Hydrophobic Polymer Films Research Articles

Investigating the impact of water capillary forces on polymer‐substrate adhesion using force spectroscopy

AbstractAtomic force microscopy (AFM) was used to characterize how water capillary forces impact polymer‐substrate adhesion in ambient conditions. We analyzed hydrophobic poly(styrene‐co‐butadiene) interacting with mica, silicon, and graphite substrates, each with distinct surface properties. Using polymer‐coated AFM tips/blank substrates, and vice versa, we explored the roles of water capillary forces and polymer‐substrate interactions on adhesion. When force spectroscopy experiments were conducted using polymer‐coated tips, adhesion was the largest on mica due to substantial water capillary forces between the tip and hydrophilic substrate. However, when using a blank tip and polymer‐coated substrates, the adhesion was largest on graphite and smallest on mica. This is because the blank tip interacted with the same hydrophobic polymer film for each experiment; therefore, water capillary forces had an equal magnitude on each substrate, allowing polymer‐substrate interactions to be compared even within ambient conditions. Moreover, single‐chain desorption events were consistently observed in these force‐distance curves since water capillary forces were significantly reduced. This study elucidated several aspects of how water capillary forces impact polymer‐substrate adhesion, which benefits applications reliant on polymer adhesion in ambient conditions and contributes to the fundamental understanding of polymer interface interactions.

Air-stable silicon hybrid solar cells constructed via hydrophobic polymer film

Silicon (Si) hybrid solar cells have advantages of solution manufacturing process and the potential for achieving low-cost fabrication compared to crystalline Si solar cells. However, the functional layer prepared by solution method usually absorbs water molecules from the air, posing a challenge to the stability of the device. Here, a PEDOT derivative, PEDOT:A, was in situ prepared through the introduction of a fluoropolymer, yielding a strongly hydrophobic film that was assembled into a PEDOT:A/Si hybrid solar cell. The PEDOT:A/Si hybrid solar cells retained 90% of its initial performance after storage in the air for 300 h, while PEDOT:PSS only retained 60% with identical device structure. Meanwhile, first principles calculations indicate that the binding energy between fluoropolymer and water molecule was 3.48 kJ/mol, whereas the binding energy between PSS and water molecule was −5.76 kJ/mol. Benefiting from the weak interaction between fluoropolymer and water molecule, the contact angle of water on PEDOT:A film was 100.84°. After optimization, PEDOT:A/Si hybrid solar cells with ITO achieved a power conversion efficiency of 6.43%, retained 97% of its initial efficiency after testing under same conditions. The development of air-stable hybrid device technology is promising in opening up practical applications of low-cost Si based solar cells.

Facile Fabrication of Hierarchical Structured Anodic Aluminum Oxide Molds for Large-Scale Production of Superhydrophobic Polymer Films.

Anodized aluminum oxide (AAO) molds were used for the production of large-area and inexpensive superhydrophobic polymer films. A controlled anodization methodology was developed for the fabrication of hierarchical micro-nanoporous (HMN) AAO imprint molds (HMN-AAO), where phosphoric acid was used as both an electrolyte and a widening agent. Heat generated upon repetitive high-voltage (195 V) anodization steps is effectively dissipated by establishing a cooling channel. On the HMN-AAO, within the hemispherical micropores, arrays of hexagonal nanopores are formed. The diameter and depth of the micro- and nanopores are 18/8 and 0.3/1.25 µm, respectively. The gradual removal of micropatterns during etching in both the vertical and horizontal directions is crucial for fabricating HMN-AAO with a high aspect ratio. HMN-AAO rendered polycarbonate (PC) and polymethyl methacrylate (PMMA) films with respective water contact angles (WCAs) of 153° and 151°, respectively. The increase in the WCA is 80% for PC (85°) and 89% for PMMA (80°). On the PC and PMMA films, mechanically robust arrays of nanopillars are observed within the hemispherical micropillars. The micro-nanopillars on these polymer films are mechanically robust and durable. Regular nanoporous AAO molds resulted in only a hydrophobic polymer film (WCA = 113-118°). Collectively, the phosphoric acid-based controlled anodization strategy can be effectively utilized for the manufacturing of HMN-AAO molds and roll-to-roll production of durable superhydrophobic surfaces.

Polymer System Based on Polyethylene Glycol and TFE Telomers for Producing Films with Switchable Wettability.

Today a lot of attention is paid to the formation of thermosensitive systems for biomedical and industrial applications. The development of new methods for synthesis of such systems is a dynamically developing direction in chemistry and materials science. In this regard, this paper presents results of the studies of a new synthesized supramolecular polymer system based on polyethylene glycol and tetrafluoroethylene telomers. The films formed from the polymer substance have the property of switching wettability depending on temperature after heating activation. It has been established that the wettability changes at 60 °C. The contact angle of activated hydrophobic polymer film reaches 143°. Additionally, the system exhibits its properties regardless of the pH of the environment. Based on data obtained by the methods of infrared and x-ray photoelectron spectroscopy, differential thermal analysis and thermal analysis in conjunction with wettability and morphology, a model of the behavior of molecules in a polymer system was built that ensures switching of the hydrophilic/hydrophobic surface state. The resulting polymer system, as well as films based on it, can be used in targeted drug delivery, implantation surgery, as sensors, etc.

Characterization of nanoscale pinhole defects in hydrophobic coatings using copper electrodeposition

Thin (∼ 100 nm thick) hydrophobic polymer films are used in a plethora of applications where water repellency is required. However, hydrophobic film implementation in industry is limited due to poor durability. Thin hydrophobic film blistering during condensation has been identified as one of the main mechanisms associated with failure. Yet, disagreement exists about the source of blister initiation. Furthermore, there is a lack of understanding about the physical defects or pinholes that facilitate vapor penetration pathways through thin hydrophobic films. These pinholes govern the nucleation of blisters on the interface between the hydrophobic polymer and metal substrate. Here, we use metal electrodeposition as a means to characterize these intrinsic pinholes in thin hydrophobic polymers. A facile method is demonstrated to locate pinholes and measure pinhole density on CFx and poly(2-chloro-p-xylylene) (Parylene C) films. Our work not only helps to understand the intrinsic defects associated with film deposition, it also provides design guidelines for the selection and development of efficient thin film hydrophobic coatings.

ENERGY- AND RESOURCE-SAVING PROCESSES INVOLVING THE POLYMER PHASE

The paper deals with the processes of application and production of various polymer materials. By coating the surface of mineral fertilizer granules with hydrophobic polymer films, fertilizers with controlled release of nutrient components were obtained. Such fertilizers can prevent the leaching of nutrients, prevent the negative impact on the environment and reduce fertilizer consumption. Methods for calculating the particle distribution function by the degree of coating characterizing the uniformity of coating on fluidized bed particles for stationary and non-stationary modes of operation of the apparatus are considered. The process of applying a thick composite coating to the surface of urea granules in a pan granulator was also investigated. A simple method for calculating the size distribution of the obtained granules with a composite shell is proposed. The actual problem of developing a method for predicting the kinetics of nutrient release from polymer-coated fertilizer granules based on a fairly simple mathematical model of the process has been solved. Studies of the combined polymerization and drying process in the synthesis of polyacrylamide and sodium methacrylate copolymer with methacrylic acid amide have shown that its use at the final stage of obtaining water-soluble acrylic polymers is very effective. This technique allows to reduce the total time of the technological cycle. The process of obtaining polyethylene powder by the method of elastic-deformation grinding of polymer gel and a two-stage process of solvent removal from polymer powder with the return of the solvent to the technological cycle has been developed. The rational technological parameters of the electrodialysis process of contaminated steam condensate of mineral fertilizers plant have been identified, which allows to obtain a more concentrated salt solution, which is used as a secondary raw material, as well as a desalinated solution used as process water. For citation: Lipin A.G., Lipin A.A. Energy- and resource-saving processes involving the polymer phase. ChemChemTech [Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol.]. 2023. V. 66. N 7. P. 203-213. DOI: 10.6060/ivkkt.20236607. 6836j.

Autonomous Self-healable Scratch-free Bilayer Anti-corrosion Film

Thin hydrophobic polymer film, which physically prevents an approach of corrosive media, has been widely used as an anti-corrosion coating for metals. Though polymer film effectively passivates surface of metal, it loses its anti-corrosion property once the film is peeled off by physical damage, such as scratches. Corrosion can be propagated from the exposed area even if the area is small. Therefore, for long-term anti-corrosion, the film should be seamless and completely cover the entire metal surface without scratches. In this study, we introduce an autonomously self-healable hydrophobic coating with superior anti-corrosion property by a combination of self-healable/fluorinated polymers. Schiff-base linkages based polydimethylsiloxane (SC-PDMS) is used as a primary protection layer against corrosive media. The SC-PDMS matrix with the dynamic imine bonds allows scratch-free metal protection layer by reproducible damage healing property. In addition, we applied polytetrafluoroethylene (PTFE) thin film at the surface of the SC-PDMS, which suppresses the reaction of imine bond with water and helps to maintain long-term anti-corrosion property. Eventually, this simple coating of bilayer structure with SC-PDMS and PTFE shows an effective scratch-free corrosive resistance, providing a new way of long-term use of metals.

Biomimetic Rose Petal Structures Obtained Using UV-Nanoimprint Lithography.

This study aims to produce a hydrophobic polymer film by mimicking the hierarchical micro/nanostructures found on the surface of rose petals. A simple and two-step UV-based nanoimprint lithography was used to copy rose petal structures on the surface of a polyurethane acrylate (PUA) film. In the first step, the rose petal was used as a template, and its negative replica was fabricated on a commercial UV-curable polymer film. Following this, the negative replica was used as a stamp to produce rose petal mimetic structures on UV curable PUA film. The presence of these structures on PUA influenced the wettability behavior of PUA. Introducing the rose petal mimetic structures led the inherently hydrophilic material to display highly hydrophobic behavior. The neat PUA film showed a contact angle of 65°, while the PUA film with rose petal mimetic structures showed a contact angle of 138°. Similar to natural materials, PUA with rose petal mimetic structures also displayed the water pinning effect. The water droplet was shown to have adhered to the surface of PUA even when the surface was turned upside down.

Surface Acoustic Wave Humidity Sensor Based on Hydrophobic Polymer Film

Surface Acoustic Wave Humidity Sensor Based on Hydrophobic Polymer Film

Outside Front Cover: Plasma Process. Polym. 7/2022

Outside Front Cover: Antibacterial activity based on the generation of reactive oxygen species (ROS) has been investigated. A doped metal oxide catalyst deposited by sputtering was postoxidized and covered by a hydrophobic plasma polymer film, allowing diffusion of water and ROS. Rapid bacterial inhibition was observed even during storage in the dark, which can be reactivated by light exposure. The developed multifunctional coating can be deposited on various materials including polymers such as catheters or nonwovens. Further details can be found in the article by Dirk Hegemann, Barbara Hanselmann, Flavia Zuber, Fei Pan, Sandra Gaiser, Patrick Rupper, Katharina Maniura-Weber, Kurt Ruffixseux, and Qun Ren (e2100246)

Characterization of critical roughness indicators by digital image processing to predict contact angles on hydrophobic surfaces

This study innovatively applies digital imaging techniques to quantify the irregular nanoscale roughness of the surfaces of plasma-etched, hydrophobic polymer films. The main objective is to verify meaningful roughness indicators that predict the surface wettability by quantifying the surface nanostructures in a simple way. Five texture parameters were extracted from SEM images by box-counting and a gray-level co-occurrence matrix (GLCM) algorithm, which together provide 2D spatial information of roughness features. Also, five parameters related to height and aspect ratio profiles of roughness were obtained using AFM analysis. The 2D texture parameters and AFM roughness profiles were statistically correlated, and either set could be used to predict surface wettability with high explanatory power. The prediction was most powerful when variables of fractal dimension, arithmetic mean height Ra of roughness features in the assessed area, and skewness Rsk of height in the assessed area were used in the regression model. This result indicates that both the height profile and 2D spatial distribution of roughness features strongly affect surface wettability. The correlation of gray levels with the neighboring pixels was statistically correlated with Ra and Rsk, and a simple predictive model was developed using fractal dimension and correlation. This research is significant in that it explored a novel analytical approach in assessing the roughness characteristics to predict surface wettability. Ultimately, we anticipate that the developed approach can be applied in designing relevant process parameters to control the wetting properties.

Plasma‐deposited AgOx‐doped TiOx coatings enable rapid antibacterial activity based on ROS generation

AbstractTo enable a rapid‐acting antibacterial mechanism without the release of biocidal substances, TiO2 catalysts have been considered based on the generation of reactive oxygen species (ROS). Doping with dissimilar metals generates electron‐hole pairs with narrow band gaps promoting the production of ROS. Here, plasma technology is investigated to deposit Ag nano islets on defective TiOx films, stabilized by plasma postoxidation suppressing Ag ion release. Importantly, ROS generation is maintained upon storage in the dark yet with diminishing efficacy; however, it can be restored by exposure to visible light. The rapid‐acting antibacterial properties are found to strongly correlate with ROS generation, which can even be maintained by functionalization with hydrophobic plasma polymer films. The cytocompatible coatings offer promising applications for implants and other medical devices.

Improving lifetime of organic light-emitting diodes using hydrophobic films as passivation layers

In this work, we have optimized the passivation process to improve the lifetime and reliability of organic light-emitting diode (OLED) devices. A hydrophobic polymer (HPP) was used as the passivation layer and characteristics of the optimized OLED devices with the film were investigated. The HPP films exhibited excellent permeating barrier properties toward water because they were hydrophobic and had low surface energy. In addition, in OLEDs, the HPP films prevented darkspot growth on the emitting area.

Foldable and washable textile-based OLEDs with a multi-functional near-room-temperature encapsulation layer for smart e-textiles

Wearable electronic devices are being developed because of their wide potential applications and user convenience. Among them, wearable organic light emitting diodes (OLEDs) play an important role in visualizing the data signal processed in wearable electronics to humans. In this study, textile-based OLEDs were fabricated and their practical utility was demonstrated. The textile-based OLEDs exhibited a stable operating lifetime under ambient conditions, enough mechanical durability to endure the deformation by the movement of humans, and washability for maintaining its optoelectronic properties even in water condition such as rain, sweat, or washing. In this study, the main technology used to realize this textile-based OLED was multi-functional near-room-temperature encapsulation. The outstanding impermeability of TiO2 film deposited at near-room-temperature was demonstrated. The internal residual stress in the encapsulation layer was controlled, and the device was capped by highly cross-linked hydrophobic polymer film, providing a highly impermeable, mechanically flexible, and waterproof encapsulation.

Design Considerations to Facilitate Clinical Radiological Evaluation of Implantable Biomedical Structures.

Clinical effectiveness of implantable medical devices would be improved with in situ monitoring to ensure device positioning, determine subsequent damage, measure biodegradation, and follow healing. While standard clinical imaging protocols are appropriate for diagnosing disease and injury, these protocols have not been vetted for imaging devices. This study investigated how radiologists use clinical imaging to detect the location and integrity of implanted devices and whether embedding nanoparticle contrast agents into devices can improve assessment. To mimic the variety of devices available, phantoms from hydrophobic polymer films and hydrophilic gels were constructed, with and without computed tomography (CT)-visible TaOx and magnetic resonance imaging (MRI)-visible Fe3O4 nanoparticles. Some phantoms were purposely damaged by nick or transection. Phantoms were implanted in vitro into tissue and imaged with clinical CT, MRI, and ultrasound. In a blinded study, radiologists independently evaluated whether phantoms were present, assessed the type, and diagnosed whether phantoms were damaged or intact. Radiologists identified the location of phantoms 80% of the time. However, without incorporated nanoparticles, radiologists correctly assessed damage in only 54% of cases. With an incorporated imaging agent, the percentage jumped to 86%. The imaging technique which was most useful to radiologists varied with the properties of phantoms. With benefits and drawbacks to all three imaging modalities, future implanted devices should be engineered for visibility in the modality which best fits the treated tissue, the implanted device's physical location, and the type of required information. Imaging protocols should also be tailored to best exploit the properties of the imaging agents.

Methods of transferring two-dimensional materials

The advent of two-dimensional (2D) materials, a family of materials with atomic thickness and van der Waals (vdWs) interlayer interactions, offers a new opportunity for developing electronics and optoelectronics. For example, semiconducting 2D materials are promising candidates for extending the Moore's Law. Typical 2D materials, such as graphene, hexagonal boron nitride (h-BN), black phosphorus (BP), transition metal dichalcogenides (TMDs), and their heterostrcutures present unique properties, arousing worldwide interest. In this review the current progress of the state-of-the-art transfer methods for 2D materials and their heterostructures is summarized. The reported dry and wet transfer methods, with hydrophilic or hydrophobic polymer film assistance, are commonly used for physical stacking to prepare atomically sharp vdWs heterostructure with clear interfaces. Compared with the bottom-up synthesis of 2D heterostructures using molecular beam epitaxy (MBE) or chemical vapor deposition (CVD), the construction of 2D heterostructures by transfer methods can be implemented into a curved or uneven substrate which is suitable for pressure sensing, piezoelectric conversion as well as other physical properties’ research. Moreover, the transfer of 2D materials with inert gas protected or in vacuum operation can protect moisture-sensitive and oxygen-sensitive 2D materials from degerating and also yield interfaces with no impurities. The efficient and non-destructive large-area transfer technology provides a powerful technical guarantee for constructing the 2D heterostructures and exploring the intrinsic physical and chemical characteristics of materials. Further development of transfer technology can greatly facilitate the applications of 2D materials in high-temperature superconductors, topological insulators, low-energy devices, spin-valley polarization, twistronics, memristors, and other fields.

Hydrophobically modified water-based polymer for slow-release urea formulation

To enhance the performance of water-based polymer-coated fertilizers and to minimize the environmental pollution caused by fertilizer overuse, a series of nano-SiO2 and water-based polymer were used to fabricate nano-modified water-based polymer-films (NW) at various temperatures and for various reaction times. Both nano-SiO2 and 1H,1H,2H,2H-perfluorooctyltriethoxysilane were used to modify the water-based polymer to prepare a biomimetic hydrophobic water-based polymer (BW) film. Water absorption, water contact angles (WCAs) and permeability experiments were used to evaluate the hydrophobic performance of films. The mechanical, chemical composition and morphological properties were determined and compared to explain the formation mechanism of the hydrophobic structures. A soil leaching test was also conducted to evaluate the nitrogen (N)-release characteristics of the coated urea. This study demonstrated that after modification, the water absorbency was decreased from 150.2 % to 21.4 %, the WCAs and tensile strength (TS) were increased from 33.3° to 120.9° and 26.21 kPa to 36.72 kPa, respectively. The urea coated with BW8 coating material exhibited an excellent release behavior of 87.52 % on the 56th day. Therefore, our work highlights the substantial potential of biomimetic hydrophobic water-based polymer coated urea (BCU) for modern agriculture.

New Approaches to the Preparation of Nanocomposite Proton Exchange Membranes for Fuel Cells

Experimental results on the development of two original approaches to obtaining new nanocomposite proton exchange membranes for low-temperature fuel cells are generalized. The first approach consists in in situ modification of the transport channels of commercial proton exchange membranes of the Nafion brand with interpenetrating polymer networks of the introduced polyelectrolyte based on cross-linked polystyrene sulfonate. The second approach is to create a proton exchange nanoscale phase based on polystyrene sulfonate in commercial hydrophobic polymer films. Polystyrene sulfonate is formed during thermal polymerization of styrene sorbed in the films without using ionizing radiation, followed by sulfonation. The influence of the conditions for obtaining membranes on the composition, morphology, transport properties, and results of testing the membranes in low-temperature fuel cells is considered.

Humidity-Resistive Optical NO Gas Sensor Devices Based on Cobalt Tetraphenylporphyrin Dispersed in Hydrophobic Polymer Matrix.

We report on an optical nitrogen oxide (NO) gas sensor device using cobalt tetraphenylporphyrin (CoTPP) dispersed in three kinds of hydrophobic polymer film matrix (polystyrene (PSt), ethylcellulose (EC), and polycyclohexyl methacrylate (PCHMA)) to improve humidity resistance. Our approach is very effective because it allows us to achieve not only high humidity resistance, but also a more than sixfold increase in sensitivity compared with CoTPP film due to the high dispersion of CoTPP in the polymer film. The limit of detection was calculated as 33 ppb for the CoTPP-dispersed EC film, which is lower than that of CoTPP film (92 ppb).

Lectins at Interfaces-An Atomic Force Microscopy and Multi-Parameter-Surface Plasmon Resonance Study.

Lectins are a diverse class of carbohydrate binding proteins with pivotal roles in cell communication and signaling in many (patho)physiologic processes in the human body, making them promising targets in drug development, for instance, in cancer or infectious diseases. Other applications of lectins employ their ability to recognize specific glycan epitopes in biosensors and glycan microarrays. While a lot of research has focused on lectin interaction with specific carbohydrates, the interaction potential of lectins with different types of surfaces has not been addressed extensively. Here, we screen the interaction of two specific plant lectins, Concanavalin A and Ulex Europaeus Agglutinin-I with different nanoscopic thin films. As a control, the same experiments were performed with Bovine Serum Albumin, a widely used marker for non-specific protein adsorption. In order to test the preferred type of interaction during adsorption, hydrophobic, hydrophilic and charged polymer films were explored, such as polystyrene, cellulose, N,-N,-N-trimethylchitosan chloride and gold, and characterized in terms of wettability, surface free energy, zeta potential and morphology. Atomic force microscopy images of surfaces after protein adsorption correlated very well with the observed mass of adsorbed protein. Surface plasmon resonance spectroscopy studies revealed low adsorbed amounts and slow kinetics for all of the investigated proteins for hydrophilic surfaces, making those resistant to non-specific interactions. As a consequence, they may serve as favorable supports for biosensors, since the use of blocking agents is not necessary.