High-performance nano-PTFE reinforced nickel mold for defect-free micro injection molding of surface micro structures

Abstract

Interest in electroformed nickel (Ni) molds has continued increasing due to their high precision, low cost and high surface finish. Nevertheless, pure Ni molds still rely on extra surface treatments employing release agents to achieve defects-free demolding and meanwhile, mitigate the residual contamination. To address these issues, lubricant-retaining Ni mold was achieved by doping low surface tension polytetrafluoroethylene (PTFE) nano-fillers into the Ni matrix via electrodeposition. The introduction of surfactant mixtures facilitated the successful incorporation of PTFE into the Ni matrix, causing them to perfectly integrate and form as a whole. Such mold exhibited excellent mechanical performance with the enhanced hardness of 452 HV (2.3-fold increase), low surface roughness of 23 nm in S_a and low surface energy of 28.1 mJ/m² (33.6% decrease), resulting in a maximum reduction of 28.6% in demolding force. This Ni-PTFE mold can withstand more than 1 500 demolding cycles without the need for additional demolding agents or the removal of residual contaminants. Importantly, no PTFE nanoparticles were detected on the produced cyclic-olefin-copolymer (COC) chips, as confirmed by energy dispersive X-ray spectroscopy analysis and Raman spectroscopy, confirming no contamination to the polymer and no lubrication degradation of such mold. Polymer chips produced from such mold displayed well-defined structures and excellent biocompatibility, rendering them suitable for microfluidic applications. Finally, this facile and cost-effective method enables creating a reusable, high-resolution mold with low surface energy, ensuring defects-free demolding for the mass production of polymer parts.

Keywords

Polytetrafluoroethylene (PTFE) nano-filler / Lubrication / Electroforming / Mold / Micro injection molding

References

[1] Battat S, Weitz DA, Whitesides GM. An outlook on microfluidics: the promise and the challenge. Lab Chip, 2022, 22: 530-536

[2] Kaur H, Kumari N, Sharma A, et al. . Optical and electrochemical microfluidic sensors for water contaminants: a short review. Mater Today Proc, 2022, 48: 1673-1679

[3] Jena R, Yue C, Lam Y, et al. . Comparison of different molds (epoxy, polymer and silicon) for microfabrication by hot embossing technique. Sens Actuators B Chem, 2012, 163: 233-241

[4] Ongaro AE, Ndlovu Z, Sollier E, et al. . Engineering a sustainable future for point-of-care diagnostics and single-use microfluidic devices. Lab Chip, 2022, 22: 3122-3137

[5] Zhou W, Dou M, Timilsina SS, et al. . Recent innovations in cost-effective polymer and paper hybrid microfluidic devices. Lab Chip, 2021, 21: 2658-2683

[6] Shakeri A, Jarad NA, Khan S, et al. . Bio-functionalization of microfluidic platforms made of thermoplastic materials: a review. Anal Chim Acta, 2022, 1209 339283

[7] Gülçür M, Romano JM, Penchev P, et al. . A cost-effective process chain for thermoplastic microneedle manufacture combining laser micro-machining and micro-injection molding. CIRP J Manuf Sci Technol, 2021, 32: 311-321

[8] Farooque R, Asjad M, Rizvi S, et al. . A current state of art applied to injection molding manufacturing process–a review. Mater Today Proc, 2021, 43: 441-446

[9] Ge J, Catalanotti G, Falzon BG, et al. . Process characteristics, damage mechanisms and challenges in machining of fibre reinforced thermoplastic polymer (FRTP) composites: a review. Compos Part B Eng, 2024, 273: 111247

[10] Zhang N, Zhang H, Zhang H, et al. . Geometric replication integrity of micro features fabricated using variotherm assisted micro injection molding. Procedia CIRP, 2018, 71: 390-395

[11] Fan Z, Hu X, Gao RX. Indirect measurement methods for quality and process control in nanomanufacturing. Nanomanuf Metrol, 2022, 5: 209-229

[12] Regi F, Doest M, Loaldi D, et al. . Functionality characterization of injection molded micro-structured surfaces. Precis Eng, 2019, 60: 594-601

[13] Bäumer S. Applications of injection-molded optics. Handbook of plastic Optics, 2010, Weinheim. Wiley: p251-286

[14] Liu C, Feng Q, Sun J. Lipid nanovesicles by microfluidics: manipulation, synthesis, and drug delivery. Adv Mater, 2019, 31: 1804788

[15] Guan T, Zaki S, Haasbroek PD, et al. . Precision electroforming of nickel nanocomposite mold for defects-free demolding in polymer micro replication: surface properties, performance validation and mold release mechanism. J Manuf Process, 2023, 94: 196-213

[16] Li A, Tang X, Zhu Z, et al. . Basic research on electroforming of Fe–Ni shell with low thermal expansion. Int J Adv Manuf Technol, 2019, 101: 3055-3064

[17] Lee DK, Kwon JY, Cho YH. Fabrication of microfluidic channels with various cross-sectional shapes using anisotropic etching of Si and self-alignment. Appl Phys A, 2019, 125: 1-7

[18] Wang Q, Yao P, Li Y, et al. . Inverted pyramid structure on monocrystalline silicon processed by wet etching after femtosecond laser machining in air and deionized water. Opt Laser Technol, 2023, 157 108647

[19] Laermer F, Franssila S, Sainiemi L, et al. Tilli M, Paulasto-Kröckel M, Petzold M, et al. . Deep reactive ion etching. Handbook of silicon based MEMS materials and technologies, 2020, 3Amsterdam. Elsevier: p417-446

[20] Hamdana G, Puranto P, Langfahl-Klabes J, et al. . Nanoindentation of crystalline silicon pillars fabricated by soft UV nanoimprint lithography and cryogenic deep reactive ion etching. Sens Actuators A Phys, 2018, 283: 65-78

[21] Lin Y, Gao C, Gritsenko D, et al. . Soft lithography based on photolithography and two-photon polymerization. Microfluid Nanofluid, 2018, 22: 1-11

[22] Ferrari E, Nebuloni F, Rasponi M, et al. . Photo and soft lithography for organ-on-chip applications. Organ-on-a-Chip: Methods and Protocols, 2022, New York. Springer: 1-19

[23] Rynes ML, Ghanbari L, Schulman DS, et al. . Assembly and operation of an open-source, computer numerical controlled (CNC) robot for performing cranial microsurgical procedures. Nat Protoc, 2020, 15: 1992-2023

[24] Li M, Chen Y, Luo W, et al. . Demolding force dependence on mold surface modifications in UV nanoimprint lithography. Microelectron Eng, 2021, 236 111470

[25] Liu J, Song D, Zong G, et al. . Fabrication of SU-8 molds on glass substrates by using a common thin negative photoresist as an adhesive layer. J Micromech Microeng, 2014, 24 035009

[26] Esch MB, Kapur S, Irizarry G, et al. . Influence of master fabrication techniques on the characteristics of embossed microfluidic channels. Lab Chip, 2003, 3: 121-127

[27] Plaza EG, López PN, González EB. Efficiency of vibration signal feature extraction for surface finish monitoring in CNC machining. J Manuf Process, 2019, 44: 145-157

[28] McGeough J, Leu M, Rajurkar K, et al. . Electroforming process and application to micro/macro manufacturing. CIRP Ann, 2001, 50: 499-514

[29] Shah NMR, Yeo CD, Choi M, et al. . Change of electrical and transport properties of nickel oxide by carrier concentration and temperature through first-principle calculations. Nanomanuf Metrol, 2023, 6: 37

[30] Ogilvie I, Sieben V, Floquet C, et al. . Reduction of surface roughness for optical quality microfluidic devices in PMMA and COC. J Micromech Microeng, 2010, 20 065016

[31] Yang X, Wu T, Liu D, et al. . 3D printing of release-agent retaining molds. Addit Manuf, 2023, 71 103580

[32] Guan T, Huang N, Song R, et al. . Toward defect-free nanoimprinting. Small, 2024, 20: 2312254

[33] Saha B, Toh WQ, Liu E, et al. . A review on the importance of surface coating of micro/nano-mold in micro/nano-molding processes. J Micromech Microeng, 2015, 26 013002

[34] Zhang N, Zhang H, Stallard C, et al. . Replication integrity of micro features using variotherm and vacuum assisted microinjection molding. CIRP J Manuf Sci Technol, 2018, 23: 20-38

[35] Calderon JC, Koch L, Bandl C, et al. . Multilayer coatings based on the combination of perfluorinated organosilanes and nickel films for injection molding tools. Surf Coat Technol, 2020, 399 126152

[36] Masato D, Sorgato M, Babenko M, et al. . Thin-wall injection molding of polystyrene parts with coated and uncoated cavities. Mater Des, 2018, 141: 286-295

[37] Bobzin K, Wietheger W, Knoch M, et al. . Heating behaviour of plasma sprayed TiOx/Cr₂O₃ coatings for injection molding. Surf Coat Technol, 2020, 399 126199

[38] Vera J, Contraires E, Brulez AC, et al. . Wetting of polymer melts on coated and uncoated steel surfaces. Appl Surf Sci, 2017, 410: 87-98

[39] Mekaru H, Yamada T, Yan S, et al. . Microfabrication by hot embossing and injection molding at LASTI. Microsyst Technol, 2004, 10: 682-688

[40] Guan T, Zhang H, Fang F, et al. . Synthesis of two-dimensional WS₂/nickel nanocomposites via electroforming for high-performance micro/nano mold tools. Surf Coat Technol, 2022, 437 128351

[41] Guan T, Lu Y, Wang X, et al. . Scaling up the fabrication of wafer-scale Ni-MoS₂/WS₂ nanocomposite molds using novel intermittent ultrasonic-assisted dual-bath micro-electroforming. Ultrason Sonochem, 2023, 95: 106359

[42] Zhang H, Guan T, Zhang N, et al. . Fabrication of permanent self-lubricating 2D material-reinforced nickel mold tools using electroforming. Int J Mach Tools Manuf, 2021, 170 103802

[43] Guan T, Gilchrist MD, Fang F, et al. . Study on mechanical and tribological properties of electroformed nickel composite mold co-deposited with nano-sized PTFE particles. J Mater Res Technol, 2023, 25: 3688-3703

[44] Guo Y, Liu G, Xiong Y, et al. . Study of hot embossing using nickel and Ni–PTFE LIGA mold inserts. J Microelectromech Syst, 2007, 16: 589-597

[45] Owens DK, Wendt R. Estimation of the surface free energy of polymers. J Appl Polym Sci, 1969, 13: 1741-1747

[46] Kaelble D, Moacanin J. A surface energy analysis of bioadhesion. Polymer, 1977, 18: 475-482

[47] Lago WSR, Aymes-Chodur C, Ahoussou AP, et al. . Physico-chemical ageing of ethylene–norbornene copolymers: a review. J Mater Sci, 2017, 52: 6879-6904

[48] Zhou N, Wang S, Walsh FC. Effective particle dispersion via high-shear mixing of the electrolyte for electroplating a nickel-molybdenum disulphide composite. Electrochim Acta, 2018, 283: 568-577

[49] Clayton KN, Salameh JW, Wereley ST, et al. . Physical characterization of nanoparticle size and surface modification using particle scattering diffusometry. Biomicrofluidics, 2016, 10 054107

[50] Barbero DR, Saifullah MS, Hoffmann P, et al. . High-resolution nanoimprinting with a robust and reusable polymer mold. Adv Funct Mater, 2007, 17: 2419-2425

[51] Matschuk M, Larsen NB. Injection molding of high aspect ratio sub-100 nm nanostructures. J Micromech Microeng, 2012, 23 025003

[52] Gopanna A, Mandapati RN, Thomas SP, et al. . Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy and wide-angle X-ray scattering (WAXS) of polypropylene (PP)/cyclic olefin copolymer (COC) blends for qualitative and quantitative analysis. Polym Bull, 2019, 76: 4259-4274

[53] Wang Y, Weng C, Fei Z, et al. . Enhancing structural replication of microfluidic chips: parameter optimization and mold insert modification. Polym Eng Sci, 2024, 64: 2082-2095

[54] Saha B, Liu E, Tor S, et al. . Improvement in lifetime and replication quality of Si micromold using N: DLC: Ni coatings for microfluidic devices. Sens Actuators B Chem, 2010, 150: 174-182

[55] Tian Y, Zhang P, Liu G, et al. . The lifetime comparison of Ni and Ni-PTFE molding inserts with high aspect-ratio structure. Microsyst Technol, 2005, 11: 261-264

[56] Pinate S, Leisner P, Zanella C. Wear resistance and self-lubrication of electrodeposited Ni-SiC: MoS₂ mixed particles composite coatings. Surf Coat Technol, 2021, 421 127400

[57] Liu H, He M, Li J, et al. . Additive manufacturing of high-performance Ni-Co coatings for micro/nanomold applications using an advanced gradient ultrasonic electrochemical deposition process. Addit Manuf, 2023, 79: 103949

[58] Takadoum J. Materials and surface engineering in tribology, 2013, Hoboken. Wiley

[59] Dhanumalayan E, Joshi GM. Performance properties and applications of polytetrafluoroethylene (PTFE)—a review. Adv Compos Hybrid Mater, 2018, 1: 247-268

[60] Reddy ARN, Reddy YN, Krishna DR, et al. . Multi wall carbon nanotubes induce oxidative stress and cytotoxicity in human embryonic kidney (HEK293) cells. Toxicology, 2010, 272: 11-16

[61] Szekely D, Brennan SC, Mun HC, et al. . Effectors of the frequency of calcium oscillations in HEK-293 cells: wavelet analysis and a computer model. Eur Biophys J, 2009, 39: 149-165

[62] Zachari MA, Chondrou PS, Pouliliou SE, et al. . Evaluation of the alamarblue assay for adherent cell irradiation experiments. Dose-Response, 2014,

[63] Al-Nasiry S, Geusens N, Hanssens M, et al. . The use of Alamar Blue assay for quantitative analysis of viability, migration and invasion of choriocarcinoma cells. Hum Reprod, 2007, 22: 1304-1309

Funding

Science Foundation Ireland(22/RP-2TF/10466)

Enterprise IRELAND(CF-2021-1635-P)

China Sponsorship Council(202008300010)

University College Dublin

RIGHTS & PERMISSIONS

The Author(s)