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![(A–B) Micro-electro-mechanical systems (MEMS) [2], (C) real lotus leaf surface [16], (D) lotus-like polymeric nano-patterns [16], (E) replicated surface of lotus leaf [18] and (F) naturally dried real lotus leaf surface [24].](profile/Cuong-Pham-13/publication/248195507/figure/fig1/AS:359775595450369@1462788595726/A-B-Micro-electro-mechanical-systems-MEMS-2-C-real-lotus-leaf-surface-16-D.png)
(A–B) Micro-electro-mechanical systems (MEMS) [2], (C) real lotus leaf surface [16], (D) lotus-like polymeric nano-patterns [16], (E) replicated surface of lotus leaf [18] and (F) naturally dried real lotus leaf surface [24].
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![Fig. 1. (A–B) Micro-electro-mechanical systems (MEMS) [2], (C) real...](profile/Cuong-Pham-13/publication/248195507/figure/fig1/AS:359775595450369@1462788595726/A-B-Micro-electro-mechanical-systems-MEMS-2-C-real-lotus-leaf-surface-16-D_Q320.jpg)
In miniaturized devices like micro/nano-electro-mechanical systems (MEMS/NEMS), the critical forces, namely adhesion and friction restrict the smooth operation of the elements that are in relative motion. MEMS/NEMS are traditionally made of silicon, whose tribological properties are not good. In this paper, we present an investigation on the approa...
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... These include a variety of sensors, actuators, motors and complex micro/ nano-devices for industrial, consumer, defense, aerospace, and biomedical applications [1]. However, the issue of smooth operation and long-term durability of these devices remains to be solved, especially of those devices in which their elements undergo relative motion. Fig. 1(a) and (b) shows micrographs of micromechanical systems that have gears [2]. For the smooth functioning of these systems, the contact between the gears must be properly lubricated. But lubrication becomes really difficult when the dimensions of machine elements decrease from macroscale to micro/nano-scale. As the sizes of the machine ...
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... friction. Working along this line, and inspired by the ''Lotus Effect'', we recently modified the surfaces of silicon wafers topographically by fabricating nano-scale polymeric asperities on them using a capillarity-directed soft lithography technique [16]. Bio-mimetic in nature, these nano-patterns mimic the protuberances of a lotus leaf [16]. Fig. 1(c) shows the surface of a real lotus (Nelumbo nucifera) leaf and Fig. 1(d) shows the biomimetic nano-patterned polymeric surface on silicon wafer [16]. These nano-patterned surfaces exhibit reduction in adhesion and friction forces by an order of magnitude at nano-scale due to their hydrophobic nature and reduced real area of contact ...
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... we recently modified the surfaces of silicon wafers topographically by fabricating nano-scale polymeric asperities on them using a capillarity-directed soft lithography technique [16]. Bio-mimetic in nature, these nano-patterns mimic the protuberances of a lotus leaf [16]. Fig. 1(c) shows the surface of a real lotus (Nelumbo nucifera) leaf and Fig. 1(d) shows the biomimetic nano-patterned polymeric surface on silicon wafer [16]. These nano-patterned surfaces exhibit reduction in adhesion and friction forces by an order of magnitude at nano-scale due to their hydrophobic nature and reduced real area of contact [16]. Owing to their excellent tribological properties, these surfaces have ...
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... area of contact [16]. Owing to their excellent tribological properties, these surfaces have been proposed as prospective tribological candidates for MEMS devices [17]. In another work, we fabricated polymeric micro-patterns by using the surfaces of real lotus (N. nucifera) and Colocasia (Colocasia esculenta) leaves as natural templates [18,19]. Fig. 1(e) shows a lotus-like micro-patterned surface so fabricated [18,19]. These biomimetic micro-patterned surfaces created by the direct replication of natural topographies have also proved to be superior tribological candidates at small-scales, by the virtue of their increased hydrophobicity and reduced real area of contact. The ...
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... the wax on the lotus leaves gives rise to their superhydrophobic property (water contact angles $1628 [22]). It has been observed earlier that the surface characteristics of these leaves, namely the protuberances and wax significantly influence their friction behavior at micro-scale, when tested in their fresh and naturally dried conditions [24]. Fig. 1(c) and (f) shows the surfaces of a real lotus leaf in its fresh and naturally dried conditions, respectively. Upon drying the morphology of the lotus leaf remains almost the same except that the surface and protuberances shrink in their size [19,24]. It was observed that the leaves in their fresh condition exhibited values of friction ...
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... of silicon micro-patterned surfaces after the tests revealed that they exhibited wear. However, it was seen that the generated wear particles were found trapped at the spaces inbetween the pillars/channels. Fig. 10(a) and (b) shows the surfaces of silicon micro-patterns taken using an optical microscope. Fig. 10(c) and (d) shows the images of the patterned surfaces taken after the tests. The arrow marks show wear particles trapped at the spaces in-between the pillars/channels. This interesting feature of the removal of wear particles from the ...
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... of silicon micro-patterned surfaces after the tests revealed that they exhibited wear. However, it was seen that the generated wear particles were found trapped at the spaces inbetween the pillars/channels. Fig. 10(a) and (b) shows the surfaces of silicon micro-patterns taken using an optical microscope. Fig. 10(c) and (d) shows the images of the patterned surfaces taken after the tests. The arrow marks show wear particles trapped at the spaces in-between the pillars/channels. This interesting feature of the removal of wear particles from the sliding interface exhibited by the patterns further contributes towards lowering their friction ...
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... wear debris on their friction property is another reason for the values of friction to be high ( Fig. 8(a) shows the worn surface of a bare silicon flat specimen where large amounts of wear debris are seen on the wear track). Compared to the wear of bare silicon flat surfaces, the DLC coated flat surfaces show fewer wear particles (Fig. 8(b)). Fig. 11 shows the results of the micro-friction tests of silicon surfaces with the dual/combined surface modification (topographically and chemically modified silicon surfaces viz. silicon micro-pillars coated with DLC and Z-DOL). Comparing this figure with Fig. 7 (chemically modified silicon flat surfaces), it could be seen that the combined ...
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... contact angles increase significantly than those of the uncoated silicon micro-pillars. Lower surface energies, indicated by the higher water contact angle values (Table 2) contribute towards lowering the friction property of the coated silicon micro-pillared surfaces through the reduction of inherent adhesion arising due to the capillary force. Fig. 12(a) and (b) shows the results of the micro-friction tests of silicon surfaces with the dual/combined surface modification i.e. silicon micro-channels coated with DLC and Z-DOL, tested in the parallel and orthogonal directions, respectively. Similar to that in the case of the coated micro-pillars as mentioned above, the coated ...
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Micro/nano electro-mechanical systems (MEMS/NEMS) are constantly attracting an increasing attention for their relevant technological applications in fields ranging from biology, medicine, ecology, energy to industry. Most of the performances of micro-nanostructured devices rely on both the design and the intrinsic properties of the constituent mate...
Citations
... Nanopatterns of PMMA with three different aspect ratios (holding time) were fabricated on silicon surfaces using simple capillary force lithography produced a contact angle of 99° [20]. Silicon micropillars and channels were fabricated using photolithography and deep reactive ion etching (DRIE) Techniques produces a WCA of 59 and 63 respectively [21]. ...
The behavior of a liquid on a solid surface has shown great interest in a variety of applications related to surfaces and its interfaces. In this paper, the wetting behavior of DI water on micropatterned silicon surfaces fabricated through photolithography and deep reactive ion etching (DRIE) is investigated. Micro pillars of both solid and hollow geometries at a varying pitch and its arrangement in an array has been examined with static contact angle measurement. However, the results concluded that the arrangement of pillars in an array plays an important role as hollow geometries in the case of chain type arrangement provide both hydrophilic and hydrophobic surface properties, while the same hollow geometries in case of zig-zag orientation experiences only hydrophobicity at a varying pitch. Decreased WCA with increased pitch has been observed in the case of a zig-zag arrangement, due to the effect of capillary and gravitation forces. Also the existence of air pockets at sharp corner in the case of hollow square assists in providing maximum contact angle (WCA = 144°) as compared to hollow circle and solid geometries; thus a non-sticky behavior would be possible between the droplet and the patterned surface, due to less adhesion force.
... In the past decade, biomimetics showed significant development due to the modernization of technology and above all the possibilities of studying the micro-and nanolevels of biological structures. On the other hand, the miniaturization of technological devices has increased the need for understanding of tribological phenomena at the micro-and nanolevel, which is the huge potential for technological innovation (Fig. 2) [22][23][24][25]. ...
Biomimetics, biomimicry and bionics are synonyms for the scientific
discipline of creating new structures inspired by nature. Biomimetics
systematically analyses the evolutionary processes of living organisms, their structural relationships, the characteristics of natural materials and it studies how this knowledge can be used to create the optimal products and new sustainable materials. In the past decade, the biomimetics has received an incentive for the development by the technology modernization, and above all, by making it possible to study the micro and nanolevels of biological structures. On the other hand, the miniaturization of technological devices has increased the need to understand the tribological phenomena on micro- and nanolevel, where is a huge potential for technological innovation. The integration of advanced research methods made it possible to discover new aspects in the structure and properties of biological materials and transfer that knowledge into new concepts or products. State-of-the-art of biomimetics progress is discussed, as well as, its goals and the potential to simultaneously achieve the financial and ecological contribution by realization of bio-inspired concepts. An overview of biomimetic researches is also provided, with special emphasis on the possibility of their tribological applications. The
characteristic examples have been presented and those examples show how the structural and mechanical properties of the material were used as the basis for developing new creative solutions to solve the problem of friction in engineering applications.
... In the past decade, biomimetics showed significant development due to the modernization of technology and above all the possibilities of studying the micro-and nanolevels of biological structures. On the other hand, the miniaturization of technological devices has increased the need for understanding of tribological phenomena at the micro-and nanolevel, which is the huge potential for technological innovation (Fig. 2) [22][23][24][25]. [25] Thanks to a better understanding of fundamental biological principles, biomimetic research activity has been directed increasingly toward the development of bioinspired materials [26][27][28]. ...
Biomimetics, biomimicry and bionics are synonyms for the scientific discipline of creating new structures inspired by nature. Biomimetics systematically analyses the evolutionary processes of living organisms, their structural relationships, the characteristics of natural materials and it studies how this knowledge can be used to create the optimal products and new sustainable materials. In the past decade, the biomimetics has received an incentive for the development by the technology modernization, and above all, by making it possible to study the micro- and nanolevels of biological structures. On the other hand, the miniaturization of technological devices has increased the need to understand the tribological phenomena on micro- and nanolevel, where is a huge potential for technological innovation. The integration of advanced research methods made it possible to discover new aspects in the structure and properties of biological materials and transfer that knowledge into new concepts or products. State-of-the-art of biomimetics progress is discussed, as well as, its goals and the potential to simultaneously achieve the financial and ecological contribution by realization of bio-inspired concepts. An overview of biomimetic researches is also provided, with special emphasis on the possibility of their tribological applications. The characteristic examples have been presented and those examples show how the structural and mechanical properties of the material were used as the basis for developing new creative solutions to solve the problem of friction in engineering applications.
... An interesting route to make surfaces water-repellent is by learning from the phenomenon of 'Lotus Effect'. Lotus has natural wax on its leaves which makes its surface water-repellent (natural superhydrophobic surface having high water contact angle and low contact angle hysteresis) [1,2]. Inspired by this fact, in this work sisal fibers have been treated with cardanol oil (derived from cashew nut shell) to make them water-repellent (i.e. less water absorbing). ...
Polymer matrix composites (PMCs) are light weight and have high strength to weight ratio, owing to which they are attractive for aviation and automotive industries. Amongst PMCs, glass fiberepoxy composites are being widely used. Replacement of synthetic materials by naturally available materials (i.e. agricultural products) as fiber and/or resin in making composites will ensure bio-degradability and eco-friendliness. In the view of developing natural fiber reinforced composites, in this work sisal fibers treated with/without cardanol oil have been investigated for their water absorption and strength characteristics. The investigation revealed that when
compared to the untreated fibers, the cardanol treated fibers exhibit (i) 35 % reduction in water absorption
and (ii) increased tensile strength property.
... An interesting route to make surfaces water-repellent is by learning from the phenomenon of 'Lotus Effect'. Lotus has natural wax on its leaves which makes its surface water-repellent (natural superhydrophobic surface having high water contact angle and low contact angle hysteresis) [1,2]. Inspired by this fact, in this work sisal fibers have been treated with cardanol oil (derived from cashew nut shell) to make them water-repellent (i.e. less water absorbing). ...
Polymer matrix composites (PMCs) are light weight and have high strength to weight ratio, owing to which they are attractive for aviation and automotive industries. Amongst PMCs, glass fiberepoxy composites are being widely used. Replacement of synthetic materials by naturally available materials (i.e. agricultural products) as fiber and/or resin in making composites will ensure bio-degradability and eco-friendliness. In the view of developing natural fiber reinforced composites, in this work sisal fibers treated with/without cardanol oil have been investigated for their water absorption and strength characteristics. The investigation revealed that when
compared to the untreated fibers, the cardanol treated fibers exhibit (i) 35 % reduction in water absorption
and (ii) increased tensile strength property.
... In recent times, 'topographical modification' of surfaces (patterning) is being explored as an alternative and effective route to mitigate friction [6,7]. Researchers are also exploring the combination of chemical and topographical modifications, known as 'hybrid modification' that has proved to be very effective in reducing friction of silicon at small-scale [8]. In this paper, the friction behavior of silicon at nano/micro-scale and of its surface modifications are presented and compared. ...
... From Fig. 3 it can be seen that the DLC coated silicon pillars have the lowest friction values at nanoscale when compared to the rest of the surfaces. Similar to these nano-pillared silicon surfaces, micro-pillared/channeled silicon surfaces when coated with DLC and ZDOL have shown lowest friction values at micro-scale [8]. The hybrid approach utilizes the combined advantages of (i) physical reduction in real area of contact via topographical modification and (ii) the lubrication effect of chemical modification. ...
Micro-Electro-Mechanical Systems (MEMS) are miniaturized devices built at nano/micro-scale. MEMS are fabricated from semiconductor silicon. At nano/micro-scale, capillary force along with asperity deformation induces friction at the surfaces of moving elements of actuators-based devices. The magnitude of friction force so generated is of the same order as that of the forces driving the moving elements. Friction therefore resists the relative mechanical motion between moving elements and reduces the useful operating lifetime of actuator devices. Solutions to reduce friction at nano/micro-scale in silicon by surface modification include: (i) chemical modification i.e. thin lubricant films/coatings, (ii) topographical modification i.e. surface patterning and (iii) hybrid modification, i.e. combination of topographical and chemical modifications. Friction behavior at nano/micro-scale of silicon and modified silicon surfaces is presented and discussed in this paper. Amongst the different surface modification approaches, the hybrid modification shows the best results in terms of friction reduction.
... In addition to hard coatings, relatively soft polymeric coatings have also been investigated. A combination of polymethylmethacrylate and perfluoropolyether nanolubricants with micro-patterns has been proposed for microelectromechanical system (MEMS) and bio-MEMS application for reduction in friction [16][17][18]. SU8, which is biocompatible and hydrophobic, has been introduced as a new type of a polymeric coating for MEMS applications [19][20][21]. Another method used to reduce friction is to fabricate textures on the surface to eliminate the particles that may cause abrasion to the contacting surfaces [13,14]. ...
Abstract The friction and deformation behaviors of ∼60-μm-diameter stainless steel micro-balls were assessed under various rolling conditions against Si specimens. In the friction tests, the micro-balls were placed between a stationary flat silicon specimen on the top and a flat or grooved silicon specimen at the bottom that was made to move in a reciprocating motion. Rectangular- and V-shaped grooves were fabricated on the silicon specimen by a photolithographic process, and the effect of groove shape on the frictional behavior of the micro-balls was investigated. Friction coefficient of 0.01 could be successfully achieved when proper rolling was attained. It was found that the number of micro-balls was not a critical factor as long as more than three balls were placed between the two flat Si specimens. Furthermore, rectangular-shaped groove resulted in lower friction than V-shaped groove. This was due to severe deformation of the micro-ball which led to increase in the contact area when the V-shaped groove was used. The results of this work were expected to aid in the development of miniature bearings for applications in small precision systems.
... Most of the other bio-inspired structures investigated in the literature to lower friction and wear are based on protruding features, e.g. pillars mimicking Lotus leave, or structures that were originally meant to ensure superhydrophobicty [12,[26][27][28]. These studies found an increase in wear resistance [27] and lower friction forces [26,29]. ...
... pillars mimicking Lotus leave, or structures that were originally meant to ensure superhydrophobicty [12,[26][27][28]. These studies found an increase in wear resistance [27] and lower friction forces [26,29]. With hexagonal surface patterns inspired by bush cricket feet, it was possible to decrease friction forces in dry and increase them in wet conditions [30]. ...
Friction, wear and the associated energy dissipation are major challenges in all systems containing moving parts. Examples range from nanoelectromechanical systems over hip prosthesis to off-shore wind turbines. Bionic approaches have proven to be very successful in many engineering problems, while investigating the potential of a bio-inspired approach in creating morphological surface textures is a relatively new field of research. Here, we developed laser-created textures inspired by the scales found on the skin of snakes and certain lizards. We show that this bio-inspired surface morphology reduced dry sliding friction forces by more than 40%. In lubricated contacts the same morphology increased friction by a factor of three. Two different kinds of morphologies, one with completely overlapping scales and one with the scales arranged in individual rows, were chosen. In lubricated as well as unlubricated contacts, the surface texture with the scales in rows showed lower friction forces than the completely overlapping ones. We anticipate that these results could have significant impact in all dry sliding contacts, ranging from nanoelectromechanical and micro-positioning systems up to large-scale tribological contacts which cannot be lubricated, e.g. because they are employed in a vacuum environment.
... Besides this, the texturing of frictional surfaces is used in a wide range of tribological applications especially in the automotive industry (mechanical seals, piston rings or thrust bearings [10]). Moreover, micro texturing is also used for hard discs [11] and is considered as a means of reducing friction in MEMS [12]. In particular, progress in the area of MEMS leads to smaller devices and new applications as sensors, actuators or micro machines. ...
... Thus, it becomes more and more important to control the properties of frictional surfaces. An advanced route to do this is to combine surface coating (to reduce adhesive forces) and surface texturing (to reduce the real area of contact) [12]. ...
... Thus the contact area A r is larger and according to equation (7) it results also in a higher coefficient of friction. An indication of the surface energy can be the water contact angle [12]. The contact angle Θ between water and ta-C was Θ ∼ 80°and silicon had a contact angle of Θ ∼ 41°indicating a higher surface energy and hydrophilic behavior of silicon. ...
We have investigated the direct laser interference patterning (DLIP) of tetrahedral amorphous carbon (ta-C) thin films in the nanometer region. In this paper we achieved texturing of ta-C from a surface swelling either by a phase change from sp3 to sp2 or thin film delamination. In contrast to surface ablation, the thin film is not removed from the silicon surface. With this technique a surface nano-swelling of ta-C with an area-speed of 1 m2 min−1 and nanometric resolution can be realized. The phase changes in the ta-C, due to DLIP material heating are undermined by thermal simulations of the patterning process. Additionally we investigated for the first time the influence of periodic nano-swelling on the coefficient of friction (COF). The COF of periodic graphitized surfaces was found to be lower (~50%) compared to as grown ta-C. This reduction of the COF can be attributed to a reduced area of contact.
... Surface texture, such as arrayed micro-grooves or micro-dimples fabricating, is an option to improve engineering materials' load capacity, wear resistance. Laser surface texturing (LST) seems to be the most advanced of all know methods of surface texturing, which provides the substantial improvement of the tribological performance under friction conditions with fluid lubricant [7][8][9][10] A c c e p t e d M a n u s c r i p t texture and surface coating. The superhydrophobic lotus leaf, the water strider's leg, the cricket's attaching foot, the gecko's gripping foot and the snake's textured skin, all offer effective ways of controlling wettability and friction. ...
