Thin Polymer Layer Research Articles

Responsive polymer thin films

Responsive polymer thin films

3D printed photocatalytic reactor for air purification

A 3D printed plastic sinusoidal reactor with a 3D printed photocatalytic lining is prepared and used to purify air, containing the test pollutants, NO2, NO, acetaldehyde and ozone. This 3D printed, air-purifying photocatalytic reactor, 3D APPR, is first UVA pre-conditioned (168 h, 1.5 mW cm−2), to render its P25 TiO2 containing photocatalytic lining active, through the destruction of the thin layer of polymer that covers the photocatalytic particles at, or near, to the surface. When testing for pollution removal, unless stated otherwise, the typical reaction conditions are, [pollutant] = ca. 1000 ppb, flow rate = 0.26 L min−1, relative humidity = 50%, UVA irradiance (352 nm) 1 mW cm−2 and irradiation time, t, = 5 h. Under these conditions the 3D APPR removes 27% of the NO2, 25.3% of the NO, but simultaneously generates 17.3% NO2 so %NOx removed is only ca. 8%. With acetaldehyde, [pollutant] = ca. 5000 ppb; 3 h irradiation, 34.2% is removed. Finally, with ozone, [pollutant] = ca. 420 ppb; 1 h irradiation; 2.8 mW cm−2 368 nm, 99% is removed. Indeed, the latter process is so effective that the small amount (47 μW cm−2) of UV in cool white fluorescent tubes is able to effect the removal of 70 % of the ozone. In all cases, the 3D APPR is more effective at removing the test pollutant than Activ™ self-cleaning glass, even though the latter has nearly 3 times the irradiated surface area and over 12 times the residence time. Long term (5 day) irradiations of the same systems produces very similar, if not enhanced, % removal values for all the pollutants tested. The potential of this type of disposable, plastic film photocatalytic reactor, made using a biodegradable plastic, polylactic acid, PLA, is discussed briefly.

Photothermal dual-responsive polymers for trypsin-free cell sheet harvesting

Cell sheet engineering has emerged to tackle cell therapy's bottlenecks and increase the likelihood of life-saving potentials of tissue engineering. In this study, Poly(N-isopropylacrylamide-co-spiropyran) (P(NIPAAm-co-Sp)) copolymer and Poly(N-isopropylacrylamide-co-styrene-co-spiropyran) (P(NIPAAm-co-St-co-Sp)) terpolymer were synthesized by free radical polymerization (FRP). Fourier transform infrared (FTIR) was utilized to characterize the chemical structure of the resultant polymers. The molecular weight and molecular weight distribution were measured by gel permeation chromatography (GPC). The reversible photosensitivity of the synthesized polymers was proved by ultraviolet–visible (UV–Vis) spectroscopy. Thin layers of polymers were spin-coated onto ultraviolet/ozone (UV-O3) and silane-modified glass slides. To confirm the coating process, the attenuated total reflection FTIR spectroscopy (ATR-FTIR) was used. The cross-sectional images of the spin-coated glass slides, obtained using field emission scanning electron microscopy (FESEM), showed thin layers about 300 to 400 nm thick. The roughness of the coated layers was examined by atomic force microscopy which were below 1 nm. The water contact angle (WCA) measurements showed that changes in the surface wettability of thin layers occurred in response to temperature alteration and light illumination. The spin-coated glass slides were used to culture the mouse fibroblast cell line L929. The cell culture results showed that the thickness of the thin layers was adequate for forming a confluent and integrated sheet of L929 cells. By reducing the temperature from 37 °C to 20 °C and illuminating the glass slide, fragments of the cell sheet were harvested. The use of light besides temperature reduction decreased the time needed for cell sheet detachment from 2 h to 1 h.

Off-Stoichiometry Thiol-Ene Polymers: Inclusion of Anchor Groups Using Allylsilanes.

The use of polymers in silicon chips is of great importance for the development of microelectronic and biomedical industries. In this study, new silane-containing polymers, called OSTE-AS polymers, were developed based on off-stoichiometry thiol-ene polymers. These polymers can bond to silicon wafers without pretreatment of the surface by an adhesive. Silane groups were included in the polymer using allylsilanes, with the thiol monomer as the target of modification. The polymer composition was optimized to provide the maximum hardness, the maximum tensile strength, and good bonding with the silicon wafers. The Young's modulus, wettability, dielectric constant, optical transparency, TGA and DSC curves, and the chemical resistance of the optimized OSTE-AS polymer were studied. Thin OSTE-AS polymer layers were obtained on silicon wafers via centrifugation. The possibility of creating microfluidic systems based on OSTE-AS polymers and silicon wafers was demonstrated.

Understanding the Composition of Layer‐by‐Layer Deposited Active Layer at Buried Bottom Surface

AbstractLayer‐by‐layer (LbL) coating is becoming a widely used method to fabricate nonfullerene active layer films for organic solar cells. However, the vertical compositional distribution of the LbL‐coated active layer, particularly at the buried bottom surface, is not clear yet. In common sense, it is believed that the LbL‐coating yields a donor–mixture–acceptor (D–m–A) vertical distribution in the active layer, i.e., a thin polymer donor layer at the bottom surface, a thin acceptor layer at the top surface and a donor‐acceptor mixture in the middle. In this study, it is shown that the LbL active layer vertically is an entire donor:acceptor mixture. A pure layer of polymer donor doesn't exist at the bottom surface. The LbL active layer delivers high performance in both conventional and inverted device structures. A thin polymer layer with different thicknesses (2, 6, 12 nm) is inserted at the bottom surface to study their effects on the device performance. Those inserted layers substantially deteriorate the device's performance. Furthermore, the assumption is further confirmed by X‐ray photoelectron spectroscopy measurement on the exposed “originally buried” surface. This study sheds light on understanding the vertical compositional distribution of active layer via layer‐by‐layer solution processing.

Substrate-free miniaturized thin-film filters for single-element coarse wavelength division multiplexing fibers.

We have created high-precision, miniaturized, substrate-free filters, based on ion beam sputtering on a sacrificial substrate. The sacrificial layer is cost efficient and environmentally friendly and can be dissolved using only water. We demonstrate an improved performance compared to filters on thin polymer layers from the same coating run. With these filters, a single-element coarse wavelength division multiplexing transmitting device for telecommunication applications can be realized by inserting the filter between fiber ends.

Improvement of the Electrical Performance of Ag/MEH-PPV/SiNWs Schottky Diode by the Insertion of a Thin Layer of MEH-PPV Polymer and Study of the Annealing Effect

Poly[2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylene vinylene] (MEH-PPV) thin layer was deposited on silicon nanowires (SiNWs) by electroless dipping method. SiNWs were obtained using Ag-assisted chemical etching process. Scanning Electron Microscopy (SEM) images reveal a vertical alignment of the SiNWs as well as the formation of MEH-PPV layer on their surfaces. The presence of MEH-PPV polymer on the SiNWs surface was confirmed by Energy-dispersive X-ray (EDX). Current–Voltage (I–V) measurements were performed for the electrical characterization of Ag/MEH-PPV/SiNWs diodes before and after annealing. The ideality factor (n), the barrier height (φb) and the series resistance (RS) are determined using the Cheung method. The diode parameters are strongly affected by the immersion duration in MEH-PPV solution as well as the annealing temperature. The rectification rate of the diodes was increased by MEH-PPV deposition. The annealing temperature has a great influence on the diode parameters by the thermal activation of carriers at Ag/MEH-PPV and MEH-PPV/SiNWs interfaces. I–V characteristics show an ohmic character for temperatures above 250 °C. The electrical parameters such as equivalent carrier concentration (ND) and built-in voltage (Vb) and other values of φb are calculated from Capacitance–Voltage (C–V) measurements.

2D optical confinement in an etchless stratified trench waveguide.

We demonstrate novel trapezoidal and rectangular stratified trench optical waveguide designs that feature low-loss two-dimensional confinement of guided optical modes that can be realized in continuous polymer thin film layers formed in a trench mold. The design is based on geometrical bends in a thin film core to enable two-dimensional confinement of light in the transverse plane, without any variation in the core thickness. Incidentally, the waveguide design would completely obviate the need for etching the waveguide core, avoiding the scattering loss due to the etched sidewall roughness. This new design exhibits an intrinsic leakage loss due to coupling of light out of the trench, which can be minimized by choosing an appropriate waveguide geometry. Finite-difference eigenmode simulation demonstrates a low intrinsic leakage loss of less than 0.15 dB/cm. We discuss the principle of operation of these stratified trench waveguides and present the design and numerical simulations of a specific realization of this waveguide geometry. The design considerations and tradeoffs in propagation loss and confinement compared with traditional ridge waveguides are discussed.

A Single Mg Ion-conductive Polymer-coated MgCo2O4 for Mg Rechargeable Batteries

A method for coating cathode active material for magnesium-ion batteries was proposed using polymer, a poly(styrene-4-sulfonyl trifluoromethane sulfonyl)imide Mg salt (PSTFSI-Mg) having a trifluoromethane sulfonyl imide side group. A cathode active material, MgCo2O4 (MCO), was used and spray-dried with PSTFSI-Mg. After preparing the cathode, the Mg battery test was performed with glyme electrolyte solution. The polymer-coated MCO cathode-based coin cell showed good cyclability with moderate discharge capacity around 45 mAh g−1, and this indicates that the polymer thin layer on the MCO surface probably acts as artificial solid electrolyte interface and prevents electrolyte decomposition.

Chemical vapor deposition of carbohydrate-based polymers: a proof of concept study

The aim of this work is to investigate if vinyl-modified carbohydrate compounds are suitable monomers for thin film polymerization via chemical vapor deposition in a proof-of-concept study. Synthetic carbohydrate-based polymers are explored as biodegradable, biocompatible, and biorenewable materials. A thin film of synthetic polymers bearing sugar residues can also offer a good surface for cell attachment, and thus might be applied in biomaterials and tissue engineering. The possibility of having such thin film deposited from the vapor phase would ease the implementation in complex device architectures. For a proof-of-concept study, sugar vinyl compound monomers are synthesized starting from methyl α-d-glucopyranoside and polymerized by initiated chemical vapor deposition (iCVD) leading to a thin polymer layer on a Si-substrate. Thus, a successful vapor polymerization of the sugar compounds could be demonstrated. Infrared spectroscopy shows that no unwanted crosslinking reactions take place during the vapor deposition. The solubility of the polymers in water was observed in situ by spectroscopic ellipsometry.Graphical abstract

Improving the Resistance of Molecularly Doped Polymer Semiconductor Layers to Solvent.

The ability to form multi-heterolayer (opto)electronic devices by solution processing of (molecularly doped) semiconducting polymer layers is of great interest since it can facilitate the fabrication of large-area and low-cost devices. However, the solution processing of multilayer devices poses a particular challenge with regard to dissolution of the first layer during the deposition of a second layer. Several approaches have been introduced to circumvent this problem for neat polymers, but suitable approaches for molecularly doped polymer semiconductors are much less well-developed. Here, we provide insights into two different mechanisms that can enhance the solvent resistance of solution-processed doped polymer layers while also retaining the dopants, one being the doping-induced pre-aggregation in solution and the other including the use of a photo-reactive agent that results in covalent cross-linking of the semiconductor and, perhaps in some cases, the dopant. For molecularly p-doped poly(3-hexylthiophene-2,5-diyl) and poly[2,5-bis(3-tetradecyl-thiophene-2-yl)thieno(3,2-b)thiophene] layers, we find that the formation of polymer chain aggregates prior to the deposition from solution plays a major role in enhancing solvent resistance. However, this pre-aggregation limits inclusion of the cross-linking agent benzene-1,3,5-triyl tris(4-azido-2,3,5,6-tetrafluorobenzoate). We show that if pre-aggregation in solution is suppressed, high resistance of thin doped polymer layers to solvent can be achieved using the tris(azide). Moreover, the electrical conductivity can be largely retained by increasing the tris(azide) content in a doped polymer layer.

Non-invasive fabrication of plasmonic nanostructures on dielectric substrates coated with transparent-conductive oxide

Modern photonics demands for high-resolution (HR) and deterministic lithography on transparent substrates. Thermal scanning-probe lithography (t-SPL) is a mask-less approach that couples a nanoscopic patterning resolution with the possibility to perform morphological characterizations without damaging delicate substrates unlike it happens for other techniques of similar resolution. In order to operate at its maximum performances, an electric bias between the scanning micromachined cantilever and the sample is needed thereby preventing, in principle, the patterning of transparent materials (that are usually insulators). In this work we demonstrate that by intercalating an ultrathin layer of a transparent conductive oxide (TCO) between an insulating and transparent substrate and the polymeric thin layer it is possible to exploit all the benefits of t-SPL also on challenging optically transparent substrates. Taking advantage of this particular lithographic configuration, we were effectively able to obtain a family of different gold plasmonic nanostructures resonating in the spectral range from the Visible to the Near-Infrared. The ensemble of the different resonators shows optical properties that encourage their exploitation in fields like sensing and thermoplasmonics.

High-performance fiber-shaped Li-ion battery enabled by a surface-reinforced self-supporting electrode.

Herein, we develop a surface-reinforced self-supporting fiber electrode via the simple-yet-reliable ink-extrusion technology to introduce a thin polymer layer at the electrode surface, which endows the fiber architecture with sufficient rigidity for the subsequent fiber cell assembly. Such fiber LiFePO4//Li4Ti5O12 full cells exhibit high linear capacity output (0.144 mA h cm-1) and energy density (0.267 mW h cm-1).

Modelling of the dependence of charge transport in organic layer, containing crystallites, on the layer morphology

A Monte Carlo simulation of the charge carrier mobility in a polymer layer with a thickness of about 100 nm, containing both nanosized crystallites and disordered (amorphous) regions, has been carried out. The mobility has a maximum at a certain energy depth of crystallites. The mobility increases along with an increase in the fraction of crystallites and can exceed its value for the case of disordered material by several orders of magnitude.. Keywords: disordered polymers, thin polymer layer morphology.

Absorption Coefficient and Optical Contrast Modulation through Side Chain Engineering of Electrochromic Polymers

Conjugated polymers can be electrochemically bleached to achieve colored-to-transmissive electrochromic switching. This work presents a side chain engineering approach to enhance colored state absorptivity of an electrochromic polymer, while maintaining high transmissivity in the bleached state. A series of dioxythiophene copolymers with systematic variations in their branched alkyl side chains have been used to understand side chain influence on solubility, aggregation, film morphology and optical constants. By increasing the chromophore density through an appropriate choice of side chains, the absorption coefficient of the colored polymer can be improved by almost 50%, with minimal influence on bleached-state absorption coefficients over the visible region. As such, solution-processed films of high absorbance can be prepared using thin polymer layers to achieve fast electrochromic switching and highly transmissive bleached states. Under optimized conditions, optical contrasts nearing 80% can be reached at the wavelength of maximum absorbance, among the highest reported for solution-processed, cathodically coloring electrochromic polymers. The improved absorption coefficients are especially useful in enhancing the electrochromic performance in the low transmittance regime (colored state transmittance <20%), providing useful insights for designing high contrast electrochromic materials.

Investigation of the Effects of Pulse-Atomic Force Nanolithography Parameters on 2.5D Nanostructures' Morphology.

In recent years, Atomic Force Microscope (AFM)-based nanolithography techniques have emerged as a very powerful approach for the machining of countless types of nanostructures. However, the conventional AFM-based nanolithography methods suffer from low efficiency, low rate of patterning, and high complexity of execution. In this frame, we first developed an easy and effective nanopatterning technique, termed Pulse-Atomic Force Lithography (P-AFL), with which we were able to pattern 2.5D nanogrooves on a thin polymer layer. Indeed, for the first time, we patterned nanogrooves with either constant or varying depth profiles, with sub-nanometre resolution, high accuracy, and reproducibility. In this paper, we present the results on the investigation of the effects of P-AFL parameters on 2.5D nanostructures' morphology. We considered three main P-AFL parameters, i.e., the pulse's amplitude (setpoint), the pulses' width, and the distance between the following indentations (step), and we patterned arrays of grooves after a precise and well-established variation of the aforementioned parameters. Optimizing the nanolithography process, in terms of patterning time and nanostructures quality, we realized unconventional shape nanostructures with high accuracy and fidelity. Finally, a scanning electron microscope was used to confirm that P-AFL does not induce any damage on AFM tips used to pattern the nanostructures.

Detection of Strong Light-Matter Interaction in a Single Nanocavity with a Thermal Transducer.

The concept of strong light-matter coupling has been demonstrated in semiconductor structures, and it is poised to revolutionize the design and implementation of components, including solid state lasers and detectors. We demonstrate an original nanospectroscopy technique that permits the study of the light-matter interaction in single subwavelength-sized nanocavities where far-field spectroscopy is not possible using conventional techniques. We inserted a thin (∼150 nm) polymer layer with negligible absorption in the mid-infrared range (5 μm < λ < 12 μm) inside a metal-insulator-metal resonant cavity, where a photonic mode and the intersubband transition of a semiconductor quantum well are strongly coupled. The intersubband transition peaks at λ = 8.3 μm, and the nanocavity is overall 270 nm thick. Acting as a nonperturbative transducer, the polymer layer introduces only a limited alteration of the optical response while allowing to reveal the optical power absorbed inside the concealed cavity. Spectroscopy of the cavity losses is enabled by the polymer thermal expansion due to heat dissipation in the active part of the cavity, and performed using atomic force microscopy (AFM). This innovative approach allows the typical anticrossing characteristic of the polaritonic dispersion to be identified in the cavity loss spectra at the single nanoresonator level. Results also suggest that near-field coupling of the external drive field to the top metal patch mediated by a metal-coated AFM probe tip is possible, and it enables the near-field mapping of the cavity mode symmetry including in the presence of a strong light-matter interaction.

Omniphobic braid-reinforced hollow fiber membranes for DCMD of oilfield produced water: The effect of process conditions on membrane performance

Recent efforts to realize appropriate hollow fiber membranes (HFMs) for treatment of complex wastewater such as oilfield produced water (PW) have resulted in designing unique surfaces like the omniphobic, for use in membrane distillation (MD) to combat pore wetting and fouling/scaling. However, HFMs, despite their unique advantages, suffer from mechanical inadequacies. The use of polyethylene terephthalate (PET) braid support to strengthen HFMs is gaining attraction for filtration membranes, although their application in MD is scarce. Herein, we report a pioneering omniphobic PET braid-reinforced HFMs (OBRMs) for application in direct contact membrane distillation (DCMD) of PW. The effects of feed type, feed flow rate, feed temperature, and prolonged testing on performance OBRMs are reported. From the obtained findings, a thin polymer (PVDF) layer (∼68 μm) with a single-layer finger-like structure allowed for good vapor flux (up to 15 kg/m2h) while omniphobic skin layer was instrumental in keeping oils and surfactants at bay. Complex PW feed is shown to have more adverse effect on strength of OBRMs than saltwater. Increased temperature negatively affects tensile strength while a turbulent flow regime keeps foulants at bay and mitigates fouling-assisted deterioration. Prolonged testing for nine DCMD cycles (72 h) of treating PW recorded flux recovery up to 85 %, with salt rejection remaining above 99.9 %, a total organic carbon (TOC) rejection up to 98 % and a decline in tensile strength of used membranes by 6.5 %.

Modification of Battery Separators via Electrospinning to Enable Lamination in Cell Assembly

To meet the requirements of today’s fast-growing Li-ion battery market, cell production depends on cheap, fast and reliable methods. Lamination of electrodes and separators can accelerate the time-consuming stacking step in pouch cell assembly, reduce scrap rate and enhance battery performance. However, few laminable separators are available on the market so far. This study introduces electrospinning as a well-suited technique to apply thin functional polymer layers to common battery separator types, enabling lamination. The method is shown to be particularly appropriate for temperature resistant ceramic separators, for which stable interfaces between separator and electrodes were formed and capacity fading during 600 fast charging cycles was reduced by 44%. In addition, a straightforward approach to apply the method to other types of separators is presented, including separator characterization, coating polymer selection, mechanical tests on intermediates and electrochemical validation in pouch cells. The concept was successfully used for the modification of a polyethylene separator, to which a novel fluoroelastomer was applied. The stability of the electrode/separator interface depends on the polymer mass loading, lamination temperature and lamination pressure, whereas poorly selected lamination conditions may cause damage on the separator. Appropriate adhesion force of 8.3 N/m could be achieved using a polymer loading as low as 0.25 g/m2. In case separator properties, coating polymer, morphology of the fibrous coating and lamination conditions are well adjusted to each other, the implementation of electrospinning and lamination allows for faster, more flexible and robust pouch cell production at comparable or better electrochemical cell behaviour.

Optical and morphological properties of ZnO and Alq3 incorporated polymeric thin layers fabricated by the dip-coating method

In this report, we present the influence of polymer matrix on morphological and optical properties of thin films containing zinc oxide (ZnO), tris(8-hydroxyquinolinato)aluminium (Alq3) and ZnO:Alq3. Polyvinylpyrrolidone (PVP) and poly(methyl methacrylate) (PMMA) dissolved in isopropanol and tetrahydrofuran, respectively, were used as polymeric matrices of fabricated composites. The analysed thin layers were deposited on Si substrates using a dip-coating method and characterized by Fourier-Transform Infrared Spectroscopy (FTIR), Energy-Dispersive X-ray spectroscopy (EDX), Atomic Force Microscopy (AFM), Scanning Electron Microscopy (SEM), Spectroscopic Ellipsometry (SE) and photoluminescence (PL). It was found that adding the polymer to Alq3 causes a blueshift in absorption compared to pure Alq3 layers. We also observed photoluminescence in the region of 2.2–2.8 eV for ZnO:Alq3:PMMA and ZnO:Alq3:PVP, as well as for Alq3:PMMA at room temperature. PL measurements showed that adding ZnO to Alq3:polymer matrix did not result in any shift in PL spectra compared to the results of Alq3:polymer layer. AFM and SEM measurements show that relatively smooth films were obtained in the case of composites based on PVP and PMMA. Moreover, a change in the size of ZnO agglomerates depending on polymer used is observed for the three-component layers. We also noticed that the values of the refractive index are higher for the samples in the PVP matrix. However, the opposite behaviour was observed in the case of the extinction coefficient.