Cyclic Olefin Copolymer Films Research Articles

Fabrication of Implantable Microelectrode Array using Cyclic Olefin Copolymer and SU-8 via Photocrosslinking Lamination.

In this work, a fabrication process for implantable electrodes using a Cyclic Olefin Copolymer (COC) substrate and a SU-8 passivation layer was presented. COC and SU-8 were shown to be suitable for implantable neural electrodes due to their biocompatibility, chemical resistance, and thermal stability. The electrodes were successfully patterned on the COC film, and the SU-8 passivation layer was coated while maintaining site-opened via photolithography. The photocrosslinking lamination of the substrate and passivation layer was used to produce electrodes with fine line widths of 20um without applying heat.

The Synergy of Electrospinning and Imprinting for Faithful Replication of Fiber Structures

AbstractElectrospinning is a powerful method to fabricate structures resembling the fibrous texture of the native extracellular matrix. However, the random fiber deposition of the process hinders a faithful reproduction of the fiber mesh morphology on multiple samples, which raises difficulties in experimental designs to systematically test and assess cell response in vitro. A multi‐replication process to precisely reproduce the fiber morphology on different cell culture substrates is developed. The process involves a decoupling of the fiber structure, material, and porosity by combining the key advantages of electrospinning and imprinting. With this, fiber patterns having a diameter between 0.4 and 2.8 µm are replicated on polycarbonate, polystyrene, poly(methyl methacrylate), and cyclic olefin copolymer films. Identical fiber morphology is, then, obtained on porous films having a pore diameter between 2 and 12 µm. Having full control over these parameters allows the multireplication process to engineer well‐characterized cell microenvironments, which can potentially be used to further investigate complex cell–material interactions.

Flexible substrate based on sandwich-structure hydrocarbon resin/aligned boron nitride composites with high thermal conductivity and low dielectric loss

Flexible circuit board materials with low dielectric constant (εr), low dielectric loss (tanδ) and high thermal conductivity (TC) were highly desired for high-frequency and high-speed electronic equipment. Herein, hexagonal boron nitride (h-BN) sheets were filled into highly elastic styrene ethylene butylene styrene (SEBS) matrix and oriented along in-plane direction regularly by hot-pressing method. SEBS/h-BN films exhibited high TC and outstanding flexibility except relatively high tanδ and water absorption. The sandwich structure was designed utilizing pure cyclic olefin copolymer (COC) films as outer surface layers and SEBS/h-BN film as interlayer. The introduction of COC films reduced the tanδ and water absorption of SEBS/h-BN film without reducing original TC obviously. Hybrid SEBS/COC/BN films owning the same components with sandwich-structure films were also fabricated to verify the advantages of designed structure. Sandwich-structure films always kept good flexibility and exhibited low εr (2.7–3.6), low tanδ (<1 × 10−3, 10 GHz), high TC (3.8–17.6 W m−1 K−1) and low water absorption (<0.1%). These films were also fabricated into flexible copper clad laminates and patch antenna operated in sub-6G band. The antenna exhibited a return loss of −32.8 dB and a gain of 7.04 dBi. The flexible substrates show great potential and satisfy large-scale production demand in high TC flexible circuit board materials field.

Broadband terahertz guided-mode resonance filter using cyclic olefin copolymer.

We propose an all-dielectric single-layer guided-mode resonance filter (GMRF) operating in the high-frequency terahertz (THz) region. For the fabrication of thin gratings to achieve strong resonance in the high-frequency region, the refractive index and absorption must be small, while the tensile strength must be high. Cyclic olefin copolymer (COC) films have a lower refractive index and absorption than polyethylene terephthalate (PET) films and a higher tensile yield strength than polytetrafluoroethylene (PTFE) films. Therefore, the COC film was found suitable to fabricate a GMRF operating in the high-frequency THz region. We fabricated COC-based single-layer GMRFs with a thickness of 50 µm and grating periods of 500, 400, 300, 200, and 100 µm; the resonance frequencies of the TE0,1 mode were 0.576, 0.712, 0.939, 1.329, and 2.759 THz, respectively. A shorter grating period caused a greater shift of the resonance to a higher frequency. In particular, the COC film enabled the fabrication of a 100-µm grating period with a ridge width of 32 µm and length of 2 mm, enabling the GMRF to operate up to 2.759 THz, which is very high frequency compared to the previous highest frequency of 0.7 THz. These results were in good agreement with a simulation using rigorous coupled-wave analysis.

Cyclic Olefin Copolymer Interleaves for Thermally Mendable Carbon/Epoxy Laminates.

Thin cyclic olefin copolymer (COC) foils were used as intrinsic thermoplastic healing agents in carbon fiber (CF)-reinforced epoxy laminates. COC films were produced by hot pressing and were interleaved in the interlaminar regions between each EP/CF lamina, during the hand layup fabrication of the laminates. Three samples were produced, i.e., the neat EP/CF laminate without COC, and two laminates containing COC layers with a thickness of 44 μm and 77 μm, respectively. It was observed that the fiber volume fraction decreased, and the porosity increased with the introduction of COC layers, and this effect was more evident when thick films were used. These two effects, combined with the sub-optimal adhesion between COC and EP, caused a decrease in the mechanical properties (i.e., the elastic modulus, flexural strength, interlaminar shear strength and interlaminar fracture toughness) of the laminates. Specimens subjected to mode I interlaminar fracture toughness test were then thermally mended under pressure by resistive heating, through the Joule effect of conductive CFs. A temperature of approximately 190 °C was reached during the healing treatment. The healing efficiency was evaluated as the ratio of critical strain energy release rate (GIC) of the healed and virgin specimens. Healed specimens containing COC layers of 44 μm and 77 μm exhibited a healing efficiency of 164% and 100%, respectively. As expected, the healing treatment was not beneficial for the neat EP/CF laminate without COC, which experienced a healing efficiency of only 2%. This result proved the efficacy of COC layers as a healing agent for EP/CF laminates, and the effectiveness of resistive heating as a way to activate the intrinsic healing mechanism.

Electrically stable polymer-only dielectrics for organic field-effect transistors with low gate leakage current

Abstract Organic-only dielectric films are needed for several electronic applications, particularly in organic field-effect transistors (OFETs). Here, cyclic olefin copolymer (COC) films with the thickness on the order of 100 nm are reported as satisfactory dielectric layers for high-performance and reliable OFETs. The COC dielectric film has a high glass-transition temperature and low free volume, which contribute to its superior insulating properties and high dielectric strength. Moreover, the smooth surface morphology and low surface energy of the COC film are responsible for the formation of highly crystalline structures of the overlying pentacene molecules. Finally, the OFETs with the COC dielectric layers are found to exhibit charge-carrier mobilities up to 1.075 ± 0.05 cm2/V and on/off ratios exceeding 106 while displaying low gate leakage current and negligible hysteresis.

Fabrication and Evaluation of Cyclic Olefin Copolymer Based Implantable Neural Electrode.

The purpose of this paper is to establish fabrication method of cyclic olefin copolymer(COC)-based neural electrode. The fabrication started with preparing COC pellets into COC films by compression molding. Metal layers were deposited on the COC film and attached to a silicon wafer. Laser ablation was used to cut the outer edges and mark alignment keys. The metal layers were patterned using standard photolithography procedures. Finally, the isolated electrodes were laminated. To ensure that the resulting electrode is safe and suitable for long-term implants, in vitro biocompatibility test, impedance evaluation, accelerated soak test, and repeated bend test were conducted. Cytotoxicity test and elution test confirmed the biocompatibility in vitro. The basic performance was not hindered compared to other polymer-based electrodes, and the longevity of the electrode was validated by accelerated soak test. However, repeated bend test revealed that the material might not be suitable for applications where constant bending is required. The COC-based neural electrode was successfully fabricated. The material showed several merits such as biocompatibility, thermoplasticity, low water absorption rate, and high transparency, but should be limited to applications where repeated bending is not required. Electrical circuits in implantable prosthetic devices must be hermetically encapsulated for a long period of time. Material such as COC with extremely low water absorption rate could have a significant impact on the longevity of these devices.

Development and characterization of cyclic olefin copolymer thin films and their dielectric characteristics as CPW substrate by means of Terahertz Time Domain Spectroscopy

We describe recent advances in the fabrication of cyclic olefin copolymer (COC) thin films and their electrical characteristics between 0.3 and 2 THz (terahertz). COC films were fabricated by dissolving the raw material in toluene at different concentrations. Three different techniques were used to fabricate thin solid films of COC: Spin Coating (SC), in-house developed technique Vacuum Solvent Desorption (VSD), and Thermic Solvent Desorption (TSD). Film characteristics such as roughness, thicknesses, and homogeneity were compared. These studies were performed to establish the technique that ensures the lowest roughness, highest homogeneity, and best control over thin film thickness. We also investigated the effect of film roughness and homogeneity on dispersion and losses related to the complex dielectric function ε(f). Then, we used Terahertz Time-Domain Spectroscopy (THz-TDS) characterization up to 2 THz to obtain the dielectric function of COC thin films fabricated by the three methods, and we compare these values with values in literature and state-of-the-art polymeric material BCB. We found that COC has low dispersion (the real part of the dielectric function is almost constant with frequency up to 2 THz), low losses regardless of the fabrication technique, and negligible losses due to roughness and non-homogeneity. Finally, we report the design of a coplanar waveguide, its loss characterization (0.1–0.6 THz), and the microfabrication process on a COC substrate. These results clearly demonstrate that COC films are serious contenders for developing low-loss and low-cost THz electronic devices and optoelectronics.

Induction-heated nanoimprint on soda-lime glass using sapphire molds

The authors developed an induction-heated high-temperature thermal nanoimprint process to directly transfer nanoscale features on sapphire molds to soda-lime glass substrates. Nanoholes of a 650-nm-period hexagonal lattice were directly imprinted in soda-lime glass using the induction-heated thermal nanoimprint configuration as an experimental demonstration. The morphology of nanostructures imprinted on glass substrates at different imprinting process parameters was characterized by scanning electron microscopy and atomic force microscopy and further numerically investigated using a finite element method. The soda-lime glass substrates imprinted with nanohole arrays were then used as secondary templates for further transferring nanostructures onto cyclic olefin copolymer films through another thermal nanoimprint process. The authors also demonstrated surface-enhanced Raman spectroscopy sensing applications on these nanostructured glass substrates after coating them with a thin layer of gold.

High performance cyclic olefin copolymer (COC) membranes prepared with melt processing method and using of surface modified graphitic nano-sheets for H2/CH4 and H2/CO2 separation

In this study, cyclic olefin copolymer (COC) composite membranes were prepared with melt processing method by using of various types of graphite nano-sheets namely graphite oxide (GO), octadecylamine (GO-ODA) and stearic acid (GO-SA) modified graphite oxides. Structural and physical characterization of the modified nano-sheets and membranes were conducted by contact angle measurements, XRD, FTIR, TGA, DMA and SEM analysis. Gas permeability (P) and ideal gas selectivity values (α) of membranes for the H2/CO2 and H2/CH4 were quantified depending on the structural features and the content of fillers. It was found that increasing amount of filler resulted in reducing of CO2 and CH4 permeability for all series of membranes. On the other hand, the H2 permeability values of membranes decreased with the increasing amount of filler in the sample series prepared with GO and GO-ODA but increased in the samples containing of GO-SA. It was also found that the ideal selectivity values of the membrane included 5wt% of GO-SA for the H2/CH4 and H2/CO2 were drastically improved to 498 and 38.6, respectively. Consequently, the ideal selectivity of GO-SA base membrane was increased by 57.5% for H2/CO2 and by 280% for H2/CH4 separation compared to the COC film. The superior separation performances of the system surpass the current permeability–selectivity tradeoff limits (Robeson, 2008 upper bound) for H2/CO2 separation.

Nanostructure transfer using cyclic olefin copolymer templates fabricated by thermal nanoimprint lithography

The authors demonstrate the application of cyclic olefin copolymer (COC) films as secondary nanoimprint templates for transferring sub-100 nm nanostructures. Featureless COC films were first patterned by a thermal nanoimprint process using silicon molds with gratings of various periods from 140 to 420 nm. Morphology of COC gratings imprinted at different processing parameters was characterized by scanning electron microscopy and atomic force microscopy and the grating transfer fidelity was systematically investigated. The nanoimprinted COC substrates were then used as secondary templates in an ultraviolet (UV)-cured nanoimprint lithography process to transfer the grating patterns onto UV-curable epoxy. The authors also demonstrate the application of using these nanoimprinted COC templates to transfer metallic nanostructures onto fiber facets. With good mechanical strength, high transparency to UV light, easy fabrication, and excellent chemical compatibility, COC is a promising material that can be used in low-cost secondary templates for large-volume nanoimprint-based manufacturing of nanostructured devices.

Fabrication of free standing microporous COC membranes optimized for in vitro barrier tissue models

This paper reports a low-cost method for micro fabrication of cyclic olefin copolymer (COC) membranes with optimized thickness and pore size for creation of in vitro tissue models. The method is capable of creating membranes satisfying the technical requirement of in vitro barrier tissue models on microfluidic chips such as small thickness, customizable pore size and pore density, and low auto fluorescence. Micro pore arrays with pore diameter of 3–5μm were created on membranes with 1–2μm thickness with free standing area of more than 3mm2. The method is based on spin coating of a polymer bilayer and hot embossing. First polyvinyl alcohol (PVA) is coated as a sacrificial layer and then COC polymer film is formed on PVA layer. The hot embossing process with a micro fabricated silicon master created indentations on the COC film. A brief oxygen plasma treatment after hot embossing eliminated the residual film in the indentations. The plasma treatment created smooth round shaped holes in the indented area. The membrane was released by dissolving the sacrificial PVA layer in water. The method is highly reproducible and simple indicating its compatibility for fabrication of disposable membranes. We also integrated the membrane in a microfluidic device to test the performance of the membrane as a support layer for cells during in vitro barrier tissue experiments. The experiments conducted with fibroblasts and endothelial cells indicated that the membrane successfully supports cell attachment and proliferation. We conclude that this fabrication method should be a useful tool to create low-cost disposable microporous membrane components for in vitro barrier tissue model systems on microfluidic chips.

Resonant infrared pulsed laser deposition of cyclic olefin copolymer films

Barrier materials on thin-film organic optoelectronic devices inhibit the uptake of water, oxygen, or environmental contaminants, and fabricating them is a major challenge. By definition, these barrier layers must be insoluble, so the usual routes to polymer- or organic-film deposition by spin coating are not problematic. In this paper, we report comparative studies of pulsed laser deposition of cyclic olefin copolymer (COC), an excellent moisture barrier and a model system for a larger class of protective materials that are potentially useful in organic electronic devices, such as organic light-emitting diodes (OLEDs). Thin films of COC were deposited by resonant and nonresonant infrared pulsed laser ablation of solid COC targets, using a free-electron laser tuned to the 3.43 μm C–H stretch of the COC, and a high-intensity nanosecond Q-switched laser operated at 1064 nm. The ablation craters and deposited films were characterized by scanning-electron microscopy, Fourier-transform infrared spectrometry, atomic-force microscopy, high-resolution optical microscopy, and surface profilometry. Thermal-diffusion calculations were performed to determine the temperature rise induced in the film at the C–H resonant wavelength. The results show that resonant infrared pulsed laser deposition (RIR-PLD) is an effective, low-temperature thin-film deposition technique that leads to evaporation and deposition of intact molecules in homogeneous, smooth films. Nonresonant PLD, on the other hand, leads to photothermal damage, degradation of the COC polymers, and to the deposition only of particulates.

Transparent cyclic olefin copolymer/silica nanocomposites

AbstractIn this work, melt blending of fumed nanosilica with cyclic olefin copolymer (COC) was carried out to prepare high strength transparent composites. The effects of various loadings (1, 2, 3 and 5 wt%) of nanosilica on the physical, mechanical, dynamic mechanical, thermal, tribological and optical properties of the COC composites were investigated in detail. The tensile test results showed that the nanocomposite with 3 wt% nanosilica content provides the highest tensile strength (55.6 MPa) compared with the nanocomposite with 5 wt% nanosilica content (54.6 MPa), which is believed to be significantly dependent on better dispersion. Moreover, the glass transition temperature (from tan δ) increased from 184 °C for pure COC to 194.3 °C for the COC composite with 3 wt% nanosilica. The scratch test and nano‐indentation results showed that addition of nanosilica increased the stiffness and hardness of the composite, providing higher scratch resistance and lower frictional coefficient. UV−visible spectroscopy measurements showed that the nanocomposites have excellent optical transparency which is similar to that of the pure COC film. © 2013 Society of Chemical Industry

Surface characterization and properties of plasma‐modified cyclic olefin copolymer/layered silicate nanocomposites

AbstractIn this study, cyclic olefin copolymer (COC)/layered silicate nanocomposites (CLSNs) were prepared by the intercalation of COC polymer into organically‐modified layered silicate through the solution mixing process. Both X‐ray diffraction data and transmission electron microscopy images of CLSNs indicate most of the swellable silicate layers were disorderedly intercalated into the COC matrix. The effect of layered silicate on the mechanical and barrier properties of the fabricated nanocomposites shows significant improvements in the storage modulus and water permeability when compared with that of neat COC matrix. Surfaces of COC and CLSN films were modified by a mixture of oxygen (O2) and nitrogen (N2) plasmas with various treated times, system pressures, and radio frequency (RF) powers. The surfaces of plasma‐modified COC and CLSN were investigated using scanning probe microscopy and contact‐angle measurements. The exposure of the COC and CLSN film to the plasmas led to the combination of etching reactions of polymer surface initiated by plasma and the following addition reactions of new functional groups onto polymer surfaces to change the topology of COC film surfaces. The surface roughness was closely related to how high and how long the RF power was input into the system. The plasmas also led to changes in the surface properties of the CLSN surfaces from hydrophobic to hydrophilic; and the contact angle of water on the surface decreases. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2745–2753, 2005