Solution-cast Films Research Articles

The Effect of Processing of Polycaprolactone Films on Degradation Process Initiated by Aspergillus Oryzae Lipase

Poly(ϵ-caprolactone) (PCL) films with Mn = 18 kDa obtained by compression molding (CM) or solution casting (SC) were subjected to Aspergillus oryzae (AO) lipase action in a phosphate buffer at pH 7 at 37°C. The appearance of randomly oriented cracks on the surface of incubated PCL films accompanied by a decrease of the weight-average molecular weight (Mw) by 10% was observed after 42 days. The increase of crystallinity and surface morphology pattern of PCL samples exposed to AO lipase action supported the fact that the degradation proceeded in the amorphous phase of the aged films. SC films were degraded faster, probably due to better accessibility of ester bonds in the amorphous phase of spherulites.

Electroactive polymer-based electrochemical capacitors using poly(benzimidazo-benzophenanthroline) and its pyridine derivative poly(4-aza-benzimidazo-benzophenanthroline) as cathode materials with ionic liquid electrolyte

A novel processing technique was used to solution cast films of poly(benzimidazo benzophenanthroline), (BBL), and the novel ladder polymer poly(4-aza-benzimidazo benzophenanthroline) (Py-BBL), which were used as cathode materials in Type IV electroactive polymer-based electrochemical capacitors (EPECs). This new processing technique involves co-casting the polymer from solution with a room temperature ionic liquid, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMIBTI). The new processing technique gave polymer films with superior transport properties and electrochemical stabilities, did not require a break-in period, and yielded higher charge capacity than the standard films. Co-cast films of BBL and Py-BBL were each incorporated into separate Type IV EPECs using poly(3,4-propylene dioxythiophene) (PProDOT) as the anode material. It was found that the PProDOT/BBL capacitors store, on average, about 50% more energy than a comparable PProDOT/Py-BBL EPEC. While PProDOT/BBL films have an energy density advantage at rates (power densities) less than 0.01 kW kg−1, PProDOT/Py-BBL EPECs are capable of delivering higher energy than the BBL EPECs at rates greater than 0.01 kW kg−1 (550 s per cycle). In fact, PProDOT/Py-BBL devices delivered more than ten times the energy density of PProDOT/BBL devices at 0.5 kW kg−1 (50 s per cycle). The PProDOT/Py-BBL EPECs were cycled for 10,000 cycles at 65% depth of discharge and maintained 96% of the initial energy and power density, whereas the PProDOT/BBL EPECs were cycled under the same conditions and lost more than 35% of the initial energy and power density after only 2300 cycles.

Brill transition of nylon-6 in electrospun nanofibers

Electrospun nylon-6 fibers were prepared from its polyelectrolyte solution in formic acid with different concentrtaions. In situ Fourier transform infrared (FTIR), wide-angle X-ray diffraction and small-angle X-ray scattering (SAXS) were performed on the nylon-6 fibers heated to various temperatures until melting. For comparison, stepwise annealing of the solution-cast film having exclusively the α-form was also carried out to elucidate the structural evolution. Our results showed that Brill transition in the electrospun fibers occurs at a lower temperature than that in the solution-cast film due to the crystal size difference. Differential scanning calorimetry heating traces on the as-spun fibers exhibited a unique crystalline phase with a melting temperature of ∼235 °C, higher than the equilibrium melting temperature of nylon-6. The content of high melting temperature (HMT) phase increased with increasing nylon-6 concentration; a maximum of 30 % of the fiber crystallinity was reached for fibers obtained from the 22 wt.% solution regardless of the heating rates used. Based on the SAXS and FTIR results, we speculated that the HMT phase is associated with thick α-form crystals developed from the highly oriented nylon-6 chains that are preserved in the skin layer of the as-spun fibers. A plausible mechanism for the formation of the skin/core fiber morphology during electrospinning was proposed.

A facile route to ordered γ phase in poly (vinylidene fluoride) via melt annealing and re-crystallization

The formation of γ phase in poly (vinylidene fluoride) is not rare from solution casting and high temperature melt crystallization. However, it is still a challenge to obtain γ phase with high melting point in a facile route. This study demonstrates that it can be readily realized via melt annealing of solution-cast films at 180°C, followed by subsequent re-crystallization upon rapid cooling in air. The re-crystallization into ordered γ phase arises from the formation of long TTTGTTTG' sequences in the melt due to transformation of TTTT conformation of initial β phase, rather than from the melt memory effects of original γ phase.

Proton Conducting Phase‐Separated Multiblock Copolymers with Sulfonated Poly(phenylene sulfone) Blocks for Electrochemical Applications: Preparation, Morphology, Hydration Behavior, and Transport

AbstractA family of multiblock copolymers consisting of alternating fully sulfonated hydrophilic poly(phenylene sulfone) and hydrophobic poly(phenylene ether sulfone) segments are prepared and characterized. The multiblock copolymers are formed by the coupling of preformed hydrophilic and hydrophobic blocks using a specially designed coupling agent. The block lengths (degree of polymerization) of both segment types were varied in order to control the ion exchange capacity. Solution cast films show spontaneous nanophase separation leading to distinct bicontinuous morphologies with correlation lengths around 15 nm. The hydrophobic phase gives the membranes their advantageous viscoelastic properties even at high temperatures under both wet and dry conditions, while proton conductivity takes place within the hydrophilic phase. Since the properties of fully sulfonated poly (phenylene sulfone)s are locally preserved within the hydrophilic domain, the membranes show very high proton conductivity and high hydrolytic stability. The very high degree of water dispersion within the hydrophilic domains leads to very low electro‐osmotic water drag. Because of their superior transport and stability properties these multiblock copolymers have a great potential for use as a substitute for perfluorosulfonic acid membranes which are used as separator materials in electrochemical applications such as polymer electrolyte membrane (PEM) fuel cells and redox flow batteries.

Enhanced electrochemical response of solution-deposited n-doping polymer via cocasting with ionic liquid

A novel cocasting approach is presented for improving electroactivity of solution-cast films of conducting polymers. Solutions of the n-doping polymer poly(benzimidazobenzophenanthroline) (BBL) were co-deposited with the ionic liquid electrolyte 1-ethyl-3-methyl-imidazolium bis(trifluoromethylsulfonyl)imide (EMIBTI). The resultant co-continuous mixture yielded highly porous polymer films (CC-BBL) upon removal of solvent and EMIBTI. Electrochemical quartz crystal microgravimetry revealed that the n-doping process in neat ionic liquid is anion-dominant, which is contrary to what is observed in dilute electrolyte solutions. The CC-BBL films exhibit a thirty-fold increase in initial current response and capacity relative to non-cocast BBL films. While current response and capacity of the non-cocast BBL improve with cycling, they level out after 800 cycles at 35% of those of the CC-BBL. CC-BBL shows high n-doping stability; no decrease in electroactivity is seen after 1000 cycles. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012

Improving the Processability of Water-soluble Films Based on Filled Thermoplastic Polyvinyl Alcohol

Abstract Melt extrusion of polyvinyl alcohol (PVOH) is desirable over commonly practiced solution film casting due to reduced energy input, environmental footprint, and processing cost, however, melt extrusion processing of plasticized polyvinyl alcohol (PVOH) presents a significant processing challenge due to inherent adhension issues of extruded PVOH film to the surface of equipment. This paper reports a method using inorganic fillers such as CaCO3 and talc to facilitate the plasticized PVOH processing for blown films. Parameters are also identified for additional process studies to optimize the mechanical properties of blown films. It was found that the preferred inorganic filler is CaCO3 for the PVOH stickiness reduction. The filled PVOH films were found to have delayed or reduced water solubility. It takes about 7 to 10 minutes for the filled PVOH films to dissolve in water whereas the neat PVOH films are soluble in water instantly. The delayed water solubility may be desirable for certain specialty applications such as packaging of pesticides during shipping and storage. With improved processability by incorporating filler, the melt extrusion produced PVOH film should cost less than the solution-cast PVOH films.

In Situ Measurement of Block Copolymer Ordering Kinetics during the Drying of Solution-Cast Films Using Small-Angle X-ray Scattering

The ordering of a poly(styrene-b-butadiene) block copolymer solution into hexagonally packed cylinders during the extraction of a neutral solvent from a solution-cast film was studied in real time ...

Blends of Zein and Nylon-6

Blends of zein and nylon-6 (55 k) in formic acid were used to produce solution cast films and electrospun fibers. When the amount of nylon-6 was 8 % or less blends were formed that had improved tensile strength and reduced solubility. The blends were analyzed using physical property measurements, DSC and IR spectra. Using between 2 and 8 % nylon-6 provided a 33 % increase in tensile strength. Young’s modulus increased by over 50 % in this range. In general elongation was lower for all formulations. Surprisingly the cast films having 0.5–8 % nylon-6 had improved solvent resistance to 90 % ethanol/water. Electrospun fibers were produced from formic acid solutions of zein and nylon-6 where the amount of nylon was 0, 2 and 6. Fibers produced from 27 % spinning solids had average diameters on the order of 0.5 μm. Reducing the spinning solids to 21 % provide slightly smaller fibers however, the fibers had more defects.

In Situ Tracking of Microstructure Spacing and Ordered Domain Compression during the Drying of Solution-Cast Block Copolymer Films Using Small-Angle X-ray Scattering

Changes in the spacing of hexagonally packed cylinders in a poly(styrene-b-butadiene) copolymer film during the continual extraction of toluene under different solvent removal conditions were studied by in situ small-angle X-ray scattering (SAXS) measurements. As the solvent is removed from the film, the structure spacing increases due to increasing segregation power and then decreases as the polymer chains become kinetically trapped while microdomains continue to deswell. The structure spacing in the vertical film direction decreases more drastically due to compression of the domains as the film thickness decreases. The degree of compression increased with increased polymer concentration because of an increase in the chain relaxation time. Increasing the drying temperature resulted in more severe domain compression, which is ascribed to faster solvent removal. Removing solvent in the presence of a sweep gas further increased the domain compression as a result of the formation of a skin at the film surfac...

Preparation and properties of peanut protein films crosslinked with citric acid

Solution cast films made from peanut proteins extracted from peanut meal and crosslinked with citric acid were found to have good dry and wet tensile properties but poor biocompatibility. Plant proteins are abundantly available, are non-immunogenic and can be used to develop films, fibers, nanoparticles and other types of materials for various applications. Previous attempts on developing films from peanut proteins have used high amounts of glycerol resulting in poor film properties. In this research, peanut proteins were made into films using 3–15% glycerol and the effect of film forming conditions on the tensile properties and thermal behavior was studied. Films were crosslinked with cytocompatible citric acid as the crosslinking agent. Ability of the crosslinked films to be used as substrates for tissue engineering was studied using mouse fibroblast cells. It was found that films developed in this research had much higher tensile strength and modulus than films previously developed from peanut proteins. Crosslinking with citric acid improved the dry and wet strengths of the films without affecting the water vapor permeability. Peanut protein films did not support the attachment and growth of mouse fibroblast cells suggesting that peanut proteins were cytotoxic.

Vacuum-processed polyethylene as a dielectric for low operating voltage organic field effect transistors

We report on the fabrication and performance of vacuum-processed organic field effect transistors utilizing evaporated low-density polyethylene (LD-PE) as a dielectric layer. With C60 as the organic semiconductor, we demonstrate low operating voltage transistors with field effect mobilities in excess of 4cm2/Vs. Devices with pentacene showed a mobility of 0.16cm2/Vs. Devices using tyrian Purple as semiconductor show low-voltage ambipolar operation with equal electron and hole mobilities of ∼0.3cm2/Vs. These devices demonstrate low hysteresis and operational stability over at least several months. Grazing-angle infrared spectroscopy of evaporated thin films shows that the structure of the polyethylene is similar to solution-cast films. We report also on the morphological and dielectric properties of these films. Our experiments demonstrate that polyethylene is a stable dielectric supporting both hole and electron channels.

Real-time measurement system for tracking birefringence, weight, thickness, and surface temperature during drying of solution cast coatings and films

This paper describes the design and performance of a new instrument to track temporal changes in physical parameters during the drying behavior of solutions, as well as curing of monomers. This real-time instrument follows in-plane and out-of-plane birefringence, weight, thickness, and surface temperature during the course of solidification of coatings and films through solvent evaporation and thermal or photocuring in a controlled atmosphere. It is specifically designed to simulate behavior of polymer solutions inside an industrial size, continuous roll-to-roll solution casting line and other coating operations where resins are subjected to ultraviolet (UV) curing from monomer precursors. Controlled processing parameters include air speed, temperature, initial cast thickness, and solute concentration, while measured parameters are thickness, weight, film temperature, in-plane and out-of-plane birefringence. In this paper, we illustrate the utility of this instrument with solution cast and dried poly (amide-imide)∕DMAc (Dimethylacetamide) solution, water based black paint, and organo-modified clay∕NMP (N-Methylpyrrolidone) solution. In addition, the physical changes that take place during UV photo polymerization of a monomer are tracked. This instrument is designed to be generic and it can be used for tracking any drying∕swelling∕solidification systems including paper, foodstuffs such as; grains, milk as well as pharmaceutical thin paste and slurries.

Morphology-induced hydrophobic behavior of electrospun polyhydroxyalkanoate membranes

ABSTRACTBiodegradable poly(3-hydroxybutyrate) -PHB- and the copolymers with poly (3-hydroxyvalerate) -PHB/HV, containing 5 and 12 mol% valerate (denoted PHB/5HV and PHB/12HV, respectively) were electrospun from chloroform solution at room temperature. The results showed that relatively low voltage and concentrations favored uniform filament formation in PHB, with filament diameters ranging from 3 to 7 micrometers. On the other hand, low molecular weight and low solution concentration favored uniform filament formation in the PHB/5HV copolymer. Strikingly, morphology of filaments and beads favored the membranes hydrophobic behavior; the membrane from PHB/12HV exhibited a water contact angle of 112°. In contrast, solution cast films from the PHAs exhibited water contact angles in the range of 65°. Analyses on the membranes morphology via scanning electron microscopy (SEM) revealed that filament diameter drives the degree of porosity and the hydrophobic behavior of the electrospun membranes.

Consecutive living polymerization from cationic to radical: a straightforward yet versatile methodology for the precision synthesis of “cleavable” block copolymers with a hemiacetal ester junction

In this paper, we provide a straightforward yet versatile methodology via two consecutive living polymerizations, from cationic to radical, to synthesize “cleavable” block copolymers whose segment junction is a hemiacetal ester (HAE). The key compound is α-halophenyl acetic acid [HOOC–CH(Ph)–X: X = halogen] used as a hetero-bifunctional initiator: the carboxylic acid is for living cationic polymerization (LCP) and the carbon–halogen bond for metal-catalyzed living radical polymerization (LRP). The carboxylic acid efficiently reacted with a vinyl ether (e.g., isobutyl vinyl ether: IBVE) to give an adduct with a hemiacetal ester bond, which was reversibly activated with a suitable mild Lewis acid (SnBr4) as a catalyst to initiate LCP of IBVE. Thus obtained poly(IBVE) quantitatively retained an α-end carbon–halogen bond from the initiator and thus worked as a macroinitiator for the LRP of methyl methacrylate (MMA) with a ruthenium catalyst, to form HAE-connected block copolymers (PIBVE-HAE-b-PMMA), whose junction can be cleaved under acidic conditions. Their solution-cast films exhibited mostly cylindrical microphase-separated structures, and both the junction cleavage and removal of the PIBVE segment were achieved in one shot, just by immersing the film into a trifluoroacetic acid solution in n-hexane without distorting film integrity with the cylinder morphology virtually intact, leading to nanoporous patterns.

Synthesis, Properties, and Processing of New Siloxane-Substituted Poly(p-xylylene) via CVD

The synthesis of a disiloxane-functionalized [2.2]paracyclophane and its polymerization to the corresponding siloxane-substituted poly(p-xylylene) via chemical vapor deposition (CVD) has been described. Because of the enhanced solubility of the siloxane substituted poly(p-xylylene) analysis of the molecular structure by NMR, molecular weight, and polydispersity by gel permeation chromatography (GPC), and processing by film casting as well as nanofiber formation by electrospinning was possible. Structural isomers were found by NMR which was expected due to the isomeric mixture of the precursor. High molecular weights at moderate polydispersities were found by GPC which was unexpected for a vapor phase deposition polymerization. The amorphous morphology in combination with a low glass transition temperature led to high elongation at break for the siloxane substituted poly(p-xylylene). Significant difference for the wetting versus water was found for as-deposited films, solution cast films, and nanofibers obtained by electrospinning with contact angles up to 135° close to superhydrophobic behavior.

The effects of cellulose nanowhiskers on electrospun poly (lactic acid) nanofibres

The effects of cellulose nanowhiskers on the microstructure and thermal behaviour of electrospun poly (lactic acid) (PLA) nanofibres have been investigated in this study. The PLA/cellulose nanowhiskers composite nanofibres are successfully produced by electrospinning the mixtures of cellulose whiskers with PLA solution. The diameters of PLA and its composites are around 300 nm. The scanning electron micrographs show that the cellulose nanowhiskers do not protrude out of the outer surfaces of PLA nanofibres. The existence of cellulose nanowhiskers in the electrospun PLA matrix nanofibres, and the microstructural evolution are investigated by using X-ray diffraction, Fourier transform infrared spectroscopy (FTIR) analysis shows the formation trend of PLA α crystal with the addition of cellulose nanowhiskers. The electrospun PLA and PLA/cellulose nanowhiskers composites reveal very low crystallinity due to the rapid solvent evaporation and relatively slow crystallisation kinetics character of PLA. The electrospun nanofibres show particularly different thermal behaviour from that of the solution cast films. The nanofibres of pure PLA and PLA/cellulose nanowhiskers experience two consecutively overlapping crystallisation processes. The cellulose nanowhiskers act as heterogeneous sites for nucleation of PLA by decreasing the cold crystallisation onset temperature. The incorporation of cellulose nanowhiskers into PLA nanofibres is expected to improve mechanical properties and bring new functionalities to the electrospun matrix nanofibres.

Synthesis and Properties of Isomerically Pure Anthrabisbenzothiophenes

The synthesis of three heptacyclic heteroacenes is described, namely anthra[2,3-b:7,6-b']bis[1]benzothiophenes (ABBTs). A stepwise sequence of aldol reactions provides regiochemical control, affording only the syn-isomer. The ABBTs are characterized by X-ray crystallography, UV-vis absorption, and emission spectroscopy, as well as cyclic voltammetry. Field effect transistors based on solution-cast thin films of ABBT derivatives exhibit charge-carrier mobilities of as high as 0.013 cm(2)/(V s).

Investigation of PLLA/PCL Blends and Paclitaxel Release Profiles

Blends of poly (L-lactide) (PLLA) and poly (ε-caprolactone) (PCL) with and without paclitaxel were prepared via solution casting. DSC analysis as well as SEM analysis of the PLLA/PCL blend solution cast films showed that these blends are all phase separated.%PLLA crystallinity was found to increase with increasing PCL content (up till 15 wt.%). The PCL phase is found to homogeneously disperse in the PLLA matrix as spherical domains where the pore diameters of the PCL domains significantly increased with increasing PCL content. The degradation profiles matched with the slower degrading component PCL rather than PLLA and also increasing PCL content of the blends increased the degradation rate relatively. The increased crystallinity of the PLLA phase with increasing PCL contents confirmed that the degradation occurred through PCL phase. Cell proliferation on PLLA/PCL blends showed that all these blends were suitable for the support of cellular growth. Apoptosis assay with the paclitaxel-loaded PLLA/PCL blends showed an increase in cell death throughout 7 days of incubation where the cell death was increased with increasing PCL contents. This was attributed to the faster release of paclitaxel which was at least partially affected by the faster degradation rate at increasing PCL contents. The paclitaxel release was shown to be degradation controlled in the initial stages followed by a faster diffusion-controlled release in the later stages. These polymer blends were found to be very suitable paclitaxel release agents for which the paclitaxel release times can be altered with the composition of the blend and the film thickness.

Dielectric properties of polyhedral oligomeric silsesquioxane (POSS)-based nanocomposites at 77k

The goal of this study is to develop dielectric nanocomposites for high energy density applications at liquid nitrogen temperature by utilizing a unique nano-material polyhedral oligomeric silsesquioxanes (POSS). A POSS molecule is consisted of a silica cage core with 8 silicon and 12 oxygen atoms and organic functional groups attached to the corners of the cage. In this study, we utilize POSS for the fabrication of nanocomposites both as a silica nanoparticle filler to enhance the breakdown strength and as a surfactant for effective dispersion of high permittivity ceramic nanoparticles in a polymer matrix. The matrix materials selected for the study are polyvinylidene fluoride (PVDF) and poly(methyl methacrylate) (PMMA). The ceramic nanoparticles are barium strontium titanate (BST 50/50) and strontium titanate. The dielectric properties of the solution-cast nanocomposites films were correlated to the composition and processing conditions. We determined that the addition of POSS did not provide enhanced dielectric performance in PVDF- and PMMA-based materials at either room temperature or 77K. In addition, we found that the dielectric breakdown strength of PMMA is lower at 77K than at room temperature, contradicting literature data.