Glass Transition Temperature Of Polystyrene Research Articles

Temperature dependence of oxygen diffusion into clay‐doped PS films

AbstractFluorescence technique was employed for the measurement of the diffusion coefficient of oxygen into polystyrene (PS) latex/modified Na‐activated bentonite (MNaLB) clay composite films. Three different MNaLB content (0, 5, and 20 wt%) composite films were prepared from PS/MNaLB mixtures by annealing them at 200°C, above the glass transition temperature of PS for 10 min. To determine the diffusivity of oxygen in PS/MNaLB composite films, diffusion measurements were performed over the temperature range from 25 to 70°C. Pyrene (P) was used as the fluorescent agent. The diffusion coefficients (D) of oxygen were determined by combining the fluorescence quenching method with Fickian transport model, and were found as a function of temperature for each MNaLB content film. The results showed that D values are strongly dependent on both temperature and clay content in composite film. It was also observed that D coefficients obey Arrhenius behavior, from where diffusion activation energies were measured. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers

Covalent polymer functionalization of graphene nanosheets and mechanical properties of composites

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.

Environmental responses of nanostructured polyaniline films based on polystyrene–polyaniline core–shell particles

This paper describes a simple method for fabricating nanostructured polyaniline (PANI) films from polystyrene (PS)–PANI core–shell particles and the environmental responses of the films. Monodisperse PS latex particles synthesized via surfactant-free emulsion polymerization were used as cores, onto whose surface aniline monomers adsorbed with the aid of sodium dodecyl sulfate and were polymerized by adding ammonium peroxydisulfate. The resulting suspensions of core–shell particles were then drop-cast onto substrates and dried. Films composed of fragments of thin PANI shells of tens of nanometers were obtained after the removal of PS by tetrahydrofuran extraction. Another kind of films was prepared by heating the core–shell particles above the glass transition temperature of PS for a short time before the extraction. The morphology was observed using scanning electron microscopy, and the UV–vis spectra were recorded by a spectrometer. Furthermore, we examined the resistance responses of the films to dry gas flow, ethanol vapor, hydrogen chloride, and ammonia. The high sensitivity and fast response should be due to the large surface area interacting with analytes and porosity that facilitates diffusion. In addition, the effect of the packing of PANI shells in the films on the responses was discussed.

Tuning the electrical switching of polymer/fullerene nanocomposite thin film devices by control of morphology

The working principles of thin film organic memory devices remain debated and tunability has been less presented. We show that the nanostructure of [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) and polystyrene (PS) allows facile tuning of switching behavior for low PCBM concentrations upon annealing above the glass transition temperature of PS. By increasing the PCBM concentration from 2 to 6 wt %, the switching voltage from off to on state during the first voltage sweep systematically decreases. In subsequent voltage sweeps negative differential resistance effect is observed. Above ca. 7 wt %, chains of PCBM clusters couple the electrodes, which leads to Ohmic behavior.

Efeito da adição de diferentes copolímeros em blendas HDPE/HIPS pós-consumo: morfologia de fases e propriedades térmicas

Blendas de poliolefinas/HIPS têm sido exploradas para obter filmes especiais com determinadas propriedades desejadas, tornando imperativo desenvolver vários estudos para um melhor conhecimento do comportamento desses materiais. Neste trabalho, efeitos da adição dos copolímeros comerciais de estireno-butadieno multibloco (SBS) e de estireno-(etileno-co-butileno)-estireno (SEBS) tribloco linear em blendas pós-consumo de HDPE e HIPS são reportados. A diminuição nas dimensões da microfase dispersa, aliada à rugosidade superficial da fase HDPE após extração seletiva do HIPS, independentemente de a fase matriz ser HIPS ou HDPE, mostraram mais eficiência do SEBS como modificador interfacial de tensão ou como surfactante entre os diferentes domínios quando comparado com o SBS. Os resultados das caracterizações térmicas, por exemplo, menor Tm e menor grau de cristalinidade do HDPE, e maior Tg do poliestireno na presença de SEBS corroboraram esta conclusão, como será discutido posteriormente.

Control of Dispersion State of Silsesquioxane Nanofillers for Stabilization of Polystyrene Thin Films

The influence of the dispersion states of the nanofillers on the dewetting behavior of the polymer thin film was investigated. Polyhedral oligomeric silsesquioxanes (POSS) with various substituents were added into polystyrene (PS) thin films as the nanofillers. The dewetting rate of the films drastically changed with the surface substituents of POSS additives. Neutron reflectivity measurements indicated that the difference of the dewetting rate was associated with the dispersion state of POSS additives in the films. POSS with phenethyl groups (PhPOSS), which homogeneously dispersed into the films, resulted in the decrease of the glass transition temperature of PS and the enhancement of the dewetting of the films. POSS with a fluoroalkyl group (CpPOSS-R f) segregated to the film surface and showed the retardation of the dewetting by the decrease of the surface energy of the film. POSS with hydroxyl groups (CpPOSS-2OH) segregated to the film surface and film-substrate interface and led to the elimination of the dewetting, suggesting the importance of the interfacial segregation for the inhibition of dewetting. These results revealed the strong relationship between the dispersion state of the nanofillers and the dewetting of the nanofilled films.

Inside Front Cover: Superhydrophobic Surfaces Generated from Water‐Borne Dispersions of Hierarchically Assembled Nanoparticles Coated with a Reversibly Switchable Shell (Adv. Mater. 1/2008)

AbstractOn p. 200, Sergiy Minko and co‐workers report on the fabrication of a superhydrophobic coating from aqueous dispersions of hybrid responsive nanoparticles with no application of surfactants and organic solvents. A suspension of the particles forms a textured hydrophilic coating upon casting. Heating above the glass transition temperature of polystyrene, or treatment in acidic water, resulted in backward and forward switching between the superhydrophobic and the hydrophilic material, respectively.

Direct Observation of Nanoparticle Embedding into the Surface of a Polymer Melt

Direct embedding of metal nanoparticles (NPs) into the surface of a polymer melt is observed by TEM and a new embedding mechanism proposed. Upon annealing above the glass transition temperature of polystyrene (PS), NPs (20 nm gold) are rapidly covered by a thin PS wetting layer, h* approximately 1.3-1.8 nm (i.e., about two or three monomers). Because it creates capillary pressure on a NP, this "universal" wetting layer is proposed to be responsible for NP embedding. The value of h* is independent of the molecular weight of PS and constant during the embedding process. The value of h* is found to be similar to the equilibrium wetting layer thickness of a polymer melt spreading on a metal substrate. Using a model that includes the spreading coefficient, long-range van der Waals interactions, and a chain-stretching penalty, h* is shown to be independent of the molecular weight of the polymer. Using this model and the measured value of h*, the interfacial energy between Au NP and PS is estimated to be 8.7 J/m2.

Morphology of side chain liquid crystalline block copolymer thin films and effects of thermal annealing

AbstractThe self‐assembly behavior of siloxane based side chain liquid crystalline block copolymer thin films are investigated via grazing incidence small angle X‐ray scattering and atomic force microscopy. The as‐spun films displayed polystyrene cylinders perpendicular to the substrate and the cylinders reoriented parallel to the surface after thermal annealing. The morphology observed in the as‐spun films is resultant from the orientation of the smectic LC mesophase relative to the substrate. Annealing above both the polystyrene glass transition temperature and the smectic to isotropic transition temperature eliminates the influence of the LC phase, leading to a reorientation of the morphology that minimizes the interfacial energy of the system. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 3263–3266, 2007

An energetic criterion to compare the evolution of thermally-excited surface disturbances and nanoindentation-induced defects on thin polymer films

A criterion is developed to predict the resulting evolution process of the following surface defects on thin (17 nm) polystyrene (PS) films on silicon (Si): (i) nanoindentation-induced indents which grow after being heated above the glass transition temperature of PS, T g, leading to dewetting; (ii) nanoindentation-induced indents which level at temperatures above the T g, resulting in a flat polymer surface and (iii) indents which are formed and grow spontaneously by thermal treatment above the T g (thermal film break up). The criterion is based on the concept of the excess surface energy, Δ F γ , which was introduced in previous reports for cases (i) and (ii). Here, a similar energetic term is used which corresponds only to the effect of the depressions, Δ F γ(D) . The effect of the rims which surround the depressions in cases (i) and (ii) is not taken into account. Measurements of Δ F γ(D) , performed by atomic force microscopy, prior to any treatment above the T g suggest that growing depressions (cases i and iii) correspond to Δ F γ(D) > 1.5 × 10 −16 J while for healing depressions (case ii) Δ F γ(D) < 1.8 × 10 −16 J. A critical region of Δ F γ(D) exists from 1.5 × 10 −16 J to 1.8 × 10 −16 J. Depressions which correspond to this, rather short, region can either grow or heal.

Characterization of Au nano-cluster formation on and diffusion in polystyrene using XPS peak shape analysis

XPS peak shape analysis is used as a novel and nondestructive method to study Au nano-cluster growth mechanism on polystyrene (PS) as a function of deposition as well as diffusion and distribution of the nano-clusters in PS as a function of subsequent annealing at temperatures in the range from room temperature to above the glass transition temperature of PS. The Au nano-cluster size and density are determined for four different amounts of Au deposition. It is shown that this nondestructive method can give all mentioned information on such a metalized polymer without the need for any other complimentary and time consuming technique such as AFM, TEM and the destructive technique XTEM. Thus this method is suitable to monitor and control the degree of intermixing of metal nano-clusters and polymers which is of high technological interest.

Thickness dependence of free‐standing thin films

AbstractBelow a critical thickness, of about 60 nm, the glass transition temperature of polystyrene (PS) films decreases with film thickness, as demonstrated using free‐standing films. A geometrical model is developed here describing this phenomenon in the case of ideal (Gaussian) chains. This model, which can be considered as an application of the free volume model, assumes that the decrease of the glass transition temperature from thick to ultrathin films is due to the modification of the interpenetration between neighboring chains. The theoretical curve deduced from the model is in excellent agreement with the PS experimental results, without using any adjustable parameters. From these results, it can be concluded that new chain motions, usually buried in bulk samples, are expressed by the presence of the surface. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 10–17, 2007

Observation of nondegenerate cavity modes for a distorted polystyrene microsphere

Nondegenerate azimuthal morphology-dependent resonances are observed for a distorted, fluorescently labeled polystyrene microsphere levitated in a quadrupole ion trap. Modeling the individual resonances by using perturbation theory allows a determination of quadrupole and octupole distortion parameters. The particle's shape changes slowly over the course of the measurement and eventually becomes spherical. The morphological changes are facilitated by laser heating of the particle above the polystyrene glass transition temperature. We demonstrate a method of transforming a trapped particle to a sphere and rendering its azimuthal modes degenerate.

Foaming of Polystyrene/Supercritical CO&lt;sub&gt;2&lt;/sub&gt; in Rapid Decompression and Cooling Process

Foaming of polystyrene (PS)/ supercritical dioxide system was studied in a batch process in order to achieve a better understanding of supercritical CO2 diffusion mechanism in polymer and foaming condition. In this study, PS sample was treated with CO2 at 5-30 MPa and 40-160°C, soaking times was about 30-120min.Using gravimetric method, the solubility of CO2 in PS was obtained. The study datum shows that the solubility of CO2 in PS increases with increment of pressures, but decreases with the increment of temperature. The sorbed amount of CO2 is from 0.02 % (7MPa,160°C) to 0.11%(30MPa,40°C).The relation of glass transition temperature, volume expansion ratio, cells density of foaming with pressure and temperature also was discussed individually. The glass transition temperature of PS swelled with CO2 is 80°C-95°C, which is lower than the glass transition temperature of pure PS by 10°C-25°C. The cell density increases as the pressure increase, and it decrease as the temperature increase.

Morphology and characterization of conductive films based on polyaniline-coated polystyrene latexes

The polyaniline (PANI)-coated polystyrene (PS) latexes were synthesized, and the electrically conductive films were prepared thereafter. The weight ratio of PANI was 5%. Thermal analysis of the latices was performed using DSC and TGA. In this study, the electrically conductive films were prepared above the PS glass transition temperature (Tg). During the film formation, the effects of the annealing temperature and atmosphere (air or N2) on the film resistance were investigated. In addition, the film morphology was observed utilizing scanning electron microscopy. The film resistance decreased in the initial heating stage due to the increasing temperature and the compaction of film. Then the film resistance increased with further annealing due to the aging of PANI. Typically, the film resistance was about 6000 Ω/sq, and the conductivity was 0.3 S/cm. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 5406–5413, 2006

The influence of hematite nano-crystals on the thermal stability of polystyrene

A synthetic procedure based on thermal hydrolysis of iron(III) chloride solutions for the preparation of hematite (α-Fe 2O 3) sol consisting of nano-crystals (NCs) is described. The α-Fe 2O 3 NCs were characterized by transmission electron microscopy and X-ray diffraction measurements. Incorporation of α-Fe 2O 3 NCs into polystyrene (PS) was based on the transfer of α-Fe 2O 3 NCs from the aqueous phase to the organic solvent. A significant shift in the glass transition temperature of PS by 17 °C towards higher temperatures was observed after incorporation of α-Fe 2O 3 NCs. Also, the thermal stability of PS was improved by about 100 °C in the presence of 3.6 wt% of α-Fe 2O 3 NCs.

Metal Nanoparticles on Polymer Surfaces: 5. Catalytic Activity of Colloidal Platinum Films Incorporated in Polystyrene Surface Layer

The fundamental possibility to enlarge Pt nanoparticles in monolayer ensembles formed on polystyrene surfaces by the adsorption from hydrosol in solution of isopropanol and K2PtCl4 is demonstrated for the first time. The enlargement of “seeding” nanoparticles is performed after their preliminary incorporation (partial embedding) into the polymer surface layer by the annealing of a system within the range between “surface” and “bulk” glass transition temperatures of polystyrene. It is shown that a colloidal film of metallic platinum with a thickness up to 200 nm is formed in the course of enlargement and it is mechanically fixed in the polymer surface layer. Such a system exhibits, over a long time, high catalytic activity in the model reaction of methyl viologen reduction with hydrogen.

Kinetics-controlled compatibilization of immiscible polypropylene/polystyrene blends using nano-SiO 2 particles

Rigid inorganic filler has been long time used as a reinforcement agent for polymer materials. Recently, more work is focused on the possibility that using filler as a compatibilizer for immiscible polymer blends. In this article, we reported our efforts on the change of phase morphology and properties of immiscible polypropylene(PP)/polystyrene(PS) blends compatibilized with nano-SiO 2 particles. The effects of filler content and mixing time on the phase morphology, crystallization behavior, rheology, and mechanical properties were investigated by SEM, DSC, ARES and mechanical test. A drastic reduction of PS phase size and a very homogeneous size distribution were observed by introducing nano-SiO 2 particles in the blends at short mixing time. However, at longer mixing time an increase of PS size was seen again, indicating a kinetics-controlled compatibilization. This conclusion was further supported by the unchanged glass transition temperature of PS and by increased viscosity in the blends after adding nano-SiO 2 particles. The compatibilization mechanism of nano-SiO 2 particles in PP/PS blends was proposed based on kinetics consideration.

Synthesis and characterization of new ion conductors based on butadiene styrene copolymers

In this work, we report the synthesis, kinetic study and microstructure characterization of a new proton conductor based on sulfonated polybutadiene–styrene copolymer (HPBS). Block copolymer ionomers were prepared through sulfonation of part of the styrene units. The free acid (HPBS-SH) sample was characterized using FT-IR spectroscopy and X-ray Photoelectron Spectroscopy (XPS) to confirm and quantify sulfonation. Microstructural characterization of the samples was carried out using Differential Scanning Calorimetry (DSC), Dynamic Mechanical Analysis (DMA), and Impedance Spectroscopy (IS). DMA and DSC analysis have shown that Tg (HPB) remains constant for all the samples studied, while glass transition temperature of polystyrene (PS) measured present an increase about 30 °C after sulfonation. Complex impedance measurements have shown that proton conductivity of HPBS-SH membrane was about 10 −3–10 −2 S cm −1, lower values were observed generally in the case of blends.

Morphology of Nylon12/natural rubber blends compatibilized by reactive processing

The reactive blending of 60 wt% polystyrene (PS) and 40 wt% natural rubber (NR) was carried out in the presence of peroxide initiator (0.5 phr; phr is part per hundred polymer bases (e.g., 60 : 40 PS/NR; 80 : 20 Nylon12/NR)), so the blend was called PSNR05. The reactive blend produced 26% gel and showed the reduction of glass transition temperature of polystyrene indicating the presence of PS-g-NR. The reactive blend PSNR05 as well as commercial styreneethylene-butylene-styrene block copolymer (SEBS) and the block copolymer with grafted maleic anhydride (SEBS-g-MA) were added to compatibilize Nylon12 (80 wt%) and NR (20 wt%) blends at various contents (1-16 phr). Interfacial tensions of the ternary blends were calculated. The reactive PSNR05 should encapsulate NR phase in Nylon12 matrix more readily than SEBS-g-MA and SEBS. In contrast to the prediction, core-shell morphology observed by SEM and TEM revealed that not only the dispersion of particles having a NR core with SEBS or PSNR05 shell occurred, but also the inclusion of Nylon12 in NR particles with PSNR05 or SEBS at the interfaces, such that Nylon12, PSNR05 and SEBS became core and NR was shell in the Nylon12 matrix of the ternary blends, while in the blend with SEBS-g-MA (which is capable of reaction between MA and the amide group in Nylon12), the core-shell morphology was as expected. The average particle sizes (including NR and compatibilizer) tended to increase with SEBS and PSNR05 content, although the sizes were still in the submicron range. On the other hand, the blends with increasing SEBS-g-MA showed reduction of the average particle sizes which were relatively lower than those of the other blends with PSNR05 and SEBS. The morphologies of ternary blends having SEBS and PSNR05 were not significantly different so that the reactive blending technique is potentially an easier way to prepare the compatibilizer.