Sub-Tg dynamics in polycarbonate by neutron scattering and its relation with secondary gamma relaxation

We have investigated the dynamics of phenylene rings in glassy bisphenol-A (BPA) polycarbonate (PC) by means of quasielastic neutron scattering. Taking advantage of selective deuteration of the samples, we have studied the incoherent scattering of hydrogens in phenylene rings on the one hand, and on the other hand the coherent quasielastic scattering of all the atoms in the sample. Two different types of neutron spectrometers, time of flight and backscattering, were used in order to cover a wide dynamic range, which extends from microscopic (approximately 10(-13) s) to mesoscopic (approximately 10(-9) s) times. Moreover, neutron-diffraction experiments with polarization analysis were carried out in order to characterize the structural features, and the relative coherent and incoherent contributions of the samples investigated. In contrast with previous studies of phenylene ring dynamics in BPA polysulfone performed by us also by neutron scattering, phenylene rings in BPA PC exhibit an "extra" motion in addition to those found for BPA polysulfone's phenylene rings. This extra motion of the rings in PC perfectly correlates with the main carbonate group motion followed by dielectric spectroscopy and allows us to (i) consistently interpret the PC's gamma relaxation in terms of two different motions; and (ii) experimentally confirm the relation between the motion of phenylene rings and carbonate groups within BPA PC formerly predicted by computational methods.     

Blends of polycarbonate and acrylic polymers: Crystallization of polycarbonate

The microstructure of amorphous polymer blends has been extensively studied in the past, but now there is a growing interest for polymer blends where one or more of the components can crystallize. In this study we investigate such blends, namely miscible polycarbonate (PC)/acrylic blends. Using small angle X-ray scattering (SAXS) measurements, combined with atomic force microscopy (AFM), electron microscopy (SEM), and optical microscopy, we demonstrate that the amorphous acrylic component mostly segregates inside the spherulites between the lamellar bundles (interfibrillar segregation). Varying the PC molecular weight or the mobility of the amorphous component (by changing its molecular weight and T_g) does not change the mode of segregation. So far qualitative predictions of the mode of segregation in semicrystalline polymer blends have been proposed using the δ parameter (the ratio between the diffusion coefficient D of the amorphous component in the blend and the linear crystallization rate G), introduced by Keith and Padden. Our results suggest that other parameters have to be considered to fully understand the segregation process. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. B Polym. Phys. 36: 2197–2210, 1998     

Invited Article. X-ray diffraction by mesomorphic comb-like polymers

This article presents a survey of the literature on X-ray diffraction by mesomorphic comb-like polymers. Special emphasis is placed upon two points: it is often possible to study the localization of the backbone in the smectic phases by considering the intensities of the Bragg reflections from the layers. It is also possible to observe different kinds of short range order and localized defects through their contribution to the X-ray diffuse scattering. For instance, the average S_A structure may be affected by layer undulations or disturbed by edge dislocations. By examining the many X-ray diffraction studies already published, it can be shown that the backbones have an ambiguous influence upon the molecular organization. They sometimes tend, for entropic reasons, to lessen the positional long range order or to create defects, whereas they sometimes promote short range order because they induce correlations among the mesogenic cores chemically linked to them.     

Multiwalled carbon nanotube promotes crystallisation while preserving co-continuous phase morphology of polycarbonate/polypropylene blend

The influence of multiwalled carbon nanotubes (MWCNTs) on phase morphology, lamellar structure, thermal stability, melting behaviour and isothermal crystallisation kinetics of polycarbonate/polypropylene (PC/PP) blend nanocomposites has been investigated. Both neat blends and PC/PP (60/40)/MWCNT nanocomposites were prepared by melt mixing method. Morphological analyses were performed by high-resolution X-ray micro-computed tomography and scanning electron microscopy. The co-continuous morphology of the blend was retained irrespective of MWCNT loading. In addition, a substantial refinement in the co-continuous structure was observed. Wide angle and small angle X-ray scattering studies were used to analyse the structural properties of the blend nanocomposites. The addition of MWCNT increases the long period of polypropylene. The influence of addition of MWCNT on the crystallisation temperature and equilibrium melting temperature (Tm°) of polypropylene was followed. The MWCNTs promote crystallisation rate of polypropylene in the blend nanocomposites.     

Polymer–polymer interactions via analog calorimetry. 2. Blends of polystyrene with bisphenol-A polycarbonate and tetramethyl bisphenol-A polycarbonate

Analog calorimetry is used as a tool to study the interaction of polystyrene, PS, with bisphenol-A polycarbonate, PC, and with tetramethyl bisphenol-A polycarbonate, TMPC. Electrostatic charge calculations were used as a guide to divide polymer repeat units and analogs into groups. A mean-field binary interaction model was used to evaluate group interaction energies. The enthalpic interaction energy obtained from this study for the PS-PC pair is 0.41 ± 0.13 cal/cm³ while that for the PS-TMPC pair is 0.19 ± 0.34 cal/cm³. The result for PS-PC blends is in good agreement with values obtained from studies using the critical molecular weight approach and the phase behavior of copolymer blends. The value for PS-TMPC does not correctly predict the phase behavior of this blend; however, its standard deviation (on both an absolute and relative basis) is large and the range of possible interaction energies includes the negative values obtained from neutron scattering. The results of this study indicate that the presence of methyl groups on the aromatic ring of TMPC repeat unit is the main factor favoring the miscibility of PS-TMPC blends. © 1997 John Wiley & Sons, Inc.     

Preparation and characterization of antimicrobial polycarbonate nanofibrous membrane

Electrospinning of polycarbonate (PC)/chloroform solution with quaternary ammonium salt (benzyl triethylammonium chloride, BTEAC) was investigated to develop antimicrobial nanofibrous membranes for ultrafiltration. With BTEAC additive, ultrafine PC fibers were continuously generated and densely mounted without the blockage of spinning tip on electrospinning. When small amounts of BTEAC were added to the PC solution, the average diameter was also decreased from several micrometers to submicron range. It was found that the conductivity of the PC solution was a major parameter affecting the morphology and diameter of the electrospun PC fibers as well as the electrospinnability of PC. The nanofibrous membranes electrospun from the PC solution with BTEAC exhibited better excellent antimicrobial activity than those prepared without BTEAC. The PC nanofibrous filter shows a good filtration efficiency to satisfy the criterion of HEPA filter, and the pressure drop of the PC filters are within the normal range. Therefore, PC nanofibrous membrane showed a great potential as a candidate for ultrafiltration, compared to a commercial HEPA filter.     

Solvent-induced phase separation in polycarbonate blends PC/TMPC

Compatibility of the polycarbonates of bisphenol A (PC) and tetramethyl bisphenol A (TMPC) was studied in glassy films cast from CH₂Cl₂ at room temperature, and above the glass-transition temperature. Blends with different compositions and of different molecular weights were analyzed by DSC and small-angle neutron scattering (SANS). Solution studies were made with light scattering and microscopy. Some of the blend films were two-phased when cast at room temperature, but all films were one-phased in equilibrium above the glass transition. The SANS data demonstrated that phase separation in the cast films was not caused by inherent incompatibility of PC and TMPC, but was induced by the solvent CH₂Cl₂. The effect is caused by a closed miscibility gap in the ternary solution system PC/TMPC/CH₂Cl₂.     

Light scattering of bisphenol-A polycarbonate in the amorphous state and at the beginning of thermal crystallization

Summary Depolarized light scattering of amorphous polycarbonate (PC) is angular independent. The amount of scattering did not give any evidence for the existence of a liquid crystal type of phase, consisting of regions with a strong orientation correlation between chain segments. Annealing of PC belowT _g does not affect its scattering behaviour. Therefore, observed changes in physical properties such as the mechanical behaviour cannot be interpreted by an appreciable increase of intermolecular orientation correlation. If PC is heated at 190 °C for several days, an angular dependent scattering component appears. This component arises from the formation of spherulites with a sheaf-like structure.With 4 figures and 1 table     

Diffuse scattering of superionic phase of CuAgSe

Summary The diffuse scattering pattern of high temperature phase of CuAgSe was investigated by X-ray powder diffraction measurements at 523 K. The wide and strong peak of diffuse scattering appeared around 20~35°. There were two contributions to the oscillatory diffuse scattering, one was the short range order of cations. The other was the correlation between thermal displacements of anion-cation and cation-cation pairs. The theoretical treatments of the diffuse scattering including the correlations among the thermal displacements of atoms were described.     

Flame retarding mechanism of polycarbonate containing methylphenyl-silicone

The thermal degradation of polycarbonate (PC) containing methylphenyl-silicone with a branched structure (SFR-PC) was investigated by the thermogravimetric analysis (TGA). The decomposition activation energies were determined using the Ozawa method. It was found that the decomposition activation energy and the degradation residue of the SFR-PC at 800 °C in air atmosphere were much higher than those of the PC. The addition of methylphenyl-silicone enhanced the thermal stability of PC and promoted the formation of char. The silicone was found effective in retarding the combustion of the PC. The limited oxygen index of the PC containing 5 wt.% of methylphenyl-silicone was 34%. Surfaces of the SFR-PC before and after combustion were analyzed by energy dispersive X-ray analysis (EDX) and infrared (IR) spectroscopy. Based on these results obtained, the flame retarding mechanism of the SFR-PC was discussed.     

Optical characterization of polycarbonate: Influence of additives on optical properties

In laser transmission welding of thermoplastics the optical properties of the joining parts determine the quality of the welding result. Especially, the scattering of laser radiation in the transparent welding part has an impact on weld seam properties. This scattering is caused by additives. For polycarbonate (PC) with different additives the transmittance, the reflectance and the collimated transmittance are measured with a UV‐VIS‐NIR spectrometer. From this data, the optical properties, such as scattering coefficient, absorption coefficient, and anisotropy factor are calculated. The calculations are made with the aid of the four‐flux model of radiation transport in the diffusive approximation. The results show that the additives have a significant influence on the scattering coefficient. For most additives under consideration the scattering is forward directed, which means that most of the radiation is transmitted into the absorbing welding part. However, the power density distribution of the transmitted radiation may differ significantly from PC without additives. So, the weld seam may also differ due to different additives. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 451–455, 2010     

Miscibility studies on blends of polycarbonate with syndiotactic polymethyl methacrylate

Miscibility of bisphenol-A polycarbonate (PC) and syndiotactic polymethyle methacrylate (sPMMA) blends was investigated by differential scanning calorimetry (DSC) and small-angle light scattering. Cloud-point measurements indicated the existence of both a lower critical solution temperature and an upper critical solution temperature, forming an immiscibility loop. This immiscibility gap was observed for PC blends with sPMMA of various molecular weights ranging from 8,300 to 55,000. The DSC study on solvent-cast and coprecipitated PC/sPMMA blends from tetrahydrofuran solutions showed a single glass transition, shifting regularly with composition. The annealing of the 50/50 composition within the immiscibility loop exhibited dual glass transitions, but the system reverted to a single phase upon annealing above the loop. Phase dissolution took place during annealing above the loop, followed by thermoxidative branching (cross-linking) reaction. Dry pellets of PC and sPMMA were melt mixed above the loop in a Mini-Max mixer/molder; these molded blends exhibited a single phase. © 1993 John Wiley & Sons, Inc.     

Dynamic aspects of phase decomposition in reactive blends of polycarbonate and syndiotactic polymethyl methacrylate

Dynamics of phase separation in bisphenol-A polycarbonate (PC)/syndiotactic polymethyl methacrylate (sPMMA) blends has been investigated by means of time-resolved light scattering. Solvent-cast films of the PC/sPMMA blends were transparent, suggestive of miscible character. Several temperature jumps were carried out at a 50/50 PC/sPMMA composition from a homogeneous state (room temperature) into a two-phase regime. The process of phase separation first occurred for some considerable period, then it was followed by phase dissolution driven by chemical reaction. The thermodegradative reaction of sPMMA triggered the dissolution process by probably forming PC/sPMMA graft or random copolymers at the interface, which eventually resulted in a single phase. However, annealing at elevated temperatures for an extended period could lead to cross-linking, and thus a two-phase structure could be fixed permanently. The early stage of spinodal decomposition was interpreted in terms of the linearized Cahn-Hilliard theory. In the late stages of spinodal decomposition, the relationship between scattering peak wavenumber and time was found to obey a power law, but the exponents showed a strong dependence on temperature jumps. The temporal universal scaling failed due to the influence of the chemical reaction. © 1995 John Wiley & Sons, Inc.     

Transesterification in polymer blends including polycarbonate at high temperatures

Miscibility of polycarbonate (PC)/poly (arylate) (PAr) was studied by differential scanning calorimetry (DSC), phase contrast microscopy with digital image analysis (DIA) system, FT-IR spectroscopy, and cloud points for the PC/PAr/methylene chloride ternary systems. PC and PAr were immiscible over the whole composition range from the thermodynamical viewpoint. However, PC/PAr is homogenized by transesterification between PC and PAr at high temperatures. There is observed a competition between phase separation due to thermodynamical factor and phase dissolution due to transesterification. The pattern of the phase separation was spinodal decomposition type and the structure was successfully analysed by DIA.     

Studies of the higher order smectic phase of the large electroclinic effect material W317

Abstract

We present studies of the large electroclinic effect material W317. We found via X-ray scattering, calorimetry and optical observation that quenching from the smectic A* phase results in several higher order phases including an orthogonal (hexatic) smectic with short range in-layer translational order and no interlayer order. We characterize the electroclinic response in the quenched phase, and determine its magnitude and response time as a function of electric field amplitude and temperature.     

Electrical conductivities of carbon nanotube-filled polycarbonate/polyester blends

Carbon nanotube (CNT)-filled polycarbonate (PC)/poly(butylene terephthalate) (PBT) and polycarbonate (PC)/poly(ethylene terephthalate) (PET) blends containing 1 wt% CNTs over a wide range of blend compositions were prepared by melt mixing in a torque rheometer to investigate the structure-electrical conductivity relationship. Field emission scanning electron microscopy was used to observe the blend morphology and the distribution of CNTs. The latter was compared with the thermodynamic predictions through the calculation of wetting coefficients. It was found that CNTs are selectively localized in the polyester phase and conductive blends can be obtained over the whole composition range (20 wt%, 50 wt% and 80 wt% PBT) for CNT-filled PC/PBT blends, while conductive CNT-filled PC/PET blends can only be obtained when PET is the continuous phase (50 wt%, 80 wt% PET). The dramatic difference in the electrical conductivity between the two types of CNT-filled PC/polyester blends at a low polyester content (20 wt%) was explained by the size difference of the dispersed phases on the basis of the transmission electron microscope micrographs.     

Hybrid silica coatings on polycarbonate: enhanced properties

Hybrid silica coatings based on 3- glycidoxypropyltriethoxysilane (GPTES), tetraethylorthosilicate (TEOS) and colloidal silica were deposited on polycarbonate (PC) by the sol–gel method, in order to obtain a material with enhanced properties with respect to raw PC (mainly scratch resistance, hydrophobicity and density), and consequently reach increased durability. The necessity of performing a N₂-plasma treatment on PC (before coating deposition) was highlighted in order to obtain a good adherence between the coating and the substrate: XPS measurements showed that after treatment, nitrogenous radicals had formed on the PC surface and were able to link covalently with the sol during its deposition. Adherence was also higher when young sols (<8-day-old) were used. Different alkoxysilanes/colloidal silica ratios were tested to optimize the coating resistance: crack resistance of the coatings was found to be greater when the ratio was high. Scratch resistance of raw PC was enhanced as soon as PC was coated, irrespective of the alkoxysilanes/colloidal silica ratio or the sol ageing time. The density of the coatings was assessed by environmental ellipsometric porosimetry and found to be very high. Water contact angle measurements showed that the hydrophobicity of the coatings was inferior to raw PC. The addition in the sol of a small wt% of octyltriethoxysilane (OTES), 1H,1H,2H,2H-perfluorooctyltriethoxysilane (FTES) and silicone surface additive (BYK-306) allowed a significant increase in hydrophobicity of the samples.     

Evaluation of physico-chemical properties of electron beam-irradiated polycarbonate film

In this work, polycarbonate (PC) film samples were irradiated with 10 MeV electrons at different doses ranging from 25 to 250 kGy. Characterization techniques viz. thermogravimetric analysis (TGA), Fourier transform infra-red spectroscopy (FTIR), X-ray diffraction analysis (XRD) and electron paramagnetic resonance (EPR) were exploited to understand the induced changes in the physico-chemical properties of the polymer. An increase in the decomposition temperature with increasing dose was observed, while the crystallinity remained unchanged as a result of the formation of cross-link bond. EPR technique characterized the stability of the free radicals in the irradiated PC. The result showed that cross-linking process occurs at low absorbed doses, whereas polymer degradation happens at higher doses.     

State of order in blends of poly(butylene terephthalate) with poly(ethylene terephthalate) or polycarbonate

Blends of PBT with PET or PC were studied by X-ray diffraction and DSC for different conditions of crystallization. PBT and PET crystallize very similarly, though they are recognized as partially compatible in the melt. In the PBT/PC blends X-ray diffraction examinations show crystallization of PC after 4 h of annealing. In the melt, both components are compatible. T_g-calculations indicate a plasticizing effect. In both kinds of blends, PBT crystallizes faster than PC or PET. Fast crystallization processes were examined by X-ray diffraction measurements with synchrotron radiation.     

Polyethyleneimine coating renders polycarbonate resistant to organic solvents

We propose a method for the modification of surfaces of microchannels in chips fabricated in polycarbonate (PC) that makes the devices resistant to a range of organic solvents. Coating of PC with branched polyethyleneimine (BPEI) with the use of trimethylpropane triglycidyl ether (TTE) as a linker renders the devices resistant to toluene, benzene, acetonitrile, tetrahydrofuran, dioxane and ethylene dichloride. The optimized procedure of modification allows for continuous operation of the chips for several hours without dissolution of PC. Additional modification with the use of Krytox? allows for the use of Fluorinert (FC-40) as the continuous phase and for generation and handling of droplets of organic solvents that are miscible with water.