Initiated Chemical Vapor Deposition Research Articles

Antimicrobial polymeric coatings synthesized by solvent-free initiated Chemical Vapor Deposition: A review

Microbial adhesion on surfaces may cause infectious diseases that seriously threaten human health, which can be controlled by antimicrobial surfaces. Antimicrobial polymeric coatings can endow surfaces with biocidal properties to address infectious diseases. Initiated Chemical Vapor Deposition (iCVD) is a novel technique to synthesize high-quality polymeric antimicrobial coatings on various surfaces. Owing to the solvent-free and mild deposition conditions, iCVD facilitates solvent-susceptible, delicate, or fragile substrates. Herein, we provided a comprehensive review of antimicrobial coatings fabricated by iCVD. First, iCVD was introduced. Then, antimicrobial iCVD coatings were discussed based on killing and antifouling strategies. The microbe-killing coatings were discussed according to release-killing and contact-killing approaches. Next, hydrophilic, hydrophobic, and amphiphilic antifouling coatings were reviewed. Finally, micro/nano-structured antimicrobial surfaces fabricated via iCVD were also discussed, followed by the future directions of iCVD coatings in the antimicrobial field.

Micropatterned Polymer Nanoarrays with Distinct Superwettability for a Highly Efficient Sweat Collection and Sensing Patch.

Wearable sweat sensor offers a promising means for noninvasive real-time health monitoring, but the efficient collection and accurate analysis of sweat remains challenging. One of the obstacles is to precisely modulate the surface wettability of the microfluidics to achieve efficient sweat collection. Here a facile initiated chemical vapor deposition (iCVD) method is presented to grow and pattern polymer nanocone arrays with distinct superwettability on polydimethylsiloxane microfluidics, which facilitate highly efficient sweat transportation and collection. The nanoarray is synthesized by manipulating monomer supersaturation during iCVD to induce controlled nucleation and preferential vertical growth of fluorinated polymer. Subsequent selective vapor deposition of a conformal hydrogel nanolayer results in superhydrophilic nanoarray floor and walls within the microchannel that provide a large capillary force and a superhydrophobic ceiling that drastically reduces flow friction, enabling rapid sweat transport along varied flow directions. A carbon/hydrogel/enzyme nanocomposite electrode is then fabricated by sequential deposition of highly porous carbon nanoparticles and hydrogel nanocoating to achieve sensitive and stable sweat detection. Further encapsulation of the assembled sweatsensing patch with superhydrophobic nanoarray imparts self-cleaning and water-proof capability. Finally, the sweat sensing patch demonstrates selective and sensitive glucose and lactate detection during the on-body test.

Influence of Silsesquioxane-Containing Ultra-Thin Polymer Films on Metal Oxide Gas Sensor Performance for the Tunable Detection of Biomarkers

Certain biomarkers in exhaled breath are indicators of diseases in the human body. The non-invasive detection of such biomarkers in human breath increases the demand for simple and cost-effective gas sensors to replace state-of-the-art gas chromatography (GC) machines. The use of metal oxide (MOX) gas sensors based on thin-film structures solves the current limitations of breath detectors. However, the response at high humidity levels, i.e., in the case of exhaled human breath, significantly decreases the sensitivity of MOX sensors, making it difficult to detect small traces of biomarkers. We have introduced, in previous work, the concept of a hybrid gas sensor, in which thin-film-based MOX gas sensors are combined with an ultra-thin (20–30 nm) polymer top layer deposited by solvent-free initiated chemical vapor deposition (iCVD). The hydrophobic top layer enables sensor measurement in high-humidity conditions as well as the precise tuning of selectivity and sensitivity. In this paper, we present a way to increase the hydrogen (H2) sensitivity of hybrid sensors through chemical modification of the polymer top layer. A poly(1,3,5,7-tetramethyl-tetravinylcyclotetrasiloxane) (PV4D4) thin film, already applied in one of our previous studies, is transformed into a silsesquioxane-containing top layer by a simple heating step. The transformation results in a significant increase in the gas response for H2 ~709% at an operating temperature of 350 °C, which we investigate based on the underlying sensing mechanism. These results reveal new pathways in the biomedical application field for the analysis of exhaled breath, where H2 indicates gastrointestinal diseases.

Ultrafast Humidity Sensing Layers Made by Two‐Photon Polymerization and Initiated Chemical Vapor Deposition

AbstractHumidity sensors are used in many applications. The design of fast sensors that can operate in explosive environments is a difficult task. Therefore, current research efforts aim at combining reliability, sensitivity and high sensing speed. The use of structured ultrathin hydrogels perfectly meets these requirements. Nanostructures are directly fabricated with a two‐photon‐polymerisation (2PP) 3D printer to use them as templates for hydrogels. After the 3D printing multiple templates are coated with ultrathin films of poly(2‐hydroxyethyl‐methacrylate) (pHEMA) using initiated chemical vapor deposition (iCVD). p(HEMA) is a humidity responsive hydrogel which changes its thickness by orders of magnitude depending on the ambient conditions. The 3D printed structures are optimized to give both a fast response time, and an optical read‐out method for visible wavelengths. Upon hydrogel swelling, the height of the nanostructure pillars increases, keeping their periodicity constant. This induces a change in intensity of the first ‐order refraction peak, which can be easily measured also at low humidity levels. The humidity response of the nanostructures is measured and an influence for different hydrogel thicknesses and humidity flow rates is observed. The ultrathin film with the lowest thickness of 50 nm shows the fastest response to relative humidity, which is much faster than commercial sensors with 8 s response time.

Tuning the Selectivity of Metal Oxide Gas Sensors with Vapor Phase Deposited Ultrathin Polymer Thin Films.

Metal oxide gas sensors are of great interest for applications ranging from lambda sensors to early hazard detection in explosive media and leakage detection due to their superior properties with regard to sensitivity and lifetime, as well as their low cost and portability. However, the influence of ambient gases on the gas response, energy consumption and selectivity still needs to be improved and they are thus the subject of intensive research. In this work, a simple approach is presented to modify and increase the selectivity of gas sensing structures with an ultrathin polymer thin film. The different gas sensing surfaces, CuO, Al2O3/CuO and TiO2 are coated with a conformal < 30 nm Poly(1,3,5,7-tetramethyl-tetravinyl cyclotetrasiloxane) (PV4D4) thin film via solvent-free initiated chemical vapor deposition (iCVD). The obtained structures demonstrate a change in selectivity from ethanol vapor to 2-propanol vapor and an increase in selectivity compared to other vapors of volatile organic compounds. In the case of TiO2 structures coated with a PV4D4 thin film, the increase in selectivity to 2-propanol vapors is observed even at relatively low operating temperatures, starting from >200 °C. The present study demonstrates possibilities for improving the properties of metal oxide gas sensors, which is very important in applications in fields such as medicine, security and food safety.

Vapor-based fabrication of PEDOT coating for wearable strain sensors with excellent sensitivity and self-cleaning capability

Poly(3,4-ethylenedioxythiophene) (PEDOT) coating is advantageous in constructing flexible sensors, due to its good flexibility, high conductivity, and excellent physical and chemical stability. Traditional solution-based coating methods, however, are difficult to retain the micro- and nanostructures of the substrates, thus decreasing the sensitivity of the resulted sensors. In this work, we prepared superhydrophobic (SHB) strain sensors using a piezoresistive composite made from consecutive vapor deposition of conformal polymer coatings, i.e. PEDOT and poly(perfluorodecyl acrylate-co-ethylene glycol diacrylate) on fabrics using oxidative and initiated chemical vapor deposition methods. Compared with the pristine fabric sample, the composite materials displayed significantly improved initial currents, which are attributed to more conductive paths created by PEDOT coating. The resulted strain sensor displayed great flexibility, large sensitivity, wide sensing range, and excellent reliability. Furthermore, the sensor has been successfully employed to monitor various human motions in real time. The hydrophobic outer layer endows the sensor self-cleaning and durability capacities, indicating possible applications under harsh environment.

Tunable and Reconfigurable Logic Gates With Electrolyte-Gated Transistor Array Co-Integrated With Neuromorphic Synapses

A tunable and reconfigurable logic gates based on an electrolyte-gated transistor (EGT) array are co-integrated with neuromorphic synapses. The tunable and reconfigurable operations of the various logic gates are controlled by analog conductance modulation with nonvolatility of the fabricated EGT. The EGT array was uniformly fabricated on an entire 4-in wafer with the aid of CMOS compatible processes. Initiated-chemical vapor deposition (i-CVD) method was adopted for the deposition of the ultrathin polyethylene glycol dimethacrylate (pEGDMA) electrolyte layer. Therefore, the logic gates could be co-integrated with synaptic devices on the same in-plane substrate for integrability. Basic inverter operation with switching threshold tunability ranging from −1 to +1 V was demonstrated with good operational stability. In addition, NAND and NOR gate operations were realized by modulating the conductance level of a specified cell in the array configuration.

59‐3: A Thin, Transparent Encapsulation Film with Excellent Gap‐filling Performance for Ultra‐High‐Resolution OLEDs via Vapor‐phase Deposited Polymeric Layer

A thin polymer film was developed by vapor‐phase deposition method, termed initiated chemical vapor deposition (iCVD) that can replace the inkjet process. The thin polymer film was integrated together with the PECVD SiNx layers to form a high performance thin film encapsulation (TFE) layer for ultra‐high resolution OLEDs, featured by excellent gap‐filling properties, full transparency in whole visible light region, and minimal shadow effect.

One‐Step Bottom‐Up Growth of Highly Liquid Repellent Worm‐Like Surfaces on Planar Substrates

AbstractHighly liquid repellent (superhydrophobic, superoleophobic) surfaces are fabricated using mostly top‐down approaches and liquid‐based processing. Top‐down approaches, like lithography and templating, are highly process‐intensive, while liquid‐based processing, like etching and fluoropolymer solution coating, rely on solvents that often damage the substrate. Ultimately, to suppress liquids from spreading, the goal is to create a surface with low surface energy and a hierarchically roughened topology. Here, a bottom‐up approach that achieves these two prerequisite criteria in one single step is demonstrated. Relying on a liquid‐free initiated chemical vapor deposition (iCVD) process, worm‐like protrusions of a semicrystalline fluoropolymer (poly(perfluorodecyl acrylate)) directly grow on flat substrates without prior surface pretreatment. The nano/microworm surfaces display super‐liquid repellency (&gt;150° contact angle) to water and oil. Worm formation (as opposed to conformal thin film formation) is attributed to preferential crystal nucleation, orientation, and growth on the substrate plane.

Surface Modification of Stainless-Steel Membrane using a Closed-Batch iCVD Reactor for Oil/Water Separation

Oil-spill is one of the major global issues facing society in this century. The aim of this study was to develop a steel-based membrane for selective separation of oil from oil/water mixture. For this purpose, a single-step, rapid and environmentally friendly closed-batch initiated chemical vapor deposition (iCVD) method was employed to deposit hydrophobic thin film on a stainless-steel mesh. Perfluorodecyl acrylate (PFDA) and tert-butyl peroxide (TBPO) were used as monomer and initiator, respectively. Owing to the inherent vapor-based nature of iCVD method provided excellent conformal coverage on the mesh with high durability. iCVD coated mesh showed 96% oil/water separation efficiency. Highly reproducible results were obtained when the oil/water separation experiments were repeated.

A Versatile Surface Modification Method via Vapor-phase Deposited Functional Polymer Films for Biomedical Device Applications.

For last two decades, the demand for precisely engineered three-dimensional structures has increased continuously for the developments of biomaterials. With the recent advances in micro- and nano-fabrication techniques, various devices with complex surface geometries have been devised and produced in the pharmaceutical and medical fields for various biomedical applications including drug delivery and biosensors. These advanced biomaterials have been designed to mimic the natural environments of tissues more closely and to enhance the performance for their corresponding biomedical applications. One of the important aspects in the rational design of biomaterials is how to configure the surface of the biomedical devices for better control of the chemical and physical properties of the bioactive surfaces without compromising their bulk characteristics. In this viewpoint, it of critical importance to secure a versatile method to modify the surface of various biomedical devices. Recently, a vapor phase method, termed initiated chemical vapor deposition (iCVD) has emerged as damage-free method highly beneficial for the conformal deposition of various functional polymer films onto many kinds of micro- and nano-structured surfaces without restrictions on the substrate material or geometry, which is not trivial to achieve by conventional solution-based surface functionalization methods. With proper structural design, the functional polymer thin film via iCVD can impart required functionality to the biomaterial surfaces while maintaining the fine structure thereon. We believe the iCVD technique can be not only a valuable approach towards fundamental cell-material studies, but also of great importance as a platform technology to extend to other prospective biomaterial designs and material interface modifications for biomedical applications.

One-step vapor deposition of fluorinated polycationic coating to fabricate antifouling and anti-infective textile against drug-resistant bacteria and viruses.

The ongoing pandemic caused by the novel coronavirus has turned out to be one of the biggest threats to the world, and the increase of drug-resistant bacterial strains also threatens the human health. Hence, there is an urgent need to develop novel anti-infective materials with broad-spectrum anti-pathogenic activity. In the present study, a fluorinated polycationic coating was synthesized on a hydrophilic and negatively charged polyester textile via one-step initiated chemical vapor deposition of poly(dimethyl amino methyl styrene-co-1H,1H,2H,2H-perfluorodecyl acrylate) (P(DMAMS-co-PFDA), PDP). The surface characterization results of SEM, FTIR, and EDX demonstrated the successful synthesis of PDP coating. Contact angle analysis revealed that PDP coating endowed the polyester textile with the hydrophobicity against the attachment of different aqueous foulants such as blood, coffee, and milk, as well as the oleophobicity against paraffin oil. Zeta potential analysis demonstrated that the PDP coating enabled a transformation of negative charge to positive charge on the surface of polyester textile. The PDP coating exhibited excellent contact-killing activity against both gram-negative Escherichia coli and gram-positive methicillin-resistant Staphylococcus aureus, with the killing efficiency of approximate 99.9%. In addition, the antiviral capacity of PDP was determined by a green fluorescence protein (GFP) expression-based method using lentivirus-EGFP as a virus model. The PDP coating inactivated the negatively charged lentivirus-EGFP effectively. Moreover, the coating showed good biocompatibility toward mouse NIH 3T3 fibroblast cells. All the above properties demonstrated that PDP would be a promising anti-pathogenic polymeric coating with wide applications in medicine, hygiene, hospital, etc., to control the bacterial and viral transmission and infection.

Solvent-Free Fabrication of Self-Regenerating Antibacterial Surfaces Resisting Biofilm Formation.

Biofilm formation on indwelling medical devices is a major cause of hospital-acquired infections. Monofunctional antibacterial surfaces have been developed to resist the formation of biofilms by killing bacteria on contact, but the adsorption of killed bacterial cells and debris gradually undermines the function of these surfaces. Here, we report a facile approach to produce an antibacterial surface that can regenerate its function after contamination. The self-regenerating surface was achieved by sequential deposition of alternating antibacterial and biodegradable layers of coating using a solvent-free initiated chemical vapor deposition method. As the top antibacterial layer gradually loses its killing ability due to the accumulation of debris, the underlying biodegradable layer degrades, shedding off the top surface layers and exposing another fresh antibacterial surface. Urinary catheters coated with monofunctional and self-regenerating antibacterial coatings both showed more than 99% bacterial killing ability at the initial antibacterial test, but the monofunctional surface lost its killing ability after continued exposure to concentrated bacterial solution, whereas the self-regenerating surfaces regained strong bacterial killing ability after prolonged exposure. Employing poly(methacrylic anhydride) and its copolymers with varied composition as the degrading layer, the degradation kinetics can be well-tailored and the self-regeneration duration spanned from minutes to days. The designed self-regenerating antibacterial surfaces could provide an effective approach to resist biofilm formation and extend the service life of indwelling medical devices.

Rational design of vapor‐deposited self‐crosslinking polymer for transparent flexible oxygen barrier coatings

AbstractTransparent flexible barrier coatings consisting of a copolymer of 2‐isocyanatoethyl methacrylate and 4‐aminostyrene were fabricated using a facile vapor‐based initiated chemical vapor deposition (iCVD) method. The isocyanate and amino groups were well reserved during deposition and reacted on the substrate surface, inducing self‐crosslinking. The resultant coating showed a fairly smooth pinhole‐free surface with more than 99% light transmittance across the visible range. With a proper compositional ratio, the synthesized coating demonstrated oxygen permeability 26 and 8 times lower than commercial PET and PVDF barrier films, respectively. The achieved barrier performance is attributed to the designed molecular structure, where interchain crosslinks are produced between a combination of both rigid and flexible side chains. Such combination enabled efficient packing of space while avoiding loose structures with low permeation resistance. The crosslinked network with rather flexible urea linkages also imparted excellent mechanical strength and high flexibility to the coating. Furthermore, the reported method is compatible with current industrial manufacturing process, thus expecting great potential in flexible electronics encapsulation.

Solvent-free fabrication of tough self-crosslinkable short-fluorinated copolymer nanocoatings for ultradurable superhydrophobic fabrics

• Tough short-fluorinated nanocoatings were fabricated by solvent-free iCVD. • Isocyanate chemistry induced self-crosslinking and fixated surface fluorinated chains. • Self-crosslinking enabled excellent dynamic water repellency and mechanical strength. • Conformal nanocoating imparted fabrics ultradurable superhydrophobicity. As long-perfluorinated side chain polymers are phasing out due to healthy and environmental concerns, short-fluorinated polymers are garnering increasing attention as a substitute for superhydrophobic coatings. Challenges, however, are to be addressed due to the poor dynamic water repellency and unsatisfactory durability of short-fluorinated polymer coatings. This work reports the fabrication of self-crosslinkable poly(perfluorohexylethyl acrylate- co -isocyanato ethyl methacrylate) nanocoating with good dynamic water repellency and high mechanical strength using a solvent-free initiated chemical vapor deposition (iCVD) method. The employment of highly reactive isocyanate groups in the coating not only facilitated covalent binding with functional groups on the substrate surface, but also enabled self-crosslinking reactions in the presence of water vapor. Crosslinking immobilized the fluorinated chains on the surface, thus alleviating the contact angle hysteresis. The crosslinked network also significantly improved the mechanical strength of the coating. Without affecting fabric morphology, the coating enabled superhydrophobicity of different fabrics with water sliding angle as low as 3˚. Such superhydrophobicity was well maintained after various harsh durability tests, including sandpaper abrasion for up to 20,000 cm, ultrasonication and boiling for more than 12 h, etc. The achieved durability was attributed to the enhanced adhesion strength and excellent mechanical property of the coating. This work thus paves a novel way towards eco-friendly fabrication of durable superhydrophobic fabrics.

Fabrication, characterization and cytocompatibility assessment of gelatin nanofibers coated with a polymer thin film by initiated chemical vapor deposition.

The presence of various functional groups in the structure of gelatin nanofibers (GNFs) has made it a suitable candidate for biomedical applications, yet its fast dissolution in aqueous media has been a real challenge for years. In the present work, we propose an efficient procedure to improve the durability of the GNFs. The electrospun GNFs were coated with poly(ethylene glycol dimethacrylate) (pEGDMA) using initiated chemical vapor deposition (iCVD) as a completely dry polymerization method. Morphological and chemical analysis revealed that an ultrathin layer formed around nanofibers (iCVD-GNFs) which has covalently bonded to gelatin chains. Against the instant dissolution of GNFs, the in vitro biodegradability test showed the iCVD-GNFs, to a large extent, preserve their morphology after 14days of immersion and did not lose its integrity even after 31days. In vitro cell culture studies, also, revealed cytocompatibility of the iCVD-GNFs for human fibroblast cells (hFC), as well as higher cell proliferation on the iCVD-GNFs compared to control made from tissue culture plate (TCP). Furthermore, contact angle measurements indicated that the hydrophilic GNFs became hydrophobic after the iCVD, yet FE-SEM images of cell-seeded iCVD-GNFs showed satisfactory cell adhesion. Taken together, the proposed method paves a promising way for the production of water-resistant GNFs utilized in biomedical applications; for instance, tissue engineering scaffolds and wound dressings.

Roll-to roll initiated chemical vapor deposition of super hydrophobic thin films on large-scale flexible substrates

In this study, a large-scale roll-to-roll initiated chemical vapor deposition (iCVD) system was developed to allow for coating superhydrophobic thin films on flexible substrates. Poly(hexafluorobutyl acrylate), which possesses a short fluorinated side-chain, was chosen as the hydrophobic finish material, while a commercial porous bamboo fabric was used as the flexible substrate. After iCVD coating, bamboo surface, which is superhydrophilic by its nature, transformed into a superhydrophobic with a water contact angle of 156° without changing its porous and flexible structure. Similar hydrophobic properties were observed against various daily liquids. Complete coverage of as-deposited films on both sides of bamboo surfaces was observed at very high roll speeds up to 225 mm/min, which allow coatings on 20 m2 flexible substrates in a single run. Large scale contact angle and chemical uniformity of coatings on fabric surfaces were evaluated using contact angle and XPS analyses.

Synthesis and characterization of thin film polyelectrolytes for solid-state lithium microbatteries

A critical challenge associated with the efficient fabrication of solid-state, three-dimensional microbatteries is the synthesis of conformal, solid-state thin film electrolytes. This study presents the synthesis of lithium ion conducting thin film polyelectrolytes based on poly(methacrylic acid-co-ethylene glycol diacrylate) using initiated chemical vapor deposition. These films are transformed to lithium-bearing polyelectrolytes through an H+/Li+ ion exchange reaction in a 1M LiOCH3 solution in methanol. Infrared spectroscopy of the vibrational stretching modes associated with the carbonyl bond in methacrylic acid confirmed that the ion exchange was successful, and quantification by x-ray photoelectron spectroscopy showed that ion exchange was nearly 100% complete. Incorporation of the crosslinking comonomer ethylene glycol diacrylate (EGDA) was necessary for physical stability of the film during the ion exchange process, and four polyelectrolyte compositions with varying crosslinking densities (ethylene glycol diacrylate content) were prepared to understand its role on ionic conductivity. The highest ionic conductivity was achieved in the polymer film with the lowest crosslinking density (9 mol. % EGDA); its conductivity was determined to be 6 × 10−9 S cm−1 at 20 °C and 1 × 10−5 S cm−1 at 100 °C. The activation energy for ionic conductivity was 0.88 eV. Using atomic force microscopy, the surfaces of thin film polyelectrolytes were shown to be continuous, smooth, and pinhole-free, suggesting that these films are suitable for integration into 3D microbatteries.

Initiated Chemical Vapor Deposition of Poly(Ethylhexyl Acrylate) Films in a Large-Scale Batch Reactor

The present study demonstrates the successful deposition of poly(ethylhexyl acrylate) thin films in a large-scale closed-batch initiated chemical vapor deposition (iCVD) system. A horizontal cylindrical stainless-steel vacuum tank, which is highly utilized in industrial vacuum applications, was used as iCVD reactor. The effects of substrate temperature, precursor ratio, and pressure on the deposition rates were studied, and the results showed that a deposition rate of 315 nm/min can be achieved in a single run at a reactor pressure of 600 mTorr. At a lower chamber pressure of 400 mTorr, deposition rate decreases, whereas film uniformity increases. By carrying out depositions at successive cycles, thicker films could be obtained, without the need for extensive monomer consumption. The yield percentage was found to be 3.5 for the films deposited in closed-batch system at 400 mTorr, which is 35-fold larger than that of the classical iCVD flow system.

Fast Optical Humidity Sensor Based on Hydrogel Thin Film Expansion for Harsh Environment.

With the application of a recently developed deposition method called initiated chemical vapor deposition (iCVD), responsive hydrogel thin films in the order of a few hundred nanometers were created. When in contact with humid air, the hydrogel layer increases its thickness considerably. The measurement of the thickness change was realized interferometrically with a laser and a broadband light source in two different implementations. The relative change in thickness with respect to humidity can be described with the Flory–Huggins theory. The required Flory–Huggins interaction parameter was determined for the actual hydrogel composition. The setup was designed without electric components in the vicinity of the active sensor layer and is therefore applicable in harsh environments such as explosive or corrosive ones. The implemented sensor prototype delivered reproducible relative humidity () values and the achieved response time for an abrupt change of the humidity s was about three times faster compared to one of the fastest commercially available sensors on the market.