Showing papers on "Polystyrene published in 2001"

Multilayered Titania, Silica, and Laponite Nanoparticle Coatings on Polystyrene Colloidal Templates and Resulting Inorganic Hollow Spheres

Abstract: The applicability of the layer-by-layer (LbL) technique for the formation of a range of polymer-core inorganic-shell particles and inorganic hollow spheres is demonstrated Titanium dioxide, silica, and Laponite nanoparticles were used as the inorganic building blocks for multilayer formation on polystyrene (PS) sphere templates Composite organic−inorganic particles were formed by the controlled assembly of the preformed nanoparticles in alternation with oppositely charged polyelectrolytes onto PS microspheres The influence of nanoparticle type, shape (spherical to sheetlike), and size (3−100 nm), and the diameter of the PS sphere templates (210−640 nm) on the formation of multilayer shells was examined by transmission and scanning electron microscopy In addition, the LbL technique for coating polymer spheres has been shown to be adaptable with small variations in the coating steps used to optimize the nanoparticle coatings of the different materials For example, the number of polyelectrolyte multilay

Preparation and Characterization of Titania-Coated Polystyrene Spheres and Hollow Titania Shells

Abstract: A procedure has been developed to coat colloidal polystyrene spheres with a smooth and well-defined layer of amorphous titanium dioxide. The thickness of the coating can be easily varied from a few nanometers upward and can be increased further by seeded growth. The resulting composite particles are very monodisperse. The core−shell particles can be turned into spherical hollow titania shells by dissolution of the polystyrene cores in suspension or by calcination of the dried particles in a furnace. Calcination also crystallizes the titania into its anatase form. The coated particles were characterized with electrophoresis, thermogravimetric analysis, X-ray diffraction, electron microscopy, and light scattering. We find that the coating strongly densifies when the particles are dried but that it is not dense and about twice as thick when the particles are still in suspension. Calcination results in spherical shells composed of a dense arrangement of TiO2 (anatase) nanocrystals. This way, we obtained collo...

Poly(methyl methacrylate) and polystyrene/clay nanocomposites prepared by in-situ polymerization

Abstract: Poly(methyl methacrylate) (PMMA) and polystyrene (PS)/clay nanocomposites were prepared via in-situ bulk polymerization. The compatibility of the initiator and monomer with the clay surface was found to profoundly affect the clay dispersion. By using a surfactant containing a polymerizable group to modify the clay surface, exfoliated PMMA and PS/clay nanocomposites were synthesized. The clay dispersion was quantified by both X-ray diffraction (XRD) and transmission electron microscopy (TEM). The dimension stability of nanocomposites was studied and related to both nanoscale (layer separation) and mesoscale (long-range distribution) clay dispersion.

Preparation of Polystyrene- and Silica-Coated Gold Nanorods and Their Use as Templates for the Synthesis of Hollow Nanotubes

Abstract: We report the preparation of polystyrene and silica-coated Au nanorods (aspect ratio 13 with 16 nm short axis). The coating resulted in a modification of the optical properties of the Au nanorods. Dissolution of the Au core from the polystyrene- and silica-coated Au nanorods using KCN enabled the formation of hollow polystyrene and silica nanotubes.

Effect of Interfacial Interactions on the Glass Transition of Polymer Thin Films

Abstract: Previous studies had demonstrated that the Tg of polymer thin films is strongly dependent on the interactions, γs, between the polymer and the underlying substrate. We present a study of the glass transition temperature, Tg, in thin films of polystyrene, PS, as a function of film thickness and as a function of γs by measuring the change in the thermal expansion using X-ray reflectivity. The Tg for PS on native silicon oxide was found to decrease with decreasing film thickness, consistent with results by others. Using random copolymers of styrene and methyl methacrylate anchored to the substrate, γs could be varied by changing the styrene fraction, f. With a constant PS film thickness of 330 A, the Tg was depressed by ∼20 °C as f was decreased from 1 to 0.75. An analysis analogous to the Gibbs−Thompson model indicated that the surface energy was not a suitable parameter to use to describe the effects of interfacial interactions on the Tg of polymer thin films. An associated local fractional change in the s...

Sonochemically Produced ZnS-Coated Polystyrene Core−Shell Particles for Use in Photonic Crystals

Abstract: Zinc sulfide films were grown on carboxyl-modified polystyrene microspheres (PS-CO2) through sonochemical deposition in an aqueous bath containing zinc acetate and sulfide, released through the hydrolysis of thioacetamide. The resulting particles were “optically hollow”, due to a large refractive index contrast between the core and shell materials. Continuous, uniform films were obtained after 3−4 h and reached a maximum thickness of 70−80 nm after 13 h of growth, as characterized by transmission electron microscopy (TEM). Aggregation was minimized by subsequent modification of the core−shell particles with mercaptoacetic acid to increase their surface charge and produce good colloidal suspensions. Oscillations in the optical spectra of dilute suspensions of the particles were indicative of interference patterns as expected from Mie light scattering calculations. X-ray diffraction (XRD) patterns match the zinc blende structure of ZnS and indicate a compression in the crystal lattice (a = 5.305 ± 0.037 A),...

Polymer nanocomposites : synthesis, characterization, and modeling

Abstract: Preface 1. Polymer Nanocomposites: Introduction 2. Commercialization of Polymer Nanocomposites 3. PMMA Nanocomposites Synthesized by Emulsion Polymerization 4. Boron Nitride Fillers for Organic Polymer Composites 5. Surface-Initiated Anionic Polymerization: Tethered Polymer Brushes on Silicate Flat Surfaces 6. Predicting the Phase Behavior of Polymer-Clay Nanocomposites: The Role of End-Functionalized Chaines 7. Carbon Black Structure and Associations in Filled Rubbers 8. An Investigative Study of Polymer Adsorption to Smectite Clay: Polyelectrolytes and Sodium Montmorillonite 9. Mesoscopic Structure of Polymer-Inorganic Nanocomposites 10. Solution and Solid-State NMR Spectroscopy of Nylon 6-Montmorillonite Clay Nanocomposites 11. Studies of Organically Modified Clays by Scattering Techniques 12. Thin Film Organically Modified Layered Silicate-Polymer Hybrid Materials 13. Influence of Layered-Silicates on the Rheological Properties of Diblock Copolymer Nanocomposites 14. Dispersion and Nucleating Effects of Clay Fillers in Nanocomposite Polymer Films 15. Molecular Simulations of Ultra-Confined Polymers: Polystyrene Intercalated in Layered-Silicates 16. A Coarse-Grained Simulation Study of Polymer Melt Intercalation in Layered Nanostructures AUTHOR INDEX SUBJECT INDEX

Effects of Chain Ends and Chain Entanglement on the Glass Transition Temperature of Polymer Thin Films

Abstract: Monodispersed polystyrene with different molecular weights, Mw, from below the entanglement molecular weight, Me (∼20K Da), to well above was studied for effects of chain ends and chain entanglemen...

FTIR Spectra, Thermal Properties, and Dispersibility of a Polystyrene/Montmorillonite Nanocomposite

Abstract: This article presents FTIR spectra, thermal properties, and dispersibility of an exfoliated polystyrene/montmorillonite (PS/montmorillonite) nanocomposite. First, the infrared bands of CTAB-montmorillonite and the PS/montmorillonite nanocomposite are assigned tentatively. FTIR results indicate that the montmorillonite is transformed into small particles and dispersed homogeneously in the PS matrix. The PS/montmorillonite nanocomposite exhibits a higher decomposition onset temperature and glass transition temperature, which may be due to the nanoscale dispersion of the montmorillonite particles. The powder sample can be perfectly dispersed in toluene and chloroform, partly dispersed in benzene, and is not dispersible in acetone.

Preparation of polystyrene–graphite conducting nanocomposites via intercalation polymerization

Abstract: In situ polymerization of styrene was conducted in the presence of expanded graphite obtained by rapid heating of a graphite intercalation compound (GIC), to form a polystyrene–expanded graphite conducting composite. The composite showed excellent electrically conducting properties even though the graphite content was much lower than in normal composites. The transition of the composite from an electrical insulator to an electrical semiconductor occurred when the graphite content was 1.8 wt%, which is much lower than that of conventional conducting polymer composites. TEM, SEM and other studies suggest that the graphite was dispersed in the form of nanosheets in a polymer matrix with a thickness of 10–30 nm, without modification of the space between carbon layers and the structure of the graphite crystallites. The composite exhibited high electrical conductivity of 10−2 S cm−1 when the graphite content was 2.8–3.0 wt%. This great improvement of conductivity could be attributed to the high aspect ratio (width-to-thickness) of the graphite nanosheets. The rolling process strongly affected the conductivity and the mechanical properties of the composite. © 2001 Society of Chemical Industry

Absolute Molecular Orientational Distribution of the Polystyrene Surface

Abstract: Vibrationally resonant sum frequency generation (VR-SFG) has been used to study the absolute molecular orientational distribution of the pendant phenyl groups at the free surface of polystyrene (PS) thin films on oxidized Si substrates. Characterization of the dependence of the VR-SFG on film thickness allows unique identification of the origin of the signal, e.g., free surface, bulk, or buried interface. For films <400 nm thick, the dominant source of vibrationally resonant signal is the PS/air interface, while the dominant source of the nonresonant background is the Si/SiO2 interface. VR-SFG of a self-assembled phenylsiloxane layer is used to calibrate the relative phase between the vibrationally resonant phenyl ring hyperpolarizability and the Si/SiO2 interface nonresonant hyperpolarizability. It is found that the phenyl groups are ordered at the PS/air interface and are oriented away from the polymer film. Quantitative analyses of the orientational distribution for both the PS free interface and the p...

Rapid FTIR method for quantification of styrene‐butadiene type copolymers in bitumen

Abstract: The mid-IR molar absorptivity for polystyrene (PS) and polybutadiene (PB) blocks were obtained for five styrene-butadiene-styrene (SBS) and SB copolymers, including linear, branched, and star copolymers, and their blends with bitumen. The average absorptivity for PS and PB blocks was 277 and 69 L mol−1 cm−1 and it was little affected by the S/B ratio or the copolymer architecture. In the presence of bitumen, Beer's law was obeyed but the respective PS and PB absorptivity was 242 and 68 L mol−1 cm−1, possibly because of weak interactions between the copolymer and bitumen. The absorptivity values were used to calculate the concentration of SB-type copolymers in blends with bitumen with an accuracy of 10% or better. The method can be used to probe the stability of bitumen–copolymer blends in storage at 165°C, to determine the copolymer concentration in commercial polymer modified bitumen (PMB), and to assess the resistance of PMB to weathering. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 1034–1041, 2001

Shape and volume of cavities in thermoplastic molecular sieves based on syndiotactic polystyrene

Abstract: The empty space in different crystalline and clathrate phases of syndiotactic polystyrene (s-PS) is evaluated by a numerical procedure. It is shown that the δ form is nanoporous and includes two identical cavities per unit cell, whose shape and volume are characterized. As a consequence of clathration, the unit cell of the δ form is enlarged and the cavity is able to include molecules definitely larger than its starting size. Sorption experiments of nitrogen at 77 K for s-PS powders in different crystalline forms are also presented. These can be interpreted by inclusion of three nitrogen molecules per cavity of the δ crystalline phase and hence give an independent estimate of its volume.

Crystal Orientation Changes in Two-Dimensionally Confined Nanocylinders in a Poly(ethylene oxide)-b-polystyrene/Polystyrene Blend

Abstract: A lamella-forming poly(ethylene oxide)-b-polystyrene (PEO-b-PS) diblock copolymer has been blended with a low molecular weight polystyrene (PS) homopolymer to form a miscible polymer blend. The PEO volume fraction is 0.32, and the order−disorder transition temperature (TODT) of this blend is 175 °C. Therefore, the PEO blocks form nanocylinders surrounded by a PS matrix below the TODT. Since the glass transition temperature of the PS is 64 °C and the PEO crystal melting occurs at ∼50 °C, the PEO-block crystallization takes place in a two-dimensionally confined glassy environment. The cylinder diameter is determined to be 13.7 nm, based on small-angle X-ray scattering (SAXS) and transmission electron microscopy results. Using simultaneous two-dimensional SAXS and wide-angle X-ray scattering techniques, the crystal orientation (the c-axes of the PEO crystals) within the nanocylinders is found to change simply depending upon the crystallization temperature (Tc). At very low Tc (<−30 °C), PEO crystals are rand...

Dewetting of Highly Elastic Thin Polymer Films

Abstract: Investigations of the opening of holes in thin, almost glassy polystyrene films deposited onto silicon wafers coated with a polydimethylsiloxane monolayer revealed strong deviations from the behavior of pure liquids. At early stages, these holes grew independent of the molecular weight of the polymer and without the formation of a rim. At later stages, a highly asymmetric rim was built up with the maximum height increasing linearly with the diameter of the hole. As the polymer cannot flow under the conditions of the experiments, our experiments demonstrate that capillary forces are able to provoke plastic deformation on a micron scale in thin quasisolid films.

Remote Oxidation of Organic Compounds by UV-Irradiated TiO2 via the Gas Phase

Abstract: The remote oxidation of organic materials via the gas phase was studied in detail. A TiO2-coated glass plate was faced to an organic film separated by a small gap (50 μm to 2.2 mm), and the TiO2 was irradiated with UV light. As a result, aromatic and aliphatic substances were oxygenated and decomposed to generate CO2 by active oxygen species that were generated at the TiO2 surface and transported in the gas phase. The amount of CO2 generated during the irradiation with 1 mol of photons was estimated to be 2 × 10-4 mol for polystyrene oxidation and 3 × 10-5 mol for polyethylene oxidation. The active oxygen species that oxidizes the organic substrates is most likely to be HO•. Strong evidence for this is the result that the organic materials were oxidized by chemically generated HO• in a similar way.

Block copolymers of poly(styrene) and poly(acrylic acid) of various molar masses, topologies, and compositions prepared via controlled/ living radical polymerization. Application as stabilizers in emulsion polymerization

Abstract: A series of well-defined diblock, triblock, and star-block copolymers composed of polystyrene and poly(acrylic acid) were synthesized by controlled/living radical polymerization and used as stabilizers in emulsion polymerization under alkaline conditions. The structure of the copolymers, the size of the blocks, and the composition were varied and their efficiency as stabilizers was correlated with their structural characteristics. The block length was varied from 10 to 30 units for the polystyrene block and from 13 to 266 units for the poly(acrylic acid) block. The copolymers appeared to be efficient stabilizers down to a block copolymer-to-monomer ratio of less than 0.5 wt %. From the comparison of the effect of the different structures and compositions, it was shown that the diblock copolymers were particularly efficient and that the optimal composition was about 10 styrene units and a maximum of 50 acrylic acid units. The triblock and star-block copolymers with external hydrophilic blocks did not behav...

Extraordinary elevation of the glass transition temperature of thin polymer films grafted to silicon oxide substrates

Abstract: We used local thermal analysis and ellipsometry to measure the glass transition temperatures (Tg) of supported thin films of poly(4-hydroxystyrene) (PHS) and hydroxy terminated polystyrene (PS-OH). The films were spuncast from solution onto silicon oxide substrates and annealed under vacuum at elevated temperatures to graft the polymer to the substrate. Grafting was verified and characterized in terms of the thickness of and the advancing contact angle of water on the residual layer after solvent extraction. For PHS, each segment of the polymer chain was capable of grafting to the substrate. The thickness of the residual layer increased with increasing annealing temperature. For this polymer the critical thickness below which the Tg of the film deviated from the bulk value was nearly 200 nm after annealing at the highest temperature (190 °C); the Tg of films 100 nm thick or less were elevated by more than 50 °C above the bulk value. For PS-OH films the polymer was only capable of grafting at one chain end...

Dendrimers and Hyperbranched Polymers as High‐Loading Supports for Organic Synthesis

Abstract: Polymeric supports have become a big necessity for automated synthesis and combinatorial chemistry, yet, the loading capacities of most polystyrene resins are very limited (typically <1.5 mmol g−1). Dendrimers and hyperbranched polymers have been discussed for this application and now became readily available. These soluble polymers can either be used directly as high-loading supports for substrates, reagents, and catalysts or alternatively in hybrid polymers linked to conventional polystyrene resins.

A self-organized network of nanochannels enhances ion conductivity through polymer films

Abstract: Graft polymers of well-defined structure consisting of monodisperse poly(sodium styrene sulfonate) graft chains and a polystyrene backbone have been synthesized by stable free radical polymerization. Proton-exchange membranes prepared from these polymers possess phase-separated nanochannels of ionic domains and exhibit larger proton conductivity compared to analogous membranes prepared from random copolymers of sodium styrene sulfonate and styrene.

Dynamics near the Glass Temperature of Low Molecular Weight Cyclic Polystyrene

Abstract: The segmental relaxation properties of a low molecular weight (4.6 kg/mol), cyclic polystyrene (PS) were characterized. The sample was obtained by fractionation using HPLC at the chromatographic critical condition, which yields a ring uncontaminated by its linear precursor. Both the glass temperature and the temperature dependence of the segmental relaxation times for the ring PS were equivalent to the high molecular weight limiting values for the linear polymer. These results are interpreted by considering the configurational mobility of a polymer lacking chain ends.