Polymer Blend Films Research Articles

Non-destructive depth-dependent morphological characterization of ferroelectric:semiconducting polymer blend films

Herein, we investigate the technologically relevant blend of the ferroelectric polymer poly(vinylidene fluoride-co-trifluoroethylene), P(VDF-co-TrFE), with the semiconducting polymer poly(3-hexylthiophene), P3HT, by means of a combination of scanning probe microscopy techniques, namely atomic force microscopy, conductive force microscopy, kelvin probe force microscopy, and piezoresponse force microscopy. This combination proves to be a powerful tool for the non-destructive morphological reconstruction of multi-functional nano-structured thin films, as those under study. Each modality allows discerning the two blend constituents based on their functionality, and, additionally, probes layers of different thickness with respect to the film surface. The depth-dependent information that is collected allows a qualitative reconstruction of the blend’s composition and morphology both in-plane and out-of-plane of the film. We demonstrate that P3HT exhibits the tendency to reside the film surface at an almost constant composition of 15%, independent of blend’s composition. Increasing the P3HT content in the blend results in the segregation of P3HT at the upper layers of the films, partially buried below a P(VDF-co-TrFE) superficial layer. The depletion of P3HT from the substrate/film interface is reflected by the poor existence of conducting pathways that connect the top and bottom planes of the film. The three-dimensional morphology of this polymer blend that is revealed thanks to the employed techniques deviates substantially from the ideal morphology proposed for the efficient performance of the targeted memory devices.

Structural, dielectric, and magnetic studies based on MWCNTs/NiFe2O4/ZnO nanoparticles dispersed in polymer PVA/PEO for electromagnetic applications

The hydrothermal and the co-precipitation methods were used for the formation of new multifunctional MWCNTs/NiFe2O4/ZnO (MNFZ) hybrid nanostructures. The MNFZ hybrid nanostructure formation was asserted by characterizing it via the X-ray diffraction (XRD) analysis and TEM. Then, the casting technique was used for preparing the MNFZ nanoparticle-doped Poly (vinyl alcohol) (PVA) and poly (ethylene oxide) (PEO) by various concentrations of MNFZ NPs as nanofiller. All polymer blend and nanocomposite films are shown by XRD studies to have a semicrystalline nature with a reduced degree of semi-crystallinity with the dopant. The infrared absorption band shift and the intensity change indicate the interaction or complexation between the blend and nanofiller is confirmed by FTIR studies. The volume percentage variation of the nanoparticles and the ferromagnetic response variation of the nanocomposite were in consistency. The dielectric characteristics and ac conductivity of the film polymer blend were higher upon adding the nanofiller because the charge carrier number was higher. Such features of MNFZ-doped PVA/PEO films prove their appropriateness as materials for electromagnetic applications.

Understanding interfacial segregation in polymer blend films with random and mixed side chain bottlebrush copolymer additives.

Bottlebrush polymers are complex macromolecules with tunable physical properties dependent on the chemistry and architecture of both the side chains and the backbone. Prior work has demonstrated that bottlebrush polymer additives can be used to control the interfacial properties of blends with linear polymers but has not specifically addressed the effects of bottlebrush side chain microstructures. Here, using a combination of experiments and self-consistent field theory (SCFT) simulations, we investigated the effects of side chain microstructures by comparing the segregation of bottlebrush additives having random copolymer side chains with bottlebrush additives having a mixture of two different homopolymer side chain chemistries. Specifically, we synthesized bottlebrush polymers with either poly(styrene-ran-methyl methacrylate) side chains or with a mixture of polystyrene (PS) and poly(methyl methacrylate) (PMMA) side chains. The bottlebrush additives were matched in terms of PS and PMMA compositions, and they were blended with linear PS or PMMA chains that ranged in length from shorter to longer than the bottlebrush side chains. Experiments revealed similar behaviors of the two types of bottlebrushes, with a slight preference for mixed side-chain bottlebrushes at the film surface. SCFT simulations were qualitatively consistent with experimental observations, predicting only slight differences in the segregation of bottlebrush additives driven by side chain microstructures. Specifically, these slight differences were driven by the chemistries of the bottlebrush polymer joints and side chain end-groups, which were entropically repelled and attracted to interfaces, respectively. Using SCFT, we also demonstrated that the interfacial behaviors were dominated by entropic effects with high molecular weight linear polymers, leading to enrichment of bottlebrush near interfaces. Surprisingly, the SCFT simulations showed that the chemistry of the joints connecting the bottlebrush backbones and side chains played a more significant role compared with the side chain end groups in affecting differences in surface excess of bottlebrushes with random and mixed side chains. This work provides new insights into the effects of side chain microstructure on segregation of bottlebrush polymer additives.

An experimental setup for dip-coating of thin films for organic solar cells under microgravity conditions.

We report the design and testing of a custom-built experimental setup for dip-coating from volatile solutions under microgravity conditions onboard an aircraft. Function and safety considerations for the equipment are described. The equipment proved to work well, both concerning the safety and the preparation of thin films. No leakage of the solvents, nor the solvent vapors, was detected, not even in a situation with a fluctuating gravitational field due to bad weather conditions. We have shown that the equipment can be used to prepare thin films of polymer blends, relevant for organic solar cells, from solution in a feasible procedure under microgravity conditions. The prepared films are similar to the corresponding films prepared under 1 g conditions, but with differences that can be related to the absence of a gravitational field during drying of the applied liquid coating. We report on some introductory results from the characterization of the thin films that show differences in film morphology and structure sizes.

Thermo‐Adaptive Block Copolymer Structural Color Electronics

AbstractFlexible electronics that enable the visualization of thermal energy have significant potential for various applications, such as thermal diagnosis, sensing and imaging, and displays. Thermo‐adaptive flexible electronic devices based on thin 1D block copolymer (BCP) photonic crystal (PC) films with self‐assembled periodic nanostructures are presented. By employing a thermo‐responsive polymer/non‐volatile hygroscopic ionic liquid (IL) blend on a BCP film, full visible structural colors (SCs) are developed because of the temperature‐dependent expansion and contraction of one BCP domain via IL injection and release, respectively, as a function of temperature. Reversible SC control of the bi‐layered BCP/IL polymer blend film from room temperature to 80 °C facilitates the development of various thermo‐adaptive SC flexible electronic devices including pixel arrays of reflective‐mode displays and capacitive sensing display. A flexible diagnostic thermal patch is demonstrated with the bi‐layered BCP/IL polymer blend enabling the visualization of local heat sources from the human body to microelectronic circuits.

A Solution Processable Dithioalkyl Dithienothiophene (DSDTT) Based Small Molecule and Its Blends for High Performance Organic Field Effect Transistors.

The 3,5-dithiooctyl dithienothiophene based small molecular semiconductor DDTT-DSDTT (1), end functionalized with fused dithienothiophene (DTT) units, was synthesized and characterized for organic field effect transistors (OFET). The thermal, optical, electrochemical, and computed electronic structural properties of 1 were investigated and contrasted. The single crystal structure of 1 reveals the presence of intramolecular locks between S(alkyl)···S(thiophene), with a very short S-S distance of 3.10 Å, and a planar core. When measured in an OFET device compound 1 exhibits a hole mobility of 3.19 cm2 V-1 s-1, when the semiconductor layer is processed by a solution-shearing deposition method and using environmentally acceptable anisole as the solvent. This is the highest value reported to date for an all-thiophene based molecular semiconductor. In addition, solution-processed small molecule/insulating polymer (1/PαMS) blend films and devices were investigated. Morphological analysis reveals a nanoscopic vertical phase separation with the PαMS layer preferentially contacting the dielectric and 1 located on top of the stack. The OFET based on the blend comprising 50% weight of 1 exhibits a hole mobility of 2.44 cm2 V-1 s-1 and a very smaller threshold voltage shift under gate bias stress.

Edible Films of Whey and Cassava Starch: Physical, Thermal, and Microstructural Characterization

The present work aimed to obtain and characterize edible films produced with liquid whey and cassava starch. The films were produced with different proportions of whey (63.75–67.50%) and cassava starch (7.50–11.25%) and characterized in relation to physical, thermal, and microstructural properties. The films showed reduced solubility with increasing concentrations of cassava starch, and those with the highest proportions of whey were more stable to thermal decomposition. The increase in concentration of cassava starch altered the microstructure of the films, making them more irregular and with an accumulation of matter. The production of biodegradable polymer blend films is an important step in the development of films for use in packaging, with the formulation of 67.50/7.50% whey/cassava starch being the best film for continued future work.

The electrical and mechanical properties of Cadmium chloride reinforced PVA:PVP blend films

In this study, pure polymer blend (PVA:PVP) film and salt (CdCl2·H2O) reinforced polymer blend films were prepared at different weight ratios (10 wt%, 20 wt%, 40 wt%) using the casting method. The effect of the salt weight ratio on the dielectric properties of the polymer blend films reinforced by CdCl2·H2O salt were investigated, and the experimental results showed that the dielectric constant and the dielectric loss factor decreased as the frequency increased for all polymer blend films. Moreover, the above-mentioned properties increased with increasing salt weight ratios at the same frequency. The experimental results also showed an increase in AC electrical conductivity with increasing frequency, for all polymer blend films, and the AC electrical conductivity also increased with an increase in the weight ratio of the salt at the same frequency. The effect of the salt weight ratio on the mechanical properties of the salt-reinforced PVA:PVP polymer blend films was also studied. The experimental results obtained from the tensile test of the salt-reinforced polymer blend films show significant change in the values of tensile strength, elongation at break, and Young’s modulus with increasing salt weight ratios; the hardness value first increases then decreases with increasing salt weight ratios, and the fracture energy value increases with increasing salt weight ratios, thus they could be good candidates for hard adhesives with low flexibility.

Study of biocompatible polymer blend films with tuneable band gap

In present communication, an attempt is made to prepare and study structural, optical, and electrical properties of biocompatible polyvinylchloride (PVC)-polyvinylpyrrolidone (PVP) blend films taken in ratio of 1:1 doped with conducting polymer Polypyrrole (PPy).The XRD spectra revealed amorphous nature of all the films under investigation. The Fourier transform infra-red spectroscopy (FTIR) study of conducting polymer doped blend films indicate a significant change in the intermolecular/intramolecular interactions taking place. The study on electrical properties of conducting polymer doped blend films show better conduction of current as compared to that of blend film without conducting polymer and dopant concentration dependent electrical conductivity and conduction mechanism. The results of optical study of conducting polymer doped blend films revealed the possibility of band gap modification from wide band gap to small band gap with suitable doping concentration. These biocompatible blend films with tuneable optical and electrical properties can be potential material for use in fields of photonic biosensors, solar cell and optoelectronics field.

Förster resonance energy transfer in organic photovoltaics devices fabricated by electric field assisted spray technique

Thin films of the ternary polymer blend (donors PCE-10 and PCDTBT with the acceptor PC71BM in chlorobenzene) were fabricated by using spray coating technique without and with applied voltage to the nozzle during deposition. The increased absorption range from 400 nm to 800 nm indicates that Förster resonance energy transfer (FRET) is occurring for the films deposited under the electric field. This is also supported by photoluminescence measurements and suggesting that under the applied voltage the orientation of polymer chains are changing at desired distances to facilitate FRET phenomenon to occur due to repulsion between uniformly charged ultrafine droplets. The size of droplets further reduced at higher applied voltage. Absorption, photoluminescence, femtosecond transient absorption spectra and Kinetics traces were recorded to elucidate the role of applied DC voltages during the deposition of these films on photovoltaic performance of bulk heterojunction organic solar cell. The effect of FRET in polymer-polymer thin film under applied voltage during the deposition is observed, which indicates enhancement in the power conversion efficiency with the maximum value of 6.86% (Jsc of 15.81 mA/cm2 and Voc of 0.77 V) at an applied voltage of 750 V.

In-situ polymerization of pyrrole in PVA-PVP matrix: Optimization of oxidant/monomer ratio and its effect on dielectric properties of polymer blend films

Free standing and flexible polymer blend films of PPy (poly pyrrole) doped in PVA (poly vinyl alcohol) – PVP (poly vinyl pyrrolidone) matrix with varying concentrations of PPy have been prepared by solution cast technique at room temperature. In-situ polymerization of pyrrole monomer (Py) in PVA-PVP matrix has been carried out using FeCl3 as oxidant. The effect of monomer amount and monomer to oxidant ratio on the dielectric parameters (such as dielectric constant, dielectric loss, loss tangent, ac conductivity, complex electric modulus, complex impedance) of PPy doped PVA-PVP polymer blend films have been studied in the frequency range of 20 Hz to 2 MHz. Two different molar concentrations (0.15 M and 0.30 M) of oxidants have been taken and for each oxidant concentration, four varying concentrations of monomer have been used to optimize the results. The blend films having oxidant to monomer molar concentration ratio of 0.5 in both the cases (i.e. 0.15 M and 0.30 M) have been found to be smooth, flexible, mechanically strong and easy to process. These films have shown very systematic change and improved values of dielectric parameters within the experimental frequency range. Enhanced dielectric parameters (complex permittivity, ac conductivity and electric modulus) values for films having oxidant to monomer molar ratio of 0.5 suggest the organized growth of PPy chain in the matrix of PVA-PVP.

Synthesis of chitosan-ferulic acid conjugated poly(vinyl alcohol) polymer film for an improved wound healing

The synthesis of a new and functionally effective antioxidant polymer film containing chitosan (CS)-dietary phenol ferulic acid (FA) and poly(vinyl alcohol) (PVA) is reported.The as-formulated CS-FA-PVA blended film was pale yellow color, flexible, non-sticky with little elastic nature. The films were characterized by FTIR, mechanical testing, SEM and TGA. The antioxidant activity of polymer blend film was evaluated by DPPH and ABTS assay; whereas antimicrobial activity was demonstrated by agar-diffusion method. The antioxidant assays have shown excellent free radical scavenging as compared to the standard ascorbic acid. The CS-FA-PVA film has shown significant antibacterial activity against Bacillus subtilis, Staphylococcus aureus and Escherichia coli. The cytotoxicity was assessed in L929 mouse fibroblast cell lines by MTT assay and the results concluded no significant cytotoxic was observed for CS-FA-PVA blend film on day 1 (< 7% toxicity). The wound-healing potential of CS-FA-PVA film was tested on L929 mouse fibroblasts by in vitro scratch assay for the effective management of the wounds. The wound healing study has reported 72 and 100 % wound closure by 25 μl of CS-FA-PVA respectively at 12 and 24 h.

Solvo-selective imprinting of a thin polymer blend film for creating multi-length scale patterns

Controlling and spatial ordering of the phase separation in ultra-thin polymer-blend films is a viable approach to create complex surface structures with unique properties. This study reports a facile solvo-selective patterning technique in a phase-separated polymer blend thin film comprising of immiscible polymers polystyrene (PS) and poly(methyl methacrylate) (PMMA). The pattern replication was achieved using capillary force lithography by imprinting the blend films with cross-linked polydimethylsiloxane stamp with grating patterns. The replication was done in the presence of 1-chloropentane or acetic acid vapours, which are selective solvents for PS and PMMA, respectively. This engendered capillary flow of only one phase while the domains of the second phase remain rigid. Depending on the initial as-cast morphology of the film which is a function of the relative proportion of PS and PMMA, a variety of structures were obtained by combining the phase-separated domains with the structure imposed by the stamp. This method can be considered as a simple, one-step technique for creating hierarchical patterns that are likely to find applications in modulating properties of soft surfaces.

Enhancement of Short-Range Ordering of Low-Bandgap Donor–Acceptor Conjugated Polymer in Polymer/Polymer Blend Films

PCPDTBT, a copolymer of cyclopentadithiophene and benzothiadiazole, is a locally ordered low-bandgap donor–acceptor conjugated polymer that has been used as a hole-transport material for polymer blend solar cells. In this study, the short-range order structure of PCPDTBT in spin-coated PCPDTBT/conjugated polymer blend films has been characterized to elucidate aggregation behaviors that arise when a locally ordered conjugated polymer is blended with other polymers. UV–vis absorption spectroscopy and grazing-incidence wide-angle X-ray scattering measurements revealed that short-range ordering of PCPDTBT is promoted when it is diluted in an amorphous conjugated polymer matrix, poly­(3-methyl-4-hexylthiophene-2,5-diyl) (P3M4HT). In a PCPDTBT/P3M4HT blend film with 10 wt % PCPDTBT, the fraction of PCPDTBT chains that form aggregates increases from 51% (in neat film) to 78%, and the correlation length of the ordered PCPDTBT chains extends from 4.6 nm (in neat film) to 7.7 nm in the chain backbone direction. The polymer matrix-assisted ordering can be explained in terms of suppression of both undesired overlap and interpenetration of PCPDTBT chains; both processes can derange the self-aggregated single-chain order of PCPDTBT. This short-range ordering enhancement would be significant for the design of efficient charge carrier transport in thin-film devices such as polymer/polymer blend solar cells that use low-bandgap donor–acceptor conjugated polymers with various blend ratios as hole- and electron-transport materials.

A Swelling Study in Different PH and Mechanical Properties of Biodegradable Films Based on Pluronic F-127/ Poly-Vinyl Alcohol

PluronicF-127/PVA polymeric biomaterials blend films plasticized with glycerin were prepared by solvent molding method. The polymer blend films were characterized using Fourier transform infrared (FTIR) spectroscopy, Field Emission Scanning Electron Microscopy and mechanical measurements. The FTIR spectra of the two polymers and their blends show that there is no chemical interaction between the PVA and the PluronicF-127. FESEM images indicate that blend homogeneous film can easily be prepared. Mechanical and swelling properties of the studied blends indicate that these can be used for medical application such as biodegradable materials and biodegradable drugs carriers and as food packaging materials.

A Cross-Linkable Electron-Transport Layer Based on a Fullerene-Benzoxazine Derivative for Inverted Polymer Solar Cells.

The synthesis, optoelectronic characterization and device properties of a cross-linkable fullerene derivative, [6,6]-phenyl-C61 -butyric benzoxazine ester (PCBB) is reported. PCBB shows all the basic photophysical and electrochemical properties of the parent compound [6,6]-phenyl-C61 -butyric methyl ester (PCBM). Thermal cross-linking of the benzoxazine moiety in PCBB resulted in the formation of cross-linked, solvent resistive adhesive films (C-PCBB). Atomic force microscopy (AFM) and optical microscopic studies showed dramatic reduction in the roughness and aggregation behaviour of P3HT-PCBM polymer blend film upon incorporation of C-PCBB interlayer. An inverted bulk heterojunction solar cell based on the configuration ITO/ZnO/C-PCBB/P3HT-PCBM/V2 O5 /Ag achieved 4.27 % power conversion efficiency (PCE) compared to the reference device ITO/ZnO/P3HT-PCBM/V2 O5 /Ag (PCE=3.28 %). This 25 % increase in the efficiency is due to the positive effects of C-PCBB on P3HT/C-PCBB and PCBM/C-PCBB heterojunctions.

PREPARATION AND OPTICAL PROPERTIES CHARACTERIZATION OF P3OT - PMMA POLYMER BLEND FILMS

The optical properties of the Poly (3 - octylthiophene) (P3OT) – Poly (methyl methacrylate) (PMMA) polymer blend films at different percentage weight ratios of P3OT polymer were prepared using casting method. The optical absorbance and transmittance spectra of these films were measured in the wavelength range 300 – 1100 nm for different weight ratios of P3OT polymer using UV-Visible double - beam spectrophotometer. These optical spectra were used to determine the optical properties of the prepared polymer films. The main optical parameters of the polymer blend film, such as, reflectance (R), absorption coefficient (α), extinction coefficient (k), refractive index (n), real and imaginary parts of dielectric constant (εr and εi), and optical energy band gap (Eg), were determined. The effect of the weight ratio of P3OT polymer on these parameters was studied. The results showed that the prepared P3OT – PMMA polymer blend films exhibited suitable optical properties for the applications of solar cells, optical sensors, and photonic devices.

Flexible Organic Electrolyte-Gated Transistors Based on Thin Polymer Blend Films of Crystalline C8-BTBT and Amorphous PTAA

Thin films of polymer blends consisting of a crystalline small-molecular semiconductor, 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C8-BTBT), and an amorphous polymer semiconductor, poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA), are studied and applied to organic electrolyte-gated transistors (OEGTs). The compositions can be easily controlled by adjusting the mixing ratios of the solutions in chloroform. In the thin-film state, PTAA acts as a structural matrix and a charge-transport bridge for C8-BTBT grains. The C8-BTBT:PTAA blends have a compositional effect on the thin-film properties and performance of OEGTs. As a result, the C8-BTBT:PTAA blend films with weight ratios of 8:2 exhibit a hole mobility twice that of pristine C8-BTBT films. Moreover, OEGTs based on the C8-BTBT:PTAA blend exhibit better charge-transport properties on flexible plastic substrates under bending conditions, compared to flat devices.

Development of Melamine Electrochemical Sensor Using Molecularly Imprinted Conducting Polyanilne-Oxalic Acid Blend as a Molecular Recognition Element

In the present work, oxalic acid doped molecularly imprinted conducting polyaniline film for melamine detection was prepared by in-situ-electrochemical polymerization on the glassy carbon electrode (GCE) using melamine as template. The optimal monomer/template molar ratio was attained to be 0.2:0.1:0.01 (aniline: oxalic acid: melamine) and molecular recognition properties towards melamine were evaluated by differential pulse voltammetry. Under optimal conditions the imprinted polymer film was used to detect different concentrations of melamine in standard solutions and real milk samples. Compared with the nonimprinted polymer (NIP), the molecularly imprinted polymer (MIP) film showed higher affinity and sensitivity towards melamine with a linear range, quantification limit and detection limit of 0.5-200 nM, 1.375 nM and 0.413 nM respectively. Furthermore, the polymer blend film showed good selectivity toward melamine, stability, reproducibility and practical applications for the determination of melamine in infant formula milk with the recovery of 92.32-102.49%. The doping of the polymer with oxalic acid enhanced the conductivity and sensitivity of the sensor.

Shear-Enhanced Stretchable Polymer Semiconducting Blends for Polymer-based Field-Effect Transistors

Solution-sheared field-effect transistors based on the blend of the high-mobility donor-acceptor conjugated copolymer poly(diketopyrrolo[3,4-c]pyrrole-co-thieno[3,2-b]thiophene) (PDBT-co-TT) and the elastic polymer poly(styrene-butadiene-styrene) (SBS) are demonstrated for stretchable electronics. In this study, PDBT-co-TT serves as a charge transport layer, and the insulating polymer SBS with double bonds is used for improving elasticity. Through combination with solution shearing, the phase separation and charge transport properties of the PDBT-co-TT/SBS blends can be manipulated. Compared with the spin-coated PDBT-co-TT/SBS blends showing lower charge mobilities (~10−3 cm2 V−1 s−1), the solution-sheared polymer-blend films with the PDBT-co-TT content of 20% maintain high mobility (>0.1 cm2 V−1 s−1). The films with 60% PDBT-co-TT can even achieve mobility as high as 2 cm2 V−1 s−1, which is higher than the pristine conjugated polymer. Furthermore, as the SBS content increases, the dichroic ratios of the solution-sheared blends increase, indicating improved alignment of the conjugated polymer chains. The PDBT-co-TT/SBS blends exhibit great stretchability and high charge mobilities even under 100% strain due to their mesh-like morphology. Moreover, solution shearing not only improves polymer alignment but also controls surface morphology to enhance stretchability. This work reveals the importance of solution shearing in high-mobility stretchable polymer semiconductor blends.