Anomalous reinforcing effects in cellulose gel-based polymeric nanocomposites

Cellulose-synthetic polymer nanocomposite films were prepared by immersion of cellulose gel in polymer solutions followed by dry casting. The cellulose hydrogel was prepared from aqueous alkali-urea solution. As the synthetic polymer, polystyrene (PS) and poly(methyl methacrylate) (PMMA) were used. The polymer content could be changed between 10 and 80% by changing polymer concentration of immersing solution. While the mechanical properties of the cellulose-PMMA composite films showed a nearly linear dependence on PMMA content, those of cellulose-PS composites showed an anomalous behavior; both tensile strength and Young’s modulus showed prominent maxima at 15–30 wt% PS contents. This anomaly may have resulted from the specific interaction between the aromatic ring of PS and the hydrophobic plane of the glucopyranoside. Both PMMA and PS composite films showed significant improvements in dimensional thermal stability; up to 25 wt% synthetic polymer content, the coefficient of thermal expansion (CTE) was as low as ca. 30 ppm/K, about 1/3 of the pure polymers. This indicates that the regenerated cellulose network is effective in suppressing thermal expansion of the synthetic polymers.     

Conducting polystyrene/polyaniline blend through template-assisted emulsion polymerization

Electrically conducting polystyrene (PS)/polyaniline blends have been prepared through a one-step “anilinium-surfactant template”-assisted emulsion polymerization at room temperature. The self-assembled cylindrical An⁺PDPSA^? micelle formed inside the PS matrix can act as a structure directing template cum dopant. Morphological observation under scanning electron microscopic studies revealed that during the progress of polymerization, the initially formed nanostructured conducting polyaniline was changed into cubic/hexagonal/lamellar particles and finally transformed into a percolated structure inside the PS matrix. Blend was further characterized by UV-Vis spectroscopy, FTIR spectroscopy, X-ray diffraction, electrical conductivity, thermal stability, dielectric property, rheological property, and electromagnetic shielding efficiency. The key finding of this work is that the conductive blend prepared through micelle-guided polymerization exhibited superior electrical conductivity (9.6 S/m) with low percolation threshold concentration (5 wt%), excellent thermal stability, electromagnetic interference (EMI) SE of 1–10 dB which makes it a promising candidate for EMI shielding and antistatic discharge matrix for the encapsulation of microelectronic devices.     

Structural and electrical characterisation of betaine-type,organic, molecular,thin evaporated films and LB multilayers

The structure and electrical properties of highly polar indandione-1,3 pyridinium betaine (IPB) derivatives have been studied in vacuum-evaporated thin films and Langmuir-Blodgett (LB) multilayer assemblies. Phase transitions induced by temperature and/or electric field have been observed in LB films of an amphiphilic derivative of IPB.The LB films of IPB, obtained at room temperature, form a Y-like structure which melts at about 50 °C to produce spherical domains, having Z-like structure, which remain stable up to 110 °C. Similar phase transitions can be induced by an electric field with ε ≥ 2 × 10⁵ V cm⁻¹ at room temperature. In the new Z-like phase of the IPB LB films, the electrical conductivity increases by some five or six orders of magnitude and the activation energy of dark conductivity decreases from 0.18 ± 0.03 eV to practically zero.The vacuum-evaporated IPB films yield low electrical conductivity (σ = 10⁻¹⁵–10⁻¹⁶S cm⁻¹), whereas in the LB multilayers a notable anisotropy of conductivity is observed. In case of coplanar cells the conductivity increases to σ = 10⁻⁸S cm⁻¹. In sandwich-type LB samples the conductivity value is similar to that of the vacuum-evaporated polycrystalline thin films.     

Magnetic applications of polymer gels

In this paper we report results of both, material preparation and magnetic characterisation, on CoFe₂O₄ particles of nanometric size formed by in‐situ precipitation within polymer gels. The size of the particles was controlled within a very narrow volume distribution and its average value was shifted from 2 to 10 nm. The existence of nanoparticles showing, at room temperature, coercive field values between 500 and 900 Oe and saturation magnetisations of about 500 emu/cm³, suggest to use these systems to get magnetic recording media with ultra high density. Poly(vinyl alcohol) (PVA) and Polystyrene (PS) films were prepared from this nanocomposite material. After a magnetic field treatment nanoparticles within the PVA films are free to rotate in response to an applied magnetic field. This PVA based nanocomposite film portends a new class of magnetic material with very little or no electrical and magnetic loss.     

Electrical and physico-chemical properties of nanolayers of Conducting polyaniline-polystyrene or camphor sulfonic acid blends

In this work we studied the physico-chemical and electrical properties of conducting blends of polyaniline (PANI) with polystyrene (PS) or camphor sulfonic acid (CSA) in an appropriate solvent such as m-cresol using various concentrations of PS. The thin films or nanolayers prepared by spin coating were analysed by ellipsometry (to measure the thickness), dynamic contact angle (to measure the surface energy), atomic force micropsopy techniques (to observe the topography and roughness of films), and by using a Keithley SMU 236 recorder under a vacuum of 10⁻³ mbar, to determine the variation of the current as a function of the voltage. Results obtained show that the variations of current I versus of the voltage V (from −15 V to +15 V) for all samples coated on silicon substrate indicate a barrier effect that becomes more and more important with the increase of the PS content, while samples prepared on a glass substrate give a linear variation of the current according to the voltage. These observations (load space limited current, Fowler-Nordheim tunneling effect, light-emitting diodes) will be described in this paper. The electrical conductivity of the PANI-CSA-PS blends at room temperature for different concentrations of polystyrene (from 0% to 50%) was measured by the four probe method as a function of the PANI weight fraction x. It seems that when x increases the electrical conductivity σ increases and reaches a threshold for x = 0.5 and σ = 8.5 S/cm.     

Ultrasonically induced microemulsion polymerization of styrene

In this paper, ultrasonically induced microemulsion polymerization of styrene was successfully performed, possessing many merits such as high polymerization rate, the formation of small latex particles with a narrow size distribution, the absence of initiator and relatively low surfactant concentration. The monomer conversion reached 70% in 1 h, and the average diameter of polystyrene (PS) latex was about 30 nm which could be prepared with 3% surfactant (sodium dodecyl sulfate, SDS) concentration. The molecular weight of PS was around 10⁶ and the poly-distribution index was 1.06, indicating a very narrow distribution. Several influencing factors were investigated in detail, showing that ultrasonically induced microemulsion polymerization is a new route to prepare PS nanoparticles.     

High-quality polythiophene films prepared by electropolymerization of thiophene in BF3-ethyl ether solution

Polythiophene films have been deposited on a platinum electrode surface by direct oxidation of thiophene in BF₃-ethyl ether solution containing a controlled amount of water (5 mM). The electric and mechanical properties of the films were studied. Experimental results demonstrated that the films prepared at low applied potentials were semiconductors with conductivities in the order of 10^?1 s cm^?1. The strengths of these films were high and comparable to those of some widely used engineering plastics such as poly(propylene) and poly(vinyl acetate). The conductivities of the PT films varied with the value of applied potential used for electrolysis and passed through a maximum of 19.13 s cm^?1 at +1.6 V. At a given applied potential, low experimental temperature, and monomer concentration led to formation of films with high quality. © 1995 John Wiley & Sons, Inc.     

Synthesis of poly(ethylene‐co‐vinyl alcohol)‐g‐polystyrene graft copolymer and their applications for ordered porous film and compatibilizer

A series of new functional poly(ethylene‐co‐vinyl alcohol)‐g‐polystyrene graft copolymers (EVAL‐g‐PS) with controlled molecular weight (M_n = 38,000–94,000 g mol^?1) and molecular weight distribution (M_w/M_n = 2.31–3.49) were synthesized via a grafting from methodology. The molecular structure and component of EVAL‐g‐PS graft copolymers were confirmed by the analysis of their ¹H NMR spectra and GPC curves. The porous films of such copolymers were fabricated via a static breath‐figure (BF) process. The influencing factors on the morphology of such porous films, such as solvent, temperature, polymer concentration, and molecular weight of polymer were investigated. Ordered porous film and better regularity was fabricated through a static BF process using EVAL‐g‐PS solution in CHCl₃. Scanning electron microscopy observation reveals that the EVAL‐g‐PS graft copolymer is an efficient compatibilizer for the blend system of low‐density polyethylene/polystyrene. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 516–524     

Structural,chemical and nanomechanical investigations of SiC/polymeric a-C:H films deposited by reactive RF unbalanced magnetron sputtering

Amorphous carbon (or diamond-like carbon, DLC) films have shown a number of important properties usable for a wide range of applications for very thin coatings with low friction and good wear resistance. DLC films alloyed with (semi-)metals show some improved properties and can be deposited by various methods. Among those, the widely used magnetron sputtering of carbon targets is known to increase the number of defects in the films. Therefore, in this paper an alternative approach of depositing silicon-carbide-containing polymeric hydrogenated DLC films using unbalanced magnetron sputtering was investigated. The influence of the C₂H₂ precursor concentration in the deposition chamber on the chemical and structural properties of the deposited films was investigated by Raman spectroscopy, X-ray photoelectron spectroscopy and elastic recoil detection analysis. Roughness, mechanical properties and scratch response of the films were evaluated with the help of atomic force microscopy and nanoindentation. The Raman spectra revealed a strong correlation of the film structure with the C₂H₂ concentration during deposition. A higher C₂H₂ flow rate results in an increase in SiC content and decrease in hydrogen content in the film. This in turn increases hardness and elastic modulus and decreases the ratio H/E and H³/E². The highest scratch resistance is exhibited by the film with the highest hardness, and the film having the highest overall sp³ bond content shows the highest elastic recovery during scratching.     

An overview of polylactides as packaging materials

Polylactide polymers have gained enormous attention as a replacement for conventional synthetic packaging materials in the last decade. By being truly biodegradable, derived from renewable resources and by providing consumers with extra end-use benefits such as avoiding paying the "green tax" in Germany or meeting environmental regulations in Japan, polylactides (PLAs) are a growing alternative as a packaging material for demanding markets. The aim of this paper is to review the production techniques for PLAs, summarize the main properties of PLA and to delineate the main advantages and disadvantages of PLA as a polymeric packaging material. PLA films have better ultraviolet light barrier properties than low density polyethylene (LDPE), but they are slightly worse than those of cellophane, polystyrene (PS) and poly(ethylene terephthalate) (PET). PLA films have mechanical properties comparable to those of PET and better than those of PS. PLA also has lower melting and glass transition temperatures than PET and PS. The glass transition temperature of PLA changes with time. Humidity between 10 and 95% and storage temperatures of 5 to 40 degrees C do not have an effect on the transition temperature of PLA, which can be explained by its low water sorption values (i.e. <100 ppm at Aw = 1). PLA seals well at temperatures below the melting temperature but an appreciable shrinking of the films has been noted when the material is sealed near its melting temperature. Solubility parameter predictions indicate that PLA will interact with nitrogen compounds, anhydrides and some alcohols and that it will not interact with aromatic hydrocarbons, ketones, esters, sulfur compounds or water. The CO2, O2 and water permeability coefficients of PLA are lower than those of PS and higher than those of PET. Its barrier to ethyl acetate and D-limonene is comparable to PET. The amount of lactic acid and its derivatives that migrate to food simulant solutions from PLA is much lower than any of the current average dietary lactic acid intake values allowed by several governmental agencies. Thus, PLA is safe for use in fabricating articles for contact with food.     

Direct spincasting of polystyrene thin films onto poly(methyl methacrylate)

The low vapor pressure solvent 1‐chloropentane was used to directly spincast polystyrene (PS) films onto poly(methyl methacrylate) (PMMA) with smooth surfaces and sharp interfaces. Interface roughness after removal of the PS layer with cyclohexane was determined with scanning force microscopy to be <1 nm. Dynamic secondary mass spectroscopy revealed an interfacial width below the resolution limit of ～10 nm. Large area bilayers with smooth surfaces could be created. In addition, direct spincasting with 1‐chloropentane allows the production of thin PS films (<15 nm) and films of low molecular weight (<5 kDa) PS, all of which would be impossible to produce for this important model system by the traditional water‐transfer method. 1‐chloropentane was confirmed to be a sufficiently selective solvent for PS by measuring the Flory–Huggins χ parameters of 1‐chloropentane with PS and PMMA, respectively, with inverse gas chromatography. In the search for a suitable selective solvent, the authors have also examined the role of vapor pressure in spin casting smooth films over a wider molecular weight (4.3–190 kDa) and thickness range (～5–500 nm) than previously reported. Only solvents with low vapor pressure produced high quality PS films. Methylcyclohexene can also be used to produce excellent, directly cast PS/PMMA bilayers, but with a smaller molecular weight and thickness window compared with 1‐chloropentane. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 3234–3244, 2006     

Highly Ordered Mesoporous Tungsten Oxides with a Large Pore Size and Crystalline Framework for H2S Sensing

An ordered mesoporous WO₃ material with a highly crystalline framework was synthesized by using amphiphilic poly(ethylene oxide)‐b‐polystyrene (PEO‐b‐PS) diblock copolymers as a structure‐directing agent through a solvent‐evaporation‐induced self‐assembly method combined with a simple template‐carbonization strategy. The obtained mesoporous WO₃ materials have a large uniform mesopore size (ca. 10.9 nm) and a high surface area (ca. 121 m² g^?1). The mesoporous WO₃‐based H₂S gas sensor shows an excellent performance for H₂S sensing at low concentration (0.25 ppm) with fast response (2 s) and recovery (38 s). The high mesoporosity and continuous crystalline framework are responsible for the excellent performance in H₂S sensing.     

Segregated reduced graphene oxide polymer composite as a high performance electromagnetic interference shield

Herein, we report the synthesis of a graphene/polymer composite via a facile and straightforward approach for electromagnetic interference (EMI) shielding applications. Polystyrene (PS) beads were added in graphene oxide (GO)/water solution followed by the addition of hydroiodic acid (HI) for in situ reduction of GO. The composite solution (rGO/PS) was filtered, hot compressed and tested for EMI shielding and dielectric measurements. A 2-mm thick segregated rGO/PS sample with 10 wt% filler loading delivered a high EMI shielding effectiveness (SE) of 29.7 dB and an AC electrical conductivity of 21.8 S m^?1, which is well above the commercial requirement for EMI shielding applications. For comparison with the segregated rGO/PS composite, a control polymer composite sample utilizing a thermally reduced graphene oxide was synthesized by following a conventional coagulation approach. The as-synthesized conventional rGO/PS yield an EMI SE of 14.2 dB and electrical conductivity of 12.5 S m^?1. The high EMI shielding of segregated rGO/PS is attributed to the better filler-to-filler contact among graphene layers surrounded by PS beads and also to the better reduction and preservation of graphene structure during reduction process that makes the low temperature chemically reduced segregated rGO/PS approach a viable route compared to high temperature thermally reduced conventional rGO/PS approach.     

Characterization and modification of polymer blend films

Films of immiscible blends of (PS) and poly(methyl methacrylate) (PMMA) were characterized by contact-angle measurements with sessile drop and atomic force microscopy (AFM). These blends showed a linear dependence of the contact angles on the composition, as predicted by Cassie's equation for ideal surfaces. The surface structure investigated by AFM showed low roughness and phase-separation features. The ratio between the drop radius and the roughness amounted to the order of 10⁴–10⁵. This magnitude seemed to be sufficient to put the PS/PMMA films close to ideality. Upon sulfonation, the wettability and the microscopic surface roughness of the PS/PMMA blends increased. The treatment with sulfuric acid yielded sulfonated PS domains on the surface, causing an increase in the surface wettability. The SO₃ ⁻ groups were evidenced by X-ray photoelectron spectroscopy. The sulfonation of the PS/PMMA blends enables the formation of multiphase surfaces with hydrophobic, charged and polar domains. Received: 11 December 2000 Accepted: 6 April 2001     

Influence of the bulk and surface morphology on adhesion of polystyrene-inter-poly-cross-2-ethylhexyl-methacrylate films and particles

The adhesion behavior of semi-interpenetrating polymer networks (semi-IPNs) of linear polystyrene (PS) in crosslinked poly-2-ethylhexylmethacrylate (EHMA) was studied by variation of the bulk and surface morphology, i.e., domain size, continuity, and concentration in the domains. Semi-IPNs were prepared by liquid-liquid demixing upon cooling of a homogeneous solution of PS in methacrylate monomer, followed by gelation of the PS-rich phase and UV polymerization of the methacrylate resin. Welding of films allowed the preparation of larger objects provided that (1) the samples were phase separated to a high degree and contained domains with a high PS concentration (>90%) and (2) polystyrene was present at the interface. For semi-IPN films, a linear dependence of the adhesion strength on the (crack healing time)^1/4 was obtained. Based on these considerations, a process was developed to obtain melt-processable semi-IPN particles, by quenching droplets of the polymer solution into a cold liquid. These particles obtained a PS-rich skin layer and showed good adhesion after blending with a thermoplast. © 1996 John Wiley & Sons, Inc.     

Effects of concentration of nonionic surfactant and molecular weight of polymers on the morphology of anisotropic polystyrene/poly(methyl methacrylate) composite particles prepared by solvent evaporation method

The effects of the concentration of polyoxyethylene octylphenyl ether (OP-10) as a nonionic surfactant and the molecular weight of polymers (polystyrene (PS) and poly(methyl methacrylate) (PMMA)) on the morphology of anisotropic PS/PMMA composite particles were investigated. In the case of polymers with lower molecular weight (M _w ≈ 6.0 × 10⁴ g/mol), the PS/PMMA composite particles have dimple, via acorn, to hemispherical shapes along with the increase of the OP-10 concentration. On the other hand, when the polymers have higher molecular weight (M _w ≈ 3.3 × 10⁵ g/mol), the morphology of PS/PMMA composite particles changed from dimple, via hemispherical, to snowman-like structure while the concentration of OP-10 was increased. Furthermore, thermodynamic analysis was first simply made by spreading coefficients, and the results indicated that both the concentration of OP-10 aqueous solution and the molecular weight of polymers were very important to the final morphology of anisotropic composite particles.     

The effect of polyvinyl alcohol (PVA) on the optical,electrical and solid state properties of copper zinc tin sulfide (CZTS) deposited by sensitive spray pyrolysis (SSP)

Recently, the use of CZTS as the basis for other generation of low cost thin films solar cells has stimulated further researches. Its excellent p-type absorber nature, relatively high absorption coefficient and ideal energy band-gap of 1.5eV motivated these efforts. Additionally, CZTS consist of earth-abundant, cheap and non-toxic elements with very low manufacturing cost. Initially, copper indium gallium selenide (CIGS) solar cell device emerged but suffered limitations in further development because of rare indium and gallium in the device structure therefore, CZTS is recently preferred as an alternative to CIGS commercial solar cell absorber layer. In this work, solution mixture of CZTS and PVA was deposited on a substrate at temperature of 150 °C. Sensitive spray pyrolysis was used to grow the thin films where calculated amount of the precursor mixture was allowed to fall and be deposited on a heated substrate to form CZTS/PVA thin films. Subsequently, the thin film samples were annealed at a temperature of 200^oCfor 1 h to achieving pure crystalline thin film formation. SEM, XRD analysis, Optical, Solid State properties and Raman analysis were studied. The XRD analysis showed that the thin films fell into the pure kesterite structure of CZTS. Results show that produced thin films exhibited higher absorption coefficient and optical conductivity than pure CZTS, 10⁶ m^?1 and 10¹⁴(S^?1) against 10⁴cm^?1 and 10¹²(S^?1) respectively. The band-gap is between 1.53eV and 1.73eV. Using a PVA concentration of 0.05 M yielded highest absorbance and optical conductivity with lowest real dielectric constant and transmittance. These improved optical, electrical and solid state properties suitably qualify these thin films as absorber layer material for solar cell applications.     

Monolayer Co3O4 Inverse Opals as Multifunctional Sensors for Volatile Organic Compounds

Monolayers of periodic porous Co₃O₄ inverse opal (IO) thin films for gas‐sensor applications were prepared by transferring cobalt‐solution‐dipped polystyrene (PS) monolayers onto sensor substrates and subsequent removal of the PS template by heat treatment. Monolayer Co₃O₄ IO thin films having periodic pores (d≈500 nm) showed a high response of 112.9 to 5 ppm C₂H₅OH at 200 °C with low cross‐responses to other interfering gases. Moreover, the selective detection of xylene and methyl benzenes (xylene+toluene) could be achieved simply by tuning the sensor temperature to 250 and 275 °C, respectively, so that multiple gases can be detected with a single chemiresistor. Unprecedentedly high ethanol response and temperature‐modulated control of selectivity with respect to ethanol, xylene, and methyl benzenes were attributed to the highly chemiresistive IO nanoarchitecture and to the tuned catalytic promotion of different gas‐sensing reactions, respectively. These well‐ordered porous nanostructures could have potential in the field of high‐performance gas sensors based on p‐type oxide semiconductors.     

Effect of nanoscale confinement on the glass transition temperature of free-standing polymer films: Novel,self-referencing fluorescence method

The effect of nanoscale confinement on the glass transition temperature, T_g, of freely standing polystyrene (PS) films was determined using the temperature dependence of a fluorescence intensity ratio associated with pyrene dye labeled to the polymer. The ratio of the intensity of the third fluorescence peak to that of the first fluorescence peak in 1-pyrenylmethyl methacrylate-labeled PS (MApyrene-labeled PS) decreased with decreasing temperature, and the intersection of the linear temperature dependences in the rubbery and glassy states yielded the measurement of T_g. The sensitivity of this method to T_g was also shown in bulk, supported PS and poly(isobutyl methacrylate) films. With free-standing PS films, a strong effect of confinement on T_g was evident at thicknesses less than 80–90 nm. For MApyrene-labeled PS with M_n = 701 kg mol⁻¹, a 41-nm-thick film exhibited a 47 K reduction in T_g relative to bulk PS. A strong molecular weight dependence of the T_g-confinement effect was also observed, with a 65-nm-thick free-standing film exhibiting a reduction in T_g relative to bulk PS of 19 K with M_n = 701 kg mol⁻¹ and 31 K with M_n = 1460 kg mol⁻¹. The data are in reasonable agreement with results of Forrest, Dalnoki-Veress, and Dutcher who performed the seminal studies on T_g-confinement effects in free-standing PS films. The utility of self-referencing fluorescence for novel studies of confinement effects in free-standing films is discussed. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 2754–2764, 2008     

Highly routinely reproducible alignment of H NMR spectral peaks of metabolites in huge sets of urines

A method to obtain high reproducibility of ¹H NMR chemical shift of peaks of biofluid metabolites, by simple acidification with HCl is evaluated. Biofluid ¹H NMR analysis is indeed spoiled by a strong chemical shift dependence of metabolite peaks on parameters such as ionic strength, concentration of some earth alkali cations and, mostly, on pH of samples. The resulting chemical shift variations, as large as 0.1 ppm, generate misalignments of homogeneous peaks, artifacts and misinterpretations.Reproducible alignment is essential in ¹H NMR based metabonomics, where peak misalignments prevent even very wide bins (i.e., 0.04 ppm, as elsewhere proposed) from being used to integrate spectral data for multivariate statistical analysis. Here is demonstrated that routine acidification with HCl to 1.2 ≤ pH ≤ 2.0 ensures highly reproducible peak alignment of urine ¹H NMR spectra. In this respect, simple inspection of citrate peaks in the urine can be used to measure pH, as it will be extensively discussed, in that at such low pH they show no dependency on other urine components as reported at higher pH. Under these conditions, in as many as 493 urine samples, in which concentrations of Ca²⁺, Mg²⁺, K⁺, Na⁺, Cl⁻, phosphate, and creatinine and ionic strength measured by means of well standardized conventional procedures, showed very wide ranges, peaks align within a SD always lower than 0.002 ppm, thus allowing the use of integration bins at least five times narrower than 0.04 ppm.