Spin-coated Polymer Research Articles

Surface-attached dual-functional hydrogel for controlled cell adhesion based on poly(N,N-dimethylacrylamide)

In this study poly(N,N-dimethylacrylamide) (PDMAA) chains that contains 5 mol% of benzophenone molecules was synthesized and coated on bare organic substrates. Upon irradiation under UV light, the photo-active benzophenone molecules enabled the formation of polymer network as well as attachment of the polymer network onto the organic substrates. From the film thickness (AFM) and photoreaction kinetics of benzophenone (UV-Vis spectroscopy), the surface density of unreacted (active) benzophenone could be controlled. Five model surfaces carrying different densities of active benzophenone were prepared by pre-irradiating approximately 1000-nm spin-coated polymer films at various irradiation energy doses. Addition of protein (laminin) as the bioactive ligands to the partially cross-linked polymeric layer followed by additional irradiation of the mixture under UV light enabled the C,H-insertion crosslinking (CHiC) process between the polymer and the bioactive ligands. This resulted in the so-called dual-functional surface that contains bioactive spots on a biopassive background. Results from immunostaining and cell adhesion experiments showed that the surface density of active benzophenone (0–2.28 × 109 molecules/nm2) played role to the bioactive properties of laminin-decorated spots, while FTIR results indicated that laminin was stable upon irradiation under UV light (365 nm) up to 18 J/cm2.

Chain dynamics in spin-coated films of poly(methyl methacrylate) in a solvent annealing process

The dynamics of poly(methyl methacrylate) chains in spin-coating films during solvent annealing was studied. The neutron reflectometry (NR) measurement revealed that the absorbed solvent molecules homogeneously distributed in the spin-coated film and the solvent fraction increased to 0.35 in toluene vapor. From the real-time NR measurement for a stacked film of deuterated and hydrogenated PMMA in thermal annealing, the diffusion dynamics of the PMMA chain was strongly dependent on the distance from the surface: the polymer chain at the substrate was restricted. On the other hand, the depth dependence of the chain dynamics was weak in the spin-coated film in the solvent annealing process. Whereas the ratio of the diffusion constants of the PMMA chain at the surface and substrate was 50 in thermal annealing, the ratio in toluene vapor was as small as 2. Therefore, the solvent annealing provides sufficient mobility to the polymer chain near the substrate. This result indicates that the solvent annealing method enables the equilibration of a spin-coated polymer film from the surface to the substrate interface. The chain dynamics in a spin-coated poly(methyl methacrylate) (PMMA) film in solvent annealing was studied by in situ neutron reflectivity. The absorbed solvent molecules homogeneously distributed in the spin-coated film and the PMMA chain even near the substrate showed sufficient mobility in the solvent annealing process, while the chain mobility was strongly restricted at the substrate in thermal annealing. This result indicates that the solvent annealing method enables the equilibration of a spin-coated polymer film from the surface to the substrate interface.

Low vacuum annealing of polymer at low temperatures towards direct and scalable growth of graphene

A transfer-free method is demonstrated for the synthesis of graphene flakes directly on insulating substrate (SiO2/Si) by carbon decomposition and diffusion through a layer of nickel. The 100 nm nickel catalyst was deposited on the top of SiO2 (300 nm)/Si substrate. The sandwich structure was prepared wherein spin-coated polymer was used as a carbon source for the graphene formation. The carbon molecules decomposed and diffused into the nickel layer during annealing of sandwich structures in low vacuum (∼5 × 10−1 Pa) at 600–750 °C for 10 min. When cooled to room temperature (25 °C), graphene is formed at the interface between Ni and SiO2/Si, the nickel film was removed by chemical etching. The observed graphene on SiO2/Si substrates is confirmed by optical microscopy, Raman spectroscopy and atomic force microscopy. The Raman spectroscopy mapping over a 55 × 55 μm2 area confirmed the good quality of graphene flakes obtained.

Toward Achieving Highly Ordered Fluorinated Surfaces of Spin-Coated Polymer Thin Films by Optimizing the Air/Liquid Interfacial Structure of the Casting Solutions.

Thin polymer films with well-assembled fluorinated groups on their surfaces are not easily achieved via spin-coating film-fabrication methods because the solution solidifies very rapidly during spin-coating, which hinders the fluorinated moieties from segregating and organizing on the film surface. In this contribution, we have proposed a comprehensive strategy toward achieving well-ordered fluorinated thin films surfaces by optimizing the molecular organization at air/liquid interface of the film-formation solutions. To validate such a route, poly(methyl methacrylate) (PMMA) end-capped with several 2-perfluorooctylethyl methacrylate (FMA) units was employed as the model polymer for investigations. The air/solution interfacial structures were optimized by systematically changing the polymer chain structures and properties of the casting solvents. It was found that the polymers that form loosely associated aggregates (e.g., FMA1- ec-PMMA65- ec-FMA1) and a solvent with better solubility to FMA while having not too low surface tension (i.e., toluene) can combine to produce solutions with well-assembled FMA at the interfaces. By spin-coating the solutions with well-organized interfaces, an ultrathin film with perfluorinated groups that were highly oriented toward the film surface was readily achieved, exhibiting surface energies as low as 7.2 mJ/m2, which is among the lowest reported so far for the spin-coated thin films, and a very high F/C ratio (i.e., 0.98).

Betulin-Constituted Multiblock Amphiphiles for Broad-Spectrum Protein Resistance.

Multiblock-like amphiphilic polyurethanes constituted by poly(ethylene oxide) and biosourced betulin are designed for antifouling and synthesized by a convenient organocatalytic route comprising tandem chain-growth and step-growth polymerizations. The doping density of betulin (DB) in the polymer chain structure is readily varied by a mixed-initiator strategy. The spin-coated polymer films exhibit unique nanophase separation and protein resistance behaviors. Higher DB leads to enhanced surface hydrophobicity and, unexpectedly, improved protein resistance. It is found that the surface holds molecular-level heterogeneity when DB is substantially high due to restricted phase separation; therefore, broad-spectrum protein resistance is achieved despite considerable surface hydrophobicity. As DB decreases, the distance between adjacent betulin units increases so that hydrophobic nanodomains are formed, which provide enough landing areas for relatively small-sized proteins to adsorb on the surface.

Semitransparent conductive carbon films synthesized by sintering spin-coated sp3-based network polymer

We synthesized semitransparent conducting thin films of amorphous carbon from sp3-rich network polymer. The films showed a reasonable optical transparency (58–73% transmission in the wavelength range of 380–2200 nm), a low electric resistivity (6.7 × 10−3 Ω cm), and durability against corrosive chemical reagents. The sintering of the amorphous films results in the formation of a carbon honeycomb lattice in the films.

Interface control between an indium–tin-oxide electrode and a hole-transport polymer via reactive self-assembled monolayers

The indium–tin-oxide (ITO) surface was modified with self-assembled monolayers (SAMs) having different terminal groups including methyl, vinyl, benzophenone, and azo units. A hole-transport layer of fluorene-phenoxazine copolymer was spin-coated on the surface and then irradiated with UV light to induce photochemical reaction at the interface between the SAMs and the polymer. It was observed that the SAMs having the benzophenone and azo terminal groups can tether the spin-coated polymer after UV irradiation. The photochemical tethering was effective in improving charge injection from the ITO anode to the hole-transport polymer as well as in improving the adhesion strength of the polymer to the substrate. It is considered that the covalent tethering can be an important factor for improving the interfacial characteristics of organic/inorganic junctions.

Opportunities and challenges in probing local composition of organic material blends for photovoltaics

Abstract

ITO-Free, Fully Solution Processed Transparent Organic Light-Emitting Electrochemical Cells on Thin Glass

Organic light emitting diodes (OLEDs) have the advantages of self-emitting property, high luminous efficiency, full-colour capability, wide viewing angle, high contrast, low power consumption, low weight and flexibility. All these capacitate OLEDs to be an attractive optical source for display and lighting applications. However, the current manufacturing cost is still relative high, which obstacle its success in the display and lighting market. The main problems are indispensable low work function material for cathode and/or electron injection layer such as Ba, LiF, which require vacuum deposition and/or inert fabrication atmosphere, and widely used anode ITO which are not solution processable. Therefore, the fully solution processing manufacturing techniques are under intense investigation in order to reduce the cost. Compared to OLEDs, its derivation, organic light-emitting electrochemical cells (OLECs), show an intrinsic advantage in fully solution processing. By mixing metal ions and a solid electrolyte with light-emitting polymers as active materials, an in-situ doping and in-situ PN-junction can be generated within a three layer sandwich device. Because of this doping effect, work function adaption is not necessary and air-stable flexible electrodes like PEDOT:PSS can be used. Hereby, a manufacturing process for fully solution-processed transparent OLECs is presented, which consist of inkjet printed PEDOT:PSS anode and cathode, spin-coated ZnO interlayer, and spin-coated yellow light-emitting polymer plus dopant. Inkjet printing the electrode give the advantages of mask-free and spin-coating provides the homogeneous active layers. Furthermore, by manufacturing on 70 µm thin glass, a relative flexible transparent light source can be realized and enable the potential emerging applications like signal display on textiles.

Isatin thiosemicarbazones promote honeycomb structure formation in spin-coated polymer films: concentration effect and release studies

Isatin thiosemicarbazone mixed biopolymer films as potential biomaterial for antibacterial and anti-inflammatory protection.

Correlation between the fine structure of spin-coated PEDOT:PSS and the photovoltaic performance of organic/crystalline-silicon heterojunction solar cells

We investigated the relationship between the fine structure of spin-coated conductive polymer poly(3,4-ethylenedioxythiphene):poly(styrene sulfonate) (PEDOT:PSS) films and the photovoltaic performance of PEDOT:PSS crystalline-Si (PEDOT:PSS/c-Si) heterojunction solar cells. Real-time spectroscopic ellipsometry revealed that there were two different time constants for the formation of the PEDOT:PSS network. Upon removal of the polar solvent, the PEDOT:PSS film became optically anisotropic, indicating a conformational change in the PEDOT and PSS chain. Polarized Fourier transform infrared attenuated total reflection absorption spectroscopy and Raman spectroscopy measurements also indicated that thermal annealing promoted an in-plane π-conjugated Cα = Cβ configuration attributed to a thiophene ring in PEDOT and an out-of-plane configuration of -SO3 groups in the PSS chain with increasing composition ratio of oxidized (benzoid) to neutral (quinoid) PEDOT, Iqui/Iben. The highest power conversion efficiency for the spin-coated PEDOT:PSS/c-Si heterojunction solar cells was 13.3% for Iqui/Iben = 9–10 without employing any light harvesting methods.

Sub-100 nm gold nanohole-enhanced Raman scattering on flexible PDMS sheets

Surface-enhanced Raman spectroscopy (SERS) is a highly sensitive vibrational spectroscopy technique enabling detection of multiple analytes at the molecular level in a nondestructive and rapid manner. In this work, we introduce a new approach to fabricate deep subwavelength-scaled (sub-100 nm) metallic nanohole arrays (quasi-3D metallic nanoholes) on flexible and highly efficient SERS substrates. Target structures have been fabricated using a two-step process consisting of (i) direct pattern transfer of spin-coated polymer films onto polydimethylsiloxane (PDMS) substrates by plasma etching with transferred anodic aluminum oxide masks, and (ii) producing SERS-active substrates by functionalization of the etched polymeric films followed by Au deposition. Such an all-dry, top-down lithographic approach enables on-demand patterning of SERS-active metallic nanoholes with high structural fidelity even onto flexible and stretchable substrates, thus making possible multiple sensing modes in a versatile fashion. For example, metallic nanoholes on flexible PDMS substrates are highly amenable to their integration with curved glass sticks, which can be used in optical fiber-integrated SERS systems. Au surfaces immobilized by probe DNA molecules show a selective enhancement of Raman scattering with Cy5-labeled complementary DNA (as compared to flat Au surfaces), demonstrating the potential of using the quasi-3D Au nanohole arrays for bio-sensing applications.

Influence of thermal annealing on a capacitive humidity sensor based on newly synthesized macroporous PBObzT2

In this work, we report on the application of a newly synthesized macroporous polythiophene derivative, benzo[b]thiophene end-capped dioctyloxy-benzene(PBObzT2), in the fabrication of a capacitive humidity sensor. The sensor has been fabricated by spin-coating polymer solution in the gap between pre-deposited aluminum electrodes to form a coplanar Al/PBObzT2/Al capacitive humidity sensor. We have also demonstrated how effectively thermal annealing has improved the physical aspects of the active layer and sensing properties of the sensor. The sensor’s capacitance is measured against RH variations at different frequencies. Particularly, at an optimum annealing temperature of 75°C, the sensor exhibits high sensitivity, fast response and low hysteresis. The hydrophobic nature of the polymer makes it highly appropriate to be used in the humidity sensors.

One-dimensional PMMA–V2O5 photonic crystals used as color indicators of chloroform vapors

The fabrication and characterization of one-dimensional photonic crystals (1D-PC) in the form of quarter-wavelength multilayered stack (Bragg stack) are presented. The 1D-PC comprises alternatively deposited spin-coated polymer PMMA (Poly(methyl methacrylate)) films as low-refractive index material that change thickness upon exposure to chloroform vapors, and both dense and porous V2O5 films providing both high optical contrast. The possibility of using PMMA–V2O5 structure as an omnidirectional reflector in both cases is confirmed experimentally. Besides, the prospect of utilizing the studied structures as optical indicators of chloroform vapors is demonstrated and discussed.

Low Bandgap Conjugated Polymers Based on a Nature-Inspired Bay-Annulated Indigo (BAI) Acceptor as Stable Electrochromic Materials

The donor–acceptor (D–A) approach, which is to incorporate alternating electron-rich (donor) and electron-deficient (acceptor) units along the conjugated polymer mainchain, has become an effective method to provide an informed search for high performance electrochromic low bandgap polymers. Herein a potent electron acceptor, namely, a much more soluble version of the nature-inspired bay-annulated indigo (BAI), was employed in the synthesis of two solution-processable donor–acceptor polymers for efficient electrochromic devices (ECDs). The devices fabricated from spin-coated polymer thin films can switch reversibly between deep blue and transmissive light green hues, with high optical contrasts in the visible and near-infrared (NIR) regions, good coloration efficiency and promising ambient stability. In particular, electrochromic devices based on the copolymer containing a carbazole donor unit exhibit optical contrasts of 41% and 59% in the visible and NIR regions, respectively, and a long-term stability o...

Organic distributed feedback laser to monitor solvent extraction upon thermal annealing in solution-processed polymer films

Solution-processed polymer films are used in multiple technological applications. The presence of residual solvent in the film, as a consequence of the preparation method, affects the material properties, so films are typically subjected to post-deposition thermal annealing treatments aiming at its elimination. Monitoring the amount of solvent eliminated as a function of the annealing parameters is important to design a proper treatment to ensure complete solvent elimination, crucial to obtain reproducible and stable material properties and therefore, device performance. Here we demonstrate, for the first time to our knowledge, the use of an organic distributed feedback (DFB) laser to monitor with high precision the amount of solvent extracted from a spin-coated polymer film as a function of the thermal annealing time. The polymer film of interest, polystyrene in the present work, is doped with a small amount of a laser dye as to constitute the active layer of the laser device and deposited over a reusable DFB resonator. It is shown that solvent elimination translates into shifts in the DFB laser wavelength, as a consequence of changes in film thickness and refractive index. The proposed method is expected to be applicable to other types of annealing treatments, polymer-solvent combinations or film deposition methods, thus constituting a valuable tool to accurately control the quality and reproducibility of solution-processed polymer thin films.

Electrooptic Kerr effect of porphyrin H-aggregates in polymer films: Polymer specific spectral blue shift

J- and H-aggregates of porphyrin molecules (TPPS4) in spin-coated polymer films have been studied by electroabsorption and circular dichroism (CD) spectroscopy. A spectral blue shift of the H-band due to the electrooptic Kerr effect was observed for the first time. This occurs only for a polyvinylpyrrolidone (PVP) film, with negligibly small spectral shift observed in polyvinyl alcohol (PVA), polyvinyl sulfate (PVS), and polyacrylic acid (PAA) films, in contrast to the red shift of the J-band which is commonly observed for any host polymers. Accordingly, the CD activity in both of J- and H-bands is more enhanced in PVP films than in PVA films. The mechanism of the blue and red shifts of the respective H- and J-bands is discussed by invoking a helical structure in micro-aggregates, which is compatible with the CD spectra, based on the molecular rearrangement model. It is proved that blue- and red-shifts occur evenly to cancel each other in the H-band if a simple helical structure is assumed, in good agreement with no spectral shifts in the H-band in PVA, PVS, and PAA films.

Solution-processed crystalline silicon double-heterojunction solar cells

Crystalline silicon double-heterojunction solar cells were fabricated using Si/organic and Si/Cs2CO3 heterojunctions. The front heterojunction is formed by spin-coating conductive polymer poly(3,4-ethyenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) on n-type Czochralski (CZ) (100) silicon, which separates the photogenerated carriers and blocks the electron dark current while allowing the photocurrent to pass through. The rear heterojunction, formed by spin-coating Cs2CO3 and polyethylenimine (PEI) dissolved in 2-ethoxyethanol and Al metal evaporation, functions as a back surface field that reduces the hole dark current while allowing the electron photocurrent to pass through. The double-heterojunction device showed a power conversion efficiency of 12.7% under AM1.5G simulated solar light exposure.

Optical, Thermal and Fluorescence Properties of Spin-Coated Solid Polymer Electrolyte Films

Polyethylene oxide (PEO) −Polyvinylpyrrolidone (PVP) blended (50/50) filled with different concentration of Co2+ ions were prepared by spin-coating method. The films were characterized by UV-Absorption, TG/DTA, SEM and Fluorescence techniques. From the UV-Vis absorption results shows that optical band gap found decreases with increase cobalt ions content, this indicates that there are electrons inter band transition taken place. The thermal stability of the polymer blend has improved after filling CoCl2 increases; this indicates that the filler acts as a plasticizer. In particular, remarkable enhancement of the fluorescence properties of CoCl2 doped polymer blend was observed in different excitation light from 350 to 476 nm. The linear optical constants such as the extinction coefficient (k), refractive index (n), real (ɛr) and imaginary (ɛi) dielectric constant, optical conductivity (σopt) are calculated. The optical properties i.e., good photostability and larger stokes shift suggesting, in order to evaluate their potentialities for their use in electrochemical display device applications.

Inkjet Printed Organic Light-emitting Electrochemical Cells for Disposable Lab-on-chip Applications Manufactured at Ambient Atmosphere

Microfluidic lab-on-a-chip devices can be used for chemical and biological analyses such as DNA tests or environmental monitoring. Such devices integrate most of the basic functionalities needed for the analysis on a microfluidic chip. When using such devices, cost and space intensive lab equipment is thus not necessary. However, in order to make a monolithic and cost-efficient/disposable sensing device, direct integration of excitation light source for fluorescent sensing is often required. Organic light emitting diodes (OLEDs) have the advantages of self-emitting property, high luminous efficiency, full-color capability, wide viewing angle, high contrast, low power consumption, low weight and flexibility. All these capacitate OLEDs to be a suitable optical source for microfluidic devices. However, low work function cathode and/or electron injection layer like Ba, LiF are indispensable for high bright OLEDs, which require vacuum deposition and inert fabrication atmosphere. Hereby we introduce a fully solution processable deviation of OLEDs, organic light-emitting electrochemical cells (OLECs) as a low-cost excitation light source for a microfluidic sensing platform. By mixing metal ions and a solid electrolyte with light-emitting polymers as active materials, an in-situ doping and in-situ PN-junction can be generated within a three layer sandwich device. Because of this doping effect, work function adaption is not necessary and air-stable cathodes like silver can be used. A manufacturing process for fully solution-processed OLECs is presented, which consist of an inkjet-printed silver cathode, spin-coated blue light-emitting polymer plus dopants and an inkjet-printed PEDOT:PSS transparent top anode. Furthermore, by replacing silver with ITO, a fully transparent blue OLEC is able to emit>2500cd/m2 light under pulsed driving mode, which fulfils requirements for simple fluorescent on-chip sensing applications.