Cyclic olefin copolymers (COC) are amorphous, transparent thermoplastics composed of cyclic olefin monomers (norbornene) and linear olefins (ethene). They are increasingly utilized as fabrication materials for microsystems and microfluidic devices, owing to their promising features of low water absorption, high electrical insulation, long-term stability of surface treatments, and resistance to a broad variety of acids and solvents. Many manufacturing processes for COC-based devices have been developed in recent decades. These methodologies are categorized as replication methods or fast prototyping as common in fabrication of thermoplastic microfluidic devices. This review gives a full discussion of the features of COCs, the various production processes, and the numerous selected applications in microfluidic platforms. The review also explores COC's composition and fundamental features, as well as fabrication processes and applications in a variety of fields, investigates the material's potential advantages and uses, and attempts to create a comprehensive list of COC's possible benefits. Due to their unique features and simplicity of fabrication, COCs are projected to advance the future of microfluidics, microsystems, and optofluidics.

This article presents a simple method to pattern the surface energy of a substrate using standard microfabrication techniques. Microfluidic devices with hydrophobic polymer substrate patterned with hydrophilic graphene oxide (GO) for the separation of liquid–liquid two-phase systems are reported. The microdevice consists of a cyclic olefin copolymer (COC) substrate bonded to a polydimethylsiloxane (PDMS) element that includes a microchannel. The patterned GO film is characterized using scanning electron, atomic force, and metallurgical microscopies. The contact angle of water on COC surface is measured to be more than 120° and is approximately 10° on the GO-patterned COC surface. Different contact angles could be achieved by tuning the GO with oxygen containing functional groups as well as using different concentrations of GO dispersions. The device is used to separate dye-water droplets dispersed in silicone oil by steering the droplets toward a designated outlet. Using GO as a patterned thin film with tunable hydrophilicity allows for on-chip continuous full separation of water droplets at different flow rates.

Selective altering of surface wettability in microfluidic channels provides a suitable platform for a large range of processes, such as the phase separation of multiphase systems, synthesis of reaction controlled, nanoliter sized droplet reactors, and catalyst impregnation. Herein we study the feasibility to tune the wettability of a flexible cyclic olefin copolymer (COC). Two methods were considered for enhancing the surface hydrophilicity. The first is argon/oxygen plasma treatment, where the effect of treatment duration on water contact angle and COC surface morphology and chemistry were investigated, and the second is coating COC with GO dispersions of different concentrations. For enhancing the hydrophobicity of GO-coated COC surfaces, three reduction methods were considered: chemical reduction by Hydroiodic acid (HI), thermal reduction, and photo reduction by exposure of GO-coated COC to UV light. The results show that as the GO concentration and plasma treatment duration increased, a significant decrease in contact angle was observed, which confirmed the ability to enhance the wettability of the COC surface. The increase in hydrophilicity during plasma treatment was associated with the increase in surface roughness on the treated surfaces, while the increase during GO coating was associated with introducing oxygen-containing groups on the GO-coated COC surfaces. The results also show that the different reduction methods considered can increase the contact angle and improve the hydrophobicity of a GO-coated COC surface. It was found that the significant improvement in hydrophobicity was related to the reduction of oxygen-containing groups on the GO-coated COC modified surface.

This brief focuses on the control of steam power plants using a nonlinear model-based controller with deadtime compensation that is efficient for narrow and wide power demand ranges. The variables to be controlled are the boiler pressure and the power generation. The challenge in controlling this system lies in the ability to overcome the strong nonlinear interactions that a power plant exhibits as well as the deadtime associated with fuel flow adjustment. The derived controller was tested for set point tracking as well as disturbance rejection cases, showing excellent performance and robustness.Index Terms-Deadtime compensation, decoupling control, feedback linearization, nonlinear control, power plant control, power plants.

“Bottom-up” additive manufacturing (AM) is the technology whereby a digitally designed structure is built layer-by-layer, i.e., differently than by traditional manufacturing techniques based on subtractive manufacturing. AM, as exemplified by 3D printing, has gained significant importance for scientists, among others, in the fields of catalysis and separation. Undoubtedly, it constitutes an enabling pathway by which new complex, promising and innovative structures can be built. According to recent studies, 3D printing technologies have been utilized in enhancing the heat, mass transfer, adsorption capacity and surface area in CO2 adsorption and separation applications and catalytic reactions. However, intense work is needed in the field to address further challenges in dealing with the materials and metrological features of the structures involved. Although few studies have been performed, the promise is there for future research to decrease carbon emissions and footprint. This review provides an overview on how AM is linked to the chemistry of catalysis and separation with particular emphasis on reforming reactions and carbon adsorption and how efficient it could be in enhancing their performance.

A new approach for droplet coalescence in microfluidic channels based on selective surface energy alteration is demonstrated. The proposed method involves patterning the surface of cyclic olefin copolymer (COC), a hydrophobic substrate attached to a polydimethylsiloxane hydrophobic microchannel, with graphene oxide (GO) using standard microfabrication techniques. Surface wettability and adhesion analyses confirmed the enhancement of the COC surface energy upon GO patterning and the stability of the GO film on COC. Three representative cases are illustrated to demonstrate the effectiveness of the method on the coalescence of droplets for different droplet flow regimes, as well as the effect of changing the size of the patterned surface area on the fusion process. The method achieves droplet coalescence without the need for precise synchronization.

An original and simple fabrication process to produce thin porous metal films on selected substrates is reported. The fabrication process includes the deposition of a thin layer of gold on a substrate, spin coating of a graphene oxide dispersion, etching the gold film through the graphene oxide layer, and removing the graphene oxide layer. The porosity of the thin gold film is controlled by varying the etching time, the thickness of the gold film, and the concentration of the graphene oxide dispersion. Images by scanning electron and metallurgical microscopes show a continuous gold film with random porosity formed on the substrate with a porosity size ranging between hundreds of nanometers to tens of micrometers. This general approach enables the fabrication of porous metal films using conventional microfabrication techniques. The proposed process is implemented to fabricate electrodes with patterned porosity that are used in a microfluidic system to manipulate living cells under dielectrophoresis. Porous electrodes are found to enhance the magnitude and spatial distribution of the dielectrophoretic force.

Recently, graphene has been explored in several research areas according to its outstanding combination of mechanical and electrical features. The ability to fabricate micro-patterns of graphene facilitates its integration in emerging technologies such as flexible electronics. This work reports a novel micro-pattern approach of graphene oxide (GO) film on a polymer substrate using metal bonding. It is shown that adding ethanol to the GO aqueous dispersion enhances substantially the uniformity of GO thin film deposition, which is a great asset for mass production. On the other hand, the presence of ethanol in the GO solution hinders the fabrication of patterned GO films using the standard lift-off process. To overcome this, the fabrication process provided in this work takes advantage of the chemical adhesion between the GO or reduced GO (rGO) and metal films. It is proved that the adhesion between the metal layer and GO or rGO is stronger than the adhesion between the latter and the polymer substrate (i.e., cyclic olefin copolymer used in this work). This causes the removal of the GO layer underneath the metal film during the lift-off process, leaving behind the desired GO or rGO micro-patterns. The feasibility and suitability of the proposed pattern technique is confirmed by fabricating the patterned electrodes inside a microfluidic device to manipulate living cells using dielectrophoresis. This work adds great value to micro-pattern GO and rGO thin films and has immense potential to achieve high yield production in emerging applications.