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Polymer–metal composite films with nanostructured metal and/or polymer interfaces show a significant perspective for optoelectronic applications, for example, as sensors or in organic photovoltaics...

Organic gradient materials are an inherent part of many functional structures in the natural world. Synthetic organic materials, like polymers, are thus the perfect choice to artificially recreate these structures for functional purposes. This work reports on new high-quality gradient copolymer films via large-area deposition from the vapor phase and circumvents thus problems related to current wet chemistry approaches. It enables furthermore for the first time the transfer of this gradient approach to the nanoscale, introducing a new class of organic gradient nanomaterials. This facilitates completely new organic gradient functionality on the nanoscale, not achievable with materials currently in use. Fully functional gradient films of 21 nm have been synthesized, which open up new pathways for many application fields. Their versatility is demonstrated by some application examples ranging from every day life (adhesion of PTFE in frypans) to advanced subwavelength devices on large-area substrates as well as complex geometries.

In this work, we demonstrate the first synthesis of photochromic polymer thin films via initiated chemical vapor deposition (iCVD) using bifunctional, crystalline styrenediazocine as a photochromic unit. Since it represents a solid compound, an innovative custom-made sublimation unit is introduced, which allows the sublimation of the chromophore as well as its transport inside the reactor chamber, maintaining the functionality of the photoswitch. Styrenediazocine was co-polymerized with 1,3,5-trivinyl-1,3,5-trimethylcyclotrisiloxane (V₃D₃), a heterocycle with triple vinyl functionality, in a radical polymerization reaction from the gas phase. The structural as well as functional properties of the resulting films were characterized by various methods, including X-ray photoelectron spectroscopy (XPS), Fourier-transform infrared (FT-IR) spectroscopy, and UV–vis spectroscopy. It could be confirmed that, via iCVD, photoswitchable polymer thin films have been obtained. The polymer is based on a copolymer structure where all photoswitchable molecules are covalently bonded in the main polymer chain. Our approach could pave the way for a completely new class of high-quality, photochromic thin films that are basically applicable on almost every kind of substrate for novel, interdisciplinary application fields, where particularly classical wet chemistry methods cannot be applied.

Metal top electrodes such as gold are widely used in organic solar cells. The active layer can be optimized by modifications of the polymer band gap via side-chain engineering, and low band gap polymers based on benzodithiophene units such as PTB7 and PTB7-Th are successfully used. The growth of gold contacts on PTB7 and PTB7-Th films is investigated with in situ grazing incidence small-angle X-ray scattering (GISAXS) and grazing incidence wide-angle X-ray scattering (GIWAXS) during the sputter deposition of gold. From GIWAXS, the crystal structure of the gold film is determined. Independent of the type of side chain, gold crystals form in the very early stages and improve in quality during the sputter deposition until the late stages. From GISAXS, the nanoscale structure is determined. Differences in terms of gold cluster size and growth phase limits for the two polymers are caused by the side-chain modification and result in a different surface coverage in the early phases. The changes in the diffusion and coalescence behavior of the forming gold nanoparticles cause differences in the morphology of the gold contact in the fully percolated regime, which is attributed to the different amount of thiophene rings of the side chains acting as nucleation sites.

This study aims at deposition and characterization of antibacterial, hydrophobic and semitransparent metal/plasma polymer nanocomposite coating, containing Ag nanoparticles, onto cotton fabrics intended to be used in medical applications. The nano composite coatings were obtained via a simple, one step and ecofriendly plasma based co-deposition approach where silver was magnetron sputtered simultaneously with plasma polymerization of hexamethyldisiloxane (HMDSO) monomer. The nanocomposite thin films containing different concentration of silver were deposited either by varying silver sputter rate or thickness of the plasma polymer matrix to obtain a good balance between optical properties of the coated fabric and its long term antibacterial performance. The obtained coatings were investigated in detail with respect to their composition, morphology, optical properties, nanoparticle size distribution, silver ion release efficiency, antibacterial performance, water contact angle and washing stability of the coating. The thickness of the plasma matrix was found to be more important in controlling the release of silver ions as well as affecting the optical properties of the coating. The water contact angle on the coated fabric was up to 145°, close to super hydrophobicity. The coating showed effective antibacterial efficacy against Staphylococcus epidermidis (a Gram positive bacterium) which was present even when fabric was subjected to 10 repeated washing cycles indicating good washing stability of the coating.

ACS applied materials & interfaces 13(47), 56663 - 56673 (2021). doi:10.1021/acsami.1c18324, Large-scale fabrication of metal cluster layers for usage in sensor applications and photovoltaics is a huge challenge. Physical vapor deposition offers large-scale fabrication of metal cluster layers on templates and polymer surfaces. In the case of aluminum (Al), only little is known about the formation and interaction of Al clusters during sputter deposition. Complex polymer surface morphologies can tailor the deposited Al cluster layer. Here, a poly(methyl methacrylate)-block-poly(3-hexylthiophen-2,5-diyl) (PMMA-b-P3HT) diblock copolymer template is used to investigate the nanostructure formation of Al cluster layers on the different polymer domains and to compare it with the respective homopolymers PMMA and P3HT. The optical properties relevant for sensor applications are monitored with ultraviolet-visible (UV-vis) measurements during the sputter deposition. The formation of Al clusters is followed in situ with grazing-incidence small-angle X-ray scattering (GISAXS), and the chemical interaction is revealed by X-ray photoelectron spectroscopy (XPS). Furthermore, atomic force microscopy (AFM) and field emission scanning electron microscopy (FESEM) yield topographical information about selective wetting of Al on the P3HT domains and embedding in the PMMA domains in the early stages, followed by four distinct growth stages describing the Al nanostructure formation., Published by Soc., Washington, DC

Ultra-thin metal layers on polymer thin films attract tremendous research interest for advanced flexible optoelectronic applications, including organic photovoltaics, light emitting diodes and sensors. To realize the large-scale production of such metal–polymer hybrid materials, high rate sputter deposition is of particular interest. Here, we witness the birth of a metal–polymer hybrid material by quantifying in situ with unprecedented time-resolution of 0.5 ms the temporal evolution of interfacial morphology during the rapid formation of ultra-thin gold layers on thin polystyrene films. We monitor average non-equilibrium cluster geometries, transient interface morphologies and the effective near-surface gold diffusion. At 1 s sputter deposition, the polymer matrix has already been enriched with 1% gold and an intermixing layer has formed with a depth of over 3.5 nm. Furthermore, we experimentally observe unexpected changes in aspect ratios of ultra-small gold clusters growing in the vicinity of polymer chains. For the first time, this approach enables four-dimensional insights at atomic scales during the gold growth under non-equilibrium conditions.

Biodegradable collagen-based materials have been preferred as scaffolds and grafts for diverse clinical applications in density and orthopedy. Besides the advantages of using such bio-originated materials, the use of collagen matrices increases the risk of infection transmission through the cells or the tissues of the graft/scaffold. In addition, such collagen-based solutions are not counted as economically feasible approaches due to their high production cost. In recent years, incorporation of marine algae in synthetic polymers has been considered as an alternative method for preparation grafts/scaffolds since they represent abundant and cheap source of potential biopolymers. Current work aims to propose a novel composite patch prepared by blending Sargassum vulgare powders (SVP) to polylactide (PLA) as an alternative to the porcine-derived membranes. SVP-PLA composite patches were produced by using a modified solvent casting method. Following detailed material characterization to assess the cytocompatibility, human osteoblasts (HOBs) and osteosarcoma cells (SaOS-2) were seeded on neat PLA and SVP-PLA patches. MTT and BrdU assays indicated a greater cytocompatibility and higher proliferation for HOBs cultured on SVP-PLA composite than for those cultured on neat PLA. SaOS-2 cells cultured on SVP-PLA exhibited a significant decrease in cell proliferation. The composite patch described herein exhibits an antiproliferative effect against SaOS-2 cells without impairing HOBs’ adhesion and proliferation.

Gas sensors are demanded in many different application fields. Especially the ever-growing field of batteries creates a great need for early hazard detection by gas sensors. Metal oxides are well known for gas sensing; however, moisture continues to be a major problem for the sensors, especially for the application in battery systems. This study reports on a new type of moisture protected gas sensor, which is capable to solve this problem. Sensitive nano-materials of CuO/Cu2O/ZnO:Fe heterostructures are grown and subsequently coated with an ultrathin hydrophobic cyclosiloxane-polymer film via initiated chemical vapor deposition to protect the sensor from moisture. The monomer 1,3,5-trimethyl-1,3,5-trivinylcyclotrisiloxane is combined with the initiator perfluorobutanesulfonyl fluoride to obtain hydrophobic properties. Surface chemistry, film formation and preservation of functional groups are confirmed by X-ray photoelectron spectroscopy and Fourier-transform infrared spectroscopy. It turns out that the hydrophobicity is retained even after annealing at 400 °C, which is ideal for gas sensing. Molecular distances in the polymer nanolayer are estimated by geometry optimization via MMFF94 followed by density functional theory. Compared with unprotected CuO/Cu2O/ZnO:Fe, the coated CuO/Cu2O/ZnO:Fe exhibit a much better sensing performance at a higher relative humidity, as well as tunability of the gas selectivity. This is highly beneficial for hazard detection in case of thermal runaway in batteries because the sensors can be used under high concentrations of relative humidity, which is ideal for Li–S battery applications.

Detection and differentiation of volatile organic compounds (VOC) is highly important since these gaseous pollutants degrade the air quality and represent, even in small amounts, a threat to human health. In this work, a simple and cost-effective method to synthesize a multilayered (CuO-Cu2O)/ZnO:Al nanostructured film forming non-planar heterojunctions for efficient detection of volatile organic compound vapors is presented. While the ZnO:Al layer with different contents of Al (∼0.1 and 0.2 at%) was deposited on a glass substrate via a synthesis from chemical solutions (SCS, at a temperature

Tailoring the optical and electronic properties of nanostructured polymer-metal composites demonstrates great potential for efficient fabrication of modern organic optical and electronic devices such as flexible sensors, transistors, diodes, or photovoltaics. Self-assembled polymer-metal nanocomposites offer an excellent perspective for creating hierarchical nanostructures on macroscopic scales by simple bottom-up processes. We investigate the growth processes of nanogranular silver (Ag) layers on diblock copolymer thin film templates during sputter deposition. The Ag growth is strongly driven by self-assembly and selective wetting on the lamella structure of polystyrene

During the last decades, metal-polymer nanocomposites have been subject to extensive research as their electrical, magnetic and optical properties are very sensitive to their specific compositions and morphological structures. Although there exist a variety of standardized and well-established production processes based on plasma-assisted physical vapor deposition methods, significant progress in the understanding of the self-organized formation process has only been achieved with the help of computer simulations. In particular, computational approaches based on kinetic Monte Carlo (KMC) and molecular dynamics (MD) simulations turned out to be successful in recent years because they offer the potential to simulate and predict the system behavior on sufficiently long time scales. In this paper, we review several formation processes of metal-polymer systems that have been investigated in joint experimental and theoretical KMC and MD studies. These comprise the growth of metallic nanocolumns in a polymer matrix and the growth of nanogranular structures on a polymer film.

The properties of materials involving polymer–solid interfaces are determined not only by the properties of the constituents but also by the interfacial region of the polymer near the solid, the so-called interphase. Here we report on positron annihilation lifetime spectroscopy (PALS) measurements of the free volume near the interface with a focused positron beam. The measurements were performed at an interface between a Teflon AF 1600 film and a 30 nm thick SiN membrane from the backside of a Si substrate which was locally etched away to expose the ultrathin SiN membrane. We were able to focus the positron beam onto the exposed region and to probe the SiN–Teflon AF 1600 interfacial region with low implantation energies, resulting in very narrow implantation profiles and excellent depth resolution. We found a pronounced decrease in orthopositronium lifetime close the interface. On the basis of modeling, we could estimate the interphase width and the average density increase in the interfacial region as ∼1...

At polymer-solid contacts with thermoplastic polymers, the chain characteristics can deviate from the bulk on a length-scale of several nanometer in the so-called interphase. Such an interphase depends on the interaction between respective macromolecule and substrate, and affects the free volume in the polymer. Here, we review our experiments on the characterization of the free volume by positron lifetime spectroscopy at planar and curved interfaces. For Teflon AF on silicon, we identify a layer of increased density, corresponding to an interphase width of some 10 nm. PEP based nanocomposites with functionalized silica show no interphase, whereas for functionalized POSS an interphase is detected.

Atomistic molecular dynamics simulations of a chemically realistic model of atactic short-chain polystyrene between gold surfaces (111) and Positron Annihilation Lifetime Spectroscopy experiments on similar polystyrene thin films on gold were performed. Results from both approaches show that the free volume voids in the film have a slightly smaller average size than in bulk polystyrene. In agreement to that the existence of an interphase of higher density at the polymer-solid substrate interface is shown both by the simulation as well as in the experiment. The average shape of the voids is similar in the bulk and the film.

Polymeric gas separation membranes frequently undergo the phenomenon of aging, that is, performance parameters like permeability decrease with storage or usage time. Here, we report on a new approach of reducing aging by incorporation of functionalized multiwalled carbon nanotubes into a polymer of intrinsic microporosity. Free volume and permeability measurements clearly show a reduced aging with incorporation of the carbon nantubes. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015, 53, 213–217

The influence of confinement in polymer-nanocomposites on free volume and glass transition of the polymer chains was studied. The molecular weight (Mw) of poly(ethylene-alt-propylene) (PEP) was varied from 3k to 200k and so the end-to end distance of the chains at fixed diameter (∼15 nm) and concentration (15%) of the silica nanoparticles increased. Thus the topological confinement increases with increasing Mw. Using hydrophobic PEP and particles functionalized with short organic molecules, we can rule out contributions of permanent adsorption of the chains. DSC showed no change in glass transition temperature. The decrease in the specific heat capacity could be explained by a simple mixing rule. By positron annihilation lifetime spectroscopy, taking properly into account contributions of the silica particles, we rule out an influence of the geometrical confinement on the free volume in the PEP nanocomposites studied here.

There is a growing market for polymeric gas separation membranes for applications such as air separation and carbon dioxide capture. One of the key properties dominating transport is the free volume between atoms, allowing gas diffusion. However, thin films, in particular, undergo aging, decreasing free volume, and, hence, performance with time. We have measured the change in free volume during aging of thin films of a polymer of intrinsic microporosity (PIM-1) by depth-resolved positron annihilation lifetime spectroscopy. For films with thickness, d, smaller than 1 μm, aging is nearly complete after 3 months, whereas for films with d > 1 μm aging continues even after several months. Aging is thickness-and time-dependent and the free volume diffuses through the film to the free surface.

Recently, there is much interest in nanocomposites consisting of metal nanoparticles dispersed in a dielectric matrix due to their novel functional properties. In many cases the formation of metal clusters is affected by chemical reactions of the metal with the host matrix material during deposition. The integration of a magnetron cluster source into a plasma deposition process allows the pre-formation of clusters in the gas phase and subsequent co-deposition with the matrix material. We chose plasma polymerization of HMDSO as deposition method for the matrix in this case. Here we focus on the composition of the nanocomposites generated by high pressure magnetron sputtering combined with a plasma polymer. The influence of magnetron power, total and HMDSO partial gas pressure on the cluster formation as well as nanocomposite film properties were investigated by ex situ X-ray photoelectron spectroscopy. Furthermore optical und morphological properties of the prepared nanocomposites have been characterized.

Ag-TiO(2) nanocomposite coatings with varying Ag content were prepared by co-sputtering from two separate sputter sources. This technique allows to prepare coatings not only with a large variation of Ag content and different gradient but also allows much better control of nanocomposite thickness and nanostructure compared with mostly used techniques based on wet chemical approaches. Various thicknesses of nanocomposite layers with different deposition parameters were studied to obtain a better understanding on the growth of Ag nanostructures in the TiO(2) films. The metal-volume-fraction was varied between 15 and 47. Structural and microstructural investigations of the nanocomposite films were carried out by transmission electron microscopy. Special attention was paid to surface segregation of Ag and its suppression. The observed segregation on TiO(2) contrasts sharply with the well known embedding tendency of Ag clusters on polymers. Functionality of the Ag-TiO(2) nanocomposites was demonstrated via UV-Vis spectroscopy and antibacterial tests. It was shown that a thin layer of TiO(2) can be used as an effective barrier to tailor the release behaviour of Ag ions.

Polymers including chromophores, which can be switched by light, have been studied extensively during the last years due to a host of potential applications which arise from the marked changes in physical properties on switching. Even though there is clear evidence that the free volume has a significant influence on the isomerization kinetics, the question of free volume changes on switching was only addressed recently. Using a pulsed low-energy positron beam the ortho-positronium lifetime tau(3) was taken as a very sensitive free volume probe, and no change in free volume was detected on isomerization in an azobenzene-polymethylmethacrylate (PMMA) copolymer containing about 8 wt of the azobenzene moiety. Here, we report for the first time on free volume changes in an azobenzene-PMMA blend with an azobenzene moiety concentration as high as 40 wt . Using the same pulsed low-energy positron beam, small but significant changes of tau(3) were observed between the structurally relaxed dark and the UV-illuminated states suggesting a decrease in free volume of the order of 10. (C) 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 49: 404-408, 2011

In this article, the authors will present a simple way to produce thin solid organic films, with a content of more than 60 wt% photoactive molecules dispersed in a polymeric matrix showing an almost complete and fully reversible photoisomerization. These high filling factors could be achieved by using branched side chains in the molecules, which prevent crystallization. The chromophores were codissolved with the polymer Polymethylmethacrylate (PMMA) of different Mw in toluene in various concentrations and spin casted onto the substrate. The effect of the Mw of PMMA on the switching kinetics and the agglomeration tendency of different molecule configurations were investigated.

Nanocomposites combine favorable features of the constituents on the nanoscale to obtain new functionalities. The present paper is concerned with the preparation of polymer-based nanocomposites consisting of metal nanoparticles in a polymer matrix and the resulting functional properties. Emphasis is placed on vapor phase deposition which inter alia allows the incorporation of alloy clusters with well defined composition and tailored filling factor profiles. Examples discussed here include optical composites with tuned particle surface plasmon resonances for plasmonic applications, magnetic high frequency materials with cut-off frequencies well above 1 GHz, sensors that are based on the dramatic change in the electronic properties near the percolation threshold, and antibacterial coatings which benefit from the large effective surface of nanoparticles and the increased chemical potential which both strongly enhance ion release.

The conductivity of polymer–metal nanocomposites close to the percolation threshold is very sensitive to changes in the metal nanoparticle distances. Here the technical feasibility of a novel type of easy to prepare polymer–metal nanocomposite sensor is explored, which shall be able to detect a unique signal for various volatile organic compounds (VOCs) exhibiting a fast and reversible response. The composite consists of a nearly 2-dimensional Au nanoparticle layer near the percolation threshold thermally embedded into a thermoplastic polymer film. The sensoric response is based on the swelling behavior of the polymeric matrix upon exposure to the organic vapor molecules. Different from conventional nanocomposite sensors that require long-range diffusion of the volatile compound into the bulk of the matrix, the electrical response here only requires the penetration of the VOC a few nanometer below the surface thus causing a rapid detection. The degree of swelling depends on the type of polymer and VOC used as well as on the vapor pressure of the VOC leading to a characteristic response of each polymer to a specific VOC. This enables a “fingerprint” detection of different VOCs by an array of different polymer nanocomposite combined into one sensoric device.

Polyethylene glycol improved the gas permeability and selectivity of Pebax ® (poly(amide-b-ethylene oxide) copolymer) membrane. To understand this, the free volume variation in these blend membranes was studied from T = −80 to T = 100 °C by positron annihilation lifetime spectroscopy (PALS). A small difference in o-positronium lifetime between pristine polymer and blend with 50 wt.% of polyethylene glycol was observed between −10 and 10 °C. However, at room temperature no significant changes of free volume are detected due to the apparent molten state of polyethylene oxide. The gas permeability measurements, PALS analysis, fractional free volume (FFV) obtained from density and the theoretical correlation between diffusion coefficient and FFV show a good agreement. Thus, we could conclude that the performance of rubbery-like block copolymer membranes can also be improved by controlling the total free volume (addition of an appropriate plasticizer), and not only by solubility selectivity increase as commonly reported.

The microstructure of the free volume and its temperature dependence were studied for amorphous Teflon AF 1600 (Tg = 160 °C) and AF 2400 (Tg = 240 °C). These copolymers consist of tetrafluoroethylene and 2,2-bis(trifluoromethyl)-4,5-difluoro-1,3-dioxole units and are used as highly permeable membrane materials. We employed positron annihilation lifetime spectroscopy (PALS) to investigate the free volume. From the lifetime spectra analyzed with the routine LT9.0 the hole size distribution, its mean size and width were calculated. Results obtained from a three and a four component analysis of lifetime spectra are compared. Both polymers show very large orthopositronium lifetimes τ3 (corresponding to large hole sizes) and glass transitions in τ3 near the expected values. AF 2400 shows an unusual behavior characterized by a nonlinear temperature dependence of the orthopositronium lifetime, extraordinarily large mean values of τ3 and the widths of the lifetime distributions σ3. Possible explanations for this w...

Low-energy ion irradiation of polymer induces different phenomena in the near surface layer, which effect strongly the metal–polymer interface formation and promotes adhesion of polymers to metals. Low-energy argon and oxygen ion beams were used to alter the chemical and physical properties of different polymers (PS (polystyrene), PαMS (poly(α-methylstyrene), BPA-PC (bisphenol-A-polycarbonate) and PMMA (poly(methyl methacrylate)), in order to understand the adhesion phenomena between a deposited Cu layer and the polymers. The resulting changes were investigated by various techniques including X-ray photoelectron spectroscopy, measurements of the metal condensation coefficient and a new technique to measure cross-linking at the polymer surface. Two types of practical adhesion strengths of Cu–polymer systems, measured using 90° peel tests, were observed: (i) peel strength increased at low ion fluences, reached a maximum and then decreased after prolonged treatment and (ii) no improvement in the peel strength on treated polymer surfaces was recorded. The improvement in the metal–polymer adhesion in the ion fluence range of 1013–1015 cm−2 is attributed to the creation of a large density of new adsorption sites resulting in a larger contact area and incorporation of chemically active groups that lead to increased interaction between metal and polymer by metal–oxygen–polymer species formation. XPS analysis of peeled-off surfaces showed that in most cases the failure location changed from interfacial for untreated polymers to cohesive failure in the polymer for treated surfaces. These observations and measurements of the metal condensation coefficients suggest that bonding is improved at the metal–polymer interface for all metal–polymer systems. However, the decrease in the peel strength at high ion fluences is attributed to the formation of a weak boundary layer in polymers. The correlation between sputter rate of polymers and altering in the peel strength for moderate ion fluences was determined. It was observed that the metal–polymer adhesion could be improved for PS and BPA-PC, which have a low sputter rate and preferentially formed cross-links in the treated surface. For degrading polymers, like PαMS and PMMA, chain scission rather than cross-linking dominates, low molecular weight species are formed and no adhesion enhancement is observed.

PPO (poly(2,6-dimethyl-1,4-phenylene oxide)) is a well-known membrane material showing good gas separation properties. The incorporation of nanoparticles can enhance or deteriorate the performance of composite membranes, sometimes depending only on the way of the composite preparation. We have modified the PPO polymer with C60 fullerenes up to a content of 2 wt %. Previous investigations showed a strong dependence of permeability on whether the C60 is simply dispersed in the polymer or chemically bonded to the polymer chains. Free volume effects were suggested as an explanation but not experimentally confirmed. Here, we present free volume studies by positron annihilation lifetime spectroscopy. An additional long positron lifetime shows the increased free volume of composite samples, while the high electron affinity of C60 helps to indicate the homogeneity of the samples. Combining the presented results with permeability measurements refines the understanding of this promising membrane material.

Recently, there is much interest in nanocomposites consisting of metal nanoparticles dispersed in a dielectric matrix due to their novel functional properties offering hosts of new applications. Polymers are particularly attractive as matrix. Consequently, various approaches have been reported to incorporate metal nanoparticles into polymers. The present review is mainly concerned with the preparation of polymer-based nanocomposites by co- and tandem sputtering of metallic and organic components and the resulting functional properties. Different from typical wet chemical approaches, this vapor phase deposition technique allows the preparation of composites which contain alloy clusters of well defined composition. Emphasis is placed on soft-magnetic high frequency materials with cut-off frequencies well above 1 GHz and optical composites with tuned plasmon resonances suitable for ultrathin color filters, Bragg reflectors, and other devices. In addition, antibacterial coatings are addressed. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

This paper describes the preparation, characterization and the permeation properties of poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) dense polymer films containing aliphatic hyperbranched polyesters, Boltorn (H20, H30, and H40). The Boltorn are dispersed in PPO at various concentrations. The gas permeability results were very different between low and high concentration of Boltorn. The gas permeability of PPO with 1.0 wt % of Boltorn is 2−3 times higher than the pure polymer, while at higher concentration (9.1 wt %) of Boltorn the permeability becomes almost 50% of the pure polymer. The gas pair selectivity, however, stays constant. The increase in permeability at low concentration of Boltorn is due to the increase of the free volume, probably due to hydrogen bonds between Boltorn and the oxygen of PPO backbone. The decreased permeability of PPO containing higher concentration of Boltorn (9.1 wt %) is due to two reasons: decrease in free volume as determined by PALS as well as phase separation. The hyperbranced polyesters form aggregates that migrate to the top surface of the membrane.

Amino group containing films of maximum 30 nm thickness were deposited on gold-coated wafers using atmospheric pressure dielectric barrier discharges (DBD) and process gases consisting of aminopropyl-trimethoxysilane (APTMS) as precursor in combination with various carrier gases including nitrogen, helium, argon, or a mixture of ammonia and nitrogen. With CD-XPS a concentration [NH2]/[C] of up to almost 6% was found. Storage of the films in air for four weeks generally led to a considerable reduction of the primary amino group concentration; however, in the case of the films produced using ammonia in nitrogen as carrier gas the concentration remained stable at just under 4%. Oxidation products according to XPS and IR data include amides and nitriles though imines may also be present.

In this work, we used co-sputtering of noble metals together with polytetrafluorethylene (PTFE) as a method for producing antibacterial metal/polymer nanocomposite coatings, where the precious metals are only incorporated in a thin surface layer. Moreover, they are finely dispersed as nanoparticles, thus saving additional material and providing a very large effective surface for metal ion release. Nanocomposite films with thickness between 100 and 300 nm were prepared with a wide range of metal filling between 10 and 40%. The antimicrobial effect of the nanocomposite coatings was evaluated by means of two different assays. The bactericidal activity due to silver release from the surface was determined by a modification of conventional disc diffusion methods. Inhibition of bacterial growth on the coated surface was investigated through a modified proliferation assay. Staphylococcus aureus and S. epidermidis were used as test bacteria, as these species commonly cause infections associated with medical polymer devices. The antibacterial efficiency of the coatings against different bacteria was demonstrated at extremely small noble metal consumption: Au: ~1 mg m−2 and Ag: ~0.1 g m−2. The maximum ability for having an antibacterial effect was shown by the Ag–Au/PTFE nanocomposite, followed by the Ag/PTFE nanocomposite.

We present a combined analysis of the free volume in polyimide membrane polymers by employing experimental measurements as well as computer simulations. The amount and distribution of free volume in polymeric membranes significantly determine the transport and separation properties. In the present work these free volume characteristics were determined directly from simulated atomistic packing models via a new method. Here a “virtual tracer sphere” probes the simulation cell to determine the unoccupied volume. As an experimental approach, positron annihilation lifetime spectroscopy was used to determine the average size of free volume cavities via a well-established correlation between orthopositronium lifetime and cavity size. We show that the results obtained from the combined analysis provide a valuable basis for the investigation of free volume properties; moreover, limitations of the standard model for the evolution of the positron lifetime data will be discussed.

The polymer sputter rate dependence on ion fluence and ion chemistry (Ar, N2, O2) at 1 keV energy was investigated using a quartz crystal microbalance (QCM) which allowed to do real time etch rate measurements and to study kinetics of sputtering. The obtained sputter rates differed drastically from polymer to polymer showing, that the chemical structure of polymer is an important factor in the polymer etch yield. A decrease in the sputter rate was observed up to ion fluence of 5 × 1014–5 × 1015 cm−2 (depending on the polymer type and ion chemistry) followed by the saturation in the rate at prolonged ion bombardment. Polymer removal was accompanied by the formation of degradation products, cross-linking or branching, modification of the surface chemical structure, which was studied in situ using XPS. The dependence of the surface glass transition temperature, Tgs on the ion fluence was studied using the method based on the embedding of metallic nanoparticles. The correlation between chemical yield data and ablation rate is discussed.

Ion–polymer interaction induces different phenomena in the near surface layer of polymers, and promotes its adhesion to metals. Using XPS, TEM and AFM, polystyrene surface was examined after 1 keV ion-beam treatments with oxygen, nitrogen and argon ions in the ion fluence range from 1012 to 1016 cm−2 to clarify the following points: chemical reaction after treatment in vacuum and after exposure to air, identification of adsorption-relevant species for metal atoms, formation of cross-links in the outermost polymer layer. The early stages of metal–polymer interface formation during metallization play a crucial role in the metal–polymer adhesion. Therefore, the influence of the ion fluence and ion chemistry on the condensation of noble metals, film growth and peel strength were measured. The peel strength showed a maximum at a certain fluence depending on ion chemistry. For example, the surface treatment with very low fluence of oxygen ions improved the adhesion between copper and polystyrene by two orders of magnitude without significantly increasing the surface roughness measured with AFM. The locus of failure changed at the same time from interfacial failure for untreated polymer surfaces to cohesive failure in the polymer for modified surfaces. A multilayer model of the metal–polymer interface after ion treatment is suggested.

The metallization of organic thin films is a crucial point in the development of organic electronic devices. There is no method established yet to detect trace amounts of metal atoms in the organic thin films after metal deposition. Radiotracer measurements are probably the most sensitive tool to study diffusion and to quantify even very small amounts of material penetrating into the bulk. So far, this has been shown for metals and polymers, but not for thin ordered molecular organic films. Here, the first application of this technique on a well-characterized organic thin film system, diindenoperylene using thermally evaporated Ag containing 110mAg radiotracers is shown. The results show that Ag is mainly adsorbed on the surface, but indicate that already at moderate substrate temperatures small concentrations of Ag can penetrate into the organic thin films and agglomerate at the interface during metallization.

Interfaces between cross-linked polymers and metals play a significant role in fields like splicing and coating, metallization of plastics, microelectronics, micro system technology and nanotechnology. In this paper, we present investigations on the interface formation due to metallization (Au, Ag, Cu and Al) by evapouration of the highly cured epoxy resin system diglycidilether of bisphenol a (DGEBA)–diethylene triamine (DETA) with the focus on the structure formation at the interface. A combination of X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), atomic force microscopy (AFM) and a radiotracer technique was used to analyze the metal/epoxy interface. While a strong metal/epoxy interaction was found for Al, the noble metals Au, Ag and Cu grow in a Volmer–Weber mode due to an interplay of surface diffusion and metal cluster growth. Nevertheless, polymer bulk diffusion of these metals is negligible.

The effect of mechanical milling on free volume was studied by means of positron annihilation lifetime spectroscopy (PALS) in polystyrene (PS) as a typical brittle polymer and in polycarbonate (PC) as a tough representative. Long-time milling increases the free volume, while a decrease is observed for short milling times. The changes are mostly irreversible in PS. The irreversible fraction is much smaller for PC. Gel permeation chromatography (GPC) measurements show a decrease of the molecular weight, which is much more pronounced in PS. The milling-induced irreversible changes in free volume are attributed to chain-end defects resulting from chain scission. In PC, other deformation-induced defects that anneal upon heat treatment above the glass transition temperature dominate.

A simple one-step vapor phase co-deposition at elevated target temperature is employed to generate optical nanocomposites (~100–300 nm) of polymer-based metallic nanoparticles with uniform size and shape. Homogeneously, three dimensionally distributed isolated Ag nanoparticles are produced with appropriate volume filling (~10–30%) in Teflon AF matrix at various co-deposition target temperatures of 120–400 °C. An extremely narrow particle size distribution of ~5–7 nm based on TEM observations is demonstrated. Different ultrathin nanocomposite color filters as a result of plasmon resonance shifting in the UV–VIS wavelength region are also generated.

Chain mobility in a near surface region at a polystyrene/vacuum interface was investigated by embedding of noble metal nanosized clusters. The embedding process was monitored in situ by X-ray photoelectron spectroscopy. The embedding of nanosized clusters needs long-range chain mobility of the polymer. Therefore, the embedding process is a probe for the glass transition in a near surface region. The clusters used in this study are formed by the dewetting of evaporated noble metals onto the polymer surface. First, methodical influences on the embedding process were investigated. An onset embedding temperature T* was defined. T* increases with a heating rate comparable to Tg(bulk) determined with a differential scanning calorimeter. Furthermore, T* increases with nominal metal coverage which results in increasing average cluster radius. The cluster size distribution was investigated by transmission electron microscopy. It is shown that T* is an upper limit for Tg in a near surface region with a depth of a f...

Various polymers were sputtered with low energy Ar+ ions of 1 keV in order to determine their etching rate. Hydrocarbons, oxygenated, fluorinated and nitrogen-containing glassy polymers with a broad range of the glass transition temperature (Tg) were chosen. The etching rate was measured using a profilometer, and X-ray photoelectron spectroscopy. At the same time the surface chemical modification, and the surface glass transition temperature were studied. Comparing the sputter rate to the various polymer properties a correlation among the Tg, cross-link density, and sputter rate was found. In addition, the sputter rate as a function of the integral ion fluence proved to exhibit a sharp increase in the initial regime of very low fluence. The results are discussed in terms of the characteristics of the polymers

A completely dry technique (VPD) for the preparation of a metal cluster onto a polymer surface or between two polymer layers opens up very good possibilities to control the two dimensional dispersion of the metal clusters and their size during variation of the deposition parameters or the polymer surface treatment. The kinetics of heterogenous nucleation and the growth of nano-size metal clusters (Ni, Ag, Cu, Au) on polymers with different chemical composition (PMDA-ODA polyimide, polystyrene and Teflon AF) are studied by X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). In contrast to preferred nucleation and significantly incomplete condensation on the surface of Teflon AF and PS random nucleation and well defined cluster distribution was observed on PMDA-ODA polyimide. It was shown that cluster size and cluster distribution can be influenced in a wide range (some order of magnitude) by the variation of the preparation parameters. Ar ion beam treatment of polymers with low ion dose (10 12 –10 16 cm � 2 ) as well as predeposition of a trace amount of a reactive metal can be successfully used to prepare a definite cluster structure due to creation of adsorption sites on polymer surface. 2003 Elsevier Science B.V. All rights reserved.

The surface characteristics of polymers are important factors determining their interfacial properties and their technological performance. Changes in physical and chemical properties of a polymer film may be induced by subjecting the material to a variety of surface modification techniques, one of which is ion-beam modification. In order to understand the underlying mechanisms X-ray photoelectron spectroscopy (XPS) was used to study the alterations of the polystyrene (PS) surface after Ar-ion treatment under well controlled conditions with low ion doses from 10 12 to 10 16 cm −2 . The ion bombardment leads to surface functionalization, loss of aromaticity, and free radical formation. Induced surface cross-linking and the formation of polar groups raised the surface glass transition temperature of PS film.

A promising solvent-free route to vapor-phase tandem evaporation is employed to produce nanoclusters of reactive Ni protected between the capping layers of Teflon AF. Independent control over the homogeneously distributed particle size (∼3−10 nm) is demonstrated while increasing the cluster-volume filling from ∼1 to 20% by following codeposition to many-sequential thermal evaporation of the two components. TEM investigations have been applied to characterize the nanocomposites.

In organic-inorganic nanocomposites, interfacial regions are primarily influenced by the dispersion uniformity of nanoparticles and the strength of interfacial bonds between the nanoparticles and the polymer matrix. The insulating performance of organic-inorganic dielectric nanocomposites is highly influenced by the characteristics of interfacial regions. In this study, we prepare polyethylene oxide (PEO)-like functional layers on silica nanoparticles through plasma polymerization. Epoxy resin/silica nanocomposites are subsequently synthesized with these plasma-polymerized nanoparticles. It is found that plasma at a low power (i.e., 10 W) can significantly increase the concentration of C–O bonds on the surface of silica nanoparticles. This plasma polymerized thin layer can not only improve the dispersion uniformity by increasing the hydrophilicity of the nanoparticles, but also provide anchoring sites to enable the formation of covalent bonds between the organic and inorganic phases. Furthermore, electrical tests reveal improved electrical treeing resistance and decreased dielectric constant of the synthesized nanocomposites, while the dielectric loss of the nanocomposites remains unchanged as compared to the pure epoxy resin.

Based on a good knowledge of the basic processes occurring in the initial stages of metal/polymer interface formation the preparation conditions can be selected to obtain a desired interfacial morphology. Very sharp or spread-out metal/ polymer interfaces can thus be formed, the cluster density on the surface can be adjusted, or metal clusters can be embedded into the polymer in a controlled manner. This may have a strong impact on the macroscopic adhesion of metal films evaporated onto polymers.

We used X-ray photoelectron spectroscopy (XPS) in combination with transmission electron microscopy to characterize the nucleation and growth of noble metals deposited onto polymers and to determine the condensation coefficients of the metals. The surface concentration of the adatoms was determined using a mathematical correction of the XPS intensity to take into account the cluster formation of noble metals on polymer surfaces. Condensation coefficients for Cu and Ag depend strongly on the chemical composition of the polymer and on temperature and can vary by more than three orders of magnitude already at room temperature. The influence of the deposition parameters and the metal/polymer morphology on the condensation coefficient will be discussed.

We compare molecular modeling results of two glassy polymer membranes and one rubbery polymer membrane with gas transport parameters and free-volume-related quantities from positronium annihilation. A simple geometric model reveals hole size distributions of asymmetric shape. Among glassy polymers, the distribution parameters show a good correlation with average hole sizes determined by positron annihilation lifetime spectroscopy. Higher permeability is measured in the glassy polymer with the higher mean value of the hole size distribution. The permselectivity of the membranes for permanent gases can be interpreted in terms of the distribution broadness via free-volume-controlled diffusion selectivity. A comparison with the rubbery polymer shows that the permeation behavior is not determined only by the free volume concentration. The thermal fluctuations of the polymer matrix play an important role for gas transport properties.

We developed a method to determine condensation coefficients, C, of noble metals on polymer surfaces and to determine cluster sizes by means of XPS only, or in combination with transmission electron microscopy (TEM). The surface concentration of the adatoms was determined using a mathematical correction of the XPS intensity that takes into account cluster growth of the noble metals on the polymer surfaces. We establish our method with experimental results of C for Cu and Ag on pyromellitic dianhydride (PMDA)–4,4′-oxydianiline (ODA) polyimide, bisphenol-A polycarbonate, trimethylcyclohexane bisphenol-A polycarbonate, polystyrene and Teflon AF 1601. Values of C for Ag determined with the XPS method agree well with those of radiotracer measurements. The condensation coefficient varies by three orders of magnitude from 1 to 0.002, depending on the deposition parameters and properties of the adsorbents. The method can be applied in general to investigate the deposition of non-wetting metals on solid surfaces. Copyright © 2000 John Wiley & Sons, Ltd.

The morphology of a metal/polymer interface is important for many properties, e.g. its adhesional strength. Starting from the basic processes occurring in the initial stages of metal/polymer interface formation, it is possible to obtain different morphologies by variation of the preparation conditions. In this report we present selected examples from our own work of how metal/polymer interfaces with different morphologies can be prepared by evaporating noble metals (Au, Ag, Cu) onto chemically different polymers, i.e. bisphenol-trimethyl cyclohexane polycarbonate (TMC-PC), pyromellitic dianhydride-oxydianiline (PMDA-ODA) polyimide (PI), and on Teflon AF 1601. The interfaces were characterized using transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM). The combination of these techniques allows one to determine morphological parameters such as the concentration and distribution of metal clusters at the surface and in the near-surface region. Usin...