Constitutive modeling for characterizing the compressive behavior of PMMA open‐cell foams

A constitutive model for evaluating the compressive behavior of Poly(methyl‐methacrylate) (PMMA) open‐cell foams is herein proposed. Specifically, the study investigates the viscoelastic and viscoplastic behaviors of the PMMA open‐cell foams. The constitutive equation is expressed in terms of the following polymer and foam properties: elastic modulus, relative density, as well as the relaxation and densification constants. PMMA open‐cell foams are manufactured using a gas foaming/particulate leaching method and uniaxial compression tests are performed. The mechanical properties and compressive stress‐strain responses obtained from the experiments are compared with those predicted by the proposed constitutive model. The results suggest that the constitutive model is an apt one for assessing and evaluating the compressive behaviors of PMMA open‐cell foams. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 436–443, 2007     

Synthesis and kinetic analysis of DPE controlled radical polymerization of MMA

The 1,1‐diphenylethene (DPE) controlled radical polymerization of methyl methacrylate was performed at 80 °C by using AIBN as an initiator and DPE as a control agent. It was found that the molecular weight of polymer remained constant with monomer conversion throughout the polymerization regardless of the amounts of DPE and initiator in formulation. To understand the result of constant molecular weight of living polymers in DPE controlled radical polymerization, a living kinetic model was established in this research to evaluate all the rate constants involved in the DPE mechanism. The rate constant k₂, corresponding to the reactivation reaction of the DPE capped dormant chains, was found to be very small at 80 °C (1 × 10^?5 s^?1), that accounted for the result of constant molecular weight of polymers throughout the polymerization, analogous to a traditional free radical polymerization system that polymer chains were terminated by chain transfer. The polydispersity index (PDI) of living polymers was well controlled <1.5. The low PDI of obtained living polymers was due to the fact that the rate of growing chains capped by DPE was comparable with the rate of propagation. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2009     

Wall-jet conductivity detector for microchip capillary electrophoresis

A new end-column ‘hybrid’ contactless conductivity detector for microchip capillary electrophoresis (CE) was developed. It is based on a “hybrid” arrangement where the receiving electrode is insulated by a thin layer of insulator and placed in the bulk solution of the detection reservoir of the chip, whereas the emitting electrode is in contact with the solution eluted from the channel outlet in a wall-jet arrangement. The favorable features of the new detector including the high sensitivity and low noise, can be attributed to both the direct contact of the ‘emitting’ electrode with the analyte solution as well as to the insulation of the detection electrode from the high DC currents in the electrophoretic circuit. Such arrangement provides a 10-fold sensitivity enhancement compared to currently used on-column contactless conductivity CE microchip detector as well as low values of noise and easy operation. The new design of the wall-jet conductivity detector was tested for separation of explosive-related methylammonium, ammonium, and sodium cations. The new detector design reconsiders the wall-jet arrangement for microchip conductivity detection in scope of improved peak symmetry, simplified study of inter-electrode distance, isolation of the electrodes, position of the wall-jet electrode to the separation channel, baseline stability and low limits of detection.     

Influence of cubic α-Fe2O3 particles on the thermal stability of poly(methyl methacrylate) synthesized by in situ bulk polymerization

Poly(methyl methacrylate)/α-Fe₂O₃ composites were prepared by in situ bulk radical polymerization of methyl methacrylate in the presence of the cubic α-Fe₂O₃ particles using 2,2′-azobisisobutyronitrile as initiator. The cubic α-Fe₂O₃ particles were synthesized by forced hydrolysis of FeCl₃ and characterized by X-ray diffraction analysis and transmission electron microscopy. The molar masses and molar mass distribution of synthesized PMMA samples were determined by gel permeation chromatography. The influence of α-Fe₂O₃ filler particles on the thermal properties of the PMMA matrix was investigated using thermogravimetry and differential scanning calorimetry. The molar mass and polydispersity of PMMA extracted from composite samples were not influenced by cubic α-Fe₂O₃ particles. The obtained composites have better thermal and thermooxidative stability than pure PMMA. On the other hand, the values of the glass transition temperature of composite samples were identical to the glass transition temperature of pure PMMA.     

Effect of ZnO and organo-modified montmorillonite on thermal degradation of poly(methyl methacrylate) nanocomposites

Since a few years ago, a topic of interest consists in developing composites filled with nanofillers to improve thermal degradation and flammability property of poly(methyl methacrylate) (PMMA). In the present work, the effects of ZnO nanoparticles and organo-modified montmorillonite (OMMT) on the thermal degradation of PMMA were investigated by thermogravimetric analysis (TGA). PMMA-ZnO and PMMA-OMMT nanocomposites were prepared by melt blending with different (2, 5, and 10 wt%) loadings. SEM and TEM analyses of nanocomposites were performed in order to investigate the dispersion of nanofillers in the matrix. According to TGA results, the addition of ZnO nanoparticles does not affect the thermal degradation of PMMA under an inert atmosphere. However, in an oxidative atmosphere, two contrary effects were observed, a catalytic effect at lower concentration of ZnO in the PMMA matrix and a stabilizing effect when the ZnO concentration is higher (10 wt%). In contrast, the presence of OMMT stabilizes the thermal degradation of PMMA whatever be the atmosphere. Differential thermal analysis (DTA) curves showed surprising results, because a dramatic change of exothermic reaction of the PMMA degradation process to an endothermic reaction was observed only in the case of OMMT. During the degradation of PMMA-ZnO nanocomposites, pyrolysis-gas chromatography coupled to mass spectrometer (Py-GC/MS) showed an increase in the formation of methanol and methacrylic acid while a decrease in the formation of propanoic acid methyl ester occurred. In the case of PMMA-OMMT systems, a very significant reduction in the quantity of all these degradation products of PMMA was observed with increasing OMMT concentration. It is also noted that during PMMA-OMMT degradation less energy was released as the decomposition is an endothermic reaction and the material was cooled.     

Focused ion beam irradiation—morphological and chemical evolution in PMMA

For poly(methyl methacrylate) (PMMA) as a representative of amorphous thermoplastic polymers, the milling effects, and the chemical changes due to ion bombardment with a focused ion beam (FIB) at normal incidence are studied with scanning force microscopy (SFM), scanning electron microscopy (SEM)/energy dispersive X‐ray (EDX), and infrared (IR) spectroscopy for varying conditions of Ga⁺ treatment, including the effect of partial water pressure. Stopping and Range of Ions in Matter (SRIM) simulation results for 30 keV Ga⁺ at normal incidence show that the zone of primary ion–polymer interaction extends ca 100 nm into the PMMA. Accordingly, this interaction region is much wider than the original beam diameter. The width of the region where the recoiled ions interact strongly with the polymer chains is larger. Secondary processes, such as fragment diffusion and phonon transport, are expected to extend even farther into the polymer. SEM and SFM reveal distinct topologies of areas milled without or in presence of water vapour. Water vapour–assisted FIB milling produces more roughness and defects. The infrared attenuated total reflection spectroscopy (IR‐ATR) spectra indicate that ion milling in PMMA damages methacrylate side groups in particular. In contrary to metals, an increase in the degree of milling is found when the beam spot overlap parameter increases. Copyright © 2009 John Wiley & Sons, Ltd.     

Atmospheric‐pressure spin plasma jets processing of polymethylmethacrylate surface using experimental design methodology

Atmospheric‐pressure spin plasma jets (APSPJs) have been developed to induce surface modifications on polymethylmethacrylate (PMMA). In this study, an experimental design methodology was used to investigate the influence of process parameters [such as radio frequency (RF) power, processing gap, and number of treatment cycles] on the characteristics of PMMA surface treated by APSPJs. It was observed from the atomic force microscope (AFM) and scanning electron microscope (SEM) results that the surface morphology of PMMA treated by direct plasma is much rougher than that treated by remote plasma. The direct plasma used in APSPJs processing created a substantial amount of nanostructure grains. Moreover, the measured XPS results showed that the O/C ratios of the PMMA surface were substantially increased and subsequently water contact angle decreased on direct plasma treatment. This decrease is due to an increase of oxygen‐containing functional groups on the PMMA surface by the APSPJs processing. From the statistical analysis, the RF power and the processing gap were found to play a major role in enhancing the hydrophilic properties of PMMA surface. In contrast, the number of treatment cycles played only a secondary role in this case. Finally, in this study the APSPJs processing was demonstrated to be an effective method for surface modification of PMMA by controlling processing parameters during the treatment process. Copyright © 2009 John Wiley & Sons, Ltd.     

A new procalcitonin optical immunosensor for POCT applications

A new immunosensor for the determination of procalcitonin was developed. A sandwich assay format was implemented on a polymethylmetacrylate optical biochip, opportunely shaped in order to obtain several flow channels and potentially suitable for point of care testing applications. The sandwich format makes use of two new rat monoclonal antibodies. The capture antibody was covalently immobilised on the surface of the plastic chip, and the detection antibody was labelled with DY647 dye. Different combinations of capture and detection antibodies were investigated, and particular attention was devoted in order to avoid the non-specific adsorption. A limit of detection of 0.088 mg L⁻¹ was achieved within the working range of 0.28–50 mg L⁻¹ in buffer samples. The assay was also implemented in human serum, and 0.2 and 0.7–25 mg L⁻¹ were the attained limit of detection and working range, respectively.     

Synthesis and biocompatibility of a novel silicone hydrogel containing phosphorylcholine

A novel poly (methyl methacrylate-co-2-methacryloyloxyethyl phosphorylcholine-co-tris(trimethylsiloxy)-3-methacryloxypropylsilane) terpolymer (PMMT) was synthesized and the anti-biofouling properties were studied in order to evaluate the potential of this silicone hydrogel to be used as contact lens material. The chemical structure was characterized by IR, ¹H-NMR and elemental analysis. Poly methyl methacrylate (PMMA) and poly (methyl methacrylate-co-tris (trimethylsiloxy)-3-methacryloxypropylsilane) (PMT) were also synthesized to compare with PMMT. Protein adsorption measurement showed that for PMMT-2 membrane (MPC: 16.6 mol%), the amount of adsorbed proteins was decreased by 75.3% and 76.8% compared with PMMA and PMT membranes, respectively. SEM pictures showed clearly that PMMT films suppressed the adhesion of platelets. Water structure in polymers was determined by differential scanning calorimetry, and PMMT-2 possessed more freezing water content than PMMT-1 (MPC: 14.5 mol%). The equilibrium water content of PMMT-2 membrane reached 55%, which might offer comfortable wear feeling, and the introduction of MPC increased the wettability of the polymer surface dramatically. Both the terpolymers PMMT-1 and PMMT-2 exhibited high transparency (relatively constant at approximately 96%) in the visible light wave range. Moreover, oxygen transmissibility (Dk/t) of the terpolymers met the requirement for a lens to be worn safely overnight. It could be concluded that the novel silicone hydrogel containing MPC unit was an effective candidate material for making biomaterials, particularly for contact lenses.