Effect of filler behavior on nanocomposite SU8 photoresist for moving micro-parts (original) (raw)

Lubrication Mechanism of SU-8/Talc/PFPE Composite

Tribology Letters, 2017

SU-8, a very promising structural polymer for the next-generation 3D fabrication of micro-electromechanical systems (MEMS), has extremely poor tribological properties. The improvement in tribological properties has been recently addressed by developing SU-8/talc (30 wt%) /perfluoropolyether (PFPE) (30 wt%) composite. This composite showed wear durability approximately five orders of magnitude greater in comparison with that of pure SU-8. This drastic increment was found to be because of the in situ lubrication mechanism provided by the PFPE liquid droplets present in the composite. In this present investigation, the lubrication mechanism for SU-8/talc (30 wt%)/PFPE (10, 20 and 30 wt%) composites was further investigated by varying sliding speed (0.1-1.0 m/s) and normal load (2 N and 4 N) using silicon nitride ball of 4 mm diameter as the counterface. The data show that the coefficient of friction and interfacial shear strength follows linear relations with the logarithm of the sliding velocity. Normal load has effect on marginally reducing the coefficient of friction.

Experimental Analysis and Modeling for Reciprocating Wear Behavior of Nanocomposite Coatings

2018

This paper presents the study of wear responses of nanocomposite coatings with a steel ball under oscillatingreciprocating state. Nanocomposite coatings for this study include: Nickel-Alumina (Ni/Al 2 O 3), Nickel-Silicon Carbide (Ni/SiC), Nickel-Zirconia (Ni/ZrO 2) and Ni/Graphene. Ni/ZrO 2 exhibited maximum wear rate followed by Ni/SiC, Ni/Al 2 O 3 and Ni/Graphene respectively which was also assured by Scanning Electron Microscopy (SEM) micrographs, grain sizes, hardness, porosity, surface stresses, frictional coefficients behaviours and "Ushaped" wear depth profiles. The "U-shaped" profiles were utilised to calculate the energy distribution (Archard factor density) along the interface. A novel mechano-wear model incorporating the energy distribution equations with the mechanics equations was developed for analysing the effects of intrinsic mechanical properties (such as grain sizes, hardness, porosity, surface stresses of the nanocomposite coatings) on the wear response. The predictions showed close agreement with the experimental results. In conclusion Ni/Graphene exhibited better anti-wear properties compared to other nanocomposite coatings. The high anti-wear behaviour of Ni/Graphene composite is due to enhanced strengthening effects in the presence of graphene. The importance of this work is evident from various industrial applications which require reliable modelling techniques to predict coatings failures due to wear. This work will bring significant impact to precision manufacturing, wind turbine industries, automotive, locomotive and aerospace in overcoming critical wear failures.

Experimental analysis and modelling for reciprocating wear behaviour of nanocomposite coatings

Wear

In Situ Lubrication of SU-8/Talc Composite with Base Oil (SN150) and Perfluoropolyether as Fillers

Tribology Letters, 2016

In this paper, pure SU-8 and SU-8/talc (30 wt%) composite were filled with two liquid lubricants, hydrocarbon base oil (SN150) and perfluoropolyether (PFPE) in different weight percentages (2, 10, 20 and 30 wt%). The composite coatings in the thickness range of *150 lm were prepared on glass substrate using spin-coater. Pure SU-8 and its self-lubricated composites were examined using pin-on-disk tribometer, 3D optical profilometer, optical microscope, micro-hardness tester, thermogravimetric analyzer and goniometer. From tribological tests, it was observed that the coefficient of friction reduced by *9-10 times after adding lubricant fillers and the wear life was [4 9 10 5 cycles for the SU-8/talc (30 wt%) with 30 wt% PFPE at 6 N normal load and 0.28 m/s sliding speed compared with zero life for without PFPE. The corresponding specific wear rate was 6.4 9 10-8 mm 3 /N-m. From surface characterization, it was observed that the surface changed from hydrophilic to hydrophobic in nature after adding PFPE, but SN150 oil-filled composite shows hydrophilic nature at higher wt%. The wear mechanism for SN150-filled composite was by delamination at high load and higher wt% of the liquid, whereas for PFPE-filled composite, it was of abrasive type. There were improvements in the elastic modulus, hardness and thermal decomposition temperature for SU-8 composites with liquid fillers over pure SU-8, and the benefit was more for composites that also contained 30 wt% of talc.

An in-situ heating effect study on tribological behavior of SU-8+PFPE composite

Wear, 2013

SU-8 polymer is an emerging structural material for micro-fabrication of MEMS/NEMS devices using photolithography process. However, poor tribological properties of SU-8 restrict its wide applications as a very reliable MEMS material. In our earlier work [1], we have developed SU-8 composites which reduced friction and enhanced wear life of SU-8 by more than four orders of magnitude. The improvements in the properties were attributed to the self-lubricating nature of the composite by continuous supply of the lubricant into the worn areas, the lubricious nature of the filler lubricant perfluoropolyether (PFPE), and possible chemical bonding between SU-8 and PFPE. In this current work, we further investigated the effect of in-situ heating on the tribological performances of the SU-8þ PFPE composite. In-situ heating from room temperature (25 1C) to 100 1C showed a strong effect on the tribological behavior of SU-8þPFPE composite by reducing its initial and steady-state friction coefficients by $ 2 and $ 7 times, respectively. Wear life (n) increased by more than three times due to in-situ heating. Greater surface area coverage by the spreading of PFPE lubricant and migration of PFPE from the bulk to surface are found responsible for this superior tribological performance of the composite at high temperatures.

SU-8 Composite Based “Lube-tape” for a Wide Range of Tribological Applications

Micromachines, 2014

In a previous work, we have developed a perflouropolyether (PFPE) lubricant droplet-filled SU-8 composite which promotes bonding between the molecules of SU-8 and PFPE and provides excellent boundary lubrication. The SU-8 + PFPE composite has enhanced the wear durability of SU-8 by more than four orders of magnitude. In this work, the same SU-8 + PFPE composite was used to fabricate a stand-alone laminate film called "Lube-tape". It has integrated two layers of approximately 90 microns thickness each; the top layer is made of SU-8 + PFPE composite and the bottom layer of pristine SU-8. Thus, a single tape can have drastically contrasting high friction and low friction properties on its two surfaces. The composite side has the initial coefficient of friction ~7 times lower and the wear life more than four orders of magnitude than those of the pristine SU-8 side. This lube tape can be used on any load bearing surface to improve the tribological performance by simply pasting the pristine SU-8 side onto the substrate.

Role of nanofiller additions on mechanical and dry sliding wear behaviour of epoxy nanocomposites

Epoxy composites reinforced with organo-modified montmorillonite (oMMT) and alumina (Al2O3) particles were prepared by incorporating nanoparticles into epoxy via high shear mixing followed by liquid molding. The effects of loading of nanoparticles on the mechanical and wear properties were studied. The results showed that the incorporation of nano-Al2O3 with nano-oMMT could effectively enhance the tensile properties of the composites. The tensile strength decreased and Young's modulus of the epoxy increased with the increasing nano-oMMT content. The enhancement effect of the nanoparticles was more significant in the hybrid reinforced composites. The compounding of the two fillers also remarkably improved the wear resistance of the composites under higher load. The average coefficient of friction also decreased in Al2O3 filled oMMT-epoxy hybrid composite. It was revealed that the excellent wear resistance of the oMMT+Al2O3-epoxy hybrid composite was due to a synergistic effect between the oMMT and Al2O3. Nano-Al2O3 carried the majority of load during the sliding process and prevented severe wear of the oMMT-epoxy. Further, the specific wear rates of the hybrid composites decreased with the increasing applied load and sliding distance. Nanoparticles distribution and their influence on properties were emphasized. Different wear mechanisms were observed on the worn surfaces of the composites, including pitting, micro-and/or macro-cracks, as well as crack propagation of the matrix in the transverse direction.

SU8Silver Photosensitive Nanocomposite

Advanced Engineering Materials, 2004

Composite materials offer a combination of properties and a diversity of applications, which cannot be obtained with metals, ceramics or polymers alone. In particular, the insertion of a conductive phase (metallic or inorganic powders or conductive polymers) in an insulating polymer matrix, can result in an enhancement of its electrical conductivity. Various studies have been focused on such electrically conductive polymer composition (ECPCs), which do not have the disadvantages of the pure metal (high density, low chemical resistance, complex manufacturing process). The powder loaded polymer becomes a functional material with specific properties, and can be used for electrical or electromagnetic applications, etc. The case of ECPCs based on epoxy resins, are of particular interest to understand the properties of binary composites (morphology, electrical and thermal conductivity), which are obtained in most cases after a heat treatment to crosslink the ECPCs materials. Their main application is conductive adhesives used in the electronic field for connecting and bonding, but it can also be used for manufacturing sensors. [3±5] In this paper we report a new conductive photosensitive composite material, allowing the direct manufacture of electrically conductive micro-components. It is based on a blend containing silver particles embedded in SU-8, an epoxy photopolymer essentially used for the fabrication of high aspect ratio structures by UV-LIGA. SU-8 components are useful for MEMS, fluidic and packaging applications, [6,7] but also as masters for micro-injection-molding .

Nanomechanical Analysis of Hybrid Silicones and Hybrid Epoxy Coatings—A Brief Review

This review article is written on the investigations of nanomechanical properties of coatings by using nanoindentation techniques. The focus is on the studies that were conducted on epoxy polymer, silicones and their hybrid materials. The article describes a large number of developmental studies that are conducted on coatings. Materials properties such as nanoindentation hardness, modulus, scratch, wear and viscoelastic behavior have been described. Moreover, the article summarizes various studies that mention the use of different nanoparticles in coating formulations that could improve the mechanical strength and service life span of the coatings. The mode and mechanism of material’s failure has been outlined and discussed.

Micro/nano-wear studies on epoxy/silica nanocomposites

Composites Science and Technology, 2013

We proposed a new method for quantifying the micro/nano-scale wear volume (i.e., volume of wear loss) to characterize the wear-resistance of nanocomposites. Effects of wear load, pass (a pattern of scan cycles), and nanoparticle content on the wear behavior of silica nanoparticle-reinforced composites (EP/SiO 2) were studied. The multiple nano-scratch patterning technique was carried out for the wear test. Images of sample surface, before/after the test, obtained using in situ scanning probe microscopy (SPM) were used to calculate the wear volume. Our results indicate that the wear mechanism transits from a plastic-deformation dominated mode to a fatigue-wear dominated mode with increased wear load and pass. The threshold at which transition occurs increases with the nanoparticle content, and correlates with improvement in wear resistance of nanocomposites. This transition threshold can be a different metric, rather than using the conventional mechanical properties (e.g., surface hardness and stiffness), to characterize the wear resistance of materials such that wear load and pass is taken into account.