1,721,023 research outputs found
Thermal studies on proton conductive copolymer thin films based on perfluoroacrylates synthesized by initiated Chemical Vapor Deposition
No full textThe thermal properties of ion-conductive materials are crucial for their use in temperature-sensitive applications such as polymer electrolyte fuel cells. In this study, 1H,1H,2H,2H,-perfluorodecyl acrylate and methacrylic acid (MAA) copolymers are synthesized by initiated Chemical Vapor Deposition. This method is a solvent-free thin film deposition technique, which allows for the preparation of polymers in distinct stoichiometric compositions. The chemical stability of the copolymers was investigated upon elevated temperatures along with other thermal properties. For this, experimental techniques such as infrared spectroscopy and ellipsometry were used. The data show that samples are chemically stable up to 150 °C, a point above which anhydride formation occurs, resulting in the loss of the conductive groups. A second order thermal transition was found at (95 ± 5) °C for polymers containing 20% MAA, which shifts towards higher temperatures as the MAA content increases. In addition, the water stability was tested. While the membranes show considerable water uptake (over 35% at 60% MAA content), mechanical stability is lacking, resulting in rupture formation and partial dissolution. A possible route to overcome this issue is found in crosslinking, with the addition of 15% ethylene glycol dimethacrylate providing sufficient stability to the polymer
Vapor-phase-synthesized fluoroacrylate polymer thin films: Thermal stability and structural properties
No full textIn this study, the thermal, chemical and structural stability of 1H,1H,2H,2H-perfluorodecyl acrylate polymers (p-PFDA) synthetized by initiated chemical vapor deposition (iCVD) were investigated. PFDA polymers are known for their interesting crystalline aggregation into a lamellar structure that induces super-hydrophobicity and oleophobicity. Nevertheless, when considering applications which involve chemical, mechanical and thermal stresses, it is important to know the limits under which the crystalline aggregation and the resulting polymer properties are stable. For this, chemical, morphological and structural properties upon multiple heating/cooling cycles were investigated both for linear PFDA polymers and for differently strong cross-linked alterations thereof. Heat treatment leaves the chemical composition of the linear PFDA polymers largely unchanged, while a more ordered crystalline structure with smoother morphology is observed. At the same time, the hydrophobicity and the integrity of the polymer deteriorate upon heating. The integrity and hydrophobicity of cross-linked p-PFDA films was preserved likely because of the lack of internal strain due to the coexistence of both crystalline and amorphous phases. The possibility to finely tune the degree of crosslinking can therefore expand the application portfolio in which PFDA polymers can be utilized
Smart surfaces by initiated chemical vapor deposition
Full text linkThe ability to modify the surface of materials with functional and responsive coatings is a powerful tool for the fabrication of smart devices for biotechnology, microfluidics, membrane technology, sensors and drug delivery systems. A recently developed method for the deposition of polymeric thin films, called initiated chemical vapor deposition (iCVD) is reviewed here. The authors will describe the high versatility of iCVD in driving application-specific properties into the material, creating a platform for the implementation of polymeric coatings into device fabrication. The significant impact of this polymerization technique lies in the possibility of obtaining polymers with chemical structure similar to the one of the polymers synthesized by conventional techniques with the advantages of a sol¬vent-free deposition, which is totally substrate independent. Deposition has been demonstrated on paper, metal, plastics, porous substrates and very recently liquids. Tuning the process parameters allows to obtain controlled and uniform thickness over 3D substrates. Future outlook and iCVD scale-up approaches are also discussed
Dry Polymerization of Functional Thin Films and Multilayers by Chemical Vapor Deposition
No full textResponsive polymers with electronic and photonic properties have recently gained a widespread interest because of their versatility and cheapness. Chemical vapor deposition (CVD) offers a method to combine the large portfolio of conventional organic polymerization with the advantages of easy thin film processing, uniformity and scalability. CVD polymerization takes place in a mild vacuum environment, the substrate is kept near room temperature and in the complete absence of solvent. This allows to deposit polymers on unconventional delicate and flexible substrates, such as paper or plastic, with control over thickness on large areas. High reflectance distributed Bragg reflectors are based on multilayer structures whose growth can be facilitated by the absence of solvent, hence without risk of swelling or dissolving the underlying material. The conformal coverage of three-dimensional feature is also a unique characteristic of CVD polymers. In this chapter, fundamental background together with successful applications of CVD polymers will be reviewed. New techniques, as initiated CVD and oxidative CVD, will be introduced and it will be emphasized how they allow to obtain polymers with high chemical specificity (i.e., large retention of chemical functionality) at elevated speed. The accent will be on the applications where all-dry-processing is critical, such as deposition of insoluble polymers (e.g., highly cross-linked) for reactive and responsive surfaces, molecular crystals of fluoropolymers, conjugated polymers, composite and multilayer structures
Different Response Kinetics to Temperature and Water Vapor of Acrylamide Polymers Obtained by Initiated Chemical Vapor Deposition
No full textThermoresponsive polymers undergo a reversible phase transition at their lower critical solution temperature (LCST) from a hydrated hydrophilic state at temperatures below the LCST to a collapsed hydrophobic state at higher temperatures. This results in a strong response to temperature when in aqueous environment. This study shows that hydrogel thin films synthesized by initiated chemical vapor deposition show fast and strong response to temperature also in water vapor environment. Thin films of cross-linked poly(N-isopropylacrylamide), p(NIPAAm), were found to have a sharp change in thickness by 200% in water vapor at temperatures above and below the LCST. Additionally, the stimuli-responsive poly(N,N-diethylacrylamide) was investigated and compared to results found for p(NIPAAm). Analysis of the swelling kinetics performed with in situ spectroscopic ellipsometry with variable stage temperature shows differences for swelling and deswelling processes, and a hysteresis in the thickness profile was found as a function of temperature and of temperature change rate
Measurements of Temperature and Humidity Responsive Swelling of Thin Hydrogel Films by Interferometry in an Environmental Chamber
Full text linkThin film thermo-responsive hydrogels have become a huge interest in applications such as smart drug-delivery systems or sensor/actuator technology. So far, mostly, the response of such hydrogels has been measured only by varying the temperature in a liquid environment, but studies of the response towards humidity and temperature are rare because of experimental limitations. Often the swelling measurements are performed on samples placed on a stage that can be heated/cooled, while vapors enter the permeation chamber at their own temperature. This thermal difference leads to some uncertainties on the exact relative humidity to which the sample is exposed to. In this study, we explored the possibility of performing swelling measurements under thermal equilibrium by placing the sample and an interferometer, as a detector, in an environmental chamber and therefore exposing the smart hydrogel to adjustable temperatures and relative humidity conditions while measuring the hydrogel’s thin film thickness changes. As a case study, we used thin films of the thermo-responsive hydrogel, poly N-vinylcaprolactam deposited by initiated chemical vapor deposition (iCVD). Similar thin films were previously characterized by in situ ellipsometry while the sample was heated on a stage and exposed to humid air produced at room temperature. The comparison between the two measurement methods showed that while measurements in the presence of thermal gradients are limited mostly to low humidity, measurements in thermal equilibrium are restricted only by the operation limits of the used environmental chamber
Initiated PECVD of organosilicon coatings: A new strategy to enhance monomer structure retention
No full textA new deposition method, initiated PECVD (iPECVD), is proposed for the formation of organosilicon polymers with enhanced monomer structure retention compared to conventional PECVD. The quasi-selective fragmentation of an initiator is driven by a low power plasma discharge, as opposed to using a hot filament for initiator decomposition as in a standard, plasma-free initiated CVD (iCVD). The weak peroxide bond (O-O) in the initiator permits the formation of radical species at very low plasma power density (0.07W·cm -2). Kinetic analysis of the deposition process indicates that the film formation rate follows the Arrhenius law, similarly to other iCVD process from organosilicon monomers. Herein we show a new deposition method, initiated-PECVD (iPECVD), as an alternative to iCVD and PECVD, for the monomers that are not easily polymerizable by iCVD (e.g., the organosilicon monomers) but where a certain structure retention is needed. The addition of a radical initiator allows to ignite a plasma discharge at plasma density as low as 0.07W·cm -2. In this condition the carbon content of the monomer molecule is completely retained and at reasonably high deposition rate. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Strategies for Drug Encapsulation and Controlled Delivery Based on Vapor-Phase Deposited Thin Films
No full textVapor-phase deposition methods allow the synthesis and engineering of organic and inorganic thin films, with high control on the chemical composition, physical properties, and conformality. In this review, the recent applications of vapor-phase deposition methods such as initiated chemical vapor deposition (iCVD), plasma enhanced chemical vapor deposition (PE-CVD), and atomic layer deposition (ALD), for the encapsulation of active pharmaceutical drugs are reported. The strategies and emergent routes for the application of vapor-deposited thin films on the drug controlled release and for the engineering of advanced release nanostructured devices are presented
Dynamic Studies on the Response to Humidity of Poly (2-hydroxyethyl methacrylate) Hydrogels Produced by Initiated Chemical Vapor Deposition
No full textThe swelling of 2-hydroxyethyl methacrylate (HEMA) hydrogels, commonly synthesized by solution polymerization, has been widely studied for its practical and fundamental importance. While a good understanding of polymer-liquid interactions has been established within the Flory-Huggins framework, little is known about polymer-water vapor interactions. In this study, the swelling of pHEMA films in response to water and humidity is investigated by means of X-ray reflectivity and spectroscopic ellipsometry. The hydrogels are synthesized by initiated chemical vapor deposition, using ethylene glycol dimethacrylate (EGDMA) as a crosslinking agent. In water, copolymers of p(HEMA-co-EGDMA) are stable for an EGDMA fraction above 17%. In a humid atmosphere, even samples with no EGDMA are stable. On increasing the EGDMA fraction, both the swellability in water and in humid environments decreases. The swelling in both environments is related to the mesh size and solubility of the hydrogel, using the Flory-Huggins theory. The mesh size (average length between two crosslinks) decreases with increasing EGDMA fraction, as expected. The interaction parameter between water vapor and the polymer decreases with increasing relative humidity and reaches 1 ± 0.1 at RH > 75%. (Figure presented.)
Thickness-Dependent Swelling Behavior of Vapor-Deposited Smart Polymer Thin Films
No full textIn this contribution, the temperature-dependent swelling behavior of vapor-deposited smart polymer thin films is shown to depend on cross-linking and deposited film thickness. Smart polymers find application in sensor and actuator setups and are mostly fabricated on delicate substrates with complex nanostructures that need to be conformally coated. As initiated chemical vapor deposition (iCVD) meets these specific requirements, the present work concentrates on temperature-dependent swelling behavior of iCVD poly(N-isopropylacrylamide) thin films. The transition between swollen and shrunken state and the corresponding lower critical solution temperature (LCST) was investigated by spectroscopic ellipsometry in water. The films' density in the dry state evaluated from X-ray reflectivity could be successfully correlated to the position of the LCST in water and was found to vary between 1.1 and 1.3 g/cm3 in the thickness range 30-330 nm. This work emphasizes the importance of insights in both the deposition process and mechanisms during swelling of smart polymeric structures
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