance to surface fouling, and enhanced stability. It showed long‐term stability and repeatability with relative standard deviations of <5% for the peak current (n = 15).     

Carbon nanotube/poly(methyl methacrylate) composite electrode for capillary electrophoretic measurement of honokiol and magnolol in Cortex Magnoliae Officinalis

This paper describes the development and the application of a novel carbon nanotube/poly(methyl methacrylate) (CNT/PMMA) composite electrode as a sensitive amperometric detector of CE. The composite electrode was fabricated on the basis of the in situ polymerization of a mixture of CNT and prepolymerized methylmethacrylate in the microchannel of a piece of fused-silica capillary under heat. The performance of this unique system has been demonstrated by separating and detecting honokiol and magnolol in traditional Chinese medicine, Cortex Magnoliae Officinalis. Factors influencing their separation and detection processes were examined and optimized. Honokiol and magnolol were well separated within 7 min in a 40 cm long capillary at a separation voltage of 15 kV using a 50 mM borate buffer (pH 9.2). The new CNT-based CE detector offered significantly lower operating potentials, yielded substantially enhanced S/N characteristics, and exhibited resistance to surface fouling and hence enhanced stability. It demonstrated long-term stability and reproducibility with RSDs of less than 5% for the peak current (n = 9) and should also find a wide range of applications in microchip CE, flowing injection analysis, and other microfluidic analysis systems.     

Fabrication of poly(methyl methacrylate) microfluidic chips by redox-initiated polymerization

In this report, a method based on the redox-initiated polymerization of methyl methacrylate (MMA) has been developed for the rapid fabrication of poly(methyl methacrylate) (PMMA) microfluidic chips. MMA containing 2-2'-azo-bis-isobutyronitrile was allowed to prepolymerize in a water bath to form a viscous prepolymer solution that was subsequently mixed with MMA containing a redox-initiation couple of benzoyl peroxide/N,N-dimethylaniline. The dense molding solution was sandwiched between a silicon template and a piece of 1-mm-thick PMMA plate. The polymerization could complete within 50 min under ambient temperature. The images of raised microfluidic structures on the silicon template were precisely replicated into the synthesized PMMA substrate during the redox-initiated polymerization of the molding solution. The chips were subsequently assembled by the thermal bonding of the channel plates and the covers. The new fabrication approach obviates the need for special equipment and significantly simplifies the process of fabricating PMMA microdevices. The attractive performance of the novel PMMA microchips has been demonstrated in connection with contactless conductivity detection for the separation and detection of ionic species.     

Preparation and characterization of poly(methyl methacrylate)/titanium oxide composite particles

Before polymerization, the introduction of double bonds onto the surface of the TiO₂ particles was achieved by the treatment of the TiO₂ particles with the silane-coupling agent. Via in-situ emulsion polymerization, the poly(methyl methacrylate) (PMMA)/titanium oxide (TiO₂) composite particles were prepared by graft polymerization of MMA from the surface of the modified TiO₂ particles. The structure of the obtained PMMA/TiO₂ composite particles was characterized using fourier transform infrared spectra (FT-IR), thermo-gravimetric analysis (TGA), differential scanning calorimetry (DSC) and size excluding chromatography (SEC). The morphology of the obtained PMMA/TiO₂ composite particles was observed by transmission electron microscope (TEM). The results of FT-IR and TGA measurements show that PMMA is successfully grafted from the surface of the TiO₂ particles and that the percentage of grafting and the grafting efficiency can reach 208.3% and 96.6%, respectively. At the same time, the TGA and DSC measurements indicate an enhancement of thermal stability. TEM images demonstrate a better dispersion of the TiO₂ particles in the composite latex. In addition, UV-visible absorption measurements show that the PMMA/TiO₂ composite particles can absorb over 95% UV light at 210–400 nm wavelength.     

Poly(ethylene-co-vinyl alcohol) and poly(methyl methacrylate) blends: Phase behavior and morphology

In this work blends of poly(ethylene-co-vinyl alcohol) (EVOH) with different ethylene contents (27, 32, 38 and 44 mol%) and poly(methyl methacrylate) (PMMA) were prepared by mechanical mixing in the melted state. The miscibility and melting behavior as a function of blend composition and the ethylene content in EVOH copolymers were investigated by means of differential scanning calorimetry (DSC) and dynamic mechanical thermal analysis (DMTA). The morphology of the cryofractured surfaces was examined by scanning electron microscopy (SEM). DSC and DMTA data show that EVOH/PMMA blends are immiscible, independent of EVOH and blend composition. The SEM analysis in agreement with DMTA analysis indicates that the morphology of phases depends on the blend composition, with phase inversion occurring as the concentration of one or other polymer component increases. However, the copolymer composition apparently does not affect the domain size distribution for blends containing 20 wt% of EVOH or 20 wt% of PMMA. A better phase adhesion is observed mainly for blends with 50 wt% of each polymer component.     

Methyl methacrylate in poly(methyl methacrylate)--validation of direct injection gas chromatography

Gas chromatography (GC) was investigated for the determination of residual methyl methacrylate (MMA) in heat-processed poly(methyl methacrylate) (PMMA) denture base material emphasizing recovery and validation. Standard solutions of MMA and emulsion-polymerized PMMA in dichloromethane were analysed, before and after distillation by a room-temperature air stream into a liquid nitrogen trap, and in the presence of PMMA by direct injection. Quantitative NMR analysis using dimethyl sulphoxide as internal calibration standard in deuterated chloroform solutions provided validation. Good concordance was observed between results under all conditions; no problems arose from direct injection of PMMA solution for GC. Good straight line responses in log-log plots were generally observed. For GC and MMA: log-log calibration curve (slope: 0.9552 +/- 0.0051, r2: 0.9992, n = 32) indicated some non-linearity (t = 8.875, p approximately 4 x 10(-10)). Distillation gave slope: 0.9751 +/- 0.0213 (NS versus unity; t = 1.172, p > 0.25). For PMMA solutions, distillation (r2: 0.9301) gave greater scatter than direct injection (r2: 0.9704). For NMR: log-log plot of calculated versus actual MMA (slope: 0.9363 +/- 0.0157, r2: 0.9969, n = 13) again indicated non-linearity (t = 4.0682, p = 0.0019). PMMA solutions gave slope: 0.9477 +/- 0.0328, r2 = 0.9858 (NS versus unity; t = 1.5941, p = 0.13). Determination of MMA in PMMA by GC is recommended.     

Radiation degradation of poly(methyl methacrylate) in the soft x-ray region

The molecular weight distribution change has been measured for the photoresist poly(methyl methacrylate) [PMMA] after in-vacuo exposure to monochromatic soft x-rays from the Canadian Synchrotron Radiation Facility [CSRF]. The experimental changes in the mo-lecular weight distribations derived from gel permeation chromatography [GPC], were compared to a simple Monte Carlo simulation model that assumes random main chain scission. Using this model a scission radiation chemical yield of G(S) = 1.28± 0.10 at room temperature was found to give the best fit at a photon energy of 621 eV. This value is similar to values reported previously in the literature using electron beam and γ-ray sources, but significantly larger than those reported for fast neutrons, α-particles, or energetically charged particles. It was found that in this soft x-ray energy regime, that degradation of PMMA involves primarily a random scission process of the main chain. The results of a least-squares fit of this soft x-ray G(S) data and all available literature values from other radiation sources, to the linear energy transfer [LET] dE/dx are discussed. © 1993 John Wiley & Sons, Inc.     

Surface modification of poly(methyl methacrylate) microfluidic devices for high-resolution separations of single-stranded DNA

While polymer-based microfluidic devices offer some unique opportunities in developing low-cost systems for a variety of application areas, the ability to sort electrophoretically with high efficiency a number of different targets has remained somewhat elusive with an example consisting of achieving single base resolution as required for DNA sequencing. While the reasons for this are many-fold, it is clear that some type of coating is required on the polymer substrate to suppress the EOF and/or minimize potential solute/wall interactions. To this end, we report on a simple grafting procedure to allow the formation of polymer coats, which in this example used linear polyarcylamides (LPAs), onto a poly(methyl methacrylate) (PMMA) microfluidic device. The procedure involved creating an amine-terminated PMMA surface by appropriately functionalizing the PMMA through either a chemical or photochemical process. The aminated surface could then be used to covalently anchor methacrylic acid, which was used as a scaffold to produce LPAs on the surface through radical polymerization of acrylamide. The resulting surfaces demonstrated EOFs that were nearly an order of magnitude smaller than native PMMA. In addition, these LPA-coated devices could produce highly reproducible migration times of over approximately 20 runs with plate numbers exceeding 10(5) m(-1). Using gel electrophoretic analysis of a single base track generated from an M13mp18 template using Sanger cycle sequencing and dye-primer chemistry, the resolution value obtained for bases 199 and 200 was 0.18 while for bases 208 and 209 it was 0.21. For the native PMMA, these bands were found to comigrate.     

Light scattering studies of stereocomplex formation of stereoregular poly(methyl methacrylate) in solutions

The structure and stereocomplex formation of multi-stereoblock poly(methyl methacrylates) in three different solvents, acetone, tetrahydrofuran (THF) and chloroform, corresponding to strongly-, weakly- and non-complexing solvent, respectively, were investigated by a combination of static and dynamic laser light scattering. Our results revealed that the stereocomplex was caused by weak interactions, and could be melted at higher temperatures. In THF, the intermolecular and intramolecular interactions could be clearly separated at lower temperatures, and the structure of aggregated chains was linear. In acetone, a more compact structure was obtained, which was corroborated by the fact that the stereocomplex had a higher melting temperature than in THF.     

Synthesis of nano-ZnO/poly(methyl methacrylate) composite microsphere through emulsion polymerization and its UV-shielding property

Nano-ZnO/poly(methyl methacrylate)(PMMA) composite latex microspheres were synthesized by in-site emulsion polymerization. The interfacial compatibility between nano-ZnO particles and PMMA were improved by treating the surface of nano-ZnO particles hydrophobically using methacryloxypropyltrimethoxysilane (MPTMS). TEM indicated that nano-ZnO particles present in nanosphere and have been encapsulated in the PMMA phase. FT-IR confirmed that MPTMS reacted with the nano-ZnO particle and copolymerized with MMA. It was clearly found from SEM that ZnO nanoparticles can be homogeneously dispersed in the PVC matrix. The absorbance spectrum of the nanocomposite polymer suggested that increasing the amount of nano-ZnO in composite particles could enhance the UV-shielding properties of the polymers. The nano-ZnO/PMMA composite particle could eliminate aggregation of ZnO nanoparticle and improve its compatibility with organic polymer. This means that the composite particles can be widely applied in lots of fields.     

Sensitive capillary electrophoretic determination of mercury species with amperometric detection at a copper electrode after cation exchange preconcentration

A capillary electrophoretic method for the separation of four mercury species with amperometric detection was developed. Inorganic Hg2+, methyl-, ethyl-, and phenyl-mercury were complexed with L-cysteine and separated in a counterelectroosmotic mode in an electrolyte solution comprised of 20 mM sodium tetraborate at pH 9.5. Amperometric detection of separated species was achieved at passivated copper electrode under electrocatalytic oxidation conditions. The four mercury species were separated in less than 8 min with LODs ranging from 170 to 450 microg/L. Cation exchange preconcentration was used to decrease the LODs down to 1.7 microg/L.     

Pyrolysis mass spectrometry analysis of polycarbonate/poly(methyl methacrylate)/poly(vinyl acetate) ternary blends

Direct insertion probe pyrolysis mass spectrometry (DIP-MS) analyses of polycarbonate/poly(methyl methacrylate)/poly(vinyl acetate), (PC/PMMA/PVAc), ternary blends have been performed. The PC/PMMA/PVAc ternary blends were obtained by coalescing from their common γ-cyclodextrin-inclusion compounds (CD-ICs), through the removal of the γ-CD host (coalesced blend), and by a co-precipitation method (physical blend). The coalesced ternary blend showed different thermal behaviors compared to the co-precipitated physical blend. The stability of PC chains decreased due to the reactions of CH₃COOH formed by deacetylation of PVAc above 300 °C, for both coalesced and physical blends. This process was more effective for the physical blend most likely due to the enhanced diffusion of CH₃COOH into the amorphous PC domains, where it can further react producing low molecular weight PC fragments bearing methyl carbonate chain ends. The decrease in thermal stability of PC chains was less significant for the coalesced ternary blend indicating that the diffusion of CH₃COOH was either somewhat limited or competed with intermolecular reactions between PMMA and PC and between PMMA and PVAc, which were detected and were associated with their close proximity in the intimately mixed coalesced PC/PMMA/PVAc ternary blend.     

Compatibilization of blends of polybutadiene and poly(methyl methacrylate) with poly(butadiene-block-methyl methacrylate)

Compatibilization of blends of polybutadiene and poly(methyl methacrylate) with butadiene-methyl methacrylate diblock copolymers has been investigated by transmission electron microscopy. When the diblock copolymers are added to the blends, the size of PB particles decreases and their size distribution gets narrower. In PB/PMMA7.6K blends with P(B-b-MMA)25.2K as a compatibilizer, most of micelles exist in the PMMA phase. However, using P(B-b-MMA)38K as a compatibilizer, the micellar aggregation exists in PB particles besides that existing in the PMMA phase. The core of a micelle in the PMMA phase is about 10 nm. In this article the influences of temperature and homo-PMMA molecular weight on compatibilization were also examined. At a high temperature PB particles in blends tend to agglomerate into bigger particles. When the molecular weight of PMMA is close to that of the corresponding block of the copolymer, the best compatibilization result would be achieved. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36 : 85–93, 1998     

Methyl methacrylate oligomerically-modified clay and its poly(methyl methacrylate) nanocomposites

A methyl methacrylate oligomerically-modified clay was used to prepare poly(methyl methacrylate) clay nanocomposites by melt blending and the effect of the clay loading level on the modified clay and corresponding nanocomposite was studied. These nanocomposites were characterized by X-ray diffraction, transmission electron microscopy, thermogravimetric analysis and cone calorimetry. The results show a mixed intercalated/delaminated morphology with good nanodispersion. The compatibility between the methylacrylate-subsituted clay and poly(methyl methacrylate) (PMMA) are greatly improved compared to other oligomerically-modified clays.     

Synthesis and micelle formation of triblock copolymers of poly(methyl methacrylate)-b-poly(ethylene oxide)-b-poly(methyl methacrylate) in aqueous solution

Amphiphilic triblock copolymers of poly(methyl methacrylate)-b-poly(ethylene oxide)-b-poly(methyl methacrylate) (PMMA-b-PEO-b-PMMA) with well-defined structure were synthesized via atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA) initiated by the PEO macroinitiator. The macroinitiator and triblock copolymer with different PMMA and/or PEO block lengths were characterized with ¹H and ¹³C NMR and gel permeation chromatography (GPC). The micelle formed by these triblock copolymers in aqueous solutions was detected by fluorescence excitation and emission spectra of pyrene probe. The critical micelle concentration (CMC) ranged from 0.0019 to 0.016 mg/mL and increased with increasing PMMA block length, while the PEO block length had less effect on the CMC. The partition constant K_v for pyrene in the micelle and in aqueous solution was about 10⁵. The triblock copolymer appeared to form the micelles with hydrophobic PMMA core and hydrophilic PEO loop chain corona. The hydrodynamic radius R_h,app of the micelle measured with dynamic light scattering (DLS) ranged from 17.3 to 24.0 nm and increased with increasing PEO block length to form thicker corona. The spherical shape of the micelle of the triblock copolymers was observed with an atomic force microscope (AFM). Increasing hydrophobic PMMA block length effectively promoted the micelle formation in aqueous solutions, but the micelles were stable even only with short PMMA blocks.     

Glass transition of thin films of poly(2-vinyl pyridine) and poly(methyl methacrylate): nanocalorimetry measurements

Glass transitions were observed in thin films of poly(2-vinyl pyridine) (P2VP) and poly(methyl methacrylate) (PMMA) using a scanning nanocalorimetry technique which has both high sensitivity (10⁻⁹ J/K) and high scan rates (10⁴-10⁵ K/s). Samples were deposited by the spin-cast method. The thickness of samples was 100-400 nm. Glass transition temperature, obtained by nanocalorimetry, is shifted toward higher temperatures by 10-20 K and activation enthalpy of glass transition is shifted to lower values by factor of 2-4. The glass transition characteristics of both polymers are discussed in terms of the standard Tool-Narayanaswamy-Moynihan (TNM) multi-parameter model.     

Absorption and photoluminescence of Buriti oil/polystyrene and Buriti oil/poly(methyl methacrylate) blends

This work reports the preparation and characterization of Buriti (Mauritia flexuosa L.) oil/polystyrene (PS) and Buriti oil/poly(methyl methacrylate) blends. The Buriti is an abundant palm tree of the Amazon region. This oil was used because of its chemical composition (high concentrations of oleic acid, tocopherols and carotenoids, especially β-carotene) and interesting optical properties, such as absorption and photoluminescence. The incorporation of the vegetable oil in the PS and PMMA matrices renders orange-colored blends, which were verified to absorb UV-Vis radiation and emit light in the green region. The intensity of these properties is proportional to the oil content in the samples. Micrographs of the blends showed that the oil is located in cavities distributed in the polymeric matrices. This work shows that it is possible to employ the Buriti oil, a cheaper and abundant natural resource, to improve absorption and light emission properties of PS and PMMA polymers.     

On oxygen diffusion in poly(methyl methacrylate) films

ESR spectroscopy has been used to follow the kinetics of decay of radicals produced by UV-radiation in PMMA films upon exposure to oxygen in the temperature range 160-210 K. In the same films and at the same conditions, decay kinetics of phenanthrene phosphorescence has been studied at 180-220 K. Both types of the experiments give the same values for diffusion coefficients of oxygen in PMMA. Thus, from the oxygen diffusion standpoint, the sites of the radical stabilization and phenanthrene molecule localization in the polymer matrix do not differ.     

Preparation of poly (methyl methacrylate)/LDH nanocomposite by exfoliation-adsorption process

Exfoliated nanocomposite based on Mg, Al layered double hydroxide (Mg,Al-LDH) and poly(methyl methacrylate) (PMMA) has been prepared by exfoliation/adsorption process with acetone as co-solvent. The product was characterized by X-ray diffraction (XRD), thermal analysis and High Resolution Transmission Electronic Microscope (HREM). The results suggest that the brucite-like sheets of LDH disperse individually in the polymer matrix, and the thermal stability of the nanocomposite increases highly.