Nickel Mold Research Articles

The design and fabrication of thermoplastic microfluidic chips with integrated micropillars for particle separation

Microfluidic technology utilizing the deterministic lateral displacement (DLD) method holds significant promise for efficiently separating micro-particles and biological cells. Despite the notable high throughput advantages associated with DLD chips, their widespread application is impeded by the substantial manufacturing costs of tens of thousands of micropillars. This study aims to explore the feasibility of employing the injection molding method for the mass production of DLD microfluidic chips. A multistage DLD chip with varied critical diameters was designed to isolate white blood cells from the human whole blood. The separation effectiveness was verified with the polydimethylsiloxane chip fabricated by standard soft lithography. Subsequently, nickel mold inserts were electroformed to fabricate thermoplastic DLD chips via the injection molding. The replication quality of micropillars under different molding parameters was studied. The capability of injection-molded chips to effectively achieve particle separation was validated. Results showed that thermoplastic chips with good replication quality were obtained, providing a scale-up production strategy for fabricating polymer-based microfluidic chips for disposable separation applications.

Pulse current electroforming of Ni-PTFE nanocomposite mold insert with long-lifetime and anti-adhesive properties

Polymeric micro features tend to deform and break under the demolding force during injection molding process, which becomes a bottleneck problem limiting its precision manufacturing. To reduce the polymer-mold interfacial adhesion, nickel-polytetrafluoroethylene (Ni-PTFE) nanocomposite molds with low surface adhesion and high wear resistance were manufactured via pulse current electroforming. The electrodeposited Ni-PTFE nanocomposite showed a good hydrophobic property and low friction coefficient (between 0.1 and 0.3) than pure nickel (0.78). Compared with direct current, pulse current electrodeposition was beneficial to reduce the crystallite size and internal stress, thus improving the wear resistance and reducing the cracking defects. The hardness of pulse current electrodeposited Ni-PTFE reached 442.3 HV, which was 51.7 % higher than that of pure nickel. Compared to nickel mold, Ni-PTFE nanocomposite mold significantly improved the dimensional accuracy of molded microfluidic chips. This study systematically investigates the Ni-PTFE nanocomposite electroforming process under both direct and pulse currents, which provides a new approach for the manufacturing of high-performance precision injection mold insert.

Enhancing structural replication of microfluidic chips: Parameter optimization and mold insert modification

AbstractThe demolding process in micro‐injection molding constitutes a critical phase, exerting a decisive influence on the quality of polymer microstructures. In this study, the demolding forces of PMMA microfluidic chips were measured under different demolding temperatures, packing pressures, and demolding speeds by using pure nickel (Ni) mold insert. The dimensional deviations of the microchannels with different aspect ratios were analyzed. In addition, the effect of mold insert modification on the demolding force was further analyzed. The results showed that the effect of demolding temperature on the demolding force was the most significant, and the peak demolding force decreased with the decrease in temperature. The width of the microchannels increased and the depth decreased after demolding, while the opposite results were observed for the micro‐mixing structures. However, the dimensional deviation of the micro‐mixing structures was larger than that of the microchannels. Using the optimal molding parameters, the peak demolding force could be reduced from 114.0 N at 110°C to 47.0 N, a decrease of 58.8%. It is noteworthy that, when the microchannel was narrower than 100 μm, achieving precise replication of microchannel dimensions became progressively more challenging as the microchannel width decreased. Using the Ni‐WS2 mold insert with low surface energy and low friction coefficient, the demolding force could be further reduced by 38.3%. The effect of the molding quality of microfluidic chip microstructures on the mixing performance of heavy metals was demonstrated by micro‐mixing experiments.Highlights Demolding temperature crucially affects microstructure dimensions. Optimal parameters and modified mold insert reduce demolding force by 38.3%. Dimensional deviation increases with the increase of microchannel aspect ratio. Optimized microfluidic chip enhances Co2+ chemiluminescence by 6.42%.

Microscale shaping and rounding of ridge arrays and star pattern features on nickel mould via electrochemical polishing

Microscale shaping and rounding of ridge arrays and star pattern features on nickel mould via electrochemical polishing

Peelable porous nanosheet fabricated by roll-to-roll coating and nanoimprinting technique

A combination of roll-to-roll coating and nanoimprinting technique is proposed for large-scale fabrication of porous nanosheets. Poly (d,l-lactic acid) (PLA) in 2-methoxy-1-methylethyl-acetate is roll-to-roll coated on polypropylene substrate to obtain nanosheets with thickness above ca. 95 nm. Roller nanoimprinting with a nickel mold is applied to fabricate pores on nanosheets with diameter of ca. 1.2 μm. The imprinted PLA nanosheets with thickness above ca. 129 nm can be directly peeled from the substrate using a polyester adhesive tape frame with open circle of 30 mm. This method shows promising potential for achieving continuous production of porous nanosheets to facilitate their application.Graphical Roll-to-roll coating and nanoimprinting techniques are employed to massively fabricate peelable porous nanosheets

Tribological properties and corrosion resistance of nickel-based composite mold inserts containing lubricant nanoparticles for micro-injection molding

During the micro-injection molding process, the lifetime of mold inserts is severely limited by high-pressure impact conditions and demolding friction. To investigate the tribological properties and durability of mold insert, nickel-based composite mold inserts have been fabricated by electroforming adding polytetrafluoroethylene (PTFE), molybdenum disulfide (MoS2) and tungsten disulfide (WS2) nanoparticles, respectively. The surface morphology of pure nickel (Ni) and composite mold inserts were characterized. The Ni grain sizes of the composite mold inserts significantly decreased without changing the grain orientation and phase composition. The maximum microhardness of Ni-WS2 mold inserts was increased from 278.2 HV of pure Ni to 456.0 HV, an increase of 1.64 times, while the minimum friction coefficient against Si3N4 ball was reduced to 0.25. In addition, Ni-WS2 mold inserts exhibited excellent tribological properties, and their wear resistances were further investigated at different sliding speeds and external loads. With the increase of sliding speed and load, the self-lubricating property of the composite mold inserts would gradually disappear and the wear rate would increase significantly. The formation of a uniform and dense friction transfer film is the key to reducing the friction coefficient and wear rate. Furthermore, the corrosion resistance of the mold inserts was improved to some extent with the addition of the three nanoparticles. In dynamic electrochemical tests, the corrosion current density of Ni-PTFE mold insert was 3.083 ± 0.228 × 10−6 A/cm2 and the corrosion rate was 0.036 ± 0.003 mm/year, which showed the best corrosion resistance.

Nanoimprint Mold Consisting of an Adhesive Lap Joint between a Nanopatterned Metal Sleeve and a Carbon Composite Roll.

Roll-to-roll nanoimprinting is an emerging technology that has revolutionized the sectors of flexible electronics, thin films, and solar cells with its high throughput. However, there is still room for improvement. In this study, a FEM analysis (in ANSYS) was carried out on a large-area roll-to-roll nanoimprint system in which the master roller consists of a large nanopatterned nickel mold joined to a carbon fiber reinforced polymer (CFRP) base roller using epoxy adhesive. Deflections and pressure uniformity of the nano-mold assembly were analyzed under loadings of different magnitudes in a roll-to-roll nanoimprinting setup. Optimization of deflections was performed with applied loadings, and the lowest deflection value was 97.69 nm. The adhesive bond viability was assessed under a range of applied forces. Finally, potential strategies to reduce deflections were also discussed, which can be helpful in increasing pressure uniformity.

Development of a fabrication process for production of diffractive optics.

In this study, a novel fabrication process, to the best of our knowledge, was developed to fabricate a glass harmonic diffractive lens. In this process, a polymethylmethacrylate master of the diffractive lens was machined using single-point diamond turning. Then an electrolytic plating process was conducted to grow a reverse nickel (Ni) mold. Precision compression molding was performed using the Ni mold to replicate the diffractive lens structures onto a glass surface. Surface measurements and optical testing show that the replicated diffractive lenses by the proposed method have high tolerances and require optical performance, demonstrating a high-volume, high-precision, and cost-effective process. The proposed method will be critical for consumer products where glass optics are increasingly used in lens assemblies.

Precision electroforming of nickel nanocomposite mould for defects-free demoulding in polymer micro replication: Surface properties, performance validation and mould release mechanism

Microinjection moulding and micro/nano hot embossing are two promising manufacturing processes for the mass production of polymer workpieces with micro/nano structures. However, adhesion and friction between polymer workpieces and mould tools can cause structural distortion and surface damage. Besides, the nickel mould's lifetime is limited by its low hardness and wear resistance. To address these issues, we proposed a new methodology to codeposit micro/nanomaterials into nickel mould for microhardness enhancement and effective mould release. In this study, polytetrafluoroethylene (PTFE) microparticles, tungsten disulfide (WS2) and molybdenum disulfide (MoS2) nanosheets were incorporated into nickel mould by electroforming. Cobalt was added as a secondary phase to improve the microhardness and wear resistance of the composite mould. The result indicated that WS2 nanosheets achieved the most significant performance enhancement among three micro/nanomaterials, represented as the microhardness improved from 191 HV for pure nickel to 564 HV for nickel/WS2 nanocomposites, along with the coefficient of friction (COF) against the polymethyl methacrylate (PMMA) pin reducing from 0.72 to 0.10 in the initial stage of the sliding. With the incorporation of micro/nanomaterials, the wettability altered from hydrophilic for pure nickel to hydrophobic for the composite moulds. The study shows that the addition of cobalt improved the microhardness of the composite moulds but meanwhile induced more adhesive wear during the pin-on-disc test. Finally, a nickel/WS2 nanocomposite mould is successfully fabricated via electroforming with feature sizes from 70 to 180 μm and its lubricating properties are validated by micro hot embossing PMMA microfluidic chips with good surface quality and structural integrity.

Maskless lithography for large area patterning of three-dimensional microstructures with application on a light guiding plate.

This paper presents a maskless lithography system that can perform three-dimensional (3D) ultraviolet (UV) patterning on a photoresist (PR) layer. After PR developing processes, patterned 3D PR microstructures over a large area are obtained. This maskless lithography system utilizes an UV light source, a digital micromirror device (DMD), and an image projection lens to project a digital UV image on the PR layer. The projected UV image is then mechanically scanned over the PR layer. An UV patterning scheme based on the idea of obliquely scanning and step strobe lighting (OS3L) is developed to precisely control the spatial distribution of projected UV dose, such that desired 3D PR microstructures can be obtained after PR development. Two types of concave microstructures with truncated conical and nuzzle-shaped cross-sectional profiles are experimentally obtained over a patterning area of 160 ×115 mm2. These patterned microstructures are then used for replicating nickel molds and for mass-production of light-guiding plates used in back-lighting and display industry. Potential improvements and advancements of the proposed 3D maskless lithography technique for future applications will be addressed.

Multi-functional terahertz metamaterials based on nano-imprinting.

This paper reports a multi-functional terahertz (THz) metamaterial based on a nano-imprinting method. The metamaterial is composed of four layers: 4 L resonant layer, dielectric layer, frequency selective layer, and dielectric layer. The 4 L resonant structure can achieve broadband absorption, while the frequency selective layer can achieve transmission of specific band. The nano-imprinting method combines electroplating of nickel mold and printing of silver nano-particle ink. Using this method, the multilayer metamaterial structures can be fabricated on ultrathin flexible substrates to achieve visible light transparency. For verification, a THz metamaterial with broadband absorption in low frequency and efficient transmission in high frequency is designed and printed. The sample's thickness is about 200 µm and area is 65 × 65 mm2. Moreover, a fiber-based multi-mode terahertz time-domain spectroscopy system was built to test its transmission and reflection spectra. The results are consistent with the expectations.

A flexible and stretchable photonic crystal film with sensitive structural color-changing properties for spoiled milk detection.

This study proposes a flexible and stretchable 3D polymer film with photonic crystals for the visible detection of spoiled milk. Thermoplastic polyurethane (TPU) was used as the substrate for the photonic crystal structure. The back barrier layer with a regular array of nanohemispheres of anodic aluminum oxide film was used as a template for electroforming a nickel mold. The nanohemisphere array was then nanoimprinted onto the TPU substrate to form a strain-controllable photonic crystal (SCPC) structure on it. Food spoilage can be easily detected by the structural color change caused by the gas it produces. Experimental results confirmed that the structural color change of the fabricated SCPC TPU film occurred when the elongation (ΔL) of the film reached 0.2mm (1.2%). Furthermore, spoiled milk detection experiments showed that the proposed SCPC TPU film is a highly intelligent and cost-effective biosensor for detecting spoiled food in a container.

Injection Molding of Thermoplastics for Low-Cost Nanofluidic Devices

Thermoplastic micro- and nanofluidics are increasing in popularity due to their favorable chemical and physical properties as an alternative to poly(dimethyl siloxane) (PDMS)-based devices, which are more widely used in academia. Additionally, their fabrication is compatible with industrial processes, such as hot embossing and injection molding. Nevertheless, producing devices with sub-micrometer channel heights and low roughness while retaining high-throughput molding remains challenging. This article details the combination of grayscale e-beam lithography (g-EBL) and injection molding as a fabrication route for capillary 3D thermoplastic nanofluidic devices with unprecedented accuracy in the sub-micrometer range. We employed g-EBL to pattern the device profile in a poly(methyl methacrylate) (PMMA)-based resist, which served as a substrate for the subsequent fabrication of a negative nickel mold by using electroforming. These molds are used to fabricate devices in PMMA and cyclic olefin polymers (COP) using injection molding. We show that the 3D height profile of the nanofluidic devices is maintained throughout the entire replication cycle within very tight tolerances, retaining its nanoscale topography on a millimeter-length scale. Moreover, somewhat surprisingly, the roughness in the inflow section of the devices was significantly reduced, which we attribute to the nickel mold fabrication. Last, we show that the capillary-driven devices can be used to size-dependently trap nanoparticles of various sizes in a reliable and facile manner while only requiring a 4 μL sample volume. The presented device and fabrication procedure paves the way for applications in various scientific fields, ranging from immunology to neurology and material science, in a cost-effective manner.

A simple electrochemical immunosensor based on a gold nanoparticle monolayer electrode for neutrophil gelatinase-associated lipocalin detection

An electrochemical immunosensor for the accurate detection of cat neutrophil gelatinase-associated lipocalin (NGAL) in urine samples based on an electrode with a monolayer of gold nanoparticles (AuNPs) was proposed in this study. To fabricate the sensing electrode, a nickel mold with concave micron hemisphere array was prepared and then used to transfer the micron hemispherical structure onto a polyethylene terephthalate (PET) film using the hot embossing technique. A gold thin film was sputtered onto the micron hemispherical structure array, after which 1,6-hexanedithol and AuNPs were uniformly deposited on the PET membrane to form a sensing electrode. The NGAL concentrations were measured by electrochemical impedance spectroscopy after attaching the anti-NGAL. Results revealed that the proposed sensing scheme exhibited a wide dynamic detection range from 1 to 100 ng/mL, which is far enough to distinguish the healthy (NGAL concentration <10 ng/mL) from the damaged kidney. A low limit of detection and high sensitivity of 0.47 ng/mL and 10261.8 Ω ng−1mL, respectively, were also measured. After performing real sample detection using urine samples from cats collected at a veterinary hospital, the results confirmed that the proposed NGAL detection approach in this research could accurately detect the concentration of NGAL in cat urine samples.

Synthesis of two-dimensional WS2/nickel nanocomposites via electroforming for high-performance micro/nano mould tools

To reduce the adhesion and friction between polymer and mould surfaces during polymeric micro/nano structures replication, we have used tungsten disulfide (WS2) nanosheets to fabricate high-performance nickel/WS2 nanocomposite mould using electroforming. However, the aggregation of WS2 nanosheets in the electroforming solution is a critical issue that influences the mechanical and tribological properties of the mould. In this study, we first propose a new strategy of combining anionic surfactant sodium dodecyl sulfate (SDS) and cationic surfactant cetyltrimethylammonium bromide (CTAB) to achieve uniform dispersion and incorporation of WS2 nanosheets in the electroformed nickel mould. Our results indicate that appropriately designing the structure of CTAB-SDS complex can achieve a stable WS2 dispersion, contributing to the uniform co-deposition of WS2 nanosheets into nickel mould. The combination of high concentration of CTAB and SDS (1.0 g/L CTAB and 1.0 g/L SDS) significantly improved the dispersibility and incorporation of WS2 into the nickel matrix, compared to individual SDS or CTAB. Consequently, the maximum hardness enhanced by 350% from 284 HV for pure nickel to 1280 HV for nickel/WS2 nanocomposite mould, along with the coefficient of friction (COF) against the polymethyl methacrylate (PMMA) pin reducing from 0.75 to 0.31. It is also found that CTAB promotes particle encapsulation while SDS improves the particle dispersion but cannot control the particle incorporation. The surface wettability of nickel/WS2 mould altered to hydrophobicity from hydrophilicity of nickel mould, where the adhesion-induced wear caused by polymer pin significantly reduced. Moreover, the surface roughness did not change much with the incorporation of WS2 into the mould, which is acceptable for mould applications. Finally, the nickel/WS2 nanocomposite mould was successfully fabricated via electroforming and its self-lubricating properties was validated by micro hot embossing PMMA microfluidic chips with good surface quality.

A two-in-one immunoassay biosensor for the simultaneous detection of Odontoglossum ringspot virus and Cymbidium mosaic virus

This study proposes a highly sensitive and label-free electrochemical immunosensor that can simultaneously detect Phalaenopsis virus, Odontoglossum ringspot virus (ORSV) and Cymbidium mosaic virus (CymMV). First, a microhemisphere array nickel mold was made using the semiconductor lithography process combined with the electroforming process. Afterward, hot embossing was used to print the microhemisphere array on a polyethylene terephthalate film. Then, to prepare the detection electrode with a nano/micro-hybrid structure, a thin gold film was sputtered on the microhemisphere array surface, followed by successively immobilizing 1,6-hexanedithiol and colloidal gold nanoparticles on the surface of the gold film. Finally, the ORSV and CymMV antibodies were mixed and immobilized on the electrode using the self-assembled monolayer method to prepare the two-in-one sensing electrode. The ORSV and CymMV were simultaneously detected using electrochemical differential pulse voltammetry. The biosensor developed in this study has a detection limit of 0.5 ng/mL. Notably, the virus can be detected even after diluting the sap of the infected leaf 100 times.

Fabrication of permanent self-lubricating 2D material-reinforced nickel mould tools using electroforming

In the replication of polymeric micro/nano structures, adhesion and friction between mould tool and polymer cause significant feature failure. For the first time, this work developed a novel strategy for the fabrication of high-hardness and self-lubricating 2D material-reinforced nickel mould tools using electroforming to achieve high precision replication of polymeric micro structures. In this study, layered 2D material, including graphene oxide (GO), molybdenum disulfate (MoS2), and tungsten disulfide (WS2), for the fabrication of self-lubricating mould tools, were systematically studied. Our results demonstrated that nickel/WS2 mould tools, followed by nickel/GO and nickel/MoS2 mould tools, presented the most significant microhardness improvement. A maximum microhardness of ∼660 HV together with a minimum crystallite size of 12 nm was achieved from 0.5 g/L WS2, indicating a 3.67 times microhardness increase and 3 times crystallite size reduction relative to the pure nickel mould tool. The enhanced microhardness can be attributed to the 2D material-induced crystal refinement, and inherent hardness and incorporation content of 2D material. Additionally, friction and wear tests revealed that a low concentration of WS2 at 0.14 g/L achieved the lowest coefficient of friction (COF) and superior wear resistance. The COFs in the initial stage and steady state stage were 0.08 and 0.18, respectively, implying decreases of 42.8% and 72.3%, respectively, and a 27-fold increase in lifetime compared with those of the pure nickel mould tool. Such a significant improvement in tribological properties was due to the formation of self-lubricating transfer film by the interlayer shear effect of few-layered 2D material nanosheets. Finally, defect-free polymeric microfluidic chips were micro hot embossed using an optimal self-lubricating nickel/WS2 mould tool for validation. This work provides significant insight into the fabrication of potential self-lubricating micro/nano mould tools for microfluidics applications.

Experimental Investigation and Molecular Dynamics Simulation on the Anti-Adhesion Behavior of Alkanethiols on Nickel Insert in Micro Injection Molding

Due to the adhesion between the polymer melt and nickel (Ni) mold insert in the micro injection molding process, deformation defects frequently occur when the microstructures are demolded from the insert. In this study, self-assembled alkanethiols were applied to modify the surface of Ni mold insert to reduce its surface energy. Experimental trials were undertaken to explore the effect of alkanethiols coating on the replication quality. After that, molecular dynamics (MD) simulation was then used to investigate the adhesion behavior between the self-assembled coating and polypropylene (PP) by establishing three different types of alkanethiol material. The interaction energy, the potential energy change and radial distribution function were calculated to study the anti-adhesion mechanism. Experimental results show that all the three coatings can effectively decrease the adhesion and therefore promote the replication fidelity. It is demonstrated in MD simulation that the adhesion mainly comes from the van der Waals (vdW) force at the interface. The arrangement of sulfur atom on the Ni surface results in different absorbing behaviors. Compared with that of the PP–Ni interface, the interfacial energy and adhesion work after surface treatment is significantly reduced.

Compression Molding and Nickel Molds for Directional Gecko-Inspired Adhesives

Abstract In the fabrication of directional gecko-inspired adhesives, a new capability made possible by the availability of metal molds is hot compression molding. This molding process allows the use of elastomers with much higher toughness than those cast at ambient temperature and pressure, as has been the common case in fabricating adhesives. In addition, it permits fast cycle times (minutes instead of hours), which is useful for volume manufacturing. We present the results of hot compression molding of elastomers in metal molds created with overhanging and tapered microscopic surface features, which give rise to anisotropic adhesion. We show that the adhesive performance so obtained is equivalent to that obtained earlier with polydimethylsiloxane (PDMS).

Self-Assembled Monolayers of Alkanethiols on Nickel Insert: Characterization of Friction and Analysis on Demolding Quality in Microinjection Molding.

When the part geometry scaling down from macro to microscale level, the size-induced surface effect becomes significant in the injection molding process. The adhesion between polymer and nickel (Ni) mold insert during the process can lead to defects in necking, warping and deformation of microstructure. In this study, the self-assembled monolayers (SAMs) with low surface energy were deposited on the Ni surface to reduce the adhesion and further improve the demolding quality of the microstructure. Results show that the alkyl mercaptan SAMs with chemical bonds and close alignment can be successfully deposited on the surface of Ni by the solution deposition method. The contact angle, surface free energy, and friction coefficient before and after anti-adhesion treatment on the surface of mold insert were measured. In addition, the anti-adhesion properties of different alkyl mercaptan materials and the correspondingly replication quality of microstructure parts after injection molding were analyzed. It is found that the Ni mold insert treated by the perfluorodecanethiol has the best wear resistance and still shows good reproducibility at the 100th demolding cycle.