Showing papers on "Polystyrene published in 2009"

Covalent polymer functionalization of graphene nanosheets and mechanical properties of composites

Abstract: For developing high performance graphene-based nanocomposites, dispersal of graphene nanosheets in polymer hosts and precise interface control are challenging due to their strong interlayer cohesive energy and surface inertia. Here we report an efficient method to functionalize graphene nanosheets. The initiator molecules were covalently bonded to the graphene surface via a diazonium addition and the succeeding atom transfer radical polymerization linked polystyrene chains (82 wt% grafting efficiency) to the graphene nanosheets. The prominent confinement effect arising from nanosheets resulted in a 15 °C increase in the glass transition temperature of polystyrene compared to the pure polymer. The resulting polystyrene nanocomposites with 0.9 wt% graphene nanosheets revealed around 70% and 57% increases in tensile strength and Young's modulus. The protocol is believed to offer possibilities for optimizing the processing properties and interface structure of graphene-polymer nanocomposites.

Cellulose Nanocrystals Grafted with Polystyrene Chains through Surface-Initiated Atom Transfer Radical Polymerization (SI-ATRP)

Abstract: This paper reports the synthesis of cellulose nanocrystals grafted by polystyrene chains via surface-initiated ATRP. Naturally occurring cellulose was first hydrolyzed to obtain cellulose nanocrystals. Their surface was then chemically modified using 2-bromoisobutyryl bromide to introduce initiating sites for ATRP. A varying extent of surface modification was achieved by changing reaction conditions. Further initiation of styrene polymerization from these modified nanocrystals with a CuBr/PMDETA (N,N,N′,N′,N′′-pentamethyldiethylenetriamine) catalytic system and in the presence of a sacrificial initiator produced polysaccharide nanocrystals grafted by polystyrene chains. A range of nanocrystals-g-polystyrene with different graft lengths (theoretical polymerization degree = 27−171) was synthesized through this method and characterized by elemental analysis, XPS, FT-IR, TEM, and contact angle measurements. We are thus able to produce cellulose nanoparticles with varying grafting densities (by altering extent...

Solvent-Vapor-Induced Tunability of Self-Assembled Block Copolymer Patterns

Abstract: 2009 WILEY-VCH Verlag Gmb Well-controlled monolayer patterns of microdomains of block copolymers (BCPs) have been widely pursued for applications in sub-30-nm nanolithography. BCP film processing is scalable and low cost, and is compatible with existing semiconductor fabrication techniques. Di-BCP with a molecular weight of a few tens to a few hundreds of kgmol 1 have been known to spontaneously form periodic arrays of well-defined nanoscale features, such as dots, holes and lines, which have been used as masks in the fabrication of arrays of nanoscale functional features after the selective elimination of one block. Long-range ordering and positional registration of the features has been imposed by using chemical or topographical templates. The morphology of the patterns has been further diversified by using multi-BCPs or employing various confinement geometries. The morphology and length scale of the microdomain arrays of BCPs are governed by the degree of polymerization of each block, and thus to obtain different geometries and feature sizes, polymers with different chain lengths or BCP–homopolymer blends have been employed. However, in terms of device fabrication, it would be advantageous to be able to manipulate the shape and dimensions of features composed of a single BCP by simply altering the processing conditions. Polymeric materials often provide an exceptional degree of controllability in their molecular configurations due to their weak intermolecular forces, which are largely based on Van der Waals interactions. Solvent vapor annealing, which has been employed to increase chain flexibility in BCPs and to promote their self-assembly into themicrophase-separated state, may be used as an effective lever to engineer the resulting structures. It has been shown that treatments with selective or nonselective vapor result in different morphologies or orientations, demonstrating solvent-induced controllability. However, precise adjustment of pattern size and morphology using controlled mixed solvent vapors has not been studied to the best of our knowledge. In this Communication, we report on the systematic tunability of the dimensions and morphology of patterns of microphaseseparated BCP; this was achieved by controlling the solventannealing conditions, where the key parameters are solvent vapor pressure and the mixing ratio of selective and partially selective solvent vapors. Vapor pressure can control the degree of solvent uptake by the film, which changes both the chainmobility and the interfacial interaction between the blocks of the BCP. We will also propose the theoretical model explaining the increasing size of the pattern period with decreasing vapor pressure. It has been recently reported that a change in the effective volume fraction of the blocks can be accomplished using selective and nonselective vapors. We will show independent control of pattern size and periodicity by using a mixed vapor containing selective (heptane) and partially selective (toluene) solvents. We will also demonstrate that a cylinder-forming BCP can be transformed into a perforated lamellar structure by increasing the portion of selective solvent in the mixed vapor. This study suggests a way to relieve the constraints, imposed by the molecular structure of BCPs, on the achievable microdomain geometries. We have previously presented high quality nanoscale lines, dots and rings composed of a poly(styrene-b-dimethylsiloxane) (PS–PDMS) di-BCP. This polymer is useful for nanolithography in that its self-assembled microdomain pattern has a large correlation length that can exceed several micrometers and a low defect density, even in the absence of templating. High etch selectivity between its two blocks is also possible due to the existence of Si in the PDMS backbone. As described in Figure 1a, a PS-PDMS BCP with a molecular weight of 45.5 kgmol 1 and 33.5 vol% PDMS was spin-coated onto a Si substrate and solvent-annealed forming a PS matrix containing a monolayer of PDMS cylinders that were parallel to the substrate. There was also a PDMS layer at the interfaces of the BCP with the substrate and air due to its lower surface energy compared to PS. Etching away the surface layer of PDMS and some of the PS matrix revealed the arrangement of the now-oxidized PDMS cylinders. We consider first the effect of solvent vapor pressure on the morphology of the cylinder patterns. The vapor pressure is characterized by the ratio between S, the surface area of the solvent while in a beaker placed within the solvent-annealing chamber, and V, the volume of air that will mix with the solvent vapor, which is equivalent to the amount of air in the chamber at atmospheric pressure. The chamber had a small leak path through which solvent vapor could escape. The amount of solvent vapor in the chamber was determined by three flux components: evaporation from the solvent surface (F1), condensation onto the solvent surface (F2), and leak flow (F3). At steady state, the concentration (C) of the solvent vapor in the chamber is given by

Morphology of Porous and Wrinkled Fibers of Polystyrene Electrospun from Dimethylformamide

Abstract: Submicron diameter fibers of polystyrene are electrospun from solutions in dimethylformamide (DMF). When electrospun in a high-humidity environment, the interior of these fibers was found to be highly porous rather than consolidated, despite the smooth and nonporous appearance of the fiber surfaces. The formation of interior porosity is attributed to the miscibility of water, a nonsolvent for the polymers in solution, with DMF. The resulting morphology is a consequence of the relatively rapid diffusion of water into the jet, leading to a liquid−liquid phase separation that precedes solidification due to evaporation of DMF from the jet. When electrospun in a low-humidity environment, the fibers exhibit a wrinkled morphology that can be explained by a buckling instability. Understanding which morphology forms under a given set of conditions is achieved through the comparison of three characteristic times: the drying time, the buckling time, and the phase separation time. The morphology has important consequ...

Graphite Oxide Flame-Retardant Polymer Nanocomposites

Abstract: Graphite oxide (GO) polymer nanocomposites were developed at 1, 5, and 10 wt % GO with polycarbonate (PC), acrylonitrile butadiene styrene, and high-impact polystyrene for the purpose of evaluating the flammability reduction and material properties of the resulting systems. The overall morphology and dispersion of GO within the polymer nanocomposites were studied by scanning electron microscopy and optical microscopy; GO was found to be well-dispersed throughout the matrix without the formation of large aggregates. Mechanical testing was performed using dynamic mechanical analysis to measure the storage modulus, which increased for all polymer systems with increased GO loading. Microscale oxygen consumption calorimetry revealed that the addition of GO reduced the total heat release and peak heat release rates in all systems, and GO−PC composites demonstrated very fast self-extinguishing times in vertical open flame tests, which are important to some regulatory fire safety applications.

Preparation of three-dimensional ordered mesoporous carbon sphere arrays by a two-step templating route and their application for supercapacitors

Abstract: A two-step template approach was demonstrated for preparation of the three-dimensional ordered mesoporous carbon sphere arrays. The ordered macroporous silica skeleton was formed from silicon alkoxide precursor templating around polystyrene (latex) spheres, and removal of the polystyrene spheres. These preforms as hard templates were infiltrated with a solution mixture of amphiphilic triblock copolymer PEO-PPO-PEO and soluble resol. By combining evaporation-induced surfactant-templating organic resol self-assembly with thermosetting, carbonization and hydrofluoric acid extraction of silica, the obtained mesoporous carbon has a pore size of 10.4 nm, interconnected window size of about 60 nm, surface area of 601 m2/g and pore volume of 1.70 cm3/g. The electrochemical properties as an electrode material for supercapacitor applications were investigated in nonaqueous electrolyte. They show rectangular-shaped cyclic voltammetry curves over a wide range of scan rates even up to 200 mV/s between 0 and 3 V, and deliver a large capacitance of 14 µF/cm2 (84 F/g), and good cycling stability with capacitance retention of 93% over 5000 cycles.

Hollow silica spheres: synthesis and mechanical properties.

Abstract: Core−shell polystyrene−silica spheres with diameters of 800 nm and 1.9 μm were synthesized by soap-free emulsion and dispersion polymerization of the polystyrene core, respectively. The polystyrene spheres were used as templates for the synthesis of silica shells of tunable thickness employing the Stober method [Graf et al. Langmuir 2003, 19, 6693]. The polystyrene template was removed by thermal decomposition at 500 °C, resulting in smooth silica shells of well-defined thickness (15−70 nm). The elastic response of these hollow spheres was probed by atomic force microscopy (AFM). A point load was applied to the particle surface through a sharp AFM tip, and successively increased until the shell broke. In agreement with the predictions of shell theory, for small deformations the deformation increased linearly with applied force. The Youngʼs modulus (18 ± 6 GPa) was about 4 times smaller than that of fused silica [Adachi and Sakka J. Mater. Sci. 1990, 25, 4732] but identical to that of bulk silica spheres (...

Self‐Supporting, Double Stimuli‐Responsive Porous Membranes From Polystyrene‐block‐poly(N,N‐dimethylaminoethyl methacrylate) Diblock Copolymers

Abstract: Asymmetric membranes are prepared via the non-solvent-induced phase separation (NIPS) process from a polystyrene-block-poly(N,N-dimethylaminoethyl methacrylate) (PS-b-PDMAEMA) block copolymer. The polymer is prepared via sequential living anionic polymerization. Membrane surface and volume structures are characterized by scanning electron microscopy. Due to their asymmetric character, resulting in a thin separation layer with pores below 100 nm on top and a macroporous volume structure, the membranes are self-supporting. Furthermore, they exhibit a defect-free surface over several 100 μm 2 . Polystyrene serves as the membrane matrix, whereas the pH- and temperature-sensitive minority block, PDMAEMA, renders the material double stimuli-responsive. Therefore, in terms of water flux, the membranes are able to react on two independently applicable stimuli, pH and temperature. Compared to the conditions where the lowest water flux is obtained, low temperature and pH, activation of both triggers results in a seven-fold permeability increase. The pore size distribution and the separation properties of the obtained membranes were tested through the pH-dependent filtration of silica particles with sizes of 12-100 nm.

A low temperature surface modification assisted method for bonding plastic substrates

Abstract: A low cost, low temperature process for sealing microfluidic devices composed of at least one organic polymeric substrate is presented. The process is based on the surface modification of the organic substrate by means of a silane solution, resulting in irreversible bonding. It is a generic method of bonding polymeric/plastic substrates, bare or structured ones, such as poly(methylmethacrylate) (PMMA), polystyrene (PS) or epoxy-type polymers, to Si-containing substrates, such as poly(dimethylsiloxane) (PDMS), Si and glass. In the case that bonding between organic polymer (PMMA, PS, etc) substrates is desired, an intermediate thin PDMS layer is required.

Tailoring elastic properties of silica aerogels cross-linked with polystyrene.

Abstract: The effect of incorporating an organic linking group, 1,6-bis(trimethoxysilyl)hexane (BTMSH), into the underlying silica structure of a styrene cross-linked silica aerogel is examined. Vinyltrimethoxysilane (VTMS) is used to provide a reactive site on the silica backbone for styrene polymerization. Replacement of up to 88 mol % of the silicon from tetramethoxyorthosilicate with silicon derived from BTMSH and VTMS during the making of silica gels improves the elastic behavior in some formulations of the cross-linked aerogels, as evidenced by measurement of the recovered length after compression of samples to 25% strain. This is especially true for some higher density formulations, which recover nearly 100% of their length after compression to 25% strain twice. The compressive modulus of the more elastic monoliths ranged from 0.2 to 3 MPa. Although some of these monoliths had greatly reduced surface areas, changing the solvent used to produce the gels from methanol to ethanol increased the surface area in one instance from 6 to 220 m(2)/g with little affect on the modulus, elastic recovery, porosity, or density.

Hollow polyaniline/Fe3O4 microsphere composites: Preparation, characterization, and applications in microwave absorption

Abstract: Hollow polyaniline/Fe3O4 microsphere composites with electromagnetic properties were successfully prepared by decorating the surface of hollow polyaniline/sulfonated polystyrene microspheres with various amounts of Fe3O4 magnetic nanoparticles using sulfonated polystyrene (SPS) as hard templates and then removing the templates with tetrahydrofuran (THF). The synthesized hollow microsphere composites were characterized by FT-IR, UV/Vis spectrophotometry, SEM, XRD, elemental analysis, TGA, and measurement of their magnetic parameters. Experimental results indicated that the microspheres were well-defined in size (1.50–1.80 μm) and shape, and that they were superparamagnetic with maximum saturation magnetization values of 3.88 emu/g with a 12.37 wt% content of Fe3O4 magnetic nanoparticles. Measurements of the electromagnetic parameters of the samples showed that the maximum bandwidth was 8.0 GHz over −10 dB of reflection loss in the 2–18 GHz range when the Fe3O4 content in the hollow polyaniline/Fe3O4 microsphere composites was 7.33 wt%.

Non-Close-Packed Crystals from Self-Assembled Polystyrene Spheres by Isotropic Plasma Etching: Adding Flexibility to Colloid Lithography

Abstract: Hexagonally ordered arrays of non-close-packed nanoscaled spherical polystyrene (PS) particles are prepared exhibiting precisely controlled diameters and interparticle distances. For this purpose, a newly developed isotropic plasma etching process is applied to extended monolayers of PS colloids (starting diameters <300 nm) deposited onto hydrophilic silicon. Accurate size, shape, and smoothness control of such particles is accomplished by etching at low temperatures (−150 °C) with small rates not usually available in standard reactive ion etching equipment. The applicability of such PS arrays as masks for subsequent pattern transfer is demonstrated by fabricating arrays of cylindrical nanopores into Si.

Confined Crystallization of PEO in Nanolayered Films Impacting Structure and Oxygen Permeability

Abstract: Layer-multiplying coextrusion or “forced assembly” of thousands of alternating polystyrene (PS) and poly(ethylene oxide) (PEO) nanolayers was used to study crystallization in a confined, two-dimens...

Nanostructure, Morphology, and Properties of Fluorous Copolymers Bearing Ionic Grafts

Abstract: In order to probe the effects of polymer microstructure on the properties of proton conducting polymer membranes, three series of fluorous−ionic graft copolymers, partially sulfonated poly([vinylidene difluoride-co-chlorotrifluoroethylene]-g-styrene) [P(VDF-co-CTFE)-g-SPS], comprising controlled graft lengths and degrees of sulfonation were synthesized. The parent building block was a poly(vinylidene difluoride-co-chlorotrifluoroethylene) [P(VDF-co-CTFE)] macroinitiator (Mn = 3.12 × 105 g/mol) synthesized to contain 1 chloro group per 17 repeat units, onto which polystyrene, having degrees of polymerization of 35, 88, and 154 units per graft, was grown by atom transfer radical polymerization (ATRP). These graft copolymers, termed short, medium, and long graft chains, were sulfonated to different extents to provide a series of polymers with varying ion exchange capacity (IEC). The resulting P(VDF-co-CTFE)-g-SPS copolymers were cast into proton exchange membranes, and their nanostructure, morphology, and pr...

Synthesis and bio-functionalization of multifunctional magnetic Fe3O4@Y2O3:Eu nanocomposites

Abstract: A facile homogenous precipitation method has been developed for the synthesis of multifunctional, magnetic, luminescent nanocomposites with Fe3O4 nanoparticles as the core and europium-doped yttrium oxide (Y2O3:Eu) as the shell. The nanocomposites showed both super-paramagnetic behavior and unique europium fluorescence properties with high emission intensity. Their surface has been modified with a bifunctional ligand, p-aminobenzoic acid (PABA), and further biofunctionalized with biotin; the nanocomposites showed specific targeting for avidin-coupled polystyrene beads.

Dispersion of cellulose crystallites by nonionic surfactants in a hydrophobic polymer matrix

Abstract: Cellulose nanoparticles obtained by acid hydrolysis of cellulose paper were used to reinforce polystyrene composite films. The nonionic surfactant sorbitan monostearate was utilized to improve the dispersion properties of the hydrophilic cellulose in hydrophobic matrix and to prevent the formation of aggregates. Turbidity tests were used to measure dispersion stability of the cellulose crystallites in the hydrophobic solvent used in the composite manufacture. A correlation was found between the dispersion stability in solvent and the formation of aggregates in the polymeric composites. Nanocomposite films were processed using a casting/evaporation technique. Thermal and mechanical properties of processed composites were studied by differential scanning calorimetry (DSC) and dynamical mechanical analyses (DMA), respectively. The results showed that the optimum addition of surfactant produced better dispersion of the cellulose particles in the polystyrene matrix and improved the mechanical properties of the resulting composite due to an enhanced compatibility. POLYM. ENG. SCI., 49:2054–2061, 2009. a 2009 Society of Plastics Engineers

A conformal nano-adhesive via initiated chemical vapor deposition for microfluidic devices.

Abstract: A novel high-strength nano-adhesive is demonstrated for fabricating nano- and microfluidic devices While the traditional plasma sealing methods are specific for sealing glass to poly(dimethylsiloxane) (PDMS), the new method is compatible with a wide variety of polymeric and inorganic materials, including flexible substrates Additionally, the traditional method requires that sealing occur within minutes after the plasma treatment In contrast, the individual parts treated with the nano-adhesive could be aged for at least three months prior to joining with no measurable deterioration of post-cure adhesive strength The nano-adhesive is comprised of a complementary pair of polymeric nanolayers An epoxy-containing polymer, poly(glycidyl methacrylate) (PGMA) was grown via initiated chemical vapor deposition (iCVD) on the substrate containing the channels A plasma polymerized polyallylamine (PAAm) layer was grown on the opposing flat surface Both CVD monomers are commercially available The PGMA nano-adhesive layer displayed conformal coverage over the channels and was firmly tethered to the substrate Contacting the complementary PGMA and PAAm surfaces, followed by curing at 70 degrees C, resulted in nano- and micro-channel structures The formation of the covalent tethers between the complementary surfaces produces no gaseous by-products which would need to outgas The nano-adhesive layers did not flow significantly as a result of curing, allowing the cross-sectional profile of the channel to be maintained This enabled fabrication of channels with widths as small as 200 nm Seals able to withstand > 50 psia were fabricated employing many types of substrates, including silicon wafer, glass, quartz, PDMS, polystyrene petri dishes, poly(ethylene terephthalate) (PET), polycarbonate (PC), and poly(tetrafluoro ethylene) (PTFE)

Enhanced Mechanical Properties of Superhydrophobic Microfibrous Polystyrene Mats via Polyamide 6 Nanofibers

Abstract: In this study, a large-scale superhydrophobic mat surface with an enhanced mechanical property by blending polystyrene (PS) and polyamide 6 (PA6) fibers was fabricated via a four-jet electrospinnin...

Recycling of polymers from plastic packaging materials using the dissolution–reprecipitation technique

Abstract: In this work, results are presented on the application of the dissolution/reprecipitation technique in the recycling of polymers from waste plastic packaging materials used in food, pharmaceuticals and detergents. Initially, the type of polymer in each packaging was identified using FT-IR. Furthermore, experimental conditions of the recycling process (including type of solvent/non-solvent, initial polymer concentration and dissolution temperature) were optimized using model polymers. The dissolution/reprecipitation technique was applied in the recycling of a number of plastic materials based on polyethylene (LDPE and HDPE), polypropylene, polystyrene, poly(ethylene terephthalate) and poly(vinyl chloride). The recovery of the polymer was measured and possible structural changes during the recycling procedure were assessed by FT-IR spectroscopy. Potential recycling-based degradation of the polymer was further investigated by measuring the thermal properties (melting point, crystallinity and glass transition temperature), of the polymer before and after recycling, using DSC, their molecular properties (average molecular weight) using viscosimetry, as well as their mechanical tensile properties. High recoveries were recorded in most samples with the properties of the recycled grades not substantially different from the original materials. However, a slight degradation was observed in a few samples. It seems that this method could be beneficial in waste packaging recycling program.

Surface-Initiated Free Radical Polymerization at the Liquid―Liquid Interface: A One-Step Approach for the Synthesis of Amphiphilic Janus Silica Particles

Abstract: Amphiphilic Janus silica particles with hydrophobic polystyrene (PS) and hydrophilic poly(sodium methacrylate) (PSMA) brushes on two hemispheres were prepared at the liquid-liquid interface by surface-initiated polymerization. After introduction of free-radical initiator modified silica particles into a mixture of styrene and water, the silica particles were adsorbed at the liquid-liquid interface. One hemisphere of a silica particle is immersed in aqueous phase, and the other one is in styrene phase. After initiation at an elevated temperature, PSMA chains grow on one hemisphere and PS chains grow on the other one. Thermogravimetric analysis and infrared spectra results confirmed the grafting of polymer brushes on the surfaces. Transmission electron microscopy was used to characterize the asymmetric surface structure and aggregation structure of the Janus particles.

Double Stimuli-Responsive Ultrafiltration Membranes from Polystyrene-block-poly(N,N-dimethylaminoethyl methacrylate) Diblock Copolymers

Abstract: We report on the formation of self-supporting, double stimuli-responsive ultrafiltration membranes via the non-solvent-induced phase separation (NIPS) process. The polymers, polystyrene-block-poly(N,N-dimethylaminoethyl methacrylate) (PS-b-PDMAEMA), were synthesized via living anionic polymerization in THF using sec-butyllithium as initiator. Two amphiphilic diblock copolymers were used, S81D1975 and S68D32100. The membranes were cast from mixtures of THF and DMF. The influence of the solvent composition, the “open-time” before immersion into the coagulation bath, and the casting film thickness onto the membrane morphology were thoroughly investigated, and flux values obtained for the different membrane systems were compared. The higher content in hydrophilic polymer for S68D32100 resulted in a better compatibility with the nonsolvent bath consisting of water, leading to a slower precipitation and thus an improved control of the phase separation occurring. Under certain conditions, ordered microphase-sepa...

Control of the entropic interactions and phase behavior of athermal nanoparticle/homopolymer thin film mixtures

Abstract: It is shown that the phase behavior of an athermal thin film nanoparticle/polymer hybrid material of polystyrene (PS) with PS-grafted gold nanoparticles is readily tailored through control of the degrees of polymerization, N and P, of the grafted and the free chains, respectively, and the relative size of the nanoparticle to the average dimensions of both the grafted and the host chains. Complete miscibility or a surface-induced phase transition, leading to segregation of the particles to an interface, is readily achieved in this system.