Thin Polymer Films Research Articles

Simulation aspects of patterning polymer films via evaporative lithography and composite substrates

The continuing development of evaporative lithography is important for many areas such as the creation of photonic crystals for optronics and microelectronics, the development of biosensors for medical applications and biotechnology, and for the formation of functional coatings for nanotechnology, including the application of thin, protective polymer coatings. The article proposes a mathematical model that allows us to explain the basic mechanisms of the formation of thin polymer films (less than 50 μm thick) during their deposition onto a composite substrate by methanol evaporation from a solution. If the thermal conductivity of the substrate is spatially non-uniform, this results in inhomogeneous evaporation along the free film surface. Therefore, as the film dries, a patterned polymer coating is left behind on the substrate. The mathematical model described here is based on the lubrication approximation and takes into account the dependence of the solution density on the concentration. The numerical computation results are in qualitative agreement with the experimental data of other authors. The article shows that solutal Marangoni flow plays a primary role in the process under consideration. This study allows us to better understand the mechanisms that can be used in evaporative lithography.

Progress in 2D/3D nanomaterials incorporated polymer thin films for refractive index engineering: a critical review

Progress in 2D/3D nanomaterials incorporated polymer thin films for refractive index engineering: a critical review

Optical characterization and dispersion analyses of plasma polymerized methyl acrylate thin films

This work reports the structural characteristics, surface morphology, linear and nonlinear optical properties of 110 to 225 nm thick plasma polymerized methyl acrylate (PPMA) thin films. X-ray diffraction analyses confirm the amorphous nature of the films. Field emission scanning electron micrographs of the films display cluster-based surface morphology. Attenuated total reflectance Fourier transform infrared spectroscopy confirms the chemical structural changes in the films. The optical properties were studied based on the absorbance, transmittance, and reflectance spectra measured by an ultraviolet–visible spectrophotometer within the wavelength ranges from 200 to 800 nm. The direct optical band gap and Urbach values are increased from 3.66 to 3.83 eV and 0.28 to 0.45 eV, respectively with increasing film thickness. The extinction coefficient and refractive index were evaluated, and discussed a correlation between the refractive index and the optical bandgap. The real and imaginary dielectric constants, volume/surface energy loss functions and skin depth were deduced. The oscillator energies and parameters were analyzed using the concept of Wemple-DiDomenico and Sellmeier models, respectively for a single oscillator. Static linear refractive index for the studied films exhibits normal dispersion behavior with film thicknesses and satisfied Moss, Ravindra-Gupta, and Herve-Vandamme rules. The linear susceptibility, third-order nonlinear susceptibility and the non-linear refractive index are considerably reduced from 0.20, 29.5 × 10−14 esu, and 5.89 × 10−12 esu with increasing optical band gap energies. The outcomes from the analyses of PPMA demonstrated their potential for usage in electronic, optoelectronic, and non-linear device applications.

Study on the High-Efficiency Preparation of Superhydrophobic Polymer Thin Films by Continuous Micro/Nano Imprinting.

In order to improve the preparation efficiency, quality stability, and large-area preparation of superhydrophobic thin films, a roll-to-roll continuous micro-nano imprinting method for the efficient preparation of superhydrophobic polymer films is proposed. A wear-resistant mold roller with hierarchical microstructure is prepared by wire electrical discharge machining (WEDM). The rheological filling model is constructed for revealing the forming mechanism of superhydrophobic polymer films during continuous micro/nano imprinting. The effects of imprinting temperature, rolling speed and the surface texture size of the template on the surface texture formation rate of polymer films are analyzed. The experimental results show that, compared with other process methods, the template processed by WEDM shows excellent wear resistance. Moreover, the optimal micro/nano imprinting parameters are the mold temperature of 190 °C (corresponding film temperature of 85 ± 5 °C), rolling speed of 3 rpm and roller gap of 0.1 mm. The maximum contact angle of the polymer film is 154°. In addition, the superhydrophobic polymer thin film has been proven to have good self-cleaning and anti-icing performance.

Ferroelectric Thin Films and Composites Based on Polyvinylidene Fluoride and Graphene Layers: Molecular Dynamics Study

This work is devoted to the study of nanosized polymer polyvinylidene fluoride (PVDF) thin ferroelectric films (two-dimensional ferroelectrics) and their composites with graphene layers, using molecular dynamics methods to (1) study and calculate the polarization switching time depending on the electric field and film thickness, (2) study and calculate the polarization switching time depending on changes of the PVDF in PVDF-TrFE film, and (3) study the polarization switching time in PVDF under the influence of graphene layers. All calculations at each MD run step were carried out using the semi-empirical quantum method PM3. A comparison and analysis of the results of these calculations and the kinetics of polarization switching within the framework of the Landau–Ginzburg–Devonshire theory for homogeneous switching in ferroelectric polymer films is carried out. The study of the composite heterostructures of the “graphene-PVDF” type, and calculations of their polarization switching times, are presented. It is shown that replacing PVDF with PVDF-TrFE significantly changes the polarization switching times in these thin polymer films, and that introducing various graphene layers into the PVDF layered structure leads to both an increase and a decrease in the polarization switching time. It is shown that everything here depends on the position and displacement of the coercive field depending on the damping parameters of the system. These phenomena are very important for various ferroelectric coatings.

Subcutaneous temperature prediction during cryogenic jet cooling by surface temperature measurements and RNNs

Accurate information of subcutaneous temperature is crucial to the effectiveness and safety of a variety of medical procedures by energy-based devices, such as cooling treatments. Numerous strategies for invasive subcutaneous temperature monitoring have been investigated; however, they are impractical mainly due to their requirements for precise heat transfer modeling. In the case of cooling treatment by cryogenic substances, heat transfer rate largely varies with their phase change and procedure condition, which prevents accurate prediction of subcutaneous temperature. In this work, we propose a non-invasive, accurate, and practical prediction of subcutaneous temperature during CO2 spray jet cooling without numerical modeling by utilizing recurrent neural networks (RNNs) with surface temperature measurements for the first time. A patchable temperature sensor array on a flexible PCB is used to measure surface temperature. With this measured surface temperature, RNNs are developed with two functionalities: extraction of thermophysical properties (thermal conductivity and thermal diffusivity) of the target substrate and prediction of temperature response at 1-mm depth from the surface, which is the typical location of pain points. Five polymer thin films are used with the reference thermocouple embedded inside to train RNNs. A porcine skin is used to validate the RNNs, which show a prediction accuracy of 99.2%.

Development of excitation power-responsive anti-stokes emission wavelength switching and their energy saving induced by localized surface plasmon resonance

We designed an external stimulus-responsive anti-Stokes emission switching using dual-annihilator-based triplet–triplet annihilation upconversion systems. This system, which was constructed by incorporating a palladium porphyrin derivative as a sensitizer and 9,10-diphenylanthracene (DPA) and 9,10-bis(triisopropylsilyl)ethynylanthracene (TIPS) as annihilators into polymer thin films, produced TIPS- and DPA-based anti-Stokes emission under low and high excitation powers, respectively. The mechanism involves the following: under low excitation power, triplet energy transfer from triplet-excited PdOEP to DPA is induced, followed by relay to TIPS. This results in the generation of triplet-excited TIPS, and the subsequent triplet–triplet annihilation between them produces TIPS-based anti-Stokes emission. Conversely, under high excitation power, the high-density triplet-excited DPA, generated through triplet energy transfer from PdOEP, undergoes triplet–triplet annihilation among themselves, resulting in the generation of DPA-based anti-Stokes emission. Additionally, we achieved energy savings by reducing the required excitation power for switching through the utilization of plasmonic metal nanoparticles. The strong local electromagnetic fields associated with the localized surface plasmon resonance of metal nanoparticles enhance the photoexcitation efficiency of PdOEP, subsequently increasing the density of triplet-excited DPA. As a result, anti-Stokes emission switching becomes feasible at lower excitation powers.

Boundary Frustration in Double-Gyroid Thin Films.

Self-consistent field theory for thin films of AB diblock polymers in the double-gyroid phase reveals that in the absence of preferential wetting of monomer species at the film boundaries, films with the (211) plane oriented parallel to the boundaries are more stable than other orientations, consistent with experimental results. This preferred orientation is explained in the context of boundary frustration. Specifically, the angle of intersection between the A/B interface and the film boundary, the wetting angle, is thermodynamically restricted to a narrow range of values. Most termination planes in the double gyroid cannot accommodate this narrow range of wetting angles without significant local distortion relative to the bulk morphology; the (211)-oriented termination plane with the "double-wave" pattern produces relatively minimal distortion, making it the least frustrated boundary. The principle of boundary frustration provides a framework to understand the relative stability of termination planes for complex ordered block polymer phases confined between flat, nonpreferential boundaries.

Electropolymerization of an EDOT-Quinoxaline Monomer for Green Electrochromic Thin Films and Devices.

In this study, we present a 5,8-bis(3,4-ethylenedioxythiophene)quinoxaline monomer with two 4-(octyloxy)phenyl side chains (EDOTPQ) that can be electropolymerized on ITO glass in standard electrolytes containing lithium salts and propylene carbonate as solvent. The electrochemically deposited PEDOTPQ layers show very good adhesion and homogeneity on ITO. The green-colored polymer thin films exhibit promising electrochromic (EC) properties and are interesting for applications such as adaptive camouflage, as well as smart displays, labels, and sensors. Novel organic-inorganic (hybrid) EC cell configurations were realized with Prussian blue (PB) or titanium-vanadium oxide (TiVOx) as ion storage electrodes, showing a highly reversible and fast color change from green to light yellow.

ИМПЕДАНСНЫЙ АНАЛИЗ ПРОЦЕССОВ ПЕРЕНОСА ЗАРЯДА В СТРУКТУРЕ МЕТАЛЛ/ПОЛИМЕР/МЕТАЛЛ

The reaserch is devoted to the experimental study of charge transfer processes in thin films of an electroactive polymer from the class of polyarylene phthalides – poly (diphenylene phthalide). The method of impedance analysis of thin polymer films was used in this work. The material is quite well studied using other methods, such as thermally stimulated methods, optical spectroscopy, etc. However, frequency measurements were carried out mainly only in the field of determining capacitance-voltage characteristics. And since the polymer is electroactive, we should expect to identify features associated with charge transfer in the alternating field mode. In this regard, the work carried out an impedance analysis of thin films of poly (diphenylene phthalide) in the frequency range from 0.1 to 106 Hz. Typically, in impedance analysis, in addition to an ac field, a small DC bias voltage is applied to the metal/polymer/metal structure. This makes it possible to obtain data on surface polarization, charge carrier mobility, and the Maxwell-Wagner effect in the case of studying multilayer films. However, taking into account the electrical activity of the studied material, even impedance analysis in an alternating field, but with an effective voltage range from 0.1 to 10 V, made it possible to evaluate some of the electrophysical characteristics of the behavior of thin films. It was found that the slope of the impedance curve depends on the mechanism of transport of charge carriers in the polymer film. As the voltage increases from 0.1 to 10 V, an increase in the slope of the graph is observed. With an increase in the magnitude of the effective voltage, a transition occurs from the ohmic to the injection mechanism of transport of charge carriers limited by traps. When reaching 2 V, a mode of complete filling of the traps is observed, as a result of which an increase in voltage ceases to affect the slope of the frequency response. The dependence of the transition frequency fc on voltage has been plotted. This frequency corresponds to the transition from the predominance of the active to the reactive component of the impedance. Here, an exponential dependence on the magnitude of the applied voltage is observed, which also indicates the dependence of the mechanisms of transport of charge carriers in the polymer film on voltage (electric field).

ДЖОНШЕРОВСКИЙ УНИВЕРСАЛЬНЫЙ ДИНАМИЧЕСКИЙ ОТКЛИК В ТОНКИХ ПЛЕНКАХ ПОЛИДИФЕНИЛЕНФТАЛИДА

It is known that the supramolecular structure of organic materials can have a significant effect on the conductivity of polymer films in both constant and alternating fields. In particular, the presence of associative supramolecular formations can lead to a significant increase in the local dielectric constant. At the same time, the presence of different types of supramolecular ordering can lead to the predominance of certain charge transfer mechanisms in polymer films, and, consequently, to the presence of a dependence of conductivity on the electric field strength. The degree of molecular ordering, both on the surface and in the bulk of a polymer film, can also have a significant effect on polarization. In this regard, studying the influence of the supramolecular structure on the conductivity of polymer films in an alternating electric field is an urgent task.Previously, using various methods, it was established that the supramolecular structure of films with a thickness of more than 300 nm is determined mainly by supramolecular formations of an associative structure. The structure of films with a thickness of 100 to 300 nm is determined by the mixed structure of globular and associative formations. The structure of films less than 100 nm thick is determined by supramolecular formations of a globular. It was also established by the method of thermally stimulated depolarization that three regions are observed on the dependence of the activation energy of capture centers on the thickness of the polymer film, corre- sponding to different supramolecular organizations.In this work, the dependence of the conductivity of poly (diphenylene phthalide) films in an alternating electric field in the low-frequency range from 0.1 to 106 Hz on the supramolecular structure of polymer films was studied. It was found that the type of dependence of the conductivity of polymer films on the frequency of an alternating field depends on the thickness and supramolecular structure of the polymer films, as well as the electric field strength. The applicability of the Jonsher’s model, which describes the conductivity of amorphous materials in an alternating electric field, for thin polymer films is discussed. A correlation between the power-law dependence index and the supramolecular structure of the polymer film and the influence of dipole polarization and injection of charge carriers into the bulk of the polymer film on the conductivity of the polymer film have been revealed.

Impact of Photoluminescence Imaging Methodology on Transport Parameters in Semiconductors.

Triplet-triplet annihilation-induced delayed emission provides a pathway for investigating triplets via emission spectroscopy. This bimolecular annihilation depends directly on the transport properties of triplet excitons in disordered organic semiconductors. Photoluminescence (PL) imaging is a direct method for studying exciton and charge-carrier diffusivity. However, most of these studies neglect dispersive transport. Early time scale measurements using this technique can lead to an overestimation of the diffusion coefficient (DT) or diffusion length (Ld). In this study, we investigated the time-dependent triplet DT using PL imaging. We observed an overestimation of Ld in classical delayed PL imaging, often 1 order of magnitude higher than the actual Ld value. We compared various thicknesses of polymeric thin films to study the dispersive nature of triplet excitons. Transient analysis of delayed PL imaging and steady state imaging reveals the importance of considering the time-dependent nature of DT for the triplet excitons in disordered electronic materials.

In-plane oxygen diffusion measurements in polymer films using time-resolved imaging of programmable luminescent tags

Oxygen diffusion properties in thin polymer films are key parameters in industrial applications from food packaging, over medical encapsulation to organic semiconductor devices and have been continuously investigated in recent decades. The established methods have in common that they require complex pressure-sensitive setups or vacuum technology and usually do not come without surface effects. In contrast, this work provides a low-cost, precise and reliable method to determine the oxygen diffusion coefficient D in bulk polymer films based on tracking the phosphorescent pattern of a programmable luminescent tag over time. Our method exploits two-dimensional image analysis of oxygen-quenched organic room-temperature phosphors in a host polymer with high spatial accuracy. It avoids interface effects and accounts for the photoconsumption of oxygen. As a role model, the diffusion coefficients of polystyrene glasses with molecular weights between 13k and 350k g/mol are determined to be in the range of (0.8–1.5) × 10–7 cm2/s, which is in good agreement with previously reported values. We finally demonstrate the reduction of the oxygen diffusion coefficient in polystyrene by one quarter upon annealing above its glass transition temperature.

Gas Permeable Protection Caps for Wafer Level Chip Scale Packaging (WLCSP) of MEMS Environmental Sensors

This work presents new porous environmental protection caps designed for wafer level chip scale packaging (WLCSP) of MEMS environmental sensors. The caps consist of gaspermeable microstructures formed from loose aluminum oxide powder solidified by a ceramic thin film, grown using atomic layer deposition (ALD). For the first time, the full process flow of the proposed approach is demonstrated by manufacture of the cap wafer followed by substrate bonding using glass-frit technology. By analyzing the influence of the caps on the response time of MEMS humidity sensors, this study proves the viability of the proposed packaging technology. In addition, the ability to further functionalize the porous caps is demonstrated by the deposition of a superhydrophobic polymer thin film by chemical vapor deposition.

Extremely short optical pulses in a thin polymer film with carbon nanotubes

Extremely short optical pulses in a thin polymer film with carbon nanotubes

Simulations of Thin Polymer Films on Flat and Curved Substrates

Simulations of Thin Polymer Films on Flat and Curved Substrates

Impact of Thermal Annealing on the Dissolution of Semiconducting Polymer Thin Films

AbstractHere, the effect of thermal annealing (TA) on the stability of solution‐sheared thin films of the semiconducting polymer poly[2,5‐bis(2‐octyldodecyl)pyrrolo[3,4‐c]pyrrole‐1,4(2H,5H)‐dione‐3,6‐diyl)‐alt‐(2,2′;5′,2′’;5′’,2′’’‐quaterthiophen‐5,5′’’‐diyl)] (PDPP4T) against the original coating solvent is studied, and it is shown that TA significantly improves the solvent resistance of semiconducting polymer films. Specifically, after the thin films are annealed at or above a critical temperature, the thin film thickness is largely retained when exposed to the original solvent, while for lower annealing temperatures material loss occurs, i.e., the thin film thickness is reduced due to rapid dissolution. The results of various techniques including grazing‐incidence wide‐angle x‐ray scattering (GIWAXS), atomic force microscopy (AFM), and ultraviolet‐visible‐near infrared (UV–vis‐NIR) absorption spectroscopy suggest physical changes as the cause for the increased solvent resistance. Such annealed films also show stable electrical characteristics in bottom‐gate, top‐contact (BGTC) organic field‐effect transistors (OFETs) even after solvent exposure. In initial tests, a multitude of technologically relevant polymers show such behavior, underlining the potential impact of such temperature treatments for the fabrication of multi‐layer polymer devices.

A triangular model of fractal growth with application to adsorptive spin-coating of polymers.

Over the last 40 years, applied mathematicians and physicists have proposed a number of mathematical models that produce structures exhibiting a fractal dimension. This work has coincided with the discovery that objects with fractal dimension are relatively common in the natural and human-produced worlds. One particularly successful model of fractal growth is the diffusion limited aggregation (DLA) model, a model as notable for its simplicity as for its complex and varied behavior. It has been modified and used to simulate fractal growth processes in numerous experimental and empirical contexts. In this work, we present an alternative fractal growth model that is based on a growing mass that bonds to particles in a surrounding medium and then exerts a force on them in an iterative process of growth and contraction. The resulting structure is a spreading triangular network rather than an aggregate of spheres, and the model is conceptually straightforward. To the best of our knowledge, this model is unique and differs in its dynamics and behavior from the DLA model and related particle aggregation models. We explore the behavior of the model, demonstrate the range of model output, and show that model output can have a variable fractal dimension between 1.5 and 1.83 that depends on model parameters. We also apply the model to simulating the development of polymer thin films prepared using spin-coating which also exhibit variable fractal dimensions. We demonstrate how the model can be adjusted to different dewetting conditions as well as how it can be used to simulate the modification of the polymer morphology under solvent annealing.

From non‐doped to dopable: The impact of methoxy functionalization on doping and thermoelectric properties of conjugated polymers

AbstractThe introduction of alkoxy side chains into the backbone of conjugated polymers is an effective way to change their properties. While the impact on the structure and optoelectronic properties of polymer thin films was well‐studied in organic solar cells and transistors, limited research has been conducted on their effects on doping and thermoelectric properties. In this study, the effects of methoxy functionalization of conjugated backbones on the doping and thermoelectric properties are investigated through a comparative study of diketopyrrolopyrrole‐based conjugated polymers with and without methoxy groups (P29DPP‐BTOM and P29DPP‐BT, respectively). Methoxy‐functionalization significantly enhances doping efficiency, converting undopable pairs to dopable ones. This dramatic change is attributed to the structural changes in the polymer film caused by the methoxy groups, which increases the lamellar spacing and facilitates the incorporation of dopants within the polymer crystals. Moreover, methoxy‐functionalization is advantageous in improving the Seebeck coefficient and power factor of the doped polymers, because it induces a bimodal orientational distribution in the polymer, which contributes to the increased splitting of Fermi and charge transport levels. This study demonstrates the impact of methoxy‐functionalization of a conjugated polymer on doping behavior and thermoelectric properties, providing a guideline for designing high‐performance conjugated polymers for thermoelectric applications.image

Selective detection of salivary cortisol using screen-printed electrode coated with molecularly imprinted polymer

A novel electrochemical sensor was developed for the detection of salivary cortisol levels. The sensor employs a combination of a molecularly imprinted polymer (MIP) and gold nanoparticles (AuNPs) that are electrodeposited onto a screen-printed electrode (SPE). The study utilised density functional theory and molecular docking techniques to determine the geometry of molecular orbitals, electrostatic potential energies, and binding energy of cortisol and the polymers. The thin film of cortisol-imprinted polymer on the SPE was created by electro-polymerizing pyrrole and thiophene-3-carboxylic acid on the electrode surface along with cortisol as the template molecule. The MIP film was characterised using scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), and electrochemical techniques. The sensor exhibited a linear response in the concentration range of 0.05 nmol L−1 to 2.5 μmol L−1, with a limit of detection of 0.01 nmol L−1, as determined by differential pulse voltammetry. This method offers a simple yet efficient and sensitive approach to detecting cortisol levels in human saliva samples.