As-cast Films Research Articles

Environmental Degradation of Biodegradable Polyesters: 3. Effects of Alkali Treatment on Biodegradation of Poly(ε-Caprolactone) and Poly[(R)-3-Hydroxybutyrate) Films in Controled Soil

The poly(e-caprolactone) (PCL) and poly[(R)-3-hydroxybutyrate] (R-PHB) films with a hydrophilic surface were prepared by the alkali treatment of their as-cast films in NaOH solutions of different concentrations. The alkali-treated PCL and R-PHB films, as well as the as-cast PCL and R-PHB films, were biodegraded in soil controlled at 25°C and the effects of alkali treatment or surface hydrophilicities on their biodegradation were investigated by the use of gravimetry, gel permeation chromatography (GPC), scanning electron microscopy (SEM), and polarization optical microscopy. It became evident that the alkali treatment enhanced the hydrophilicities and biodegradabilities of the PCL and R-PHB films in soil. The biodegradabilities of the as-cast aliphatic polyester films in controlled soil decreased in the following order: PCL > R-PHB > PLLA, in agreement with that in controlled static seawater.

Synthesis of Gold Nanoparticles Coated with Well-Defined, High-Density Polymer Brushes by Surface-Initiated Living Radical Polymerization

The synthesis of a gold nanoparticle (AuNP) coated with a well-defined polymer is reported. The AuNP coated with an initiator group for living radical polymerization was prepared by the simple one-pot reduction of tetrachloroaurate with sodium borohydrate in the presence of an initiator group-holding disulfide. The surface-initiated living radical polymerization of methyl methacrylate (MMA) mediated by a copper complex was carried out with the initiator-coated AuNP in the presence of a “sacrificial” free initiator. Living polymerization proceeded exhibiting a first-order kinetics of monomer consumption and an evolution of molecular weight of the graft polymer proportional to monomer conversion, thus providing well-defined, low-polydispersity graft polymers with an approximate graft density of 0.3 chains/nm2. Transmission electron microscopic observations of as-cast films of the AuNPs coated with PMMAs (PMMA−AuNPs) revealed that the particles were well dispersed in the polymer matrix without forming aggreg...

Gas permeability and n‐butane solubility of poly(1‐trimethylgermyl‐1‐propyne)

AbstractThe gas permeability and n‐butane solubility in glassy poly(1‐trimethylgermyl‐1‐propyne) (PTMGP) are reported. As synthesized, the PTMGP product contains two fractions: (1) one that is insoluble in toluene and soluble only in carbon disulfide (the toluene‐insoluble polymer) and (2) one that is soluble in both toluene and carbon disulfide (the toluene‐soluble polymer). In as‐cast films, the gas permeability and n‐butane solubility are higher in films prepared from the toluene‐soluble polymer (particularly in those films cast from toluene) than in films prepared from the toluene‐insoluble polymer and increase to a maximum in both fractions after methanol conditioning. For example, in as‐cast films prepared from carbon disulfide, the oxygen permeability at 35 °C is 330 × 10−10 cm3 (STP) cm/(cm2 s cmHg) for the toluene‐soluble polymer and 73 × 10−10 cm3 (STP) cm/(cm2 s cmHg) for the toluene‐insoluble polymer. After these films are conditioned in methanol, the oxygen permeability increases to 5200 × 10−10 cm3 (STP) cm/(cm2 s cmHg) for the toluene‐soluble polymer and 6200 × 10−10 cm3 (STP) cm/(cm2 s cmHg) for the toluene‐insoluble polymer. The rankings of the fractional free volume and nonequilibrium excess free volume in the various PTMGP films are consistent with the measured gas permeability and n‐butane solubility values. Methanol conditioning increases gas permeability and n‐butane solubility of as‐cast PTMGP films, regardless of the polymer fraction type and casting solvent used, and minimizes the permeability and solubility differences between the various films (i.e., the permeability and solubility values of all conditioned PTMGP films are similar). © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2228–2236, 2002

Nanopatterned surfaces obtained with semicrystalline ABC triblock copolymers

The surface patterns resulting from fast crystallization of as-cast and annealed thin films (ca. 100 nm) of two polystyrene- b-polybutadiene- b-poly(ε-caprolactone) ABC triblock copolymers is investigated through atomic force microscopy (AFM). Two different substrates are used: silicon and mica. The behaviour is compared with the bulk morphology obtained through transmission electron microscopy (TEM). AFM images of the as-cast films revealed surfaces with lamellar patterns. Based on the observation of T-shaped grain boundaries between lamellae, and on a comparison of the microdomain dimensions obtained by TEM and AFM, the surface pattern is rationalized as being formed by amorphous and crystalline polycaprolactone (PCL), with the PCL/PB block copolymer interfaces located parallel to the susbstrate. The formation of islands and holes in annealed films with a lamellar ‘floor’, depending on the conmensurability between film thickness and long period, is also observed, indicating a parallel orientation of the block copolymer lamellae.

Control of mesh pattern of surface corrugation via rate of solvent evaporation in solution casting of polymer film in the presence of convection

A polygonal mesh pattern was observed on an as-cast polymer film when cast from a dilute solution on a hot plate. It was found that the pattern was ascribed to surface corrugation. In the dilute solution, a similar polygonal mesh pattern due to convection was present. A possible imprinting mechanism of the convection pattern on the as-cast polymer film as the surface corrugation was investigated by real time observation using the so-called shadowgraph technique. For this purpose poly(styrene-ran-butadiene) random copolymer was used as a solute and toluene as a solvent. Furthermore, control of the mesh size via the rate of solvent evaporation was examined. It was found that the mesh size was increased with an increase of the rate in the regime of the lower evaporation-rate (regime I) and that it was decreased tremendously with an increase of the rate in the regime of the higher evaporation-rate (regime II). These regimes can be referred to as a kinetic control regime and a temperature-gradient control regime, respectively.

Short- and Long-Range Interactions in Thin Films of Polymer Blends in Microchannels

We present the surface structures formed under the void microchannels of an elastomeric mold when thin films of polystyrene/polybutadiene (PS/PB) blends are annealed with the mold placed on the film. Exactly opposite types of structure result under identical annealing conditions, depending only on the height difference in the as-cast thin film between the PS and PB phases. Recessed patterns form under the microchannel by long-range interactions when this height is more than 60 nm; the usual protruding patterns result in the void microchannels due to the short-range interactions of capillarity when the height is less than 40 nm. The height of fully developed meniscus of the mobile PB in solid PS is believed to be the factor that determines the type of pattern formation.

Defect study of crystallized amorphous Co-rich magnetic alloy

Microstructure of Co-rich amorphous magnetic alloy, Co 74.26Fe 4.74B 18.9Si 2.1, formed by planar casting process was characterized using transmission electron microscopy (TEM) and auger electron spectroscopy (AES) to determine the cause of deterioration of the magnetic properties during extended manufacturing trial of the strip as domain wall pinned sensors. TEM analysis showed that micro-crystalline SiC particle contamination has caused the metastable B 4Si crystallites to nucleate at the wheel (cold) side of the as-cast film. The B 4Si crystals depleted the metalloids at the interface, which in turn, resulted in premature precipitation and excessive growth of Co grains at the perimeter of B 4Si particles. Such microstructural inhomogeneity remained on the wheel side of the film even after field-annealing, which adversely affected the domain pinning. AES depth analysis also indicated that the as-cast film had a steep concentration gradient with the wheel side, being depleted of B and Si. The gradient flattened slightly during annealing. As the microstructural and compositional inhomogeneities disrupt the layered structure essential for the magnetic sensor, it is critical to control the processing parameters to eliminate the sources of such defects discussed above.

MORPHOLOGIES OF MELT-CRYSTALLIZED THIN FILMS OF NYLON-6, NYLON-6,6, AND THEIR BLENDS AS REVEALED BY TRANSMISSION ELECTRON MICROSCOPY

Thin films of nylon-6 (N6), nylon-6,6 (N66), and their blends (N6/N66 = 70/30, 50/50, and 30/70) were prepared by casting from solution (1.0 wt%) in formic acid under ambient conditions. The dried films were melted at 260°C or 280°C and then isothermally crystallized at 200°C. Morphological observations and selected-area electron diffraction (SAED) by transmission electron microscopy (TEM) of the resulting films revealed the following results: All specimen films (N6/N66 = 100/0, 70/30, 50/50, 30/70, and 0/100) had fibrillar entities that were undoubtedly crystalline judging from SAED and dark-field (DF) imaging. Some of the fibrillar entities were constituents of a spherulite or a sheaflike structure (namely, an immature spherulite). To delete the “memory” of the structures of the N66 component that were formed in as-cast films, the films have to be melted at 280°C. As to isothermal crystallization of the blends at 200°C after melting at 280°C, it is postulated that the N66 component first starts to crystallize, and then the N6 one starts to crystallize afterward.

Crystallization within Melt Ordered Semicrystalline Block Copolymers: Exploring the Coexistence of Microphase-Separated and Spherulitic Morphologies

The crystalline and microphase-separated morphology of semicrystalline block copolymers are compared in bulk (0.5-1 mm) and thin films (5-0 Im), as characterized by transmission electron microscopy (TEM) and polarized light microscopy (PLM). Bulk films of a triblock copolymer of polystyrene, polybutadiene, and polycaprolactone, (PS)0.35(PB)0.15(PCL)0.5, where the subscripts denote the mass fraction, show a lamellar-cylindrical microphase-separated morphology with a lamellar repeat of =62 nm, as observed by TEM. Bulk films of a diblock copolymer consisting of (PB)0.2(PCL)0.8 show an imperfect cylindrical microphase-separated structure by TEM coexisting with crystalline lamellae of PCL. For both bulk specimens, the PLM shows a speckle pattern of birefringence that confirms the PCL is crystallized within the microphase-separated structure, but no large-scale spherulites are observed by PLM. The microstructure in the as-cast thin films (5-10 Im) by TEM is lamellar-cylindrical for the triblock copolymer and cylindrical for the diblock copolymer, as described above for the bulk specimens. Upon thermal treatment of these thin films, large and well-defined PCL spherulites are observed by PLM for both block copolymers. TEM of the thermally treated triblock copolymer thin films shows that, after the formation of spherulites, the microphase structure is no longer lamellar-cylindrical but entirely dominated by PCL lamellar crystals. In contrast, TEM of the thermally treated diblock copolymer thin films shows that the PCL lamellar crystals coexist with the PB microphase-separated cylinders after the formation of PCL spherulites. Bulk specimens could not be induced to form spherulites under similar thermal treatment conditions.

Gas permeability and hydrocarbon solubility of poly[1-phenyl-2-[p-(triisopropylsilyl)phenyl]acetylene

The effects of film thickness, physical aging, and methanol conditioning on the solubility and transport properties of glassy poly[1-phenyl-2-[p-(triisopropylsilyl) phenyl]acetylene] are reported at 35 °C. In general, the gas permeability coefficients are very high, and this polymer is more permeable to larger hydrocarbons (e.g., C3H8 and C4H10) than to light gases such as H2. The gas permeability and solubility coefficients are higher in as-cast, unaged films than in as-cast films aged at ambient conditions and increase to a maximum in both unaged and aged as-cast films after methanol conditioning. For example, the oxygen permeability of a 20-μm-thick as-cast film is initially 100 barrer and decreases to 40 barrer after aging for 1 week at ambient conditions. After methanol treatment, the oxygen permeabilities of unaged and aged films increase to 430 and 460 barrer, respectively. Thicker as-cast films have higher gas permeabilities than thinner as-cast films. Propane and n-butane sorption isotherms suggest significant changes in the nonequilibrium excess free volume in these glassy polymer films due to processing history. For example, the nonequilibrium excess free volume estimated from the sorption data is similar for as-cast, unaged samples and methanol-conditioned samples; it is 100% higher in methanol-conditioned films than in aged, as-cast films. The sensitivity of permeability to processing history may be due in large measure to the influence of processing history on nonequilibrium excess free volume and free volume distribution. The propane and n-butane diffusion coefficients are also sensitive to film processing history, presumably because of the dependence of diffusivity on free volume and free volume distribution. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1474–1484, 2000

Effect of physical aging of poly(1-trimethylsilyl-1-propyne) films synthesized with TaCl5 and NbCl5 on gas permeability, fractional free volume, and positron annihilation lifetime spectroscopy parameters

The effect of physical aging on the gas permeability, fractional free volume (FFV), and positron annihilation lifetime spectroscopy (PALS) parameters of dense, isotropic poly(1-trimethylsilyl-1-propyne) (PTMSP) films synthesized with TaCl5 and NbCl5 was characterized. As-cast films were soaked in methanol until an equilibrium amount of methanol was absorbed by the polymer. When the films were removed from methanol, film thickness initially decreased rapidly and was almost constant after 70 h in air for both catalysts. This timescale was much longer than the timescale for complete methanol desorption (ca. 5 h). From the film-thickness data, the reduction in FFV with time was estimated. For samples prepared with either catalyst, the kinetics of FFV reduction were well-described by a simple model based on the notion either that free-volume elements diffuse to the surface of the polymer film and are subsequently eliminated from the sample or that lattice contraction controls polymer densification. Methane permeability decreased rapidly during the first 70 h, which was the same timescale for the thickness change. The decrease in methane permeability was smaller in films prepared with NbCl5 than with TaCl5. The logarithm of methane permeability decreased linearly as reciprocal FFV increased, in accordance with free-volume theory. The PALS results indicate that the concentration of larger free-volume elements (as indicated by the intensity I4) decreased with aging time and that the other PALS parameters were not strongly influenced by aging. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1222–1239, 2000

Porous biodegradable polyesters. I. Preparation of porous poly(L-lactide) films by extraction of poly(ethylene oxide) from their blends

Porous poly(L-lactide) (PLLA) films were prepared by water extraction of poly(ethylene oxide) (PEO) from solution-cast PLLA and PEO blend films. The dependence of blend ratio and molecular weight of PEO on the porosity and pore size of films was investigated by gravimetry and scanning electron microscopy. The film porosity and extracted weight ratio were in good agreement with the expected for porous films prepared using PEO of low molecular weight (Mw = 1 × 103), but shifted to lower values than expected when high molecular weight PEO (Mw = 1 × 105) was utilized. The maximum pore size was larger for porous films prepared from PEO having higher molecular weight, when compared at the same blending ratio of PLLA and PEO before water extraction. Differential scanning calorimetry of as-cast PLLA and PEO blend films revealed that PLLA and PEO were phase-separated at least after solvent evaporation. On the other hand, comparison of blend films before and after extraction suggested that a small amount of PEO was trapped in the amorphous region between PLLA crystallites even after water extraction and hindered PLLA crystallization during solvent evaporation. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 629–637, 2000

A Study of Three-Phase Structures in ABC Triblock Copolymers

The microdomain structure of an ABC triblock copolymer consisting of poly(2-hydroxyethyl methacrylate), poly(tert-butyl methacrylate) and poly(2-(perfluorobutyl) ethyl methacrylate) was investigated by means of small-angle X-ray scattering (SAXS) and energy-filtered transmission electron microscopy (EF-TEM) which is based on inelastically scattered electrons by a specific element (F atoms in this case) and known as element spectroscopic imaging (ESI). A three-phase lamellar structure was observed with good contrast for an unstained ultrathin section of the as-cast film of the triblock copolymer by imaging the inelastically scattered electrons at energy-loss of 100 eV. The microdomain structure can be interpreted in accordance with the EF-TEM result. A peculiar SAXS profile where the intensity of the first-order peak was weaker than that of the second-order was observed for the triblock copolymer. Theoretical calculation of the SAXS intensity with a paracrystal model of the four-layer lamellae successfully reproduced the observed SAXS profile.

Mechanical Properties and Structure of Poly(p-phenylenevinylene) Films Prepared by the Zone-Reaction Method

The “zone-reaction method”, consisting of zone drawing (ZD) and zone reaction (ZR), was applied to chemically synthesized poly(p-phenylenevinylene) (PPV) precursor films under various applied tensions (σ) and heater temperatures (Th). The changes in the structure, tensile, and viscoelastic properties of the resulting films were investigated. It was found that orientation function (f) of the ZD films increased with draw ratio (DR), regardless of the Th and σ values, and attained 0.862 (DR = 9). ZR was subsequently performed on the ZD film. The molecular orientation and PPV content were strongly affected by the Th: The film obtained at Th = 240 °C exhibited the highest f value, as high as 0.894, while a further increase in the Th resulted in a disorientation of molecular chains. On the other hand, the absorption ratio between 632 cm-1 (C−S stretch) and 965 cm-1 (trans-vinylene C−H out-of-plane bend) (A632/A965) became almost zero at Th above 240 °C. The Young's modulus and tensile strength for the resulting ZR film respectively increased to 69.4 and 1.3 GPa from 2.1 and 0.04 GPa of as-cast original film. The dynamic storage modulus for the ZR film was the value as high as 74.7 GPa and held 40 GPa even at 350 °C, which were considerably higher than those of the typical engineering plastics.

Surface modification and functionalization of electroactive polymer films

Surface modification of electroactive polyaniline (PANi) films by gas plasma treatment, corona discharge treatment, vacuum ultra-violet (VUV) exposure, and surface graft copolymerization has been carried out. Exposure of the nigraniline-like films of PANi to argon plasma, oxygen plasma, corona discharge and VUV, followed by atmospheric exposure, resulted in the oxidation of the carbon atoms to various extents. Carbon oxidation, in turn, caused a decrease in the intrinsic oxidation state ([N/[NH] ratio) of the aniline polymer. The as-cast and noncrosslinked emeraldine (EM-25) film of PANi exhibited a surface micro-hardness of about 1 GPa. The hardness was further enhanced to about 6 GPa in the highly crosslinked EM (EM-150) film after one cycle of acid–base treatment. Surface modification of the crosslinked EM film via surface graft copolymerization with acrylic acid or styrenesulfonic acid could give rise to semi-conductive and super-hard-surfaced PANi films having micro-hardness values approaching 20 GPa. This surface hardness is comparable to those reported for the super-hard-surfaced conventional polymers from high-energy ion-beam bombardment. Copyright © 1999 John Wiley & Sons, Ltd.

The influence of annealing on thermal transitions in a nematic copolyester

Thermal transitions of a glassy, main chain, liquid crystalline, random copolyester, HIQ-40, have been characterized. HIQ-40 is made from 40 mol percent p-hydroxybenzoic acid (HBA) and 30 mol % each of p-hydroquinone (HQ) and isophthalic acid (IA). This polymer is soluble in organic solvents, permitting the preparation of thin, solution-cast films that are in a glassy, metastable, optically isotropic state. On first heating of an isotropic HIQ-40 film in a calorimeter, one glass transition is observed at low temperature (approximately 42°C), and is ascribed to the glass/rubber transition of the isotropic polymer. A cold crystallization exotherm centered near 150°C is observed. This is associated with the development of low levels of crystalline order. A broad melting endotherm is centered at about 310°C; this endotherm marks the melting of crystallites and the transformation to a nematic fluid. A nematic to isotropic transition was not observed by calorimetry. After quenching from the nematic melt, a T g is observed in the range of 110-115°C and is associated with the glass/rubber transition of the nematically ordered polymer. Annealing optically isotropic films at temperatures above the isotropic glass transition results in the systematic development of axial order. In these annealed samples, T g increases rapidly until it is near the annealing temperature, then T g increases more slowly at longer annealing times. In as-cast films annealed at 120-135°C, the light intensity transmitted through a sample held between crossed polarizers in an optical microscope (a qualitative measure of birefringence and, in turn, axial order) initially increases rapidly and uniformly throughout the sample and, at longer annealing times, approaches asymptotic values that are higher at higher annealing temperatures. The increase in transmitted intensity is ascribed to the development of axial order. The uniform increase in transmitted intensity suggests that ordering occurs by a rather global process and not via a nucleation and growth mechanism.

Photocontrol of Alignment of Liquid Crystals Using a Polymethacrylate bearing Azobenzene.

Films of poly[4-(2-methacryloylethoxy)azobenzene] irradiated with linearly polarized light induced homogeneous alignment of liquid crystals (LC) like a rubbed polyimide film, because of surface anisotropy generated by photoreorientation of azobenzene moieties. Films annealed before irradiation needed more exposure energies of incident light to induce homogeneous LC alignment, than as-cast films. And also photo-rewriting from the initial LC alignment required a large energy to change, in the case of films contacting with LC layers. While a film without LC layers during irradiation caused photo-rewriting of LC alignment at an extraordinarily small energy (10mJ cm-2).

Architecture of polymeric superstructures formed by locking cubic lattices of core-shell polymer microspheres

Poly (4-vinylpyridine) (P4VP) core-policy (α-methylstyrene) shell polymer microspheres have been synthesized by cross-linking the P4VP spherical microdomains of poly (α-methylstyrene-b-4-vinyl-pyridine) diblock copolymer films with 1,4-dibromobutane. These microspheres formed a lattice with a body-centred cubic structure near the overlap concentration. In the bulk of as-cast film of microspheres, this structure changed to a face-centred cubic lattice. After these microspheres formed a cubic lattice in methyl methacrylate (MMA) monomer, the polymeric superstructures were constructed by locking permanently ordered lattice in a solid matrix by means of free radical polymerization of MMA monomer. This technique is one of the best methods for creating nanoscopic polymeric superstructures composed of three phase-separated microdomains. © 1997 Elsevier Science Ltd.

Synthesis, thermal, and mechanical characterization of liquid-crystalline polyhydroxyethers

High molecular weight liquid-crystalline polyhydroxyethers, containing functional hydroxy groups, were synthesized from an aromatic diol and the diglycidylether of an aromatic diol. The polymers showed a liquid-crystalline melt when about 70% or more of the aromatic units in the chain were biphenyl units. Tensile modulus values varied from 3 GPa for as-cast films to 6 GPa for drawn films. These polymers are potentially suitable candidates to reinforce common thermoplastics by reactive blending. For this purpose polyhydroxyethers have been prepared, having a liquid-crystalline melt in the processing range of PET, viz. 260–290°C. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 1971–1978, 1997

Long-term permeation properties of poly(1-trimethylsilyl-1-propyne) membranes in hydrocarbon?Vapor environment

Poly(1-trimethylsilyl-1-propyne) (PTMSP), a high free-volume glassy di-substituted polyacetylene, has the highest gas permeabilities of all known polymers. The high gas permeabilities in PTMSP result from its very high excess free volume and connectivity of free volume elements. Permeability coefficients of permanent gases in PTMSP decrease dramatically over time due to loss of excess free volume. The effects of aging on gas permeability and selectivity of PTMSP membranes continuously exposed to a 2 mol % n-butane/98 mol % hydrogen mixture over a period of 47 days are reported. The permeation properties of PTMSP membranes are quite stable when the polymer is continuously exposed to a gas mixture containing a highly sorbing organic vapor such af n-butane. The n-butane/hydrogen selectivity was essentially constant for the 47-day test period at a value of 29, or 88% of the initial value of the as-cast film of 33. Condensable gases such as n-butane may serve as a “filler” in the nonequilibrium free volume of the polymer, thereby preserving the high level of excess free volume. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 1483–1490, 1997