PMMA‐based core‐shell nanoparticles with various PTFE cores

Polytetrafluoroethylene (PTFE) latices with spherical and rod‐like particles in the submicrometer size range, were employed as seeds in the emulsifier‐free methylmethacrylate (MMA) emulsion polymerization to obtain PTFE‐polymethylmethacrylate (PMMA) core‐shell nanoparticles. Stable latices were generally obtained. No residual PTFE was found at the end of the reaction. By appropriately choosing the ratio between MMA and PTFE in the reaction mixture, particles with predetermined size and monodisperse or narrow size distribution were prepared. The high structural regularity of the core‐shell samples allows the preparation of film with a periodic distribution of the cores thus ultimately leading to a well structured 2D colloidal crystal. A very peculiar crystallization behavior was observed because of the PTFE compartmentalization in the composite. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2928–2937, 2009     

The brittle–ductile transition induced by thermal ageing of toluene cast poly(2,6‐dimethyl‐1,4‐phenylene oxide) as observed by interfacial friction

The interfacial shear stress of toluene cast poly(2,6‐dimethyl‐1,4‐phenylene oxide) films has been studied as a function of annealing temperature. The surface topography of these films was studied by scanning probe microscopy following a single sliding pass. Casting from toluene results in a semicrystalline film with a rigid amorphous phase and containing a small amount of residual solvent that exhibits a higher interfacial shear stress than a high temperature annealed solvent‐free amorphous film. Films containing small amounts of toluene exhibit a wear pattern consisting of ripples oriented perpendicular to the sliding direction following a single sliding pass. These results support the notion that the interfacial shear stress is a function of the shear yield stress, and, that during sliding friction tensile stresses must form at the polymer surface. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1637–1643, 2009     

Reactive adsorption of aminosilane onto the glycidyl methacrylate graft‐copolymerized poly(tetrafluoroethylene) film surface for adhesion enhancement with evaporated copper

Surface modification of argon‐plasma‐pretreated poly(tetrafluoroethylene) (PTFE) film via UV‐induced graft copolymerization with glycidyl methacrylate (GMA) was carried out first. Reactive adsorption of γ‐aminopropyltriethoxysilane (APS) onto the GMA graft‐copolymerized PTFE (GMA‐g‐PTFE) film surface was performed by the simple immersion of the film in the APS solution. The adsorption process was studied as a function of the APS concentration, the immersion time of the graft‐modified PTFE film in the APS solution, and the washing protocol. The chemical composition and morphology of the silane‐modified surfaces were characterized by X‐ray photoelectron spectroscopy and atomic force microscopy, respectively. The performance of the silane‐modified PTFE surface in adhesion promotion was investigated. The T‐peel adhesion strength of the evaporated Cu on the PTFE film with the reactively adsorbed organosilane increased significantly to about 12.5 N/cm. This adhesion strength was more than twice that of the assembly involving evaporated Cu on the GMA‐g‐PTFE film and about 10 times that of the assembly involving evaporated Cu on the Ar‐plasma‐treated PTFE film. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 80–89, 2000     

Molecular orientation of a ZnS‐nanocrystal‐modified M13 virus on a silicon substrate

The surface structure and cast film formation process of a ZnS‐nanocrystal‐modified M13 bacteriophage (ZnS–M13) were investigated. A ZnS–M13 film oriented under the influence of a capillary force was obtained on both single‐crystal and polycrystalline substrates. The film formation process was investigated with atomic force microscopy and scanning electron microscopy. The surface images showed that the degree of orientation of the molecular long axes greatly depended on the direction of force and the concentration of aqueous solutions. Controlling the aqueous solution concentration yielded a highly oriented ZnS–M13 film on an indium tin oxide plate. The ability to control the orientation of virus‐based films may lead to new types of hybrid materials in which the components are organized on several length scales. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 629–635, 2004     

Simulation of phase‐separated structures of liquid‐crystalline polymer/flexible polymer blends

The phase‐separation kinetics of liquid‐crystalline polymer/flexible polymer blends was studied by the coupled time‐dependent Ginzberg–Landau equations for compositional order parameter ? and orientational order parameter S_ij. The computer simulations of phase‐separated structures of the blends were performed by means of the cell dynamical system in two dimensions. The compositional ordering processes of phase separation are demonstrated by the time evolution of ?. The influence of orientational ordering on compositional ordering is discussed. The small‐angle light scattering patterns are numerically reproduced by means of the optical Fourier transformation of spatial variation of the polarizability tensor α_ij, and the azimuthal dependence of the scattering intensity distribution is interpreted. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2915–2921, 2001     

Long‐term growth of core‐set curl in poly(ethylene terephthalate) film

Solid polymeric films (plates) commonly exhibit only partial recovery after being subjected to a bending moment for some finite duration. This phenomenon, generally called bending recovery or core‐set, has been described and successfully modeled in past studies using the viscoelastic plate bending theory. In this study, the viscoelastic theory of core‐set curl was extended to account for physical aging effects during the bending recovery test. The contribution of physical aging was incorporated into the model through the effective time theory and assuming a thermorheologically simple behavior. The model was tested against long‐term core‐set data for a biaxially oriented poly(ethylene terephthalate) (PET) film under ambient conditions and was then used to map the effect of sample age on the evolution of core‐set curl over long times. The predictions of the model agreed favorably with the data, and the results underscored the strong retarding effect of physical aging on the rate of acquisition of core‐set curl in PET film at ambient temperature. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 1957–1967, 2001     

Integrated mechanism for the morphological structure development in HDPE melt‐blown and machine‐direction‐oriented films

The morphologies of a series of blown films and machine‐direction‐oriented (MDO) films, all produced from high density polyethylene, were characterized. In the blown film process, the crystalline morphology develops while the melt is under extensional stress. In the MDO process, drawing takes place in the solid state and deforms the crystalline morphology of the starting film. The films were characterized by wide‐angle X‐ray scattering (WAXS), small‐angle X‐ray scattering (SAXS) and atomic force microscopy to determine the lamellar morphology. The effect of the type of deformation on the lamellar morphology was studied and relationships were developed between the lamellar and polymer chain morphology using SAXS and WAXS. Blown and MDO films were found to have very different morphologies. However, an integrated mechanism was developed linking the sequential events in the deformation and morphology development in blown and MDO films. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1834–1844, 2007     

The effect of film thickness on the depth‐wise chain orientation of rod‐shaped polyimide

Controlling the chain orientation of polyimide is important because it affects the physical and electrical properties of the film. When a polyimide film is thick, the chain orientation has an inhomogeneous distribution along the thickness direction. In this study, poly(amic acids), the precursor of polyimide, with different coating thicknesses are dried, and the distribution of chain orientation in the thickness direction is investigated by measuring the residual solvent content with Raman spectroscopy. The effect of film thickness on the imidization rate is also studied by measuring the depth‐wise degree of imidization at the curing step. With the final cured polyimide film, the depth‐wise chain orientation is quantified by introducing the Fraser distribution function using polarized Raman spectroscopy. The thicker film has a lower degree of in‐plane orientation of polyimide chains, particularly near the substrate. This distribution of polyimide chain orientation in the thickness direction is similar to that of poly(amic acid) after drying. Fast imidization with higher solvent content for thick polyimide retards the formation of a well‐ordered structure with a high degree of in‐plane orientation. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 848–857     

Relationship between fracture toughness and intrinsic deformation parameters in isotropic and flow‐oriented linear low‐density polyethylene

The fracture toughness of isotropic and flow‐oriented linear low‐density polyethylene (LLDPE) is evaluated by the Essential Work of Fracture (EWF) concept, with a special setup of CCD camera to monitor the process of deformation. Allowing for the molecular orientation, flow‐oriented sample, prepared via melt extrusion drawing, is stretched parallel (oriented‐0°) and perpendicular (oriented‐90°) to its original melt extrusion drawing direction, respectively. The obtained values of specific EFW w_e are 34.6, 10.2, and 4.2 N/mm for the oriented‐0°, isotropic and oriented‐90° sample, respectively. With knowledge of intrinsic deformation parameters deduced from uniaxial tensile tests, moreover, a relationship between specific EFW w_e the ratio of true yield stress to strain hardening modulus σ_ty/G is well established. It means that the fracture toughness of polyethylene is determined by both crystalline and amorphous parts, rather than by one of them. Moreover, the true yield stress seems to be nondecisive factors determining the fracture toughness of polyethylene. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 2880–2887, 2006     

Simulated glass transition in free‐standing thin polystyrene films

In this article, we investigate the glass transition in polystyrene melts and free‐standing ultra‐thin films by means of large‐scale computer simulations. The transition temperatures are obtained from static (density) and dynamic (diffusion and orientational relaxation) measurements. As it turns out, the glass transition temperature of a 3 nm thin film is ～60 °K lower than that of the bulk. Local orientational mobility of the phenyl bonds is studied with the help of Legendre polynomials of the second‐order P₂(t). The α and β relaxation times are obtained from the spectral density of P₂(t). Our simulations reveal that interfaces affect α and β‐relaxation processes differently. The β relaxation rate is faster in the center of the film than near a free surface; for the α relaxation rate, an opposite trend is observed. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1160–1167, 2010     

Prediction and phase segregation in thin‐film of conjugated polymer blends

Blending conjugated polymers is an efficient method to improve the properties of the films. The phase diagram of poly(9,9‐dihexylfluorene) (PF) and poly(2‐methoxy‐5‐(2′‐ethyl‐hexyloxyl)‐p‐phenylene vinylene) (MEHPPV) was predicted by a modified Flory–Huggins theory based on the topological method (graph theory) for the structure‐property correlations. It shows that the two polymers have a strong trend to separate. Atomic/friction force microscopy (AFM/FFM) measurements show there exist microphase separations in film prepared at room temperature. After annealing at 160 °C, serious phase segregations took place in both the lateral and vertical direction. The photoluminescence of the thin films was also measured by a fluorophotometer. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1382–1391, 2005     

Novel UV‐induced photografting process for preparing poly(tetrafluoroethylene)‐based proton‐conducting membranes

A novel process comprising the UV‐induced photografting of styrene into poly(tetrafluoroethylene) (PTFE) films and subsequent sulfonation has been developed for preparing proton‐conducting membranes. Although under UV irradiation the initial radicals were mainly generated on the surface of the PTFE films by the action of photosensitizers such as xanthone and benzoyl peroxide, the graft chains were readily propagated into the PTFE films. The sulfonation of the grafted films was performed in a chlorosulfonic acid solution. Fourier transform infrared and scanning electron microscopy were used to characterize the grafted and sulfonated membranes. With a view to use in fuel cells, the proton conductivity, water uptake, and mechanical properties of the prepared membranes were measured. Even through the degree of grafting was lower than 10%, the proton conductivity in the thickness direction of the newly prepared membranes could reach a value similar to that of a Nafion membrane. In comparison with γ‐ray radiation grafting, UV‐induced photografting is very simple and safe and is less damaging to the membranes because significant degradation of the PTFE main chains can be avoided. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2624–2637, 2007     

Pulsed‐laser–deposited and plasma‐polymerized polytetrafluoroethylene (PTFE)‐like thin films: A comparative study on PTFE‐specific properties

Glass‐like and structural first‐order phase transitions are investigated in polytetrafluoroethylene (PTFE) foils and PTFE‐like films prepared by pulsed‐laser deposition (PLD) and plasma polymerization (PP). A structural comparison of the investigated polymers is performed by infrared spectroscopy and dielectric dilatometry. It is shown that dielectric dilatometry (the measurement of the susceptance vs. temperature) provides a simple and elegant means for detecting volumetric transitions in thin nonpolar polymer films. In conventional PTFE foils, the known glass‐like and structural first‐order phase transitions are identified. The structure of pulsed‐laser deposited PTFE strongly depends on the target material, ranging from highly crystalline films showing only structural phase transitions to films strongly deviating from PTFE foils, with structural characteristics comparable to plasma‐polymerized fluorocarbons. The dielectric loss of the highly crystalline PLD films compares favorably with conventional PTFE foils, making the films attractive for new applications in miniature electret devices. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2115–2125, 1999     

Patterned immobilization of biomolecules by using ion irradiation‐induced graft polymerization

A new method for biomolecular patterning based on ion irradiation‐induced graft polymerization was demonstrated in this study. Ion irradiation on a polymer surface resulted in the formation of active species, which was further used for surface‐initiated graft polymerization of acrylic acid. The results of the grafting study revealed that the surface graft polymerization using 20 vol % of acrylic acid on the poly(tetrafluoroethylene) (PTFE) film irradiated at the fluence of 1 × 10¹⁵ ions/cm² for 12 h was the optimum graft polymerization condition to achieve the maximum grafting degree. The results of the fluorescence microscopy also revealed that the optimum fluence to achieve the maximum fluorescence intensity was 1 × 10¹⁵ ions/cm². The grafting of acrylic acid on the PTFE surfaces was confirmed by a fluorescence labeling method. The grafted PTFE films were used for the immobilization of amine‐functionalized p‐DNA, followed by hybridization with fluorescently tagged c‐DNA. Biotin‐amine was also immobilized on the acrylic acid grafted PTFE surfaces. Successful biotin‐specific binding of streptavidin further confirmed the potential of this strategy for patterning of various biomolecules. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 6124–6134, 2009     

Water‐sorption behaviors of poly(3,4′‐oxydiphenylene pyromellitimide) films depending on the thickness variation

The effect of film thickness on the water‐sorption behaviors of poly(3,4′‐oxydiphenylene pyromellitimide) (PMDA‐3,4′ODA) films was gravimetrically investigated and interpreted with a Fickian diffusion model in films. The diffusion coefficient increased with increasing film thickness, whereas the water uptake and the activation energy decreased. Overall, the water‐sorption behaviors of PMDA‐3,4′ODA films are strongly dependent on the changes in morphological structure, which originated from the variation in the film thickness. As the film thickness increased, the molecular in‐plane orientation decreased, consequently leading to the increased diffusion coefficient and decreased activation energy. In contrast, the water uptake decreased with increasing film thickness because of the increase in the out‐of‐plane packing order. The diffusion coefficient and activation energy were strongly dependent on the in‐plane orientation in the films. © 2001 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 669–676, 2001     

Confocal microscopy studies of shear‐induced coalescence in blends of poly(butyl methacrylate) and poly(2‐ethylhexyl methacrylate)

This article reports the results of confocal fluorescence microscopy studies of shear‐induced coalescence in binary blends of poly(2‐ethylhexyl methacrylate) (PEHMA; 90 wt %) and poly(butyl methacrylate) (PBMA; 10 wt %). We prepared the blends by casting a mixture of latex dispersions of the components onto a substrate and allowing the film to dry under ambient conditions. The initial morphology of the film was a dispersion of 120‐nm PBMA spheres in a continuous PEHMA matrix. One‐fifth of the PBMA particles were labeled with anthracene, the emission of which we observed with confocal microscopy. The blends were sheared in a parallel‐plate rheometer at 80 and 100 °C for 1 and 10 h. Careful image analysis allowed us to estimate the mean size of the dispersed phase and the width of the size distribution. The results were compared with the theoretical limits of Wu and Taylor. After 10 h of shearing, the mean particle size decreased and the particle distribution became narrower in comparison with the results obtained after 1 h of shearing. We explain this result by inferring that before the sample reached steady‐state morphology, its rate of coalescence was greater than the rate of particle breakup. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2317–2332, 2001     

Anionic polymerization of 4‐phenyl‐1‐buten‐3‐yne derivatives bearing electron‐withdrawing groups

The anionic polymerization of derivatives of 4‐phenyl‐1‐buten‐3‐yne was carried out to investigate the effect of substituents on the polymerization behavior. The polymerization of 4‐(4‐fluorophenyl)‐1‐buten‐3‐yne and 4‐(2‐fluorophenyl)‐1‐buten‐3‐yne in tetrahydrofuran at −78 °C with n‐BuLi/sparteine as an initiator gave polymers consisting of 1,2‐ and 1,4‐polymerized units in quantitative yields with ratios of 80/20 and 88/12, respectively. The molecular weights of the polymers were controlled by the ratio of the monomers to n‐BuLi, and the distribution was relatively narrow (weight‐average molecular weight/number‐average molecular weight < 1.2), supporting the living nature of the polymerization. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 1016–1023, 2001     

Development of oriented structure and properties on drawing of poly(vinylidene fluoride) by solid‐state coextrusion

Gel films of poly(vinylidene fluoride) (PVDF) consisting of α‐form crystals were drawn uniaxially by solid‐state coextrusion to extrusion draw ratios (EDR) up to 9 at an optimum extrusion temperature of 160 °C, about 10°C below the melting temperature (T_m). The development of an oriented structure and mechanical and electrical properties on coextrusion drawing were studied as a function of EDR. Wide‐angle X‐ray diffraction patterns showed that the α crystals in the original gel films were progressively transformed into oriented β‐form crystals with increasing EDR. At the highest EDR of 9 achieved, the drawn product consisted of a highly oriented fibrous morphology with only β crystals even for the draw near the T_m. The dynamic Young's modulus along the draw direction also increased with EDR up to 10.5 GPa at the maximum EDR of 9. The electrical properties of ferroelectricity and piezoelectricity were also markedly enhanced on solid‐state coextrusion. The D–E square hysteresis loop became significantly sharper with EDR, and a remanent polarization P_r of 100 mC/m² and electromechanical coupling factor along the thickness direction k_t of 0.27 were achieved at the maximum EDR of 9. The crystallinity value of 73–80% for the EDR 9 film, estimated from these electrical properties, compares well with that calculated by the ratio of the crystallite size along the chain axis to the meridional small‐angle X‐ray scattering (SAXS) long period, showing the average thickness of the lamellae within the drawn β film. These results, as well as the appearance of a strong SAXS maximum, suggest that the oriented structure and properties of the β‐PVDF are better explained in terms of a crystal/amorphous series arrangement along the draw axis. Further, the mechanical and electrical properties obtained in this work are the highest among those ever reported for a β‐PVDF, and the latter approaches those observed for the vinylidene fluoride and trifluoroethylene copolymers. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 1371–1380, 2001     

Enhanced electrical properties of highly oriented poly(vinylidene fluoride) films prepared by solid‐state coextrusion

Oriented poly(vinylidene fluoride) (PVDF) films with β‐form crystals have been commonly prepared by cold drawing of a melt‐quenched film consisting of α‐form crystals. In this study, we have successfully produced highly oriented PVDF thin films (20 µm thick) with β‐crystals and a high crystallinity (55–76%), by solid‐state coextrusion of a gel film to eight times the original length at an established optimum extrusion temperature of 160°C, some 10°C below the melting temperature. The resultant drawn films had a highly oriented (orientation function f_c = 0.993) fibrous structure, showing high mechanical properties of an extensional elastic modulus of 8.3 GPa and tensile strength of 0.84 GPa, along the draw direction. Such highly oriented and crystalline films exhibited excellent ferroelectric and piezoelectric properties. The square hysteresis loop was significantly sharper than that of a conventional sample. The sharp switching transient yielded the remnant polarization P_r of 90 mC/m², and the electromechanical coupling factor k_t was 0.24 at room temperature. These values are about 1.5 times greater than those of a conventional β‐PVDF film. Thus, solid‐state coextrusion near the melting point was found to be a useful technique for the preparation of highly oriented and highly crystalline β‐PVDF films with superior mechanical and electrical properties. The morphology of the extrudate relevant to such properties is discussed. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2549–2556, 1999