Showing papers on "Polystyrene published in 2005"

Electrospun poly(styrene-block-dimethylsiloxane) block copolymer fibers exhibiting superhydrophobicity.

Abstract: Block copolymer poly(styrene-b-dimethylsiloxane) fibers with submicrometer diameters in the range 150-400 nm were produced by electrospinning from solution in tetrahydrofuran and dimethylformamide. Contact angle measurements indicate that the nonwoven fibrous mats are superhydrophobic, with a contact angle of 163 degrees and contact angle hysteresis of 15 degrees . The superhydrophobicity is attributed to the combined effects of surface enrichment in siloxane as revealed by X-ray photoelectron spectroscopy and surface roughness of the electrospun mat itself. Additionally, the fibers are shown by transmission electron microscopy to exhibit microphase-separated internal structures. Calorimetric studies confirm the strong segregation between the polystyrene and poly(dimethylsiloxane) blocks.

Functionalization of single-walled carbon nanotubes with well-defined polystyrene by "click" coupling.

Abstract: Covalent functionalization of alkyne-decorated SWNTs with well-defined, azide-terminated polystyrene polymers was accomplished by the Cu(I)-catalyzed [3 + 2] Huisgen cycloaddition. This reaction was found to be extremely efficient in producing organosoluble polymer-nanotube conjugates, even at relatively low reaction temperatures (60 °C) and short reaction times (24 h). The reaction was found to be most effective when a CuI catalyst was employed in the presence of 1,8-diazabicyclo[5.4.0]undec-7-ene as an additive. IR spectroscopy was utilized to follow the introduction and consumption of alkyne groups on the SWNTs, and Raman spectroscopy evidenced the conversion of a high proportion of sp2 carbons to sp3 hybridization during alkyne introduction. Thermogravimetric analysis indicated that the polymer-functionalized SWNTs consisted of 45% polymer, amounting to approximately one polymer chain for every 200−700 carbons of the nanotubes, depending on polymer molecular weight. Transmission electron microscopy an...

Synthesis of SiO2/Polystyrene Nanocomposite Particles via Miniemulsion Polymerization

Abstract: The SiO2/polystyrene nanocomposite particles were synthesized through miniemulsion polymerization by using sodium lauryl sulfate surfactant (SLS), hexadecane costabilizer in the presence of silica particles coated with methacryloxy(propyl)trimethoxysilane. Core−shell or other interesting morphology composite particles were obtained depending on the size of the silica particles and the surfactant concentration employed. By adjusting these parameters, it was possible to control the size and morphology of the composite particles.

Gold nanoshells on polystyrene cores for control of surface plasmon resonance.

Abstract: A method is presented for synthesizing core-shell structures consisting of monodisperse polystyrene latex nanospheres as cores and gold nanoparticles as shells. Use of polystyrene spheres as the core in these structures is advantageous because they are readily available commercially in a wide range of sizes, and with dyes or other molecules doped into them. Gold nanoparticles, ranging in size from 1 to 20 nm, are prepared by reduction of a gold precursor with sodium citrate or tetrakis(hydroxymethyl)phosphonium chloride (THPC). Carboxylate-terminated polystyrene spheres are functionalized with 2-aminoethanethiol hydrochloride (AET), which forms a peptide bond with carboxylic acid groups on their surface, resulting in a thiol-terminated surface. Gold nanoparticles then bind to the thiol groups to provide up to about 50% coverage of the surface. These nanoparticles serve as seeds for growth of a continuous gold shell by reduction of additional gold precursor. The shell thickness and roughness can be controlled by the size of the nanoparticle seeds as well as by the process of their growth into a continuous shell. By variation of the relative sizes of the latex core and the thickness of the gold overlayer, the plasmon resonance of the nanoshell can be tuned to specific wavelengths across the visible and infrared range of the electromagnetic spectrum, for applications ranging from the construction of photonic crystals to biophotonics. The position and width of the plasmon resonance extinction peak are well-predicted by extended Mie scattering theory.

Nanoparticle‐Induced Phase Transitions in Diblock‐Copolymer Films

Abstract: Incorporation of nanoparticles into self-assembled block copolymers has been explored as an efficient way for improving the mechanical strength, electrical conductivity, and optical properties of materials at the nanometer scale. Recent computer simulations predict that the cooperative self-organization of nanoparticles and block copolymers should yield a wide variety of structures with well-controlled particle arrangements. Such nanostructures may make it possible to fabricate novel functional materials, such as photonic bandgap materials, nanostructured solar cells, highly efficient catalysts, and high-density magnetic storage media. In particular, gold nanoparticles have attracted much interest for applications as catalysts as well as building blocks for electronic devices that operate at the single-electron level. Over the years, several experimental methods have been developed for incorporating inorganic nanoparticles into polymeric nanostructures. These can be divided into two approaches. The first approach involves synthesizing nanoparticles in situ within preformed block-copolymer structures. Preformed micelles of block copolymers containing metal precursors are used as nanoreactors to synthesize nanoparticles selectively in block copolymers. For example, Boontongkong et al. produced micropatterned silver nanoparticles in a poly(styrene-b-acrylic acid) block-copolymer template using this approach. Such an approach is simple and can be easily extended to yield large-area samples. However, controlling the arrangement of the nanoparticles within the periodic structure of the block copolymer is difficult. A second approach, recently proposed as a way to avoid some of the drawbacks of the method described above, uses cooperative self-organization of nanoparticles and block copolymers. Based on theoretical predictions of the morphology of inorganic–organic hybrid materials by Balazs and coworkers, Bockstaller et al. demonstrated hierarchical pattern formation using block copolymers and binary mixtures of different sized hydrophobic nanoparticles. More recently, our previous work showed how grafting different polymers to particle surfaces can be used to precisely control the placement of particles either at the center of one of the block-copolymer domains or at the interface dividing the two block-copolymer domains. This approach exploits enthalpic interactions between the block copolymer and functionalized nanoparticle surfaces to achieve precise particle placement. Such precise control of nanoparticle position in block-copolymer thin films is important for developing highly organized hybrid materials. A particularly interesting example is the work of Russell and co-workers, who showed that the orientation of block-copolymer domains in thin films could be controlled by introducing surface-active nanoparticles that preferentially segregated to the surface of high-surface-energy domains. However, the introduction of particles into block copolymers can also have profound effects on the overall morphology of nanocomposites, especially if the particle loading is high. Nevertheless, the effect of high particle loading on the overall composite morphology has not been explored in previous experimental studies. In this communication, we report a nanoparticle-induced phase transition in a block-copolymer thin film as well as the formation of different structures of gold nanoparticles. When gold nanoparticles are coated with short polymer chains that are chemically identical to one of the copolymer blocks (in what follows we refer to such particles as simply Au particles, but it should be understood that in all cases they are coated with short polymer chains), the particles can self assemble near the center of that copolymer domain, as shown in Figure 1a. In this case, due to the coating of polystyrene (PS) chains on gold particles, the interaction between gold particles and one of the polymer blocks (PS) is neutral, but the interaction between the gold particles and the other block (P2 VP) is very unfavorable. In this report, we show that the lamellar morphology remains unchanged only if the gold nanoparticle volume fraction, cau, is below some critical value, cau,cr. For cau > cau,cr, the local concentration of gold nanoparticles varies along the thickness of the film, and different coexisting morphologies emerge as a function of sample depth. For these experiments, symmetric block copolymers of polystyrene-b-poly(2-vinylpyridine) (PS-b-P2VP) with total molecular masses, Mn, of 59 kg mol –1 and 114 kg mol were used. Gold nanoparticles with an average diameter of 2.5 nm were stabilized by short thiol end-functionalized PS chains (PS-SH; Mn = 1.3 kg mol ) that were grafted to the nanoparticle surfaces to make them compatible with the PS block and to prevent aggregation. The transmission electron microscopy (TEM) image in Figure 1a shows the cross-sectional morphology of the film for cau = 0.14 (< cau,cr) cast from toluene. The lamellae lie parallel to the film surface, as expected. Since the P2VP was preferentially stained by iodine vapor, it appears darker than the PS in C O M M U N IC A TI O N S

Nanochannel array plastics with tailored surface chemistry.

Abstract: The utilization of nanoporous substrates in applications such as selective ion transport, biomolecule separation, seeded templating, and catalysis necessitates the ability to efficiently control pore surface properties. We approached this task by preparing nanoporous polymer monoliths from ABC triblock copolymer precursors that assemble into a cylindrical morphology, where the A block constitutes matrix, C is the removable minor component, and B provides the functionality on the surface of the pores. Polystyrene−polydimethylacrylamide−polylactide (PS−PDMA−PLA) triblock copolymers were prepared by a combination of controlled ring-opening and free-radical polymerization techniques. After selective etching of the PLA cylinders from shear-aligned monoliths, a nanoporous polystyrene matrix containing a hexagonally packed array of hydrophilic, PDMA-coated channels was obtained. Extremely high degrees of alignment and order could be attained, and nanoporous substrates with second-order orientation factors of as ...

Gold nanoparticle/polymer nanocomposites: dispersion of nanoparticles as a function of capping agent molecular weight and grafting density.

Abstract: The dispersion of polymer-covered gold nanoparticles in high molecular weight (MW) polymer matrixes is reported. Complete particle dispersion was achieved for PS125−Au in the polystyrene (PS) matrixes studied (up to and including Mn = 80 000 g/mol). PS19−Au, on the other hand, exhibits complete dispersion in a low MW PS matrix (Mn = 2000 g/mol) but only partial dispersion in higher MW matrixes (up to 80 000 g/mol). Similarly, PEO45−Au is fully dispersed in a low MW poly(ethylene oxide) (PEO) matrix (Mn = 1000 g/mol) but only partially in a higher MW PEO matrix (Mn = 15 000 g/mol). Wetting of the polymer−Au brushes by the polymer matrix is associated with dispersibility. Theory predicts that, for dense polymer brushes, wetting is achieved when the MW of the polymer brush equals (and is greater than) that of the polymer matrix. The observed partial dispersion of the PS19−Au and PEO45−Au nanoparticles in matrixes whose MW is greater than the brush MW is attributable to the existence of a high volume fraction...

Inorganic oxide core, polymer shell nanocomposite as a high K gate dielectric for flexible electronics applications.

Abstract: Organic/inorganic core shell nanoparticles have been synthesized using high K TiO2 as the core nanoparticle, and polystyrene as the shell. This material is easy to process and forms transparent continuous thin films, which exhibit a dielectric constant enhancement of over 3 times that of bulk polystyrene. This new dielectric material has been incorporated into capacitors and thin film transistors (TFTs). Mobilities approaching 0.2 cm2/V·s have been measured for pentacene TFTs incorporating the new TiO2 polystyrene nanostructured gate dielectric, indicating good surface properties for pentacene film growth. This novel strategy for generating high K flexible gate dielectrics will be of value in improving organic and flexible electronic device performance.

Preparation of Homogeneously Dispersed Multiwalled Carbon Nanotube/Polystyrene Nanocomposites via Melt Extrusion Using Trialkyl Imidazolium Compatibilizer

Abstract: Well-dispersed multiwalled carbon nanotube (MWNT)/polystyrene nanocomposites have been prepared via melt extrusion, using trialkylimidazolium tetrafluoroborate-compatibilized MWNTs. Quantification of the improvement is realized via transmission electron microscopy and laser scanning confocal microscopy image analysis. Differential scanning calorimetry and Fourier-transform infrared and X-ray diffraction analysis show evidence for a π-cation, nanotube-imidazolium interaction and the conversion from an interdigitated bilayer, for the imidazolium salt, to an ordered lamellar structure, for the imidazolium on the surface of the MWNTs.

Synthesis and proton conductivity of partially sulfonated poly([vinylidene difluoride-co-hexafluoropropylene]-b-styrene) block copolymers

Abstract: A series of novel, amphiphilic block copolymers comprising of sulfonated poly([vinylidene difluoride-co-hexafluoropropylene]-b-styrene) [P(VDF-co-HFP)-b-SPS] were synthesized. The number-average molecular weights of the fluorous and polystyrene segments were 17 900 and 8100 g/mol, respectively. Sulfonation of the polystyrene segment to different extents provided a series of polymers which were cast into films to yield proton exchange membranes with varying ion exchange capacity (IEC). Proton conductivity of the membranes increased significantly when the IEC was increased from 0.5 to 1.2 mmol/g. For 0.9−1.2 mmol/g IEC membranes, the conductivity was similar to Nafion 117, significantly higher than random copolymers of polystyrene and sulfonated polystyrene, and twice that of nonfluorous block copolymer membranes based on sulfonated poly(styrene-b-[ethylene-co-butylene]-b-styrene) (S-SEBS) and sulfonated hydrogenated poly(butadiene-b-styrene) (S-HPBS) copolymers. TEM revealed a disruption in ordered morphol...

Functionalization of Single-Walled Carbon Nanotubes with Well-Defined Polymers by Radical Coupling

Abstract: Polystyrene and poly[(tert-butyl acrylate)-b-styrene] with well-defined molecular weights and polydispersities were prepared by nitroxide-mediated free-radical polymerization. The homopolymers and block copolymers were used to functionalize shortened single-walled carbon nanotubes (SWNTs) through a radical coupling reaction involving polymer-centered radicals generated at 125 °C via loss of the stable free-radical nitroxide capping agent. The resulting polymer−SWNT composites were fully characterized and were found to be highly soluble in a variety of organic solvents. This solubility could also be altered through chemical modification of the appended polymers. The tert-butyl groups of appended poly[(tert-butyl acrylate)-b-styrene] could be removed to produce poly[(acrylic acid)-b-styrene]-functionalized carbon nanotubes. The resulting composite was found to form aggregates in a mixture of chloroform/methanol (v/v: 1/1) as determined by dynamic light scattering.

Preparation of Fluorescent Carboxyl and Amino Functionalized Polystyrene Particles by Miniemulsion Polymerization as Markers for Cells

Abstract: Summary: A series of fluorescent polystyrene latex particles with carboxyl and amino functionalities on their surface were synthesized by the miniemulsion technique. The fluorescent dye N-(2,6-diisopropylphenyl)perylene-3,4-dicarboximide (PMI) was incorporated into the copolymer nanoparticles formulated from styrene and acrylic acid or styrene and aminoethyl methacrylate hydrochloride. The resulting latexes were stable and showed a monodisperse size distribution. The particle size depended on the amount and nature of the functional comonomer and was in the range 100–175 nm. All latexes were characterized by transmission electron microscopy (TEM), dynamic light scattering, UV-Vis spectroscopy and zeta potential measurements. The amount of surface functional groups was determined by electrolyte titration. Furthermore, the functionalized fluorescent particles were utilized as markers for HeLa cells and cell uptake was visualized using fluorescence microscopy. The correlation of the uptake of nanoparticles with the surface charge was determined by FACS measurements. Confocal fluorescent microscopy of HeLa cells after the uptake of amino functionalized particles (green).

Uptake of Polychlorinated Biphenyls (PCBs) from an Aqueous Medium by Polyethylene, Polyvinyl Chloride, and Polystyrene Films

Abstract: The sorption of selected polychlorinated biphenyl (PCB) congeners (from tri to deca chlorinated) by three food-packaging plastic films [polyethylene, polyvinyl chloride (PVC), and polystyrene] from...

Asymmetrically modified silica particles : A simple particulate surfactant for stabilization of oil droplets in water

Abstract: Spherical silica particles that are able to assemble at a phase boundary of a dual-phase mixture of water and an immiscible organic solvent were prepared by a partial modification of their surface hydroxyl groups with an alkylsilylation agent. Scanning electron microscopic observation of these particles in which their remaining surface hydroxyl groups had been selectively modified with colloidal gold particles revealed that each particle has an asymmetric surface structure: one side of the surface is hydrophilic and the other is hydrophobic. We found that these particles could form a micellar structure in water in the presence of an organic solution of a toluene/polystyrene mixture. The micellar structure was evidenced by formation of golf-ball-like polystyrene particles with dimples imprinting morphologies of the hydrophobic part of modified silica particles.

The effect of foam polystyrene granules on cement composite properties

Abstract: Crumbled recycled foam polystyrene waste as well as spherical large and fine blown polystyrene waste is used to produce the filler for a light thermo-insulating composite, the matrix of which is light foam cement. For better cohesion, fillers are hydrophilizated with foam cement surfactant solution. Polystyrene granules and foam cement concrete interaction schemes are discussed. The investigation of foam cement concrete and polystyrene granule contact zone showed that the contact of these two materials is very close, without any fractures or microcracks. Adherence of the two components depends on the size and shape of granules used. When a polystyrene granule is ripped out of foam cement concrete, the emerged “hole” closely repeats the structure of the granule and there is some polystyrene residue left in it. This proves the fact that foam cement concrete contact zone is stronger than the polystyrene granule material. When fine polystyrene granules are used, it disintegrates along the contact zone. Such composite has the lowest adhesion strength, however, it is stronger in comparison with a composite, made with different foam polystyrene granules, provided by better macrostructure. Strength and thermal conductivity of the composite depend on its density, the filler, its sort and amount used, and is defined by regression equations.

Cross-Linked, Monodisperse, Micron-Sized Polystyrene Particles by Two-Stage Dispersion Polymerization

Abstract: It is well-known that cross-linking agents such as divinylbenzene (DVB) interfere with the dispersion polymerization of styrene in ethanol, a reaction carried out in the presence of polymeric stabilizers such as poly(vinylpyrrolidone). Small amounts of DVB broaden the particle size distribution and lead to irregular particles, whereas modest amounts lead to coagulation. We report that many of these problems can be avoided if one delays the addition of the cross-linking agent until after the end of the nucleation stage of the reaction (e.g., at less than 5% monomer conversion). In this way one can obtain monodisperse polystyrene particles containing 1 wt % ethylene glycol dimethacrylate (EGDMA) as a cross-linker. A second set of problems arises if the cross-linking agent is consumed too early in the reaction, presumably because early network formation limits the swellability of the growing particles. These problems can be overcome by feeding DVB into the reaction over 12 h or by adding EGDMA in successive ...

Amphiphilic Gold Nanoparticles Grafted with Poly(N-isopropylacrylamide) and Polystyrene

Abstract: Two types of amphiphilic gold nanoparticles (AuNP-1 and -2) grafted with a mixture of poly(N-isopropylacrylamide) (PNIPAM) and polystyrene (PS) chains in two different compositions have been successfully prepared with the “grafting-to” method in a homogeneous THF phase. These AuNPs were thoroughly characterized by FTIR, 1H NMR, UV−vis, high-resolution transmission electron microscopy, thermogravimetric analysis, and dynamic light scattering to determine the total number of polymer chains bound to the gold nanoparticles, the ratio between PNIPAM and PS chains, and the size of the gold core. Langmuir monolayer experiments at the air−water interface of the two types of AuNPs revealed different compression isotherms of the surface pressure vs particle area (π−A curve) conducted at 20 °C. These amphiphilic gold nanoparticles can be regarded as analogues of amphiphilic diblock copolymers at the air−water interface. The compression isotherm of AuNP-2 with a PNIPAM:PS ratio of 2:1 showed several characteristic re...

Nuclear magnetic resonance monitoring of chain‐end functionality in the atom transfer radical polymerization of styrene

Abstract: The evolution of the bromine end functionality during the bulk atom transfer radical polymerization (ATRP) of styrene [in the presence of the catalyst CuBr/4,4'-di-(5-nonyl)-2,2'-bipyridine] was monitored with 600-MHz 1 H NMR. A decrease in the functionality versus the conversion was observed. The loss of functionality was especially significant at very high conversions (>90%). The experimental data were compared with a kinetic model of styrene ATRP. The latter indicated that the loss of chain-end functionality was partly due to bimolecular terminations but was mainly due to β-H elimination reactions induced by the copper(II) deactivator. These elimination reactions, which occurred later in the reaction, did not significantly affect the polymer molecular weights and the polydispersity. Therefore, a linear evolution of the molecular weights and low-polydispersity polymers were still observed, despite a loss of functionality. Understanding these side reactions helped in the selection of the proper conditions for reducing the contribution of the elimination process and for preparing well-defined polystyrene (number-average molecular weight ∼10,000 g mol -1 ; weight-average molecular weight/number-average molecular weight ∼1.1) with a high functionality (92%).

Coating noble metal nanocrystals (Ag, Au, Pd, and Pt) on polystyrene spheres via ultrasound irradiation.

Abstract: The method of ultrasound irradiation is used for anchoring metallic nanocrystals (Ag, Au, Pd, and Pt) onto the surface of polystyrene spheres. In former studies, almost all the sonochemically prepared, coated metallic nanomaterials were formed as amorphous nanoparticles (Pol, V. G.; et al. Langmuir 2002, 18, 3352; Pol, V. G.; et al. Chem. Mater. 2003, 15, 1111; Zhong, Z. Y.; et al. Chem. Mater. 1999, 11 (9), 2350; Pol, V. G.; et al. Chem. Mater. 2003, 15, 1378), which were coated on various substrates (silica spheres, carbon spherules, titania, and alumina). On the other hand, the noble metal nanoparticles deposited on polystyrene spheres via ultrasound irradiation yielded nanocrystalline Ag, Au, Pd, and Pt particles on the surface of polystyrene as as-synthesized materials. The sonochemical mechanism is proposed based on chemical interactions between the particles.

Carbon Nanotube-Adsorbed Polystyrene and Poly(methyl methacrylate) Microspheres

Abstract: Monodisperse and spherical PS and PMMA microspheres, which are only conducting on the surface by the adsorption of carbon nanotubes, were used as the dispersed phase of electrorheological fluids.

Hybrid Dissymmetrical Colloidal Particles

Abstract: Colloidal particles with a controlled morphology combining both organic and inorganic parts were synthesized through a seeded emulsion polymerization process. Silica seed particles from 50 to 150 nm were first surface-modified by adsorption of an oxyethylene-based macromonomer or covalent grafting of a trialkoxysilane derivative. Then, emulsion polymerization of styrene was carried out in the presence of these particles, the formation of polystyrene nodules being highly favored at the silica surface in such conditions. While varying different experimental parameters, we have demonstrated that the ratio between the number of silica seeds and the number of growing nodules is a key parameter in controlling the morphology of the final hybrid nanoparticles. For instance, in the particular case when this ratio was close to 1, dumbbell-like or snowman-like particles were obtained. Further selective surface modification of their silica moiety was also tested successfully, indicating a potential application of these hybrid particles as original building blocks toward supraparticulate assemblies

Preparation of Core‐Sheath Nanofibers from Conducting Polymer Blends

Abstract: Summary: Core-sheath nanofibers with conductive polyaniline as the core and an insulating polymer as the sheath were prepared by electrospinning of blends of polyaniline with either polystyrene or polycarbonate. These unique core-sheath structures offer potential in a number of applications including nanoelectronics. When polyaniline was blended with poly(methyl methacrylate) and poly(ethylene oxide), only isolated domains of polyaniline in beadlike structures were formed. The phase morphology of electrospun fibers is thought to be dependent on the high-surface tension of the solution and the molecular weight of the polymers. Incompatibility of the polymers and low molecular weight of compositions played a key role in the formation of core-sheath structures, as opposed to co-continuous morphologies. TEM image of electrospun polyaniline/polystyrene nanofiber after staining by OsO4. The dark regions are polyaniline.