Thin Polymer Films Research Articles

Electronic and optical properties of Sc2C(OH)2 with phenylsulfonic groups: A first-principles study

Polystyrene sulfonic acid (PSS) polymer thin film can be applied to the surface passivation of Si-based semiconductor devices because of its low cost and the ability to be fabricated without the need for extreme temperatures or high vacuum. Here, the phenylsulfonic groups (–pSO3H, a typical part of PSS) were grafted onto the Sc2C(OH)2 the surface to form Sc2C(OH)2–pSO3H. The electronic structure and optical properties were investigated by first-principles calculations. The results show that Sc2C(OH)2–pSO3H is a direct bandgap semiconductor material with a bandgap of 0.99 eV, which is higher than that of Sc2C(OH)2. The bandgap of Sc2C(OH)2–pSO3H has a small change by replacing cation H of –pSO3H with Li, Na and K, indicating that the Sc2C(OH)2–pSO3H maintains its semiconductor properties. The reason is that the conduction band minimum (CBM) state and the valence band maximum (VBM) are mainly determined by the contribution of C 2p states and Sc 3d states of the main body Sc2C(OH)2. Versus the conventional photovoltaic material Si, the absorption coefficient of Sc2C(OH)2–pSO3H is very high, thus resulting in a maximum photoelectric conversion efficiency of up to 31 %. These results suggest promising 2D visible light absorption materials that are photovoltaics in solar cells.

Spectral (in)dependence of nonequilibrium charge carriers lifetime and density of states distribution in the vicinity of the band gap edge in F8BT polymer

Photoelectric properties of the F8BT polymer are investigated by the Constant photocurrent method (CPM) based on the photocurrent spectra Δjph(hν) and absorption spectra αCPM(hν). The negligibly weak dependence of charge carriers lifetime on the photon energy is found for hν = 2.2–2.7 eV. The peculiarities of the absorption spectra and the photoconductivity spectra are revealed to be determined mainly by the Gaussian distribution of the density of states (DOS). The density of trap states in the F8BT polymer thin films in the exponential DOS is estimated to be 103 times higher than in the Gaussian DOS.

Flexible membranes fabricated by initiated chemical vapor deposition for water treatment, battery, and drug delivery

With the development of advanced yet structurally complex systems, flexible membranes have attracted increasing attention. Initiated chemical vapor deposition (iCVD), an emerging, facile, scalable technique to deposit high-quality polymer thin films on arbitrary substrates, holds great promise in the fabrication of flexible membranes. iCVD features solvent-free, gentle deposition conditions that enable the processing of various solvent-susceptible, fragile, or delicate substrates. The mechanical flexibility, precisely controlled morphology, and abundant physiochemical property of iCVD polymer films enable the design and optimization of membrane characteristics for diverse applications. Herein, we provide a comprehensive review of the fabrication and applications of iCVD flexible membranes. First, we introduce the deposition mechanism and parameters of iCVD. We then critically discuss the applications of iCVD membranes in water treatment, battery, and drug delivery, elaborating their processing–property–performance interrelationships. Finally, we discuss the scale-up and commercialization of iCVD, followed by the limitations and future directions in the field.

Charge carrier transport mechanism in plasma polymerized methyl acrylate thin films

Plasma-polymerized methyl acrylate thin films (PPMA) of thicknesses 115 to 290 nm were prepared using a capacitively coupled glow discharge plasma reactor. The current density-voltage (J-V) characteristics of the Aluminum/PPMA/Aluminum sandwich configuration were studied between 0.1 and 75 V over the temperature region from 298 K to 398 K for various thicknesses of PPMA thin films. J-V curves show that the conduction current follows Ohm's law in the low voltage area, but that in the high voltage range, the behavior is attributed to be space charge-limited conduction (SCLC) in PPMA thin films. The free carrier density, the trap density and carrier mobility have been determined to be around 1.77 × 1023 to 5.86 × 1023 m−3, 2.84 × 1024 to 3.77 × 1024 m−3, and 3.87 × 10−18 to 69.7 × 10−18 m2V−1s−1, respectively for various thicknesses of PPMA thin films. For the higher temperature and lower temperature areas, the activation energies were found in the range from 0.60 to 0.84 eV and 0.28 to 0.40 eV, respectively for 5 V in Ohmic region and from 0.61 to 0.98 eV and 0.27 to 0.34 eV, respectively for 60 V in SCLC (Non-Ohmic) region, respectively. It is observed that SCLC mechanism in PPMA thin films is dominated by a single dominant trap level/discrete trap level distribution. The PPMA thin films are promising candidates in manufacturing optoelectronic devices.

A thin-film polymer heating element with a continuous silver nanowires network embedded inside

This study presents a method for fabricating a film-based heating element using a polymer material with an array of intersecting conductive elements embedded within it. Track-etched membranes (TM) with a thickness of 10 μm were used as the template, and their pores were filled with metal, forming a three-dimensional grid. Due to the unique manufacturing process of TM, the pores inside intersect with each other, allowing for contacts between individual nanowires (NWs) when filled with metal. Experimental results demonstrated that filling the TM pores with silver allows for heating temperatures up to 78 degrees without deformation or damage to the heating element. The resulting flexible heating element can be utilized in medical devices for heating purposes or as a thermal barrier coating.

Multicolor Conjugated Polymer Thin Films with Tunable Responsivity to Oxidative and Reductive Environments.

Dynamic colors that respond to environmental changes are of great interest for diverse areas of science and technology ranging from chemical and biological sensors to smart information display. Here, we demonstrate a multitude of responsive colors from a conjugated polymer film arising from a thin-film interference. This mechanism provides an excellent control over the thin-film color by varying the film thickness, type of substrate, and degree of polaron population and is generally applicable to various conjugated polymers for further color variation. Furthermore, multiple sets of responsive colors are achieved from a single polymer layer by patterning the underlying substrate to spatially modify the interference conditions. Using this system, we demonstrate the reversible color changes induced by an oxidative or reductive environment with color responsivity controllable with the nature of the polaron state.

The Enhanced Thermoforming Stability of ITO Transparent Electrode Film by Using the Conducting Polymer Thin-Film

The Enhanced Thermoforming Stability of ITO Transparent Electrode Film by Using the Conducting Polymer Thin-Film

Application of surface-layer matrix-assisted laser desorption/ionization mass spectrometry imaging to pharmaceutical-loaded poly(ester urea) films

Polymer thin films are often used in transdermal patches as a method of continuous drug administration for patients with chronic illness. Understanding the drug segregation and distribution within these films is important for monitoring proper drug release over time. Surface-layer matrix-assisted laser desorption/ionization mass spectrometry imaging (SL-MALDI-MSI) is a unique analytical technique that provides an optical representation of chemical compositions that exist at the surface of polymeric materials. Solvent-free sublimation is employed for application of matrix to the sample surface, so that only molecules in direct contact with the matrix layer are detected. Here, these methodologies are utilized to visualize variations in drug concentration at both the air and substrate interface in pharmaceutical-loaded polymer films.

Interplay between Side Chain Density and Polymer Alignment: Two Competing Strategies for Enhancing the Thermoelectric Performance of P3HT Analogues.

A series of polythiophenes with varying side chain density was synthesized, and their electrical and thermoelectric properties were investigated. Aligned and non-aligned thin films of the polymers were characterized in the neutral and chemically doped states. Optical and diffraction measurements revealed an overall lower order in the thin films with lower side chain density, also confirmed using polarized optical experiments on aligned thin films. However, upon doping the non-aligned films, a sixfold increase in electrical conductivity was observed for the polythiophene with the lowest side chain density compared to poly(3-hexylthiophene) (P3HT). We found that the improvement in conductivity was not due to a larger charge carrier density but an increase in charge carrier mobility after doping with 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ). On the other hand, doped aligned films did not show the same trend; lower side chain density instead led to a lower conductivity and Seebeck coefficient compared to those for P3HT. This was attributed to the poorer alignment of the polymer thin films with lower side chain density. The study demonstrates that optimizing side chain density is a synthetically simple and effective way to improve electrical conductivity in polythiophene films relevant to thermoelectric applications.

Anomalous magnetoresistance in a nonconjugated radical polymer glass.

Macromolecules bearing open-shell entities offer unique transport properties for both electronic and spintronic devices. This work demonstrates that, unlike their conjugated polymer counterparts, the charge carriers in radical polymers (i.e., macromolecules with nonconjugated backbones and with stable open-shell sites present at their pendant groups) are singlet cations, which opens significant avenues for manipulating macromolecular design for advanced solid-state transport in these highly transparent conductors. Despite this key point, magnetoresistive effects are present in radical polymer thin films under applied magnetic fields due to the presence of impurity sites in low (i.e., <1%) concentrations. Additionally, thermal annealing of poly(4-glycidyloxy-2,2,6,6- tetramethylpiperidine-1-oxyl) (PTEO), a nonconjugated polymer with stable open-shell pendant groups, facilitated better electron exchange and pairwise spin interactions resulting in an unexpected magnetoresistance signal at relatively low field strengths (i.e., <2 T). The addition of 4-hydroxy-2,2,6,6-tetramethylpiperidin-N-oxy (TEMPO-OH), a paramagnetic species, increased the magnitude of the MR effect when the small molecule was added to the radical polymer matrix. These macroscopic experimental observables are explained using computational approaches that detail the fundamental molecular principles. This intrinsic localized charge transport behavior differs from the current state of the art regarding closed-shell conjugated macromolecules, and it opens an avenue towards next-generation transport in organic electronic materials.

Development and testing of novel functionalized polymeric thin-films for equilibrium passive sampling of PFAS compounds in water

The demand for an accurate assessment of exposure and risk from the presence of per- and polyfluoroalkyl substances (PFAS) in the aquatic environment has created the need for new methods of measurements in water at sub-parts per trillion concentrations. We explored the concept of equilibrium passive sampling for PFAS using the strategy developed for other organic compounds. Equilibrium passive sampling should predict the concentration of the chemically labile fraction of PFAS in water based on equilibrium partitioning into the sampler, without the need for site-specific calibration. Our goals were to identify sampler materials with the potential to mimic PFAS partitioning into animals and sediments and provide reversible sorption in a time frame appropriate for in situ samplers. To achieve this goal, we tested a range of candidate materials, including three broad classes of polymers embedded with suitable sorbents for PFAS. The most promising synthesized thin films were activated carbon (AC) embedded in agarose, silica-bonded human serum albumin (s-HSA) embedded in Agarose, WAX embedded in cellulose acetate, and HLB embedded in PDMS, which yielded log sampler–water partition coefficients close to 3 for many PFAS compounds. Sampler equilibration time in water was approximately one week. Investigation of the isotherms suggested that the sorption can be described across the concentration range of interest, from the ng/L range commonly found in natural uncontaminated waters to the ug/L concentrations found in contaminated sites. Also, the selected films exhibited relatively rapid desorption of PFAS, indicating that the sorbents are capable of reversible, equilibrium measurements. The present study demonstrates a potential new approach to passive sampling of PFAS.

Semiconductor quantum dots as a mechanism to enhance charge transfer processes in polymer solar cells

The light trapping capability of thin film polymer solar absorber, composed of poly (3-hexylthiophene) and [6,6]–phenyl C61- butyric acid methyl ester (P3HT:PC60BM) blend, is improved using ZnS semiconductor quantum dots (QD) as third donor-acceptor (D:A) component. The inherent characteristics of the microwave-assisted synthesized ZnS QD, such as quantum size effect, and multiple exciton generation were leveraged in harvesting high energy photons, which resulted in a better exciton generation, dissociation, and effective charge transport in the polymer medium. The synthesized QD exhibited good phase purity, effective kinetic enhancement, and control of the aggregation process. Hence, the impact of ZnS QD on the performance of thin film polymer solar cells (TFPSC) is evident by a remarkable improvement in the measured photovoltaic parameters. Nonetheless, it is observed that the device performances are generally dependent on the concentration of the QD in the absorber layer. Consequently, the power conversion efficiency has increased by 58% at 3% concentration of QDs by weight. This is an interesting development of TFPSC fabricated under an ambient environment.

Ultrahigh Capacitive Energy Density in Stratified 2D Nanofiller-Based Polymer Dielectric Films.

Dielectric capacitors are critical components in electronics and energy storage devices. The polymer-based dielectric capacitors have the advantages of device flexibility, fast charge-discharge rates, low loss, and graceful failure. Elevating the use of polymeric dielectric capacitors for advanced energy applications such as electric vehicles (EVs), however, requires significant enhancement of their energy densities. Here, we report a polymer thin film heterostructure-based capacitor of poly(vinylidene fluoride)/poly(methyl methacrylate) with stratified 2D nanofillers (Mica or h-BN nanosheets) (PVDF/PMMA-2D fillers/PVDF), that shows enhanced permittivity, high dielectric strength, and an ultrahigh energy density of ≈75 J/cm3 with efficiency over 79%. Density functional theory calculations verify the observed permittivity enhancement. This approach of using oriented 2D nanofillers-based polymer heterostructure composites is expected to be versatile for designing high energy density thin film polymeric dielectric capacitors for myriads of applications.

Steady-state simulation of the film-casting process for Newtonian and viscoelastic fluids

Thin polymeric films are usually produced in an extensional flow between an extrusion head and a chill roll. The final product is prone to several defects, such as reduced width and non-uniform thickness, and a better understanding of the whole process can improve the final product quality and reduce wastes. This work revisits the film-casting process by exploring the scaling relation between different variables, with particular focus on the width reduction (neck-in). The numerical simulations are carried out for Newtonian, Upper-Convected Maxwell and Giesekus fluids in isothermal and steady-state conditions, for varying film aspect ratio (AR; film width over length), draw ratio (DR) and Deborah number (De). The governing equations are discretized with finite-volumes in their full form (3D model) and using an approximate 2.5D model. However, the latter has been mainly used in this study, as it offered similar accuracy as the 3D model, at a much lower computational cost. The results show that the normalized film shape is independent of the aspect ratio for sufficiently high values of this parameter and that the film thickness scales with DR according to the theoretical prediction for planar and uniaxial extensional flows, in the centre and edge regions, respectively. The neck-in grows logarithmically with the draw ratio for high AR, with a De-dependent growth rate (higher De leads to lower neck-in and lower dependence on DR). There is a reasonable correlation between the neck-in and the ratio between the planar and uniaxial extensional viscosities, as well as between the neck-in and dimensionless variable M = ln(DR)/(De+δ), where δ is a constant which depends on the fluid rheology. However, none of the correlations offer a perfect fit to the neck-in and the search for such a correlation (or master curve) shall be pursued in future works.

Simultaneous quantification of Young’s modulus and dispersion forces with nanoscale spatial resolution

Many advances in polymers and layered materials rely on a precise understanding of the local interactions between adjacent molecular or atomic layers. Quantifying dispersion forces at the nanoscale is particularly challenging with existing methods often time consuming, destructive, relying on surface averaging or requiring bespoke equipment. Here, we present a non-invasive method able to quantify the local mechanical and dispersion properties of a given sample with nanometer lateral precision. The method, based on atomic force microscopy (AFM), uses the frequency shift of a vibrating AFM cantilever in combination with established contact mechanics models to simultaneously derive the Hamaker constant and the effective Young’s modulus at a given sample location. The derived Hamaker constant and Young’s modulus represent an average over a small (typically <100) number of molecules or atoms. The oscillation amplitude of the vibrating AFM probe is used to select the length-scale of the features to analyse, with small vibrations able to resolve the contribution of sub-nanometric defects and large ones exploring effectively homogeneous areas. The accuracy of the method is validated on a range of 2D materials in air and water as well as on polymer thin films. We also provide the first experimental measurements of the Hamaker constant of HBN, MoT2, WSe2 and polymer films, verifying theoretical predictions and computer simulations. The simplicity and robustness of the method, implemented with a commercial AFM, may support a broad range of technological applications in the growing field of polymers and nanostructured materials where a fine control of the van der Waals interactions is crucial to tune their properties.

Mixed Metal-Organic Framework Mixed-Matrix Membranes: Insights into Simultaneous Moisture-Triggered and Catalytic Delivery of Nitric Oxide using Cryo-scanning Electron Microscopy.

The fundamental chemical and structural diversity of metal-organic frameworks (MOFs) is vast, but there is a lack of industrial adoption of these extremely versatile compounds. To bridge the gap between basic research and industry, MOF powders must be formulated into more application-relevant shapes and/or composites. Successful incorporation of varying ratios of two different MOFs, CPO-27-Ni and CuBTTri, in a thin polymer film represents an important step toward the development of mixed MOF mixed-matrix membranes. To gain insight into the distribution of the two different MOFs in the polymer, we report their investigation by Cryo-scanning electron microscopy (Cryo-SEM) tomography, which minimizes surface charging and electron beam-induced damage. Because the MOFs are based on two different metal ions, Ni and Cu, the elemental maps of the MOF composite cross sections clearly identify the size and location of each MOF in the reconstructed 3D model. The tomography run was about six times faster than conventional focused ion beam (FIB)-SEM and the first insights to image segmentation combined with machine learning could be achieved. To verify that the MOF composites combined the benefits of rapid moisture-triggered release of nitric oxide (NO) from CPO-27-Ni with the continuous catalytic generation of NO from CuBTTri, we characterized their ability to deliver NO individually and simultaneously. These MOF composites show great promise to achieve optimal dual NO delivery in real-world medical applications.

Quantitative X‐ray scattering and reflectivity measurements of polymer thin films with 2D detectors

AbstractWe describe a fully open‐sourced Python package to process raw X‐ray scattering data using a GANESHA SAXSLAB facility, and review in this manuscript the connection of X‐ray scattering theories with the open‐sourced package. This package affords researchers more flexibility in analyzing and visualizing X‐ray scattering and reflectivity data from what is now a commonplace facility at many universities and research laboratories engaged in polymer research. We briefly review the applications of X‐ray scattering and diffraction, followed by the scattering theories. A pedagogical introduction to processing X‐ray scattering data is provided using the modules in the Python package. We compare conventions to visualize and interpret transmission and grazing‐incidence scattering data using self‐assembled lamellar morphology of bottlebrush copolymers as an example, then describe how area detectors measure specular and off‐specular reflectivity. Examples of in‐house reflectivity and grazing incidence scattering for the metrological examination of a grating are provided, where the full pitch and pitch height of a line pattern is measured easily without needing to simulate the full scattering intensity profile.

ICVD Polymer Thin Film Bio‐Interface‐Performance for Fibroblasts, Cancer‐Cells, and Viruses Connected to Their Functional Groups and In Silico Studies

AbstractThin polymer coatings are used to improve the interface between biological species and functional materials. Their interaction is significantly influenced by the functional groups and roughness of the polymer film and prediction of the interaction is thus of great interest. However, for conventional polymer films, this cannot be examined independently because of the interplay of defects, residual solvent molecules, roughness, and functional groups. Solvent‐free polymer films prepared by initiated chemical vapor deposition (iCVD) exhibit conformal, defect‐free characteristics and enable precise tailoring of the functional groups. This facilitates to isolate the contribution of functional groups on the bio‐interface performance. Consequently, in silico studies can enable a prediction of ligand interaction in anti‐viral activity for SARS‐CoV‐2 based on defined polymer and key protein structures. Furthermore, the cell viability of human fibroblasts can be traced back to the functional groups of the repeating units. For human liver cancer cell culture, it turns out that more sophisticated models are needed. The insilico‐iCVD approach can enable precise tailoring of complex polymer films optimized for the respective interfaces. In addition, this first big scan of the bio‐interface performance of iCVD films enables a solid starting point in areas like anticancer, antiviral, and biocompatibility for future studies.

Synthesis and Application of Polypyrrole/DBSA/Boron Nitride Ternary Composite as a Potential Chemical Sensor for Ammonia Gas Detection

The present study demonstrates the self-assembly method of chemical oxidative polymerization of polypyrrole (PPy), polypyrrole/boron nitride (PPy/BN), and polypyrrole/dodecylbenzene sulfonic acid/boron nitride (PPy/DBSA/BN) thin films for ammonia (NH3) gas detection. The PPy, PPy/BN, and PPy/DBSA/BN thin films were comprehensively characterized using Attenuated Total Reflectance Fourier-Transform Infrared Spectroscopy (ATR-FTIR), Scanning Electron Microscopy (SEM), X-ray diffractometry (XRD) and conductivity measurement. ATR-FTIR revealed all the pertinent peaks of PPy, BN, and DBSA present in the PPy/DBSA/BN. SEM images of PPy/DBSA/BN depict well-organized morphology. PPy/DBSA/BN recorded the highest conductivity of 4.771 x 10-6 S cm-1 among the prepared polymer thin films. The obtained characterization results are in good agreement with the NH3 gas sensor measurements conducted on the PPy/DBSA/BN composite. The linear correlation coefficient between the two was found to be R2 = 0.9916, indicating a strong relationship. Furthermore, the PPy/DBSA/BN thin film demonstrated a low limit of detection (LOD) of 5.8 ppm, surpassing the OSHA threshold value for NH3 gas. This suggests that the sensor is highly sensitive to trace amounts of NH3 gas. Moreover, the PPy/DBSA/BN thin film exhibited exceptional reusability, with the ability to be used for up to 10 cycles without a significant decrease in performance. The sensor also demonstrated selectivity towards NH3 gas in the presence of common interfering species. Additionally, it exhibited long-term stability, maintaining its performance over a period of 7 days. The proposed self-assembled gas sensor has showcased remarkable performance in detecting NH3 gas at room temperature, making it a promising candidate for industrial applications.

Femtosecond nonlinear optical investigations of nitro chalcones-doped PMMA thin films for optical limiting and photonic applications

Herein we present the linear and third-order nonlinear optical properties of two nitro substituted chalcone derivatives [3-(4-fluorophenyl)− 1-(3-nitrophenyl) prop-2-en-1-one and (2E,4E)− 1-(3-nitrophenyl)− 5-phenylpenta-2,4-dien-1-one; abbreviated as F3NC and Ci3NC, respectively] doped PMMA polymer thin films. The chemical spray pyrolysis method was adopted to prepare the films at three different doping concentrations (5 wt%, 10 wt%, 15 wt%). The linear optical studies were performed using UV-Visible-NIR spectra, and surface roughness using AFM technique. Hirshfeld surface analysis was adopted to understand the intermolecular interactions. The third-order nonlinear optical properties were investigated using Z-scan method under Ti:Sapphire femtosecond (fs) laser pulses (∼150 fs, 80 MHz, 800 nm). Open and closed aperture Z-scan curves indicated the presence of two-photon assisted reverse saturable absorption and self-defocusing effect, respectively. The calculated nonlinear refraction (n2), nonlinear absorption (β) coefficients and third-order susceptibility [χ(3)] were found to be in the order ∼10−12 cm2 W−1, ∼10−8 cm W−1 and ∼10−11 e.s.u., respectively. We observed increase in nonlinearity of the films with increased chalcone doping concentration. Among the doped chalcones, F3NC doped films exhibit a higher nonlinearity than Ci3NC doped films. The observed results reveal that chalcone-doped PMMA thin films are possible materials for optical limiting and photonic applications.