Cast Polymer Films Research Articles

Multifunctionally-doped PEDOT for organic electrochemical transistors

Organic Electrochemical Transistors (OECTs) are suitable for developing ultra-sensitive bioelectronic sensors. In the organic electrochemical transistors architecture, the source-drain channel is made of a conductive polymer film either cast from a formulated dispersion or electrodeposited from a monomer solution. The commercial poly(3,4-ethylenedioxidethiophene)/poly(styrene sulfonate) (PEDOT:PSS) water dispersion is the workhorse of organic bioelectronics for its high conductance, low impact and ease of processability. In this study, a hybrid organic electrochemical transistors channel fabrication strategy is presented, where electrochemical deposition of a PEDOT/X (with X indicating the counterion) is performed on a dispersion-cast PEDOT:PSS film. Six different counterions where used: X = PSS, Nafion, Hyaluronate, Dextran sulfate, Dexamethasone phosphate and tauroursodeoxycholic acid, each potentially endowing organic electrochemical transistors with additional functions such as ion exchange and pharmacological activity upon release of X. The PEDOT/X-PEDOT:PSS bilayers were characterized by means of electrochemical impedance spectroscopy (EIS), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and focused ion beam tomography combined with scanning electron microscopy (FIB-SEM). In addition, their respective organic electrochemical transistorss were characterized and compared to PEDOT:PSS organic electrochemical transistors. Our results show that the hybrid bilayer strategy is viable to fabricate multifunctional organic electrochemical transistorss with biologically-relevant function, thereby retaining the outstanding figures of merit of commercial PEDOT:PSS.

Laser activated room-temperature excimer delayed fluorescence of difluoroboron β-diketonate complexes in polymer matrix

Great potential has been discovered in the development of materials with a long afterglow (phosphorescence at room temperature and delayed fluorescence) for the purposes of luminescent sensing, bioimaging, information encryption and OLED. Here, we report the long-lived (lifetime up to 1.5 s) laser-induced room-temperature excimer delayed fluorescence (RTEDF) of difluoroboron β-diketonate complexes (BF2bdks) already at concentrations of 0.05% in solution cast polymer films. The emission centers of RTEDF of BF2bdks can retain for a long time in the polycarbonate matrix (>3 months) and can be repeatedly re-excited with a low-intensity ultraviolet light source. These results provide a foundation for the design of materials with applications in optical information storage and data encryption and decryption.

Facile preparation of a slippery oil-infused polymer surface for robust icephobicity

This work concentrated on the fabrication of effective slippery liquid-infused porous surfaces (SLIPSs) to robustly resist ice adhesion by using facile method and smart composition. Firstly, poly(methyl methacrylate) (PMMA), polyhedral oligomeric silsesquioxane end-functionalized PMMA (POSS-ef-PMMA) and polydimethylsiloxane-blocked PMMA (PDMS-b-PMMA) were synthesized. Secondly, micro-sized pores arranged in a three-layer honeycomb-like array at a thickness of ca. 10 μm were elicited on each surface of these three cast polymer films by breath-figure (BF) method. After a separate infiltration of polydimethylsiloxane (PDMS), poly (hydrogenmethylsiloxane) (PHMS) and hexadecane (HD) into the porous matrixes, typical SLIPSs were formed. PDMS-b-PMMA matrix with preferential lipophilicity towards PDMS endowed the obtained SLIPS with better icephobicity. However, HD-induced SLIPSs performed the lowest sliding angles at 6° for 3 μL of water droplet, the lowest ice adhesional strength ranging from 40.8–46.3 kPa and the most robust anti-icing properties of resisting more than 30 icing/de-icing cycles without changing the ice adhesional strength. Such effective anti-icing performance was ascribed to the better liquid nature of HD in contact with water and the solid nature of HD under freezing condition, which could decrease the interfacial friction and abrasion of HD against water or ice.

Plastic drawing response in the biaxially oriented polypropylene (BOPP) process: polymer structure and film casting effects

Abstract Processing isotactic polypropylene (iPP) from cast film into biaxially oriented polypropylene (BOPP) involves plastic drawing of a semi-crystalline morphology in the melting range of iPP, where the crystal phase is reduced and the polymer has high mobility. The literature claims that plastic drawing in general and at elevated temperatures in particular depends predominantly on the structure of the amorphous entanglement network. We investigated this aspect using laboratory-scale biaxial drawing experiments. Three iPP homopolymer types differing in chain isotacticity and molecular weight distribution were extruded into 200-μm-thick primary sheets using 10 different extrusion settings. The sheets were biaxially drawn on a laboratory stretcher at 157°C and 160°C, recording the respective stress-strain curves. These curves were evaluated according to a rubber elasticity model to obtain the network modulus, G N, of the entanglement network. The effects of iPP type, the extrusion parameters, the resulting cast film properties, and the draw temperature on G N are discussed.

Modeling and simulation for the investigation of polymer film casting process using finite element method

Film casting is an important forming technological method for the manufacturing of single or multi-layer films for the electronics, medical and packing products. In polymer film casting process, the processing conditions can significantly influence the performance and dimension of final products. However, proper control of practical processing conditions is still a difficult task. In the study, the mathematical model of three-dimensional film casting process is established using a membrane model. The corresponding finite element formulations is derived based on standard Galerkin method and the details of numerical schemes are introduced. The essential flow characteristics and the variation of film parameters in polypropylene film casting process are investigated based on the proposed mathematical model and numerical methods, which show good agreement with corresponding experimental observations. The evolutions of neck-in and edge bead phenomena are successfully predicted and the influences of processing conditions as draw ratio and air gap length are further discussed.

Plasma assisted formation of 3D highly porous nanostructured metal oxide network on microheater platform for Low power gas sensing

A facile and versatile approach that integrates highly porous metal oxide nanostructured network with a low power microheater platform is presented for the creation of low-power, miniaturized gas sensors. Highly porous nanostructured metal oxide network is formed by oxygen plasma treatment of a metal containing polymer film followed by a heat treatment. A generalized aqueous metal precursor solution allows a large variety of metal salts to be incorporated into cast polymer films, thus forming nanostructured metal oxide network with various compositions. Gas sensing behavior is demonstrated for Co3O4 -based devices, exhibiting high sensitivity, low detection limit, and fast response and recovery towards formaldehyde gas. The overall fabrication process is flexible and highly scalable. This facile and flexible fabrication method can be used to reproducibly fabricate a variety of low power gas sensors with tunable performances for many applications and has great potential for mass production.

Non-isothermal process of viscoelastic polymer fi lm casting

The steady-state non-isothermal process of viscoelastic fl at polymer fi lm casting is considered. The polymer melt is extruded through a fl at die, subjected to uniaxial stretching and at the same time air cooling, and then fi nally cooled down on a chill roll. It is assumed that the fi lm is wide enough, the distance between the extruder die and the cooling roller is minimal to such an extent that it is possible to neglect change of width of a fi lm in the course of longitudinal stretching. It is also believed that the forces of gravity, inertia and surface tension can be ignored. From a rheological standpoint, polymer melt is the viscoelastic fl uid. The upper-convective Maxwell model with temperature-dependent viscosity is used. The problem is solved by a numerical method of fi nite diff erences.

Metallo-Supramolecular Polymers Made of Cobalt and 3,4-Propylenedioxythiophene-Bisterpyridine Complexes for Electrochromic Applications

In this study, a series of organometallic hybrid polymers were synthesized through the complexation of cobalt metal ions with bisterpyridine derivatives bearing substituted 3,4-propylenedioxythiophene. The prepared polymers exhibited specific color changes from orange to dark green based on the metal-to-ligand charge transfer transitions. Cyclic voltammograms of the polymers showed a reversible redox wave according to the redox reaction of the cobalt metal ions. In addition, the electrochromic devices containing the polymer film cast on an indium-tin-oxide electrode exhibited good electrochromic properties, with reversible and stable spectral transitions of the cobalt-bisterpyridine complexes.

Mean‐squared‐error‐based method for parameter ranking and selection with noninvertible fisher information matrix

Two approaches are developed to rank and select model parameters for estimation in complex models when data are limited, the Fisher information matrix (FIM) is noninvertible, and accurate predictions are desired at key operating conditions. These approaches are evaluated using synthetic data sets in a linear regression example to examine the influence of several factors including: the quality of initial parameter guesses, uncertainty ranges for initial parameter values, noise variances, and the operating region of interest. It is shown that using a reduced FIM with full rank leads to more reliable model predictions for a variety of cases than the alternative approach using the pseudoinverse of the FIM. The proposed reduced‐FIM methodology also provides better predictions than related techniques that do not consider the operating region where reliable predictions are required. The methodology is illustrated using a nonlinear differential equation model of a polymer film casting process. © 2015 American Institute of Chemical Engineers AIChE J, 62: 1112–1125, 2016

A new rigid planar low band gap PTTDPP-DT-DTT polymer for organic transistors and performance improvement through the use of a binary solvent system

We report the synthesis of a new low band gap planar polymer of poly(2,5-bis(2-decyltetradecyl)-3-(5-(dithieno[3,2-b:2′,3′-d]thiophen-2-yl)thieno[3,2-b]thiophen-2-yl)-6-(thieno[3,2-b]thiophen-2-yl)-2,5-dihydropyrrolo[3,4-c]pyrrole-1,4-dione) (PTTDPP-DT-DTT) for use in organic thin film transistors (OTFTs). The polymer backbone is highly planar and well-conjugated, facilitating interchain stacking. The PTTDPP-DT-DTT-based OTFTs were fabricated and carrier mobilities were improved by using a binary solvent system: chloroform (CF):toluene (Tol), CF:chlorobenzene (CB), and CF:o-dichlorobenzene (DCB). The addition of higher boiling point solvents promoted film crystallinity with more edge-on orientations. Thus, the use of CF:DCB yielded the highest carrier mobility obtained among the devices tested. Thermal annealing further enhanced the mobility of the CF:DCB device. Atomic force microscopy images disclosed the most fibrous feature in the thermally annealed polymer film cast from CF:DCB solution. This work highlights that both the proper selection of a binary solvent and thermal annealing can manage film morphology of rigid planar conjugated polymer semiconductors effectively for high-performance OTFTs.

The effective flux through a thin-film composite membrane

Composite membrane structures, used extensively in separation processes, comprise an ultra-thin selective polymer film cast over a porous support, whose pores partially obstruct transport out of the top film. Here, we model the composite as a finite thickness slab with a periodic array of circular absorbing patches in an otherwise reflective surface and study the effective transport properties of the composite. We obtain an analytical approximation for the effective diffusive flux as a function of the geometrical parameters, namely the film thickness, the support porosity and the pore size. We find a good agreement with full numerical solutions, and that a good effective rate is achievable with a relatively small number of pores.

Influence of casting solvent on phenyl ordering at the surface of spin cast polymer thin films

Controlling the surface molecular structure of spin cast polymer films is important for the rational design of surface properties. However, the relationship between spin casting parameters and film surface molecular structure is poorly understood. We report that the surface molecular structure of spin cast homopolymers which contain phenyl groups is influenced by the solvent aromaticity, investigated by a nonlinear optical spectroscopy, sum frequency generation (SFG) vibrational spectroscopy. When phenyl groups were located in a linear polymer backbone, spin casting with aromatic solvents enhanced the phenyl SFG signal relative to when a non-aromatic solvent was used which suggests that the aromatic solvent induced the surface phenyl groups to be more ordered and/or to lie more perpendicular to the film surface. In addition, when alkyl structures were believed to be present at the solvent/air interface, alkyl structures were observed at the film/air interface which suggests that molecular structure at the solvent/air interface was carried to the film surface. The effects of solvent aromaticity on phenyl ordering at spin cast film surfaces can be explained by different molecular structures of polymer chains at solvent/air interfaces, preferential solvation of functional groups during evaporation, and re-orientation of bulky side groups at the polymer film/air interface.

Application and Evaluation of the Performance of Poly (Vinyl Alcohol) and its Blend with Nitrocelulose in Leather Top Coating

A 5% aqueous solution of polyvinyl alcohol (PVA) (m.wt. 125, 000), nitrocellulose and PVA/nitrocellulose blend were applied as a topcoat on dyed goatskin leather. The FT-IR spectroscopy of the cast polymer films indicated that each of the films in dry state consist of only pure polymer. The microscopic and physical characteristics of the coatings were also determined. The PVA coatings were found to have a glossy appearance, smooth handle and good extensibility, with excellent rubbing fastness and light fastness properties. However, the coatings have only a moderate adhesion of finish and have poor heat fastness and flexing endurance properties. The properties were found to improve when PVA was used in blend with nitrocellulose emulsion. The nitrocellulose coatings were, however, found to exhibit an almost all round superior coating property.

Mathematical modeling of polymer film casting under biaxial stretching taking into account heat transfer

Polymer film casting is studied using a modified Vinogradov-Pokrovskii rheologicalmodel with heat transfer taken into account. Dependences of the film temperature, velocity, and width on the distance to the extruder exit was obtained and the effect of model parameters on these dependences was examined.

Multifunctional Coating Films by Layer-by-Layer Deposition of Cellulose and Chitin Nanofibrils

An environmentally benign surface modification process for plastic films was demonstrated by fabricating composite coatings through layer-by-layer assembly with green solid materials: aqueous dispersions of two kinds of crystalline polysaccharide nanofibrils. Anionic cellulose nanofibrils were obtained by the TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl radical)-mediated oxidation of native cellulose, while cationic β-chitin nanofibrils were prepared by the protonation of squid pen chitin. Uniform layer depositions, driven by electrostatic attraction and enhanced by hydrogen bonding, were observed on silicon wafers and then reproduced onto poly(ethylene terephthalate) films. Contact angle measurements and dyeing tests on the resulting films revealed their hydrophilic nature and the sorption of both charged and uncharged substances. Antireflection properties were also confirmed via the light transmittance measurements. As might be presumed from all these properties, this composite coating exhibited its unique behavior largely due to its structure, which was distinct from both those of nanofibril cast films and polymer films.

Influence of film casting method on block copolymer ordering in thin films

We study the orientation of the cylinder phase of the block copolymer (BCP) poly(styrene-block-methylmethacrylate) (PS-b-PMMA) in thin spun-cast films having a range of film thicknesses and temperatures and compare to our earlier observations on flow-coated films of the same BCP under similar thermodynamic conditions. As in our former measurements on flow-coated films, morphology maps of our spun-cast BCP films reveal distinct ordering regimes where the cylinders orient predominantly perpendicular or parallel to the interface and an ‘intermediate’ regime where these morphologies are mixed. However, we find that the locations of these morphology lines in the temperature–film thickness plane are greatly influenced by the method of film formation. We hypothesize that the slow solvent evaporation of the flow-coated films leads to films having higher residual stresses than spun-cast films because of a relatively inhibited transport of the solvent out of the film during drying, and annealing measurements on both types of cast films provide supporting evidence that the BCP surface morphology change is associated with residual stresses within the films. Contrary to our initial expectations, spun-cast films showed little sensitivity to film casting speed so that residual stress effects associated with the comparatively violent fluid flow conditions of spin-casting appear to be small. Instead, residual stresses arising from slow film evaporation appear to be implicated. Residual stress effects arising during the course of film casting and drying are relevant to other fabrications involving cast polymer films, such as in organic photovoltaic devices where flow-coating or similar industrial film casting method is normally employed for film formation.

Alternating stilbene copolymers with negative birefringence

A new alternating copolymer of stilbene and N-(2-methylphenyl) maleimide) [I] was prepared and exhibited a strong negative birefringence in cast polymer films. The negative birefringence is proposed to result from the sterically crowded backbone which restricts the free rotation of the ortho-methyl phenyl substituent of the enchained maleimide monomer and forces the phenyl ring to exist normal to the plane of the imide ring. Alternating copolymers of styrene with I and stilbene with N-phenylmaleimide did not exhibit similar negative birefringence properties.

Poly-3-hydroxyoctanoate P(3HO), a Medium Chain Length Polyhydroxyalkanoate Homopolymer from Pseudomonas mendocina

Pseudomonas mendocina was found to produce a unique homopolymer of poly(3-hydroxyoctanoate), P(3HO), rather than a copolymer, when grown on sodium octanoate as the sole carbon source. Although this polymer has been produced by other organisms, interestingly this is the first time an absolute homopolymer has been produced by a wild type organism. In addition, a detailed study on the effects of different extraction methods on the yield, molecular weight, thermal properties, and lipopolysaccharide content of P(3HO) has been carried out. The organism was able to accumulate P(3HO) up to 31.38% of its dry cell weight within 48 h in mineral salt medium. Characterization of the monomer was carried out using FTIR, GC-MS, (13)C, (1)H, and HSQC NMR spectroscopy. The polymer had a crystallinity of 37.5%, Young's modulus value of 11.6 MPa and contact angle of 77.3°. Microstructural studies of solvent cast polymer films revealed a smooth surface topography with a root-mean-square roughness value of 0.238 μm.

Permeability of Cellulose Polymers: Water Vapour Transmission Rates

The water vapour transmission rates (WVTR) through solvent cast polymer films prepared from cellulose acetate, cellulose acetate propionate, and cellulose acetate butyrate have been determined. They were influenced by the relative humidity, the substituent type and the extent of substitution. Increasing the relative humidity from 32 to 90% increased the WVTR 3 to 5 times depending on the polymer used. The WVTR increased in the order of butyrate less than propionate less than acetate. An increase in the extent of substitution with acetyl and/or butyryl groups resulted in an exponential decline in the WVTR.

Biomedical Application of Surface Science: Honeycomb Patterned Polymer Films as Novel Biomedical Materials

This report describes universities-industries collaborations on biomedical applications of self-organized honeycomb-patterned polymer films, which are prepared by using physical surface phenomena based on water droplet condensation during evaporation processes of polymer film casting. The film company has established engineering processes of regularly porous polymer film fabrication. The textile company has developed high-performance adhesion preventing polymer films having asymmetric nano-honeycomb structure under collaboration with the film company. Covered biliary stents are newly developed and released by the medical device company. Honeycomb-patterned polymer films are supplied to the medical device company from the film company.