Properties of well aligned SWNT modified poly (methyl methacrylate) nanocomposites

The PMMA/SWNT composites with good uniformity, dispersion and alignment of SWNT were fabricated in a stretching process. The semidried mixture was stretched along one direction at a draw ratio of 50 before it was dried, and then folded along the same direction stretching repeatedly for 100 times. The TEM and SEM observation demonstrated that SWNT in the PMMA/SWNT composite tend to align in the stretching direction. The electrical conductivity and the mechanical properties of composite rise with the increase of SWNT concentration, composite films showed higher conductivity and higher mechanical draw ratios along the stretched direction than perpendicular to it. The TGA revealed that embedding the SWNTs into the PMMA matrix also improves the thermal stability of the composite.     

Effect of hydrophilic–hydrophobic balance on biocompatibility of poly(methyl methacrylate) (PMMA)–hydroxyapatite (HA) composites

The purpose of this study is to put in evidence the correlation between hydrophilic/hydrophobic balance and biocompatibility of PMMA–HA composites, in order to select the best composites for futures clinical applications. For this purpose, PMMA–HA cements with different compositions were prepared and static contact angle measurements, water absorption and gingival fibroblasts cell culture were performed and discussed.     

Feasibility study of friction spot welding of dissimilar single-lap joint between poly(methyl methacrylate) and poly(methyl methacrylate)-SiO2 nanocomposite

In this work, the feasibility of friction spot welding (FSpW) of a commercial poly(methyl methacrylate) (PMMA) GS grade and a PMMA 6 N/2 wt% silica (SiO₂) nanocomposite was investigated. Single-lap joints welded at rotational speeds of 1000, 2000 and 3000 rpm were produced. The analysis of the joint microstructure and material flow pattern indicated that joints could be produced using all of the tested welding conditions. However, the joint produced at 1000 rpm displayed sharp weld lines (weak links), indicating insufficient heat input, while the welds produced at 3000 rpm displayed excessive plastic deformation (bulging of the bottom plate), volumetric defects and a lack of material mixing in the welded area, associated with higher heat input. The weld produced at a rotational speed of 2000 rpm resulted in improved material mixing, which was indicated by the absence of weld lines and volumetric defects due to the more correct heat input. This welding condition was selected for further mechanical testing. Lap shear testing of PMMA GS/PMMA 6 N/2 wt% SiO₂ nanocomposite single lap joints welded at 2000 rpm resulted in an average ultimate lap shear strength of 3.9 ± 0.05 MPa. These weld strength values are equal to or better than those obtained using state-of-the-art welding techniques for PMMA materials, thereby demonstrating the potential of friction spot welding for thermoplastic nanocomposites.     

石墨烯量子点/CdS/CdSe共敏化太阳能电池

以三维锐钛矿TiO₂微球为上层光散射层材料, 以商业纳米TiO₂为下层连接材料, 采用刮刀法制备了一种新颖的双层TiO₂薄膜, 并应用于量子点敏化太阳能电池(QDSSC)。其中, 石墨烯量子点(GQDs)采用滴液法引入, CdS/CdSe量子点采用连续离子层吸附法(SILAR)制备。采用场发射扫描电镜、透射电镜、X射线衍射、紫外-可见漫反射光谱及荧光光谱对样品进行表征。实验还制备了CdS/CdSe量子点敏化及石墨烯量子点/CdS/CdSe共敏化太阳能电池, 并研究了石墨烯量子点及CdS不同敏化周期及对电池性能影响。研究结果表明, 石墨烯量子点及CdS不同敏化周期对薄膜的光学性质、电子传输及载流子复合均有较大影响。优选条件下, TiO₂/QGDs/CdS(4)/CdSe电池的光电转换效率为1.24%, 光电流密度为9.47 mA/cm², 显著高于TiO₂/CdS(4)/CdSe电池的这些参数(0.59%与6.22 mA/cm²)。这主要是由于TiO₂表层吸附石墨烯量子点后增强了电子的传输, 减少了载流子的复合。     

Modification on crystallization of poly(vinylidene fluoride) (PVDF) by solvent extraction of poly(methyl methacrylate) (PMMA) in PVDF/PMMA blends

The crystallization modification of poly(vinylidene fluoride) (PVDF) was investigated for the blend films of PVDF and poly(methyl methacrylate) (PMMA). The mass crystallinity (χ_c) and further, the β-phase content (F_(β)) of PVDF, were studied for the as-prepared blend films with different mass ratios. In addition, the variations of χ_c and F_(β) were systematically probed once the PMMA component was removed from the related blend systems. DSC, FTIR and XRD measurements all indicated that 1) χ_c, F_(β) and even the content of α-phase (F_(α)) decreased with the addition of PMMA; 2) with the extraction of PMMA, both χ_c and F_(β) increased while F_(α) decreased. It is worth noting that the increase of χ_c and F_(β) depended on the relative amount of extracted PMMA (E_PMMA), i.e., the more PMMA was removed, the more χ_c and F_(β) increased. These results reveal the hindrance effect from the PMMA constituent to the crystallization of PVDF, and consequently, this restriction would be released when the PMMA was extracted.     

Adhesion and degradation of hard coatings on poly (methyl methacrylate) substrates

The adhesion and time dependent crack growth behavior of polysiloxane based hard coatings on poly (methyl methacrylate) substrates were investigated. The adhesive fracture energies for different coatings were quantitatively characterized and varied between 1.4 J/m² and 22 J/m². Significant time dependent crack growth in various moist environments was observed and was consistent with a viscoelastic crack growth model. The effect of selected weathering treatments was also examined and resulted in a significant drop in coating adhesion. The coatings were analyzed using surface sensitive techniques; structural changes in the coatings resulting from various exposure doses were studied and mechanisms responsible for the observed degradation in adhesion were discussed.     

A simple lithographic method employing 172 nm vacuum ultraviolet light to prepare positive- and negative-tone poly(methyl methacrylate) patterns

We successfully prepared both positive- and negative-tone patterns by applying poly(methyl methacrylate) (PMMA) as a photoresist. A positive-pattern was prepared by lithography through a photomask using 172 nm vacuum ultraviolet (VUV) light under the pressure of 10³ Pa. A negative-pattern was prepared using the same VUV light under the reduced pressure of 10 Pa, followed by rinsing with toluene solution. At 10³ Pa, the irradiated PMMA was effectively decomposed and eliminated. On the other hand, at 10 Pa, the irradiated PMMA became cured and resistant to etching. We subsequently utilized these positive- and negative-tone patterns as templates on indium–tin-oxide surfaces to electrodeposit copper microstructures with 10 µm lines and spaces.     

Polybutylacrylate/poly(methyl methacrylate) Core-Shell Elastic Particles as Epoxy Resin Toughener: Part I Design and Preparation

Polybutylacrylate (PBA)/poly(methyl methacrylate) (PMMA) core-shell elastic particles (CSEP), whose rubbery core diameter ranged from 0.08 μm to 1.38μm, were synthesized by using conventional emulsion polymerization, multi-step emulsion polymerization, and soapless polymerization. Allyl methacylate (ALMA) and ethylene glycol dimethacrylate (EGDMA) were selected as crosslinking reagents for core polymerization. Methacrylic acid (MAA) was used as functional co-monomer with methyl methacrylate as shell component. The content of vinyl groups in PBA rubbery core increased with the amount of crosslinking reagents. The core-shell ratio affected great on the morphology of the complex particles. Furthermore, the amounts of carboxyl on the surface of core-shell particles, copolymerized with acrylic acid, were determined by potentiometric titration. Results showed that methylacrylic acid was distributed mostly on the surface of particles.     

Properties of biocomposites from waste seashells and poly(methyl methacrylate)

The paper presents the preparation of biocomposites from waste seashells as reinforcement and poly(methyl methacrylate), abbreviated as PMMA as the matrix. The used seashells belong to the snow‐white Bahamian species of tiger lucine (Codakia orbicularis) from the Island of Coco Cay. Seashells were grinded and homogenized with poly(methyl methacrylate) powder, with the seashell powder content ranging between 2 and 14 wt%, and finally hot pressed. Morphology of prepared composites was analyzed by scanning electron microscopy, and it was determined that the particle distribution was homogenous with no agglomeration. Mechanical properties (microhardness, compressive strength, Young's modulus) of biocomposite materials produced from different amount of waste seashells in poly (methyl methacrylate) were determined and analyzed. The best overall combination of mechanical properties was achieved when 6 wt% of seashell particles below 50 μm size were added to poly (methyl methacrylate).     

Study of d.c. electrical conductivity of paranitroaniline doped (1:1) polyvinylchloride and poly(methyl methacrylate) polyblends

Electrical properties of PVC, PMMA and their 1: 1 polyblends, before and after adding paranitroaniline into them, have been investigated as a function of temperature, electric field and dopant concentration, to study the mechanism of electrical conduction. The current was measured by applying d.c. voltage in the range 25–800 V at various thermostatically controlled temperatures (313–373 K). The results obtained predict the Schottky-Richardson conduction mechanism to be operative and d.c. conductivity of the blend lies intermediate between those of individual components. Further, the conductivity of the blend increases with temperature and applied electric field and also with the increase in concentration of dopant. To identify the mechanism governing the conduction, the activation energies in low temperature (LTR) and high temperature (HTR) regions have been calculated. The dielectric constant of the sample at various temperatures have been calculated which increased with increase in temperature. This is indicative of the diffusion of ions in space charge polarization at higher temperature. The study of XRD and FTIR supports the changes occurring in the conductivity of the blend.     

Nickel (II) ions sensing properties of dimethylglyoxime/poly(caprolactone) electrospun fibers

A novel dimethylglyoxime (DMG)/poly(caprolactone) (PCL) blend was electrospun into fibers to serve as an optical sensor for the nickel detection based on the formation of a red Ni(DMG)₂ complex. DMG was mixed with PCL at 10, 20 and 30% (w/w) in a mixture of N, N-dimethylformamide (DMF) and dichloromethane (DCM) (50/50, v/v) prior electrospunning process. The best fibers were prepared under an electric field of 20 kV and a distance between needle and collector of 20 cm. From scanning electron microscopy (SEM), the average diameter of the fibers remained nearly constant with increasing amount of DMG. The optimum mass ratio of DMG and PCL was found to be 20:80 as it produced fibers with the smallest diameter distribution and the best sensing property. The formation of the Ni(DMG)₂ complex was confirmed by Fourier transform infrared spectroscopy (FT-IR). The colorimetric response of the PCL/DMG electrospun fibers were then tested against the nickel ions over a concentration range of 1-10 ppm using reflectance spectroscopy. Good linearity between the reflectance values at 547 nm and the concentrations was obtained (R² = 0.9925). These proposed DMG and PCL fibers could be used as the naked-eye sensor for nickel in waste water.     

Preparation and Compaction Behaviour of Poly(methyl methacrylate) Coated Iron Microparticles

The poly(methyl methacrylate)(PMMA) coatings onto surface of iron particles were electrochemically prepared and the effect on both surface structure and internal structure of the resulted material after compaction was carried out.The electrochemical polymerization treatment was performed in a fluidized bed electrolyzer using sulphuric acid solution containing potassium persulphate and methyl methacrylate(MMA).The surface topography and the microstructure of the samples were observed by scanning electron mic...     

Si+ and N+ ion implantation for improving blood compatibility of medical poly(methyl methacrylate)

Si⁺ and N⁺ ion implantation into medical poly(methyl methacrylate) (PMMA) were performed at an energy of 80 keV with fluences ranging from 5×10¹² to 5×10¹⁵ ions/cm² at room temperature to improve blood compatibility. The results of the blood contacting measurementsin vitro showed that the anticoagulability and anticalcific behaviour on the surface morphology were enhanced after ion implantation. No appreciable change in the surface morphology was detected by scanning electron microscopy (SEM). X-ray photoelectron spectroscopy (XPS) analysis indicated that ion implantation broke some original chemical bonds on the surface to form some new Si- and N-containing groups. These results were considered responsible for the enhancement in the blood compatibility of PMMA.     

聚甲基丙烯酸甲酯/二氧化硅复合材料的热性能

聚甲基丙烯酸甲酯/二氧化硅(PMMA/Si O_2)复合材料可以通过简便的单体浇铸、本体聚合方法制备,二氧化硅用硅烷偶联剂3-(异丁烯酰氧)丙基三甲氧基硅烷(γ-MPS)进行表面修饰,并用红外光谱表征其甲苯抽提后的组成。当加入量为11.76%时,PMMA/Si O_2复合材料的导热率达到0.23 W/(m·K),比基体PMMA提高了27.78%。用PMMA红外光谱的侧甲基弯曲振动峰(δCH3)与羰基(νC=O)的伸缩振动峰比值可以表示PMMA大分子的偶合终止与歧化终止的比例,随着二氧化硅含量的增加,歧化终止比例升高,从而使PMMA/Si O_2复合材料的热稳定性提高,与热重分析结果一致。     

Dielectric characterization of poly(methyl methacrylate) geometrically confined into mesoporous SiO2 glasses

Characteristics of the dielectric relaxation mechanisms (γ,β,β′,α andρ) in poly(methyl methacrylate) (PMMA) and hybrids of PMMApolymerized into 5 nm SiO₂ pore matrices were studied by means of the thermally stimulated depolarization currents (TSD) technique, applied in the range 10–460 K. Low frequency relaxations (10 μHz–10 mHz) were investigated by measuring the isothermal discharging current, with the loss factorɛ”(f) determined using a new development of the Hamon method. Compared to pure PMMA, the hybrids presented a 14 to 18 degrees reduction of the TSDβ-relaxation maximum (T_β) and a drastic high temperature shift of the prominent syndiotacticα-peak. The average energy barrier for dipole (re)orientation (W) slightly decreases for both theα andβ relaxations. The latter observations, as well as the time evolution of the TSD spectra, are discussed in terms of the variation of the initiator (azobisisobutyronitrile) content and the effects of polymerization in spatial confinements (e.g. reduced monomer-to-polymer conversion at high initiator loadings and interaction effects). The shifts reflect the presence of several antagonistic mechanisms controlling the molecular dynamics of the polymeric phase. The extent of the polymer-SiO₂ hydrogen bonding interaction induces an increase of the energy barrier for the activation of the motions of the carboxymethyl lateral groups (β-process) and parts of the main chain (α-process). On the other hand, the reduction of the chain entanglements (due to the pore-directed propagation of polymerization) loosens several steric hindrances on the rotational motion of the side group, explaining the accompanying decrease of W. Received: 9 October 2000 / Reviewed and accepted: 10 October 2000