Thermal birefringence in freely quenched multilayered slabs of amorphous polymers: Experiment and simulation

The simulation of the gapwise distribution of the thermally‐induced residual birefringence and stresses in freely‐quenched PS‐PC‐PS and PC‐PS‐PC multi‐layered slabs in water was carried out to calculate the gapwise distribution of the transient and residual birefringence. The modeling was based on the linear viscoelastic and photoviscoelastic constitutive equations combined with the first‐order rate equation for volume relaxation. The master curves for the Young's relaxation modulus and strain‐optical coefficient functions obtained earlier for PS and PC were used in the simulations. The obtained numerical results provided the evolution of the thermally‐induced stress and birefringence with time during and after quenching. The predicted gapwise residual birefringence distribution in these slabs was found to be in a fair agreement with the measured results. In addition, the gapwise distribution of the thermally‐induced residual birefringence in the multi‐layered PS‐PMMA‐PS, PMMA‐PS‐PMMA, PMMA‐PC‐PMMA, and PC‐PMMA‐PC slabs quenched from different initial temperatures was measured. Explanations were provided for the observed gapwise distribution of the thermal residual birefringence in each layer of these slabs including the effect of the initial temperature. POLYM. ENG. SCI., 54:2097–2111, 2014. © 2013 Society of Plastics Engineers     

Effect of confinement on glass dynamics and free volume in immiscible polystyrene/high‐density polyethylene blends

The effect of confinement on glass dynamics combined with the corresponding free volume changes of amorphous polystyrene (PS) in blends with semi‐crystalline high‐density polyethylene (HDPE) have been investigated using thermal analyses and positron annihilation lifetime spectroscopy (PALS). Two different glass transition temperatures (T_g) were observed in a PS/HDPE blend due to the dissimilarity in the chemical structure, consistent with an immiscible blend. However, T_g of PS in the incompatible PS/HDPE blend showed an upward trend with increasing PS content resulting from the confinement effect, while T_g of the semi‐crystalline HDPE component became lower than that of neat HDPE. Moreover, the elevation of T_g of PS was enhanced with a decrease of free volume radius by comparing annealed and unannealed PS/HDPE blends. Positron results showed that the free volume radius clearly decreased with annealing for all compositions, although the free volume hole size agreed well with linear additivity, indicating that there was only a weak interaction between the two components. Combining PALS with thermal analysis results, the confinement effect on the glass dynamics and free volume of PS phase in PS/HDPE blends could be attributed to the shrinkage of HDPE during crystallization when HDPE acted as the continuous phase. © 2015 Society of Chemical Industry     

Weld‐line sensitivity of injected amorphous polymers

The effects of the processing parameters on the weld‐line mechanical properties of polystyrene (PS) and polycarbonate (PC) were investigated. PS was very sensitive to the presence of a weld line, showing property reductions of up to 70%. However, this sensitivity was mainly connected to the surface notch at the weld line. When this notch was removed, behavior close to that of unwelded specimens was obtained. The injection temperature was the main processing parameter because it affected the macromolecular diffusion speed and, therefore, influenced the weld quality. A direct relationship between the distance of molecular diffusion and the fracture mechanism was established. PC had a low weld‐line sensitivity, despite being an amorphous polymer like PS. The difference between these materials was connected to the different sizes of the surface defects and to the different entanglement densities, which influenced the relaxation time and the global behavior (brittle–ductile). © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 644–650, 2004     

Birefringence and interface in sequential co‐injection molding of amorphous polymers: Simulation and experiment

Modelings of the interface distribution and flow‐induced residual stresses and birefringence in the sequential co‐injection molding (CIM) of a center‐gated disk were carried out using a numerical scheme based on a hybrid finite element/finite difference/control volume method. A nonlinear viscoelastic constitutive equation and stress‐optical rule were used to model the frozen‐in flow stresses in disks. The compressibility of melts is included in modeling of the packing and cooling stages and not in the filling stage. The thermally induced residual birefringence was calculated using the linear viscoelastic and photoviscoelastic constitutive equations combined with the first‐order rate equation for volume relaxation and the master curves for the relaxation modulus and strain‐optical coefficient functions of each polymer. The influence of the processing variables including melt and mold temperatures and volume of skin melt on the birefringence and interface distribution was analyzed for multilayered PS‐PC‐PS, PS‐PMMA‐PS, and PMMA–PC–PMMA molded disks obtained by CIM. The interface distribution and residual birefringence in the molded disks were measured. The measured interface distributions and the gapwise birefringence distributions in CIM disks were found to be in a fair agreement with the predicted interface distributions and the total residual birefringence obtained by the summation of the predicted frozen‐in flow and thermal birefringence. POLYM. ENG. SCI., 55:88–106, 2015. © 2014 Society of Plastics Engineers     

PPO–PC block‐copolymers used as compatibilizers in PS/PC blends

Block‐copolymers containing poly(2,6‐dimethyl‐1,4‐phenylene oxide) (PPO) and polycarbonate of bisphenol A (PC) segments were employed as compatibilizers in polystyrene (PS)/PC blends. Block‐copolymers were prepared starting from oligomeric diols‐terminated PPO and PC. The poly(phenylene ethers) was obtained by oxidative coupling of 2,6‐dimethyl‐phenol in presence of tetramethyl bisphenol A. The copolymers were obtained with a chain extension reaction between the starting oligomers using bischloroformate of bisphenol A or phosgene as coupling agent. PS/PC blends, cast from chloroform solutions or mixed by melt, were studied by differential scanning calorimeter (DSC), dynamic‐mechanical thermal analysis (DMTA), and optical microscopy (OP). The thermal and morphological analyses showed a clear compatibilization effect between PS and PC, if PPO–PC copolymer is added when blending is performed in the melt; in addition, also mechanical properties are increased when compared with blends without PPO–PC. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4654–4660, 2006     

Microindentation studies at the near surface of glassy polymers: Influence of molecular weight

The viscoelastic‐plastic properties of various amorphous, glassy polymers [polystyrene (PS), poly(styrene‐acrylonitrile) copolymer (SAN), poly(methyl methacrylate) (PMMA), poly(vinyl chloride) (PVC), polycarbonate (PC)] in the micron and submicron range were investigated by means of load‐displacement analysis from depth‐sensing experiments. Hardness and Young's modulus values decrease rapidly with increasing depth up to a few microns. New data on the glass transition temperature correlation with microhardness are presented. The influence of annealing below the glass transition temperature upon the microhardness for various glassy polymers is pointed out. For PS, the influence of the molecular weight variation and molecular weight distribution on the microhardness is reported. Results are discussed on the basis of an entanglement network model, recently developed to explain the fine structure of crazes in amorphous polymers. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 1951–1956, 2004     

Positron annihilation lifetime spectroscopy for miscibility investigations of styrene–butadiene–styrene copolymer/polystyrene blends

The free volume parameters of styrene–butadiene–styrene copolymer/polystyrene (SBS/PS) blends were investigated with positron annihilation lifetime spectroscopy (PALS) in this study. The behaviors of free volume distribution, average free volume, and relative fractional free volume revealed the difference of interfacial miscibility. Based on different models, inter‐chain interaction parameter β, geometric factor γ, and hydrodynamic interaction parameter α obtained from free volume data were employed to further determine the effect of molecular architecture and styrene content on the miscibility. The results suggest the better miscibility in star‐shaped SBS/PS blends than that of corresponding linear SBS/PS systems, even than that of systems containing more styrene unit. In addition, differential scanning calorimetry, dynamic mechanical analysis, and scanning electron microscopy, which are sensitive to heterogeneities in larger domain size, give different results of miscibility from free volume data. It should be attributed the difference of characterization scale. The mechanical property corroborates the results of miscibility. POLYM. ENG. SCI., 54:785–793, 2014. © 2013 Society of Plastics Engineers     

Application of Design of the Experiment in Preliminary Investigations on the end Milling of Low Temperature Co‐fired Ceramics

The formation of three‐dimensional shapes is one of the most important technological steps in low temperature co‐fired ceramics (LTCC) process. Channels and chambers qualities and the process speed are strongly affected by the shaping procedure. There are three main machining techniques: laser cutting, punching, and milling. This article is dedicated to end milling process of LTCC tapes. The determined PS/DK 2³ experiment design was used in the investigations and its procedure is described in this article. The used procedure is a very flexible method to achieve much useful information about the influence of the process parameters on the output. The PS/DK 2³ experiment design enables analysis of the influence of: the three input parameters on the output (minimal obtained feature) and the interaction between the input parameters on the output (minimal obtained feature). Moreover, PS/DK 2³ experiment design enables to obtain the mathematical model of the milling process and to decrease the number of measurements demanded to achieve the correct model. Hence, the design is suitable to decrease the time and costs of the experiment. The influence of the following input parameters: spindle rotational speed, spindle feed rate, vertical spindle step, and cutter diameter on minimal obtained feature of LTCC tapes is analyzed in this article.     

Co‐(POSS#‐styrene) nanocomposites reduced the glass‐transition temperature,rubbery modulus,and melt viscosity of entangled polystyrene

The addition of polyhedral oligomeric silsesquioxane‐styrene copolymers, co(POSS#‐sty), to entangled polystyrene (PS) reduced (1) the glass‐transition temperature, T_g,blend, (2) the rubbery modulus, and (3) the melt viscosity. POSS#‐sty copolymers with # = 15, 25, and 45 wt% POSS were blended with PS. The blends were miscible and T_g,blend decreased with POSS#‐sty content. Strikingly, POSS#‐sty copolymers also reduced the melt viscosity, up to an order of magnitude reduction. The reductions of T_g,blend and melt viscosity were driven by the type of POSS#‐sty copolymer, POSS45‐sty producing the largest decrease of T_g,blend. Linear viscoelasticity and the time–temperature superposition (TTS) principle (using T_ref = T_g + 50 K to ensure iso‐frictional conditions) revealed that POSS#‐sty induced up to an order of magnitude reduction of the rubbery modulus G_e. The increase of free volume f_g promoted by POSS#‐sty induced the reduction of T_g,blend and G_e, as revealed by TTS analysis. The increase of free volume promoted by POSS#‐sty induced chain intercalation (TEM showed that POSS domains were smaller than the molecular mesh) and these are key factors for the chain disentanglement with the consequent rubbery modulus and melt viscosity reductions. The use of low‐molecular weight polystyrene alone will not produce increase of free volume and tube dilation. POLYM. ENG. SCI., 59:2377–2386, 2019. © 2019 Society of Plastics Engineers     

A study of the effect of surfactants on the properties of polystyrene‐montmorillonite nanocomposites

Polystyrene‐Organo Montmorillonite (PS‐MMT) nanocomposites were prepared by suspension free radical polymerization of styrene in the dispersed organophilic montmorillonite. The results of X‐ray diffraction (XRD) and Transmission Electron Microscopy (TEM) indicated that exfoliated nanocomposites were achieved. The effect of organic modifiers (surfactants) on the properties of the synthesized nanocomposites was studied. It is found that polystyrene‐MMT nanocomposite with 5.0 wt% of organo‐MMT gave the greatest improvement in thermal stability, and polystyrene‐MMT nanocomposites with 7.5 wt% of organo‐MMT showed the greatest improvement in mechanical properties, compared with that of pure polystyrene (PS) in our experimental conditions. The alkyl chain length of surfactant used in fabricating organo‐MMT affects the synthesized PS nanocomposites: the longer the alkyl chain length that the surfactant possesses, the higher the glass transition temperature of the PS nanocomposite, However, the organoclay in the nanocomposites seems to play a dual role: (a) as nanofiller leading to the increase of storage modulus and (b) as plasticizer leading to the decrease of storage modulus. This results in a lower storage modulus of PS‐TMOMMT and PS‐TMTMMT nanocomposites than that of PS‐TMDMMT and PS‐TMCMMT nanocomposites. Further study is needed to confirm the above hypothesis.     

Increasing the resistance of poly(ether imide) to solvents by blending with poly(trimethylene terephthalate)

We studied the sorption behavior of poly(ether imide) (PEI) upon the addition of minor amounts (10 and 30%) of miscibilized poly(trimethylene terephthalate) (PTT) under acetone and other common solvent environments. Significant solvent sorption (maximum solvent sorption = 8–12 wt %) and changes in mechanical properties were observed only in the case of acetone. The sorption of acetone was Fickian and partially irreversible. Both sorption and solubility decreased markedly upon PTT addition to PEI, most likely as a result of a blending‐induced decrease in the free volume. The decreases in the modulus were attributed to plasticization, and the mixed effects on the elongation at break were attributed to the combined effects of fast plasticization and slower swelling. The joint effects of applied stress and the presence of acetone were studied with creep tests. In these tests, a combination of a free volume increase, plasticization, and superficial cracking of PEI was proposed to occur. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Characterization of thermotropic liquid crystalline polyester/polycarbonate blends: Miscibility,rheology, and free volume behavior

Miscibility, rheology, and free volume properties of blends of thermotropic liquid crystalline polymers (TLCPs) (Vectra A950) and polycarbonate (PC) are studied in this work. Despite the unusual increase in T_g of the PC phase, the blends are found to be generally immiscible. Transesterification may occur during blending and be the cause of the increase of T_g of the PC phase and the partial miscibility of the blends at high TLCP concentrations. With regard to the melt rheology of these materials, according to a three‐zone model, dynamic moduli of Vectra A950 show plateau‐ and transition‐zone behavior, while PC exhibits terminal‐zone behavior. The blends show only terminal‐zone behavior at low Vectra A950 contents (≤50%) and terminal‐ and plateau‐zone behavior at higher Vectra A950 contents. The relaxation time of Vectra A950 is much longer than PC and the blends have relaxation times greater than additivity. Both the complex and steady shear viscosities of the blends increase with the addition of Vectra A950. This is attributed to interfacial association, which retards the reorientation and alignment of the Vectra A950 phase in the molten state. The Cox–Merz rule holds true for PC but not for Vectra A950 and the blends. Free volume properties on an angstrom scale evaluated by positron annihilation lifetime spectroscopy (PALS) indicate that Vectra A950 has smaller, fewer free volume cavities than PC and the variation of free volume behavior in the blends can be explained in terms of blend miscibility. The measured densities of the blends agree well with the free volume fractions of the blends determined from PALS. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 2319–2330, 2000     

Hybrid organic inorganic nylon‐6/SiO2 nanocomposites: Transport properties

Organic‐inorganic hybrid membranes of nanosized SiO₂‐filled polyamide composites were prepared via film casting and their transport properties were studied. Gas permeation measurements were performed at room temperature, and the membrane exhibited an increase in membrane permeability performance. In contrast to the performance of traditional dense filled polymer systems, the permeability increased with an increased number of nanosilica particles. The nanocomposites were studied using positron annihilation lifetime spectroscopy (PALS). From the ortho‐positronium (o–Ps) lifetime (τ₃), the size of the local free volume (holes) was estimated. The increase in permeability is ascribed to the additional free volume obtained. This is created by the presence of nanoparticles that alter the PA chain packing. Furthermore, wide angle X‐ray diffraction (WAXD) patterns revealed that the incorporation of silica induced the structural modification of polymer chains by modifying the degree of crystallinity in comparison with the neat polymer. Polym. Eng. Sci. 44:1240–1246, 2004. © 2004 Society of Plastics Engineers.     

Structural and antibacterial properties of a γ‐radiation‐assisted,in situ prepared silver–polycarbonate matrix

A silver–polycarbonate (Ag–PC) matrix was prepared by a γ‐radiation‐assisted diffusion method, and its antibacterial properties were studied. Rutherford backscattering spectroscopy, X‐ray diffraction, and transmission electron microscopy results showed the diffusion of good, crystalline‐structured (face‐centered cubic) silver nanoparticles (AgNPs) inside polycarbonate (PC) after irradiation. Ultraviolet–visible spectroscopic results indicated a blueshift in the surface plasmon resonance of the AgNPs; this revealed a particle size decrease with increasing γ‐radiation dose. This was also supported by the scanning electron microscopy results. The microstructure of the pristine PC and silver‐doped PC was monitored with positron annihilation spectroscopy, and it showed decreases in the free‐volume hole size and fractional free‐volume for Ag–PC and γ‐ray‐irradiated PC. This corroborated the Doppler broadening spectroscopy results. The thermal degradation temperature of PC was increased because of the diffusion of AgNPs in PC. The antibacterial activity of the synthesized Ag–PC matrix was evaluated by the zone of inhibition, and the results demonstrated its bacterial growth inhibition ability. The results indicate the potential to produce an Ag–PC matrix for various applications in medical and food industries. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43729.     

Effect of physical ageing on enthalpy relaxation and isothermal contraction in bisphenol-A polycarbonate

The intention of this paper is to correlate the decrease of free volume and the enthalpy relaxation which occur in high polymers during annealing. We used a simple correlation relation, with one chief parameter (the ‘equilibrium temperature’ ?), which can be deduced from different models. Data on polycarbonate (PC) show no correlation between enthalpy relaxation and isothermal contraction using that relation: the assumption that the decrease of free volume in PC in the glassy state obeys a Williams-Landel-Ferry (WLF) type equation could not be confirmed. Moreover, it seems that the changes of configuration occurring during annealing cannot be described with only one parameter.     

Structure development in melt‐spinning syndiotactic polystyrene and comparison to atactic polystyrene

Syndiotactic polystyrene (s‐PS) and atactic polystyrene (a‐PS) were melt‐spun into filaments. The s‐PS filaments exhibited increasing amounts of crystallinity and orientation with increasing drawdown ratio and spinline stress. The a‐PS filaments were amorphous but exhibited birefringence. The birefringence and Hermans orientation factors for a‐PS were proportional to this spinline stress. In ice water and at low drawdown ratios, the s‐PS is glassy or mesomorphic. At higher drawdown ratios and spinline stresses, it crystallized. The crystalline form was the zigzag TTTT hexagonal α‐form. The birefringence and orientation factors of the s‐PS filaments were higher than those of the a‐PS filaments and the difference of the birefringence increased with increasing spinline stress. Mechanical testing results showed that the Young's modulus and tensile strength generally increased with increasing spinline drawdown ratio for both a‐PS and s‐PS filaments. The elongation to break was enhanced for both materials by increased chain orientation. Polym. Eng. Sci. 44:2141–2147, 2004. © 2004 Society of Plastics Engineers.     

The effect of UV‐irradiation and molten medium on the mechanical and thermal properties of polystyrene–polycarbonate blends

Polymer materials with improved properties can be obtained through polymer blends. As a polymer mixture is generally immiscible and incompatible, it is necessary to develop new methods to improve the interfacial adhesion. The aim of this work is to find formulations and associated processes to upgrade engineering polystyrene (PS) and polycarbonate (PC) polymer blends with the objective of using the best “process‐formulation” couple. In this study, blends of PS/PC were prepared in molten medium using reactive extrusion after UV‐irradiation. The effects of UV‐irradiation on some properties of blends under molten medium were investigated by differential scanning calorimetry (DSC), fourier transform infrared (FTIR), and thermogravimetric analysis (TGA). The data showed that the presence of polycarbonate in the blend increased the tensile strength and elongation at break with respect to pure PS. The mechanical properties of the blends were improved after irradiation. All irradiated blends are thermally more stable than those nonirradiated. Chemical changes can be clearly seen in FTIR spectra through two bands assigned to C?O and OH groups. The mutual influence between the PS/PC polymer blends compositions during UV‐irradiation was studied. PS and PC have different photo‐mechanisms due to the larger UV absorption of polystyrene and formation of more stable tertiary carbon radicals. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Creation of Controlled Defects Inside Colloidal Crystal Arrays with a Focused Ion Beam

In this work the reliability of the focused-ion-beam (FIB) patterning on polystyrene (PS) colloidal crystals at different scales is determined. Ordered arrays of PS spheres (465 nm) are successfully modified by selectively removing a single sphere. The water-vapor assisted FIB milling is crucial to obtain this result. Furthermore, isolated PS spheres are FIB drilled with or without chemically enhanced milling aiming at the exploration of the limits of such a technique. These controlled defects created using the FIB-assisted techniques may be helpful in preparing mockups of photonic crystals, sensors or as colloidal masks for diverse lithographic processes.     

Phase behavior of ternary blends containing dimethylpolycarbonate,tetramethylpolycarbonate and poly[styrene‐co‐(methyl methacrylate)] copolymers (or polystyrene)

The miscibility and phase behavior of ternary blends containing dimethylpolycarbonate (DMPC), tetramethylpolycarbonate (TMPC) and poly[styrene‐co‐(methyl methacrylate)] copolymer (SMMA) have been explored. Ternary blends containing polystyrene (PS) instead of SMMA were also examined. Blends of DMPC with SMMA copolymers (or PS) did not form miscible blends regardless of methyl methacrylate (MMA) content in copolymers. However, DMPC blends with SMMA (or PS) blends become miscible by adding TMPC. The miscible region of ternary blends is compared with the previously determined miscibility region of binary blends having the same chemical components and compositions. The region where the ternary blends are miscible is much narrower than that of binary blends. Based on lattice fluid theory, the observed phase behavior of ternary blends was analyzed. Even though the term representing the Gibbs free energy change of mixing for certain ternary blends had a negative value, blends were immiscible. It was revealed that a negative value of the Gibbs free energy change of mixing was not a sufficient condition for miscible ternary blends because of the asymmetry in the binary interactions involved in ternary blends. Copyright © 2004 Society of Chemical Industry     

Highly grafted polystyrene‐modified natural rubber as toughener for polystyrene

A polystyrene‐modified natural rubber (SNR) with 80% degree of grafting was evaluated against natural rubber (NR) in their blends with polystyrene (PS). The rubber loading of the PS‐SNR and PS‐NR blends was varied from 5 to 20% by volume. At 10–15% rubber loading, the PS‐SNR blends were found to be approximately 8–10% higher in tensile strength and 7–13% higher in Young's modulus than the PS‐NR blends. Over the range of rubber loading investigated, it was also observed that the PS‐SNR blends were 5–42 and 14–36% higher in flexural strength and flexural modulus, respectively. The most pronounced difference between the two blend systems is in their impact strength, where the former is about 55–230% higher than the latter. Relative to the pure PS, the PS‐NR and PS‐SNR blends are approximately 50–250 and 140‐1050% higher, respectively, in impact strength. Morphological observations, which are consistent with the relative tensile, flexural, and impact properties of the two systems, indicate that SNR is more compatible with PS than NR and more homogeneously dispersed in the PS matrix. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 1660–1665, 2004