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The separation of oil from water and filtration of aqueous solutions and dispersions are critical issues in the processing of waste and contaminated water treatment. Membrane-based technology has been proven as an effective method for the separation of oil from water. In this research, novel vertical nanopores membrane, via oriented cylindrical block copolymer (BCP) films, suitable for oil/water filtration has been designed, fabricated and tested. We used a ?100 nm thick model poly(styrene-block-methymethacrylate) (PS-b-PMMA) BCP as the active top nanofiltration layer, processed using a roll-to-roll (R2R) method of cold zone annealing (CZA) to obtain vertical orientation, followed by ultraviolet (UV) irradiation selective etch of PMMA cylinders to form vertically oriented nanopores as a novel feature compared to meandering nanopores in other reported BCP systems. The cylindrical nanochannels are hydrophilic, and have a uniform pore size (?23 nm), a narrow pore size distribution and a high nanopore density (?420 per sq. micron). The bottom supporting layer is a conventional microporous polyethersulfone (PES) membrane. The created asymmetric membrane is demonstrated to be effective for oil/water extraction with a modestly high throughput rate comparable to other RO/NF membranes. The molecular weight dependent filtration of a water soluble polymer, PEO, demonstrates the broader applications of such membranes. This publication is made possible by NPRP grant 10-0127-170269 from the Qatar National Research Fund (a member of Qatar Foundation). A. K. would like to acknowledge the funding support supported by the National Science Foundation (NSF) via Grant DMR-1905996. The statements made herein are solely the responsibility of the authors. Scopus

Defect-assisted nonlinear absorption (NLA) and optical limiting (OL) performance of hexagonal boron nitride nanosheets (h-BNNS) in aqueous suspension and in polymethyl methacrylate matrix (PMMA) as nanocomposite films were studied using open-aperture Z-scan method. To evaluate the transmission in open-aperture Z-scan data, a theoretical model accounting one photon absorption (OPA), two photon absorption (TPA), free carrier absorption (FCA) and saturation of each process was considered. Defect-assisted NLA coefficients and saturation intensity thresholds were extracted from the fitting of the experimental results for 532 and 1064 nm pulse wavelengths. Strong defect-assisted NLA response of h-BNNS was observed while NLA at 532 nm was considerably stronger. This is attributed to the excitation of a greater number of defect states over a wider energy range. Our findings showed that h-BNNS/PMMA nanocomposite films feature highly required properties in OL applications and can function in OL applications in a wide spectral range (?200–1064 nm). © 2021 Elsevier B.V.

Glacial forefields host young, poorly developed soils with highly unstable environmental conditions. Root system contribution to soil stabilization is a well-known phenomenon. Identifying the functional traits and root morphology of pioneer vegetation that establish on forefields can provide information useful in the practical application of plants in land restoration of high altitude mountain sites.This study aims to gather information on the root morphology and biomechanical characteristics of the 10 most dominant pioneer plant species of the forefield of Lys Glacier (NW Italian Alps).X-ray Computed Tomography (X-ray CT) was used to visualize and quantify non-destructively the root architecture of the studied species. Samples were cored directly from the forefield. Data on root traits such as total root length, rooting depth, root diameter, root length density and number of roots in relation to diameter classes as well as plant height were determined and compared between species. Roots were also tested for their tensile strength resistance.X-ray CT technology allowed us to visualize the 3D root architecture of species intact in their natural soil system. X-ray CT technology provided a visual representation of root-soil interface and information on the exact position, orientation and elongation of the root system in the soil core. Root architecture showed high variability among the studied species. For all species the majority of roots consisted of roots smaller than 0.5. mm in diameter. There were also considerable differences found in root diameter and total root length although these were not statistically significant. However, significant differences were found in rooting depth, root length density, plant height and root tensile strength between species and life forms (dwarf shrub, forb, graminoid). In all cases, root tensile strength decreased with increasing root diameter. The highest tensile strength was recorded for graminoids such as Luzula spicata (L.) DC. and Poa laxa Haenke and the lowest for Epilobium fleischeri Hochst.The differences in root properties among the studied species highlight the diverse adaptive and survival strategies plants employ to establish on and thrive in the harsh and unstable soil conditions of a glacier forefield. The data determined in this study could provide a significant contribution to a database that allow those who are working in land restoration and preservation of high altitude mountain sites to employ native species in a more efficient, effective and informed manner.

A serial of tests were carried out to evaluate the effect of specimen mass on the test results for PMMA conducted in a micro-scale combustion calorimeter. Seven heating rates were used to test specimens of mass ranging from 0.5 to 6.0 mg with nominal interval of 0.5 mg. Eighty-five specimens were tested. Heat release rate, onset temperature, temperature at maximum heat release rate, total heat release, and heat release capacity were determined. The influence of specimen mass at each heating rate was analyzed. Specimen mass influences the maximum heat release rate, onset temperature, and temperature at maximum heat release rate significantly. The higher the heating rate, the greater the influence. Reliable results could be obtained as long as the specimen mass is more than 1 mg with oxygen concentration above 5 %; thus, the oxygen concentration limit might be extended from 10 to 5 %.

We report the synthesis of a well-defined molecular bottlebrush polymer with stereoregular side chains (i.e., syndiotactic PMMA). The simultaneous control over the molecular weight, side-chain tacticity, and architecture allows the macromolecule to stereocomplex with the complementary linear stereoregular polymers (i.e., isotactic PMMAs) in controlled manners. By modulating the feed ratio of the complexing materials and chain length of the linear assembling component, a variety of crystalline materials with different sizes and morphologies, including discrete spherical nanoparticle, multiple-particle assembly, and cross-linked network structure, can be produced. Among these, uniformed sized, stable nanocrystals that exhibit temperature-induced solution assembly and disassembly properties can be derived from a combined process of PMMA triple-helix stereocomplex formation and polymer architecture-directed intramolecular crystallization. This work has established a new, facile synthetic protocol toward stimuli-responsive organic nanocrystals, which is applicable to the fabrication of a wide variety of functional crystal nanomaterials with practical applications. Refereed/Peer-reviewed

A mixed-effects statistical model has been developed to understand the nanoparticle (NP)-cell interactions and predict the rate of cellular uptake of NPs. NP-cell interactions are crucial for targeted drug delivery systems, cell-level diagnosis, and cancer treatment. The cellular uptake of NPs depends on the size, charge, chemical structure, and concentration of NPs, and the incubation time. The vast number of combinations of these variable values disallows a comprehensive experimental study of NP-cell interactions. A mathematical model can, however, generalize the findings from a limited number of carefully designed experiments and can be used for the simulation of NP uptake rates, to design, plan, and compare alternative treatment options. We propose a mathematical model based on the data obtained from in vitro interactions of NP-healthy cells, through experiments conducted at the Nanomedicine and Advanced Technologies Research Center in Turkey. The proposed model predicts the cellular uptake rate of silica, polymethyl methacrylate, and polylactic acid NPs, given the incubation time, size, charge and concentration of NPs. This study implements the mixed-model methodology in the field of nanomedicine for the first time, and is the first mathematical model that predicts the rate of cellular uptake of NPs based on sound statistical principles. Our model provides a cost-effective tool for researchers developing targeted drug delivery systems.

The chirality of nanoparticles (NPs) and their assemblies has been investigated predominantly for noble metals and II-VI semiconductors. However, ceramic NPs represent the majority of nanoscale materials in nature. The robustness and other innate properties of ceramics offer technological opportunities in catalysis, biomedical sciences, and optics. Here we report the preparation of chiral ceramic NPs, as represented by tungsten oxide hydrate, WO3-x·H2O, dispersed in ethanol. The chirality of the metal oxide core, with an average size of ca. 1.6 nm, is imparted by proline (Pro) and aspartic acid (Asp) ligands via bio-to-nano chirality transfer. The amino acids are attached to the NP surface through C-O-W linkages formed from dissociated carboxyl groups and through amino groups weakly coordinated to the NP surface. Surprisingly, the dominant circular dichroism bands for NPs coated by Pro and Asp are different despite the similarity in the geometry of the NPs; they are positioned at 400-700 nm and 500-1100 nm for Pro- and Asp-modified NPs, respectively. The differences in the spectral positions of the main chiroptical band for the two types of NPs are associated with the molecular binding of the two amino acids to the NP surface; Asp has one additional C-O-W linkage compared to Pro, resulting in stronger distortion of the inorganic crystal lattice and greater intensity of CD bands associated with the chirality of the inorganic core. The chirality of WO3-x·H2O atomic structure is confirmed by atomistic molecular dynamics simulations. The proximity of the amino acids to the mineral surface is associated with the catalytic abilities of WO3-x·H2O NPs. We found that NPs facilitate formation of peptide bonds, leading to Asp-Asp and Asp-Pro dipeptides. The chiroptical activity, chemical reactivity, and biocompatibility of tungsten oxide create a unique combination of properties relevant to chiral optics, chemical technologies, and biomedicine.

With the growing use of X-ray computed tomography (X-ray CT) datasets for modelling of transport properties, comes the need to define the representative elementary volume (REV) if considering three dimensions or the representative elementary area (REA) if considering two dimensions. The resolution used for imaging must be suited to the features of interest in the sample and the region-of-interest must be sufficiently large to capture key information. Polymer electrolyte fuel cells have a hierarchical structure, with materials spanning multiple length scales. The work presented here examines the nature of the REA throughout a 25 cm2 membrane electrode assembly (MEA), focusing specifically on the micron length scale. Studies were carried out to investigate key structural (volume fraction, layer and penetration thickness, pore diameters) and transport (effective diffusivity) properties. Furthermore, the limiting current density of the nine regions was modelled. Stochastic heterogeneity throughout the sample results in local variations throughout. Finally, effects of resolution were probed by imaging using a range of optical magnifications (4× and 20×). The correlated and competing effects of voxel resolution and sampling size were found to cause difficulties where loss of clarity in the boundaries between phases occurs with larger imaging volumes. Jennifer Hack acknowledges a studentship from the EPSRC Centre for Doctoral Training in Advanced Characterisation of Materials (EP/LO15277/1) and the hydrogen and fuel cell research in the Electrochemical Innovation Lab (EIL) is supported through EPSRC projects (EP/M014371/1, EP/S018204/2, EP/R023581/1, EP/P009050/1, EP/L015749/1, EP/M009394/1, EP/M023508/1). Paul R. Shearing acknowledges funding from the Royal Academy of Engineering (CiET1718/59). Pablo A. García-Salaberri thanks the support from the STFC Early Career Award (ST/R006873/1) during his stay at the EIL.

Display Omitted Study of a new electron beam resist, SML.Contrast is as high as PMMA.Dense grating with linewidth from ~5 to 8nm demonstrated in SML and ZEP.Etch resistance equivalent to ZEP resist. We present study on a novel, positive-tone electron beam lithography (EBL) resist known as SLM and compare its lithographic performance to well-established positive resists such as 950K polymethyl methacrylate (PMMA) and ZEP 520A. SML has been fabricated to have processing parameters similar to PMMA, but with enhanced functionality. Processing parameters such as film deposition, baking temperatures as well as the developers used for PMMA work well with SML resist.Contrast curve measurements were generated for different thicknesses of SLM and exposure voltages. Two temperature variants were employed for developing the resist with 7:3 IPA:water co-solvent developer, viz. room temperature and 0?C. To verify the resolution of SML resist, dense gratings of single pixel lines were compared to those fabricated using 950K PMMA and ZEP 520A resists. Fundamental pattern transfer skills of metal lift-off and dry etching were compared with ZEP. Metal lift-off was carried out using 5-10nm thick chromium metal and Microposit 1165 resist remover. The resilience of the SML resist to dry etching (ICP etching system with SF6 and C4F8 gas mixture) was compared to ZEP and PMMA resists and then dense gratings on ZEP and SML were etched into Si.The data obtained from the contrast curves show high contrast of the new resist. From the grating results, SML demonstrates very high resolution like ZEP and PMMA. The pattern transfer abilities of SML are also similar and in some aspects even outdo that of ZEP resist.

High-molecular-weight (MW) symmetrical multiblock copolymers, based on the hydrophobic monomers styrene (Sty) and methyl methacrylate (MMA), and the more polar monomer, 2-vinyl pyridine (2VPy), were prepared using stepwise reversible addition-fragmentation chain transfer polymerization. All copolymers shared a common poly(ethylene glycol) (PEG) midblock, introduced as a bifunctional macromolecular chain transfer agent. In total, five ABA triblock copolymers, five ABCBA pentablock terpolymers, and two ABCDCBA heptablock quaterpolymers (comprising four different monomer types) were synthesized. The MWs of the multiblock polymers were determined using gel permeation chromatography (GPC) and proton nuclear magnetic resonance (1H NMR) spectroscopy, with the latter values being closer to the theoretically expected, whereas GPC MW distributions were relatively narrow, broadening with the number of blocks. The compositions of the synthesized polymers, as determined by 1H NMR spectroscopy, were also close to the expected values. Finally, films cast from chloroform solutions of the pentablock terpolymers P2VPy-b-PSty-b-PEG-b-PSty-b-P2VPy, PSty-b-PMMA-b-PEG-b-PMMA-b-PSty, and P2VPy-b-PMMA-b-PEG-b-PMMA-b-P2VPy examined using transmission electron microscopy exhibited PSty and PMMA cylinders (first two) and lamellae (third terpolymer). © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 4957–4965

Sessile marine creatures are known for their adhesion on diverse range of materials from naturally occurring rocks to synthetic material surfaces. The current work compares morphological variation in the adhesion of barnacles (Amphibalanus reticulatus) on a natural patterned surface such as the shells of a green mussel (Perna viridis) and a synthetic polymeric surface such as polymethylmethacrylate. The elemental analysis in conjunction with characterization of the protein in both these cements brings out the biochemical differences as a function of the attached substrate. � 2012 Elsevier Ltd. All rights reserved.

The magnetic-poly(divinylbenzene-4-vinylpyridine) [m-poly(DVB-4VP)] microbeads (average diameter: 180–212 μm) were synthesized by copolymerizing of divinylbenzene (DVB) with 4-vinylpyridine (4VP) and by mixing this copolymer with Fe 3 O 4 nanoparticles. The resultant material was characterized by N 2 adsorption/desorption, ESR, elemental analysis, scanning electron microscope (SEM) and swelling studies. After functionalized with sulfonic acid, m-poly(DVB-4VP-SO 3 H) was characterized by FT-IR and TGA analysis. The results showed that both of Fe 3 O 4 and –SO 3 H are bonded to the polymer successfully. N 2 adsorption/desorption isotherms of synthesized samples had the hysteresis behaviour associated with mesoporous materials (pore diameter: 3.73 nm). Sulfonic acid functionalized mesoporous m-poly(DVB-4VP-SO 3 H) has been demonstrated to have higher reactivity than commercially available solid acid catalysts for the conversion of propionic acid to methyl ester. The apparent activation energy was found to be 38.5 kJ mol −1 for m-poly(DVB-4VP-20%SO 3 H). The catalyst showed negligible loss of activity after four repetitive cycles.

Polystyrene, poly(methylacrylate) and poly(methyl methacrylate) four and three-arm stars were synthesized by Reversible Addition Fragmentation chain-Transfer (RAFT) polymerization by using two new dithioester-derived chain transfer agents [CTA or R-S-(C = S)Z]), CTA-1 and CTA-2. CTA-1 is a four arm CTA while CTA-2 is a three-arm CTA. These were easily synthesized from commercially available reagents and were characterized by spectroscopic techniques such as 1H-NMR, 13C-NMR, IR and mass spectrometry. It is demonstrated that the two new CTAs enable the growth of arms away from the core (i.e., core first approach). An attempt has been made to study the effect of the structure of the R-group, which is present as the core in the CTA, on the polymerization, by analyzing the detailed kinetics. This study suggests that CTA-2, with a benzylic R group, enables the controlled star polymerization of styrene while CTA-1, with a R group similar in structure to the propagating radical derived from the polymerization of methyl acrylate (MA), enables the controlled polymerization of MA although to a lesser extent. This study also reveals that the temperature of free radical initiated RAFT (star) polymerization should be chosen in such a way that it is a compromise between reasonable rate of homolysis of the initiator and the CTA (R-group). � Taylor & Francis Group, LLC.

Micro-optical sensors based on optical waveguides are widely used to measure temperature, force and strain but also to detect biological and chemical substances such as explosives or toxins. While optical micro-sensors based on silicon technology require complex and expensive process technologies, a new generation of sensors based completely on polymers offer advantages especially in terms of low-cost and fast production techniques. We have developed a process to integrate micro-optical components such as embedded waveguides and optical interconnects into polymer foils with a thickness well below one millimeter. To enable high throughput production, we employ hot embossing technology, which is capable of reel-to-reel fabrication with a surface roughness in the optical range. For the waveguide fabrication, we used the thermoplastic polymethylmethacrylate (PMMA) as cladding and several optical adhesives as core materials. The waveguides are characterized with respect to refractive indices and propagation losses. We achieved propagation losses are as low as 0.3 dB/cm. Furthermore, we demonstrate coupling structures and their fabrication especially suited to integrate various light sources such as vertical-cavity surface-emitting lasers (VCSEL) and organic light emitting diodes (OLED) into thin polymer foils. Also, we present a concept of an all-polymer and waveguide based deformation sensor based on intensity modulation, which can be fabricated by utilizing our process. For future application, we aim at a low-cost and high-throughput reel-to-reel production process enabling the fabrication of large sensor arrays or disposable single-use sensing structures, which will open optical sensing to a large variety of application fields ranging from medical diagnosis to automotive sensing. © 2016 SPIE. DFG/CRC/PlanOS

Large scale, planar optronic systems allowing spatially distributed functionalities can be well used in diverse sensor networks, such as for monitoring the environment by measuring various physical quantities in medicine or aeronautics. In these systems, mechanically flexible and optically transparent polymeric foils, e.g. polymethyl methacrylate (PMMA) and polyethylene terephthalate (PET), are employed as carrier materials. A benefit of using these materials is their low cost. The optical interconnections from light sources to light transmission structures in planar optronic systems occupy a pivotal position for the sensing functions. As light sources, we employ the optoelectronic components, such as edgeemitting laser diodes, in form of bare chips, since their extremely small structures facilitate a high integration compactness and ensure sufficient system flexibility. Flexographically printed polymer optical waveguides are deployed as light guiding structures for short-distance communication in planar optronic systems. Printing processes are utilized for this generation of waveguides to achieve a cost-efficient large scale and high-throughput production. In order to attain a high-functional optronic system for sensing applications, one of the most essential prerequisites is the high coupling efficiency between the light sources and the waveguides. Therefore, in this work, we focus on the multimode polymer waveguide with a parabolic cross-section and investigate its optical coupling with the bare laser diode. We establish the geometrical model of the alignment based on the previous works on the optodic bonding of bare laser diodes and the fabrication process of polymer waveguides with consideration of various parameters, such as the beam profile of the laser diode, the employed polymer properties of the waveguides as well as the carrier substrates etc. Accordingly, the optical coupling of the bare laser diodes and the polymer waveguides was simulated. Additionally, we demonstrate optical links by adopting the aforementioned processes used for defining the simulation. We verify the feasibility of the developed processes for planar optronic systems by using an active alignment and conduct discussions for further improvements of optical alignment. © 2016 SPIE. DFG/CRC/TR 123

The issue of plastic pollution in the marine environment is of increasing global concern. As plastics typically have an intrinsic durability, water insolubility and slow degradation rates, debris has now become both ubiquitous and persistent in the marine environment. Overtime, plastic ultimately result in the generation of microplastics via photolytic, thermal and biological degradation processes. Although the potential threat of microplastics on marine ecosystems is well recognized, there is no baseline data available for the Arabian Gulf. The Environmental Science Center of Qatar University has now documented the first evidence for the prevalence of microplastics within the Arabian Gulf, specifically in the marine waters of Qatar Exclusive Economic Zone (EEZ). Qatar has an arid climate and is situated midway along the western coast of the semi-enclosed Arabian Gulf. Qatar's coastline is particularly susceptible to marine debris due to the county's rapid urbanization and economic development. Surface seawater samples were collected from 12 stations during May 2015 research cruise of the RV Janan. An optimized and validated protocol was developed for the extraction of microplastics from plankton-rich samples without loss of microplastics present. Plankton present in seawater samples may readily mask the identification of microplastics and lead to an underestimation of the quantity of microplastics present. The protocol involved sample digestion using solutions of 1M NaOH, 10M NaOH, and 16M HNO3 in conjunction at different temperatures. Twenty mL of each solution was spiked with known quantities of reference polymer pellets, of varying diameters (63 μm to 4.70 mm) and used to digest the plankton biomass. The use of 1M NaOH proved to be a more efficient digestion treatment than 10M NaOH and 16M HNO3 solutions. Although 10M NaOH, and 16M HNO3 have been proven effective to mineralize plankton biomass, these solutions also resulted in some structural damage and discoloration of reference polymers with a low pH tolerance: polyvinyl alcohol, polyvinyl chloride, polystyrene, polyethylene, and nylon. After extraction, the microplastics were characterized using Attenuated Total Reflectance-Fourier Transform Infrared (ATR-FTIR) spectroscopy. In total 30 microplastics were isolated from the mineralized samples, with an average concentration of 0.71 particles m− 3 (range 0–3 particles m− 3). Nine out of 30 were identified as polypropylene, with the majority either granular, sizes ranging from 125 μm to 1.82 mm, or fibrous, sizes from 150 μm to 15.98 mm. Microplastics were more prevalent in areas where nearby anthropogenic activities, including oil-rig installations and shipping operations, are present.

Polystyrene / polymethyl methacrylate (PS-PMMA) thin films were analyzed for detecting phase separation as well as probing their electrical responses by XPS. It was also shown that electrical parameters like resistance or capacitance can also be extracted using dynamical XPS measurements. A Kratos ES300 electron spectrometer was used for XPS measurements, and a nearby filament provided low-energy electrons for charge neutralization. The results show that under a positive stress, low-energy electrons are attracted to the sample and yield less positive charge on the sample, due to partial neutralization.

Composites of poly(methyl methacrylate) and various nanoscale inorganic particles (zinc oxide, titanium dioxide, zirconium dioxide, silicon dioxide, and aluminum nitride) were prepared by in-situ bulk polymerization using 2,2′-azobis(isobutyronitrile) as initiator. The particles of ZnO, TiO 2, and ZrO2 were surface-modified by alkylphosphonic acids to render them dispersible in the monomer. The effect of these nanoparticles on the free radical polymerization was investigated. Regardless of chemical nature and size, the particles suppress the autoacceleration which would otherwise occur in the bulk free-radical polymerization of methyl methacrylate (MMA). A degenerative chain transfer is proposed to take place between surface-adsorbed water on the particles and propagating chain radicals. This reaction competes with normal termination. Formation of vinylidene chains ends originating from disproportionation is suppressed. In consequence, thermal stability of PMMA produced in the presence of particles is improved. Aggregation of individual particles upon polymerization has been observed and presumably is due to interparticle depletion attraction, even though the particles are individually dispersed in the monomer. Formation of particle clusters is suppressed when a difunctional monomer (e.g., ethylene glycol dimethacrylate) is used as comonomer. The cross-linked medium slows down the diffusion of the particles and therefore interferes with particle aggregation via a depletion mechanism.

A series of amphiphilic conetworks of methacrylic acid (MAA) and methyl methacrylate (MMA) were synthesized using group transfer polymerization (GTP). The MAA units were introduced via the polymerization of tetrahydropyranyl methacrylate (THPMA), followed by the removal of the protecting tetrahydropyranyl group by acid hydrolysis after network formation. 1,4-Bis(methoxytrimethylsiloxymethylene)-cyclohexane (MTSCH) was used as a bifunctional GTP initiator, while ethylene glycol dimethacrylate (EGDMA) served as the cross-linker. Nine of the conetworks were model conetworks, comprising copolymer chains between the cross-links of precise molecular weight and composition. Eight of the model conetworks were based on ABA triblock copolymers, while the ninth was based on a statistical copolymer. The tenth conetwork was not model but randomly cross-linked. The molecular weight and the composition of the linear conetwork precursors were analyzed by gel permeation chromatography and 1H NMR, respectively, and were found to bear values close to the theoretically expected. FTIR spectroscopic analyses indicated complete polymerization of the EGDMA cross-linker vinyl units and complete hydrolysis of the THPMA units. The degrees of swelling (DS) of all the conetworks were measured in water and in THF as a function of the degree of ionization (DI) of the MAA units. The DSs in water increased with the DI of the MAA units (and the pH), while the DSs in THF presented the opposite trend. Finally, small-angle neutron scattering and atomic force microscopy confirmed nanophase separation in a triblock copolymer-based model conetwork and lack of it in its statistical copolymer counterpart. © 2007 American Chemical Society. 40 6 2192 2200 Cited By :67

Locate full-text(opens in a new window)|Full Text(opens in a new window)|View at Publisher| Export | Download | Add to List | More... Macromolecules Volume 40, Issue 4, 20 February 2007, Pages 1089-1100 Optical properties of composites of PMMA and surface-modified zincite nanoparticles (Article) Demir, M.M.a, Koynov, K.a, Akbey, Ü.a, Bubeck, C.a, Park, I.ab, Lieberwirth, I.a, Wegner, G.a a Max Planck Institute for Polymer Research, Ackermannweg 10, D-55128 Mainz, Germany b Seoul National University, School of Chemistry, Korea, South Korea View references (65) Abstract Composites that show visible light transmittance, UV absorption, and moderately high refractive index, based on poly(methyl methacrylate) (PMMA) and zinc oxide (zincite, ZnO) nanoparticles, were prepared in two steps. First, surface-modified ZnO nanoparticles with 22 nm average diameter were nucleated by controlled precipitation via acid-catalyzed esterification of zinc acetate dihydrate with pentan-1-ol. The surface of growing crystalline particles was modified with tert-butylphosphonic acid (tBuPO3H2) in situ by monolayer coverage. Particle size and graft density of -PO3H 2 on the particle surface were controlled by the amount of surfactant applied to the reaction solution. Second, the surface-modified particles were incorporated into PMMA by in-situ bulk polymerization. Free radical polymerization was carried out in the presence of these particles using AIBN as initiator. Volume fraction (0) of the particles was varied from 0.10 to 7.76% (0.5 to 30 wt %). Although the particles are homogeneously dispersed in monomer, segregation of the individual particles upon polymerization was observed. Optical constants of the films ca. 2.0 μm including absorption and scattering efficiencies, indices of refraction, and dispersion constants were determined. The absorption coefficient at 350 nm increases linearly with ZnO, obeying Beer's law at low particle contents. However, it levels off toward a value of about 5000 cm-1 and shows a negative deviation at high concentrations because of aggregation of the individual particles. Waveguide propagation loss coefficients of the composite films were examined by prism coupling. A steep increase of the loss coefficient was found with a slope of 52 dB cm-1 vol %-1 as the volume fraction of the particle increases. The refractive index of the composites depends linearly on volume fraction of ZnO and varies from 1.487 to 1.507 (φ = 7.76%) at 633 nm. The dispersion of refractive index was found to be consistent with Cauchy's formula.

A fast transient fluorescence technique was used to study latex film formation induced by organic solvent vapor. Mixtures of pyrene (P)- and naphthalene (N)-labeled and/or pure naphthalene-labeled latex films were prepared separately from poly(methyl methacrylate) (PMMA) particles. Then these pure and mixed latex films were exposed to vapor of various chloroform-heptane mixtures in seven different experiments. In both films, fluorescence lifetimes from N were monitored during vapor-induced film formation. It was observed that N lifetimes decreased as the vapor exposure time is increased. A Stern-Volmer kinetic analysis was used for low quenching efficiencies to interpret the decrease in N lifetimes. A Prager-Tirrell model was employed to obtain back-and-forth frequencies, v, of reptating PMMA chains during latex film formation induced by solvent vapor. In both pure and mixed latex films, v values were found to be correlated with the chloroform content in the vapor mixture. It was observed that polymer interdiffusion obeyed a t(1/2) law during film formation. Publisher's Version Q1 WOS:000232815500012 PubMed ID: 16009372

The multiarm star-shaped ABC triblock terpolymers of the (ABC)n type and their linear counterparts were synthesized by group transfer polymerization (GTP). The linear and star ABC triblock and statistical terpolymers as well as their homopolymer, diblock and triblock terpolymer precursors were characterized by gas permeation chromatography (GPC) in terms of their molecular weight distributions (MWD). The synthesis was performed using sequential GTP of three monomers and the cross-linker. The synthetic procedure for the preparation of the ABC star terpolymer with structure DMAEMA10-b-HEGMA10-b-MMA10-star was presented. The star terpolymers were soluble in water, exhibiting cloud points from 55 to 77°C. 38 3 1021 1024 Cited By :14

This work reports a steady state fluorescence (SSF) technique for studying film formation from mixture of Al2O3 and polystyrene (PS) latex particles. The composite films were prepared from dispersion of pyrene (P)-labeled PS particles in Al2O3 solution at room temperature and annealed at elevated temperatures in 10-min time interval above glass transition (Tg) temperature of polystyrene. Nine different composites film were studied in various latex contents. Fluorescence intensities (IP) from P were measured after each annealing step to monitor the stages of film formation. No variations in IP were detected for the films prepared with higher than 33 wt% Al2O3 content. However films prepared below 33 wt% Al2O3 content show considerable increase in IP above the certain onset temperature called minimum film forming temperature, T0. Healing temperatures Th, were determined from the maxima of IP. Void closure and interdiffusion stages were modeled and related activation energies were determined and found to be 20 and 97 kJ.mol–1, respectively. POLYM. COMPOS., 26:352–360, 2005. © 2005 Society of Plastics Engineers

The two-dimensional flow field in the vicinity of the interface between laminae of a solid oxidizer and solid fuel under steady-state conditions is solved for empirical inputs, taking into account the nonplanarity of the burning surfaces of the two laminae. The experimentally observed nonplanar burning surface under steady-state conditions is used to prescribe the upstream boundary conditions to the gas phase domain. The regression rate of the burning surface along the laminar interface, determined experimentally, is also used as an input. This decouples the condensed phase energy balance from the gas phase fluid dynamics, and assigns the distribution of surface temperature along the burning surface. The equation for two-dimensional energy conservation in the condensed phase is also solved, with the heat flux balance giving a boundary condition across the burning surface. A distribution of heat release rate is assumed in the gas phase, and the gas phase energy equation is solved iteratively with a convergence criterion set by the interfacial heat flux balance across the burning surface. This obviates the need for a knowledge of the chemical kinetic details of the gas phase flame. The goal is to determine a realistic distribution of heat release rate which satisfies the burning surface profile and its regression rate, measured for a laminar system of ammonium perchlorate and polymethyl methacrylate at pressures below the self-deflagration limit of the former. The results indicate lateral heat conduction in the condensed phase from the oxidizer lamina to the fuel lamina. The computed distribution of heat release rate in the gas phase indicates the need to include heat release near the surface, as well as farther downstream at typical stand-off distances for the flame. ? 2003 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

In the field of modern information technology, optoelectronics are being widely used, and play an increasingly important role. Meanwhile, the demand for more flexible circuit carriers is rapidly growing, since flexibility facilitates the realization of diverse functions and applications. As a potential candidate, transparent polymer substrates with a thickness of about a hundred micrometers by virtue of their low cost and sufficient flexibility are getting more attention. Thus, accomplishing an integration of optoelectronic components into polymer based flexible circuit systems increasingly is becoming an attractive research topic, which is of great significance for future information transmission and processing. We are committed to developing a new microchip bonding process to realize it. Taking into account the fact that most economical transparent polymer substrates can only be processed with restricted thermal loading, we designed a so-called optode instead of a widely adopted thermode. We employ UV-curing adhesives as bonding materials; accordingly, the optode is equipped with a UV irradiation source. An investigation of commercial optoelectronic components is conducted, in which their dimensions and structures are studied. While selecting appropriate transparent polymer substrates, we take their characteristics such as UV transmission degree, glass transition temperature, etc. as key criterions, and choose polyethylene terephthalate (PET) and polymethyl methacrylate (PMMA) as carrier materials. Besides bonding achieved through the use of adhesives cured by the optode, underfill is accordingly employed to enhance the reliability of the integration. We deposit electrical interconnects onto the polymeric substrate to be able to bring the optoelectronic components into electrical operation. In order to enlarge the optical coupling zone from component to substrate within the proximity of the adhesive or underfill, we employ transparent interconnects made of indium-tin-oxide. We present the results of the performance tests, including the contact resistances, mechanical tests and environmental tests. © 2015 SPIE. DFG/CRC/TR 123

cited By 0; International audience; The viscoelastic behavior of poly(methyl methacrylate) (PMMA) homopolymer and poly(methyl methacrylate-co-methyl acrylate) random copolymers was characterized by dynamic mechanical analysis and nanoindentation. Differential scanning calorimetric results showed only one glass transition, indicating the random distribution of comonomers in the copolymers. The a relaxation temperature (Tα) and activation energy (Hα) decreased with increasing content of methyl acrylate monomers (CMA%). The β relaxation temperature (Tβ) also decreased whereas the activation energy (Hβ) showed only small variations compared with Hα. Moreover, the indention displacement and creep compliance strongly depended on CMA%. Two creep stages were found in the creep compliance curves. Copyright © Taylor and Francis Group, LLC.

Electrospun microfibrous membranes comprised of poly(methyl methacrylate)-poly((2-diethylamino)ethyl methacrylate) random copolymers (PMMA-co-PDEAEMA) of various chemical compositions blended together with a commercially available PMMA have been fabricated with diameters between 4.0-6.4 μm and further evaluated as adsorbents for bacteria removal from aqueous media. The morphology and thermal stability of the membranes were determined by scanning electron microscopy (SEM) and thermal gravimetric analysis (TGA), respectively. Tensile tests were also performed in order to investigate their mechanical properties. Membrane evaluation as adsorbents against two Gram-negative bacteria namely Pseudomonas aeruginosa and Advenella species revealed that the membranes containing the highest percentage of the cationic moieties (DEAEMA) exhibited the highest adsorption efficiency. The bacteria removal by the microfibrous membranes was studied by UV-vis spectrophotometry upon measuring the optical density (OD) of the microorganisms. The highest recorded bacteria removal percentages after 8 h were approximately 70% and 45%, for the Pseudomonas aeruginosa and Advenella species respectively, whereas in both cases complete (100%) bacteria removal was observed after 24 h of membrane immersion in bacteria-containing aqueous solutions. The experimental adsorption isotherms for P. aeruginosa and Advenella sp. were well-fitted with the Langmuir isotherm model indicating a monolayer adsorption process. SEM was also used to confirm the adhesion of the bacteria onto the electrospun microfibers. Most importantly, these materials exhibited great performance for the removal of microorganisms from urban wastewater as determined via the standard plating technique prepared by agar. © The Royal Society of Chemistry. 5 83 67617 67629 Cited By :3

Polymethyl methacrylate-based bone cements are used worldwide by the orthopaedic surgeons to secure joint implants with the skeleton. However, the clinical use of this cement is accompanied by complications such as exothermic heat produced during the polymerization reaction, lack of bone bonding ability and shrinkage to name a few. In the present work, the effect of incorporation of calcium-deficient hydroxyapatite nanoparticles on the properties of a commercially available orthopaedic bone cement matrix has been investigated. Initial and final setting time of the cement has been found to decrease with calcium-deficient hydroxyapatite nanoparticles addition. The exothermic heat dissipation during the polymerization has been found to significantly decrease with the calcium-deficient hydroxyapatite nanoparticle incorporation in the bone cement. Contact angle study revealed that with the increasing percentage of calcium-deficient hydroxyapatite nanoparticle, the composite cement becomes more hydrophilic. In vitro biomineralization study confirmed the bioactivity of the nanocomposite bone cement with the formation of primary and secondary apatite on the cement surface. Present study suggests that the incorporation of calcium-deficient hydroxyapatite nanoparticle into the orthopaedic bone cements could help to overcome some of the shortcomings of the orthopaedic cement. � SAGE Publications.

We report on an incidence angle influence on inscription of the Fiber Bragg Gratings in Polymethyl methacrylate (PMMA) microstructured polymer optical fibers. We have shown experimentally that there is a strong preference of certain angles, labeled Gamma K, over the other ones. Angles close to Gamma K showed fast start of inscription, rapid inscription and stronger gratings. We have also shown that gratings can be obtained at almost any angle but their quality will be lower if they are not around Gamma K angle. Our experimental results verify earlier numerical and experimental predictions of Marshall et al. (C)2015 Optical Society of America

A series of model networks based on cross-linked star polymers of poly(ethylene glycol) methacrylate (PEGMA) and tetrahydropyranyl methacrylate (THPMA), a protected form of methacrylic acid (MAA), were synthesized by group transfer polymerization (GTP), covering various compositions (homopolymers and copolymers), arm architectures (homopolymer, block and statistical copolymers), and star architectures (heteroarm and star block). The synthesis took place in tetrahydrofuran (THF) using tetrabutylammonium bibenzoate (TBABB) as the catalyst and 1-methoxy-1-(trimethytsiloxy)-2-methyl-propene (MTS) es the initiator, and comprised a four- or six-step procedure: first, the formation of linear polymer chains upon the GTP of the monomer(s) next, the interconnection of the linear segments to star polymers ("arm-first" stars) by the in situ polymerization of the ethylene glycol dimethacrylate (EGDMA) cross-linker, followed by the addition of monomer(s) for a second time to grow new chains from the cores of the stars outward ("in-out" stars) finally, the cross-linking of the "in-out" stars to a network with the addition of more EGDMA. The molecular weights (MWs) and molecular weight distributions (MWDs) of all the linear and the star precursors to the networks were determined using gel permeation chromatography (GPC). The networks which contained THPMA were hydrolyzed under acidic conditions to convert the THPMA units to MAA units and thus to obtain polyelectrolytic, double-hydrophilic model networks. The aqueous degrees of swelling of all the networks were measured as a function of pH. At low pH, where MAA is protonated, low degrees of swelling were obtained, which increased with the network content in PEGMA. An increase of the degrees of swelling was observed at high pH. These high pH degrees of swelling were found to be dependent on both the composition and the structure of the network. 35 13 4903 4911 Cited By :44

Imidazole-containing polymers were prepared and characterized in terms of their hydrolytic activity. Unlike similar materials synthesized in the 1960s, the polymers are of precise molecular weight and controlled structure (random or block) afforded by the group transfer polymerization (GTP) chemistry used in the synthetic procedure. The size and composition of the copolymers were determined by gel permeation chromatography (GPC) and proton nuclear magnetic resonance spectroscopy, respectively. Aqueous solutions of the polymers were evaluated in terms of their ability to hydrolyze 4-nitrophenyl acetate. The effects of pH, polymer concentration, substrate concentration, polymer size, and structure were investigated and discussed with reference to the nucleophilicity of imidazole and the self-assembly of the block copolymers into micelles. A series of model networks based on imidazole homopolymers were also prepared and characterized in terms of their aqueous degree of swelling. Copyright (C) 2000 Elsevier Science B.V. Imidazole-containing polymers were prepared and characterized in terms of their hydrolytic activity. Unlike similar materials synthesized in the 1960s, the polymers are of precise molecular weight and controlled structure (random or block) afforded by the group transfer polymerization (GTP) chemistry used in the synthetic procedure. The size and composition of the copolymers were determined by gel permeation chromatography (GPC) and proton nuclear magnetic resonance spectroscopy, respectively. Aqueous solutions of the polymers were evaluated in terms of their ability to hydrolyze 4-nitrophenyl acetate. The effects of pH, polymer concentration, substrate concentration, polymer size, and structure were investigated and discussed with reference to the nucleophilicity of imidazole and the self-assembly of the block copolymers into micelles. A series of model networks based on imidazole homopolymers were also prepared and characterized in terms of their aqueous degree of swelling. 167 1-2 61 72 Manufacturers: Aldrich, United Kingdom Cited By :30

In this research a prediction model for the cellular uptake efficiency of nanoparticles (NPs), which is the rate that NPs adhere to a cell surface or enter a cell, is investigated via an artificial neural network (ANN) method. An appropriate mathematical model for the prediction of the cellular uptake rate of NPs will significantly reduce the number of time-consuming experiments to determine which of the thousands of possible variables have an impact on NP uptake rate. Moreover, this study constitutes a basis for targeted drug delivery and cell-level detection, treatment and diagnosis of existing pathologies through simulating NP-cell interactions. Accordingly, this study will accelerate nanomedicine research. Our research focuses on building a proper ANN model based on a multilayered feed-forward back-propagation algorithm that depends on NP type, size, surface charge, concentration and time for prediction of cellular uptake efficiency. The NP types for in-vitro NP-healthy cell interaction analysis are polymethyl methacrylate (PMMA), silica and polylactic acid (PLA), all of whose shapes are spheres. The proposed ANN model has been developed on MATLAB Programming Language by optimizing a number of hidden layers (HLs), node numbers and training functions. The datasets are obtained from in-vitro NP-cell interaction experiments conducted by Nanomedicine and Advanced Technology Research Center. The dispersion characteristics and cell interactions with different NPs in organisms are explored using an optimal ANN prediction model. Simulating the possible interactions of targeted NPs with cells via an ANN model will be faster and cheaper compared to the excessive experimentation currently necessary.

We present two novel, homologous, pyridine-based monomers, 2-(pyridin-2-yl)ethyl methacrylate (PyEMA) and (pyridin-2-yl)methyl methacrylate (PyMMA), which, despite their structural similarity, the former can be readily thermolyzed to methacrylic acid, while the latter remains intact under the same conditions. This was most dramatically demonstrated in the present work, where PyEMA and PyMMA were randomly terpolymerized with a dimethacrylate cross-linker using reversible addition-fragmentation chain transfer polymerization to yield weakly double-cationic polyelectrolyte hydrogels of three different compositions which, upon thermal treatment, they were readily converted to polyampholyte hydrogels. While the parent double-cationic polyelectrolyte hydrogels exhibited a swelling response only to low-pH conditions, the daughter polyampholyte hydrogels presented swelling responses to both high- and low-pH conditions. Owing to the relative values of the effective pKa's of the weakly acidic and weakly basic units, with the latter being lower than the former ("inverse polyampholyte" behavior), the swelling profiles of the daughter hydrogels were insensitive to polyampholyte composition. © 2014 American Chemical Society. 47 5 1819 1827 Cited By :11

Six amphiphilic diblock copolymers based on the hydrophilic monomer 2-(1-imidazolyl)ethyl methacrylate (ImEMA) and the hydrophobic monomer styrene (Sty) were prepared by sequential reversible addition-fragmentation chain transfer (RAFT) polymerization. RAFT polymerization was performed via the use of 4-cyano-4-(dodecylsulfanylthiocarbonylsulfanyl)pentanoic acid (CDP) as the chain transfer agent and glacial acetic acid as the solvent. Amphiphilic diblock copolymers with a range of compositions were prepared, with ImEMA first blocks of constant (nominal) degree of polymerization (DP) equal to 100, and Sty second blocks of a DP between 18 and 482, having ImEMA contents between 15 and 80 mol%, as measured by 1H NMR spectroscopy in CDCl3. Only the Sty-rich (≥51 mol%) diblock copolymers were fully soluble in the solvent for gel permeation chromatography (GPC), tetrahydrofuran GPC analysis of these copolymers indicated molecular weights in the range of 15 to 34 kDa, and molecular weight dispersities ranging from 1.1 to 1.6. At room temperature, the side-group of the ImEMA units was stable in an acidic environment but hydrolyzed slowly under alkaline conditions. In bulk neutral samples, the ImEMA side-group was thermally stable up to ∼250 °C. Finally, dynamic light scattering and polarized light microscopy indicated that the Sty-rich diblock copolymers formed spherical micelles in chloroform, whereas all diblock copolymers formed anisotropic nanophases in water. © 2014 the Partner Organisations. 5 14 4339 4347 Cited By :4

This article overviews the work by our Group at the University of Cyprus on the attempted controlled polymerization of several biobased unsaturated esters. These were esters of tiglic acid, itaconic acid, fumaric acid, maleic acid and methylene malonic acid, whereas the method employed for their polymerization was group transfer polymerization (GTP), a type of quasi-living oxyanionic polymerization, capable of the rapid, room-temperature polymerization of α,β-unsaturated carbonyl compounds. Since the methyl ester of tiglic acid resisted GTP as well as conventional and controlled radical polymerizations, the monomer 2-(tigloyl)ethyl methacrylate was prepared and smoothly (co)polymerized by GTP from the methacrylate functionality, yielding various homopolymers, block copolymers and star polymers of well-defined structure. Although not polymerizable to high conversion by GTP, 1-2 units of di(n-butyl) itaconate could consistently be added to living GTP polymethacrylates, allowing their efficient end-functionalization. Similar observations were also made with diethyl maleate and diethyl fumarate. In contrast, the diethyl ester of the lower homologue of itaconic acid, methylene malonic acid, would spontaneously polymerize, probably via a mechanism of anionic polymerization initiated by moisture. © 2012 Elsevier Ltd. All rights reserved. 49 4 761 767 Cited By :5

The magnetic-poly(divinylbenzene-1-vinylimidazole) [m-poly(DVB-VIM)] microbeads (average diameter 53-212 mu m) were synthesized and characterized; their use as adsorbent in removal of Cr(VI) ions from aqueous solutions was investigated. The m-poly(DVB-VIM) microbeads were prepared by copolymerizing of divinylbenzene (DVB) with 1-vinylimidazole (VIM). The m-poly(DVB-VIM) microbeads were characterized by N-2 adsorption/desorption isotherms, ESR, elemental analysis, scanning electron microscope (SEM) and swelling studies. At fixed solid/solution ratio the various factors affecting adsorption of Cr(VI) ions from aqueous solutions such as pH, initial concentration, contact time and temperature were analyzed. Langmuir, Freundlich and Dubinin-Radushkvich isotherms were used as the model adsorption equilibrium data. Langmuir isotherm model was the most adequate. The pseudo-first-order, pseudo-second-order, Ritch-second-order and intraparticle diffusion models were used to describe the adsorption kinetics. The apparent activation energy was found to be 5.024 kJ mol(-1), which is characteristic of a chemically controlled reaction. The experimental data fitted to pseudo-second-order kinetic. The study of temperature effect was quantified by calculating various thermodynamic parameters such as Gibbs free energy, enthalpy and entropy changes. The thermodynamic parameters obtained indicated the endothermic nature of adsorption of Cr(VI) ions. Morever, after the use in adsorption, the m-poly(DVB-VIM) microbeads with paramagnetic property were separeted via the applied magnetic force. The magnetic beads could be desorbed up to about 97% by treating with 1.0 M NaOH. These features make the m-poly(DVB-VIM) microbeads a potential candidate for support of Cr(VI) ions removal under magnetic field.

Seven cyclolinear polymers bearing the tertiary-butyl α-(hydroxymethyl)acrylate (TBHMA) ether dimer were prepared using reversible addition–fragmentation chain transfer (RAFT) polymerization. Of the seven polymers, five were cyclolinear homopolymers of the TBHMA ether dimer with different degrees of polymerization, one was an “arm-first” star homopolymer, and the other was an amphiphilic linear copolymer based on the positively ionizable hydrophilic 2-(dimethylamino)ethyl methacrylate (DMAEMA) and the TBHMA ether dimer. For comparison, two more polymers were prepared using RAFT polymerization where the TBHMA ether dimer was replaced by tertiary-butyl methacrylate (tBuMA). In particular, an amphiphilic linear DMAEMA–tBuMA diblock copolymer and a tBuMA arm-first star homopolymer were also synthesized. All polymers were characterized in terms of their molecular weights and composition using gel permeation chromatography and 1H NMR spectroscopy, respectively. Subsequently, the tertiary-butyl groups of the TBHMA ether dimer units and those of the tBuMA units were cleaved by hydrolysis to yield carboxylic acid groups. The successful removal of the tertiary-butyl groups was confirmed using 1H and 13C NMR and attenuated total reflectance-Fourier transform infrared spectroscopies. The hydrolyzed (co)polymers exhibited pK values of the carboxylic acid groups of around 4.5, and glass transition temperatures, Tg, of around 200 °C, which were 50 °C higher than those of their nonhydrolyzed precursors. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012

Four well-defined end-linked triblock polyampholyte conetworks composed of positively ionizable 2-(dimethylamino)ethyl methacrylate (DMAEMA) repeating units and negatively ionizable methacrylic acid (MAA) repeating units were synthesized using one-pot, sequential reversible addition-fragmentation chain transfer (RAFT) polymerization, by employing 1,4-bis[2-(thiobenzoylthio)prop-2- yl]benzene (1,4-BTBTPB) as the chain transfer agent, and ethylene glycol dimethacrylate (EGDMA) as the cross-linker. From the four end-linked conetworks, three were based on ABA triblock polyampholytes with polyDMAEMA midblocks with a constant degree of polymerization (DP) and polyMAA end-blocks of different DPs. The fourth end-linked polyampholytic conetwork was based on an equimolar BAB triblock polyampholyte with a polyMAA midblock. Furthermore, two polyampholyte networks were also prepared: one based on an end-linked equimolar statistical polyampholyte, and one with a randomly cross-linked, rather than an end-linked, architecture. Finally, the two homopolymer networks based on the DMAEMA and the MAA monomers were also synthesized. The MAA units were introduced in the (co)networks via the polymerization of 2-tetrahydropyranyl methacrylate (THPMA) followed by its acid hydrolysis after (co)network formation. The linear precursors to the (co)networks were found to have molecular weights and compositions close to the expected values, whereas the extractables from the (co)networks were determined to be lower than 30%. In water, the degrees of swelling (DS) of all the polyampholyte (co)networks presented a characteristic minimum at intermediate pH values, around the (co)network isoelectric point (pI), while they increased at acidic and basic pHs. The pI values of the ampholytic (co)networks were estimated as the midpoints of the regions of reduced swelling and ranged between 5.3 and 6.8, decreasing with the increase of the MAA content in the (co)networks. Finally, small-angle neutron scattering (SANS) studies of the polyampholyte (co)networks swollen in D2O provided SANS profiles without any peaks but broad shoulders whose location was consistent with the spacing of the cross-linking cores. © 2011 American Chemical Society. 44 13 5352 5362 Cited By :34

Four linear amphiphilic multiblock copolymers based on 2-(dimethylamino) ethyl methacrylate (DMAEMA, hydrophilic) and methyl methacrylate (MMA, hydrophobic), bearing from two to five blocks, were synthesized using reversible addition - fragmentation chain transfer polymerization and stepwise monomer additions. The degree of polymerization of each hydrophilic poly DMAEMA block was ~50, while that of the hydrophobic polyMMA blocks was ca. 20. The stepwise monomer addition procedure secured that each higher multiblock was composed of its immediately lower homologue plus exactly one extra block. The molecular weights (MW) of the synthesized (co)polymers, as measured by gel permeation chromatography (GPC), were close to the theoretically expected. GPC also indicated rather narrow molecular weight distributions which, however, broadened with the number of blocks. The compositions of the copolymers, as determined by proton nuclear magnetic resonance spectroscopy, were also close to the expected values. The cloud points of the copolymers, measured by turbidimetry, were found to increase with the number of blocks. The sizes of the micelles formed by the copolymers in aqueous solution were characterized using dynamic light scattering and small-angle neutron scattering. The determined values of the hydrodynamic radii, the radii of gyration, and the aggregation numbers of the micelles increased slightly with the block number from the triblock to the pentablock copolymer, implying extensive folding of the chains of the tetrablock and the pentablock copolymers in their micelles. The aggregation number of the tetrablock copolymer was approximately one-half that of the diblock copolymer whose unimer MW was onehalf that of the tetrablock, suggesting that the micellar cores of these two types of micelles were composed of the same number of hydrophobic units. © 2010 American Chemical Society. 43 6 2713 2720 Cited By :33

Five linear amphiphilic multiblock copolymers based on 2-(dimethylamino) ethyl methacrylate ("D") and methyl methacrylate ("M"), bearing from two to six blocks, were synthesized using sequential group transfer polymerization. All copolymers were obtained from the same polymerization flask (by the withdrawal of a sufficient amount of sample and appropriate adjustment of subsequent monomer loadings) to ensure better comparison between the various multiblocks. A theoretical degree of polymerization (DPth) of 20 was targeted for all D blocks, whereas a DPth of 10 was aimed for the M blocks. Upon characterization using gel permeation chromatography and H NMR spectroscopy, the copolymers were confirmed to have the expected values of molecular weights and compositions. Subsequently, the aqueous micellization behavior of these copolymers was probed using dye solubilization, dynamic light scattering, and small-angle neutron scattering. Dye solubilization experiments indicated that micelles readily formed at low copolymer concentrations equal to or less than 0.03% w/w. The scattering measurements revealed that despite the differences in their overall DPth values, the triblock, the tetrablock, and the pentablock copolymers selfassembled in water to form micelles with radii of gyration and hydrodynamic radii very similar to each other, suggesting chain looping and the formation of flowerlike micelles, which is in agreement with recent Monte Carlo simulations. © 2009 American Chemical Society. 42 15 5492 5498 Cited By :28

A detailed analysis of the unburned material heat-up during upward flame spread over small slabs of PMMA is provided using a numerical model. The two-dimensional time-dependent Favre-averaged Navier–Stokes equations coupled with sub-models for turbulence, combustion, soot formation, and radiation are solved for the gas phase. The modelling of condensed phase processes is based on the one-dimensional heat conduction equation and pyrolysis is treated as a phase change using the latent heat approach. Pyrolysis heights, xp, up to 0.6 m are considered. Model results agree with data on the pyrolysis front trajectory and heat release rate per unit width, Q ˙ ′ , as a function of xp from experiments in which the lateral air entrainment is expected to have no significant effect on flame spread. It is shown that the average luminous flame height, xfl, defined by the height at which the total wall heat flux is equal to 10 kW/m2, correlates with Q ˙ ′ 1.25 for Q ˙ ′ 20 kW / m , whereas it correlates with Q ˙ ′ 2 / 3 for Q ˙ ′ 20 kW / m , as deduced from experiments. Appropriate scaling of the total wall heat flux distribution is found in terms of ξ = ( x - x p ) / ( x fl - x p ) . This scaling allows us to locate the continuous flame region between ξ=0 and 0.4 and the plume region above ξ=1.6, the intermittent flame region being located between the two. Both continuous and intermittent flames are found to play an important role in the process of heating the unburned solid fuel whereas the plume contribution is negligible.

A series of experiments is performed to determine the local burning rate of vertically oriented burning slabs of PMMA (poly(methyl methacrylate)) under steady-state conditions. The burning rate is essential for the determination of flame temperatures, flame lengths, and burnout, all critical parameters to establish fire growth. The experimental procedure consists of a postprocessing of digitized images obtained with three CCD cameras placed on the sides of the PMMA slabs. The cameras are used to establish the displacement of the regressing surface as a function of time. The PMMA/gas interface is characterized by a bubbling layer that scatters light, making the bubbles visible. The video images are processed by establishing a gray-level intensity threshold that defines the depth of the bubbling layer. The local burning rate is then computed from the time derivative of the surface regression. Local burning rates for PMMA slabs, 30 cm high, 3 cm thick, and 2.5, 5, 10, 15, and 20 cm in width are obtained. Three-dimensional effects appear for 2.5-cm-wide slabs. For wider slabs, the local burning rate along the centre line is found not to be width-dependent and to be in good agreement with literature data. Results show that the pyrolyzing surface divides vertically into four regions. In the lowest region (0 < x < 4 cm), the local burning rate increases with the distance from the leading edge, x. For 4 < x < 10 cm, the local burning rate follows a power-law decay. For slabs wider than 2.5 cm, the exponent approximates -0.35. This is higher than that predicted by the two-dimensional laminar boundary layer theory, i.e., -0.25. For 2.5-cm-wide slabs, the local burning rate decreases faster, with a power law dependency of -0.8. From x = 10 to 18 cm, the local burning rate is approximately constant, which is believed to correspond to the laminar/turbulent transition region. In the upper region, the flow becomes fully turbulent and the burning rate increases weakly with x. © 2007 The Combustion Institute.

The recent development of table top extreme ultraviolet (EUV) lasers have enabled new applications that so far were restricted to the use of large facilities. These compact sources bring now to the laboratory environment the capabilities that will allow a broader application of techniques related to nanotechnology and nanofabrication. In this paper we review the advances in the utilization of EUV lasers in nanopatterning. In particular we show results of the nanopatterning using a table-top capillary discharge laser producing 0.12-mJ laser pulses with 1.2-ns time duration at a wavelength λ = 46.9 nm. The nanopatterning was realized by interferometric lithography using a Lloyd's mirror interferometer. Two standard photoresists were used in this work, polymethyl methacrylate (PMMA) and hydrogen silsesquioxane (HSQ). Pillars with a full width half maximum (FWHM) diameter of 60 nm and holes with FWHM diameter of 130 nm were obtained over areas in excess of 500×500 μm2. © 2008 Versita Warsaw and Springer-Verlag Berlin Heidelberg. Fil:Capeluto, M.G. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina. Fil:Marconi, M.C. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.

Flame height is defined by the experimentalists as the average position of the luminous flame and, consequently is not directly linked with a quantitative value of a physical parameter. To determine flame heights from both numerical and theoretical results, a more quantifiable criterion is needed to define flame heights and must be in agreement with the experiments to allow comparisons. For wall flames, steady wall flame experiments revealed that flame height may be defined by a threshold value on the wall heat flux. From steady wall flame measurements, three definitions of flame height from wall heat flux are retained: the first is based on the continuous flame while the two others are based on threshold values of 4 kW/m2 and 10 kW/m2. These definitions are applied to determine flame heights from a two-dimensional time-dependent CFD model used to describe flame spread on a vertical slab of PMMA. Results show that the predicted flame heights are consistent with the available data of the literature. Defining flame height by threshold values on the wall heat flux of 4 and 10 kW/m2 allows the correlation of the wall heat flux in terms of (x-xp)/(xfl-xp), which is the dimensionless characteristic length scale for upward flame spread. It is also found that the continuous flame is not a characteristic length for the heat transfer to the unburnt fuel and is not really appropriate to define flame height in upward flame spread. © 2007 Elsevier Ltd. All rights reserved.

A compact, cleavable acylal dimethacrylate cross-linker, 1,1-ethylenediol dimethacrylate (EDDMA), was synthesized from the anhydrous iron(III) chloride-catalyzed reaction between methacrylic anhydride and acetaldehyde. The ability of EDDMA to act as cross-linker was demonstrated by using it for the preparation of one neat cross-linker network, four star polymers of methyl methacrylate (MMA), and four randomly cross-linked MMA polymer networks using group transfer polymerization (GTP). For comparison, the corresponding polymer structures based on the commercially available ethylene glycol dimethacrylate (EGDMA) cross-linker (isomer of EDDMA) were also prepared via GTP. The number of arms of the EDDMA-based star polymers was lower than that of the corresponding EGDMA polymers, whereas the degrees of swelling in tetrahydrofuran of the EDDMA-based MMA networks were higher than those of their EGDMA-based counterparts. Although none of the EDDMA-containing polymers could be cleanly hydrolyzed under basic or acidic conditions, they could be thermolyzed at 200 °C within 1 day giving lower molecular weight products. ©2007 Wiley Periodicals, Inc. 45 24 5811 5823 Cited By :16

Group transfer polymerization (GTP) chemistry was employed for the preparation of polymethacrylate networks of controlled structure (quasi-model networks) of three different types: (a) regular quasi-model networks, in which all polymer chains were linked at their ends, leaving, in principle, no free chain ends, (b) crosslinked star polymer quasi-model networks, in which star polymers were interlinked via half of their chains, letting the other half free (dangling), and (c) shell-crosslinked polymer quasi-model networks, in which the outer part of the network contained polymer arms (dangling chains). Combination of hydrophilic and hydrophobic monomers led to amphiphilic networks whose aqueous swelling behavior was characterized gravimetrically. © Springer-Verlag 2007. 58 1 185 190 Cited By :29

This paper describes the results of investigations on giant negative magnetoresistance (GMR) in nanocomposite aligned fibers prepared using electrospinning. The nanocomposite contains polymethylmethacrylate (PMMA) matrix and the nanoparticles of polymer (PMMA) grafted magnetite, Fe3 O4 (PGM). Even for the low magnetic field (1 T) a GMR of about 50% was observed for low loading (5 wt %) of PGM at room temperature. The fibers were characterized using scanning electron microscope and high resolution transmission electron microscope. X-ray diffraction (XRD) patterns were recorded for clean PMMA fibers, PMMA granules, and PGM nanoparticles. The dc conductivity was calculated from the I-V characteristics for the fibers at room temperature. � 2007 American Institute of Physics.

Seven model networks of a new structure, that of cross-linked "in-out"\star polymers, were synthesized by the group transfer polymerization of the Hydrophobic monomers methyl methacrylate (MMA) and n-butyl methacrylate (BuMA) and the cross-linker ethylene glycol dimethacrylate in a one-pot preparation. From the seven networks, two were the homopolymer networks of MMA and BuMA, while the remaining five were based on equimolar MMA-BuMA copolymer stars of different architectures: heteroarm (two), star block (two), and statistical. The synthesis of the networks involved at least four steps, starting from the synthesis of the linear polymers, proceeding to the preparation of the "arm-first" and "in-out" star polymers, and being completed with the cross-linking of the stars into a network. All the precursors to the networks were characterized in terms of their molecular weights using gel permeation chromatography. The sol fraction extracted from the networks was found to be equal to or lower than 20%. The degrees of swelling (DSs) in n-hexane/tetrahydrofuran (THF) mixtures of all networks increased with the solvent content in THF, a nonselective solvent, and this trend was confirmed by thermodynamic calculations. The DS in a 50-50 n-hexane-THF mixture of the statistical network was found to be the same as those of the segmented networks, suggesting absence of microphase separation in the latter type of networks, a trend confirmed by thermodynamic predictions. © 2006 American Chemical Society. 39 4 1560 1568 Cited By :30