Research in Biomimetics related to Tribology: An Overview

R. Arvind Singh,윤의성 대한기계학회 2008 대한기계학회 춘추학술대회 Vol.2008 No.5

Biomimetically Engineered Polymeric Surfaces for Micro-scale Tribology

Singh R. Arvind,Kim Hong-Joon,Kong Ho-Sung,Yoon Eui-Sung Korean Tribology Society 2006 KSTLE International Journal Vol.7 No.1

In this paper, we report on the replication of surface topography of natural leaf of Lotus onto thin polymeric films using a capillarity-directed soft lithographic technique. PDMS molds were used to replicate the surface. The replication was carried out on poly(methyl methacrylate) (PMMA) film coated on silicon wafer. The patterns so obtained were investigated for their friction properties at micro-scale using a ball-on-flat type micro-tribo tester, under reciprocating motion. Soda lime balls (1 mm diameter) were used as counterface sliders. Friction tests were conducted at a constant applied normal load of $3000{\mu}N$ and speed of 1mm/s. All experiments were conducted at ambient temperature ($24{\pm}1^{\circ}C$) and relative humidity ($45{\pm}5%$). Results showed that the patterned samples exhibited superior tribological properties when compared to the silicon wafer and non patterned sample (PMMA thin film). The reduced real area of contact projected by the surfaces was the main reason for their enhanced friction property.

Photolithographic Silicon Patterns with Z-DOL (perfluoropolyether, PFPE) Coating as Tribological Surfaces for Miniaturized Devices

Singh, R. Arvind,Pham, Duc-Cuong,Yoon, Eui-Sung Korean Tribology Society 2008 KSTLE International Journal Vol.9 No.1

Silicon micro-patterns were fabricated on Si (100) wafers using photolithography and DRIE (Deep Reactive Ion Etching) fabrication techniques. The patterned shapes included micro-pillars and micro-channels. After the fabrication of the patterns, the patterned surfaces were chemically modified by coating Z-DOL (perfluoropolyether, PFPE) thin films. The surfaces were then evaluated for their micro-friction behavior in comparison with those of bare Si (100) flat, Z-DOL coated Si (100) flat and uncoated Si patterns. Experimental results showed that the chemically treated (Z-DOL coated) patterned surfaces exhibited the lowest values of coefficient of friction when compared to the rest of the test materials. The results indicate that a combination of both the topographical and chemical modification is very effective in reducing the friction property. Combined surface treatments such as these could be useful for tribological applications in miniaturized devices such as Micro/Nano-Electro-Mechanical-Systems (MEMS/NEMS).

Artificial Adhesive Surfaces Mimicking Gecko Setae: Novel Approaches in Surface Engineering

Singh, R. Arvind,Yoon, Eui-Sung Korean Tribology Society 2008 KSTLE International Journal Vol.9 No.1

Surface Engineering is a field closely related to Tribology. Surfaces are engineered to reduce adhesion, friction and wear between moving components in engineering applications. On the contrary, it is also necessary to have high adhesion between surfaces so as to hold/stick surfaces together. In this context, surface engineering plays an important role. In recent times, scientists are drawing inspiration from nature to create effective artificial adhesive surfaces. This article provides some examples of novel surface engineering approaches conducted by various research groups worldwide that have significantly contributed in the creation of bio-inspired artificial adhesive surfaces.

Friction of chemically and topographically modified Si (100) surfaces

Singh, R. Arvind,Yoon, Eui-Sung Elsevier 2007 Wear: An international journal on the science and Vol.263 No.7

<P><B>Abstract</B></P><P>Silicon (Si (100)) is a typically used material in micro/nano-scale devices, such as micro/nano-electromechanical systems (MEMS/NEMS). However, Si (100) does not have good tribological properties and hence its surface needs to be treated either chemically or topographically to enhance its tribological performance. In this paper, the micro/nano-frictional property of chemically and topographically modified Si (100) surfaces was studied. Chemically modified surfaces of Si (100) include coating of diamond-like carbon (DLC) films (two different thicknesses) and two self-assembled monolayers (SAMs). Topographically modified surfaces of Si (100) include nano-patterned poly(methyl methacrylate) (PMMA) on silicon wafer, fabricated by the process of a capillarity-directed soft lithographic technique. At the nano-scale, friction was measured using an atomic force microscope (AFM) and at the micro-scale it was measured using a ball-on-flat type micro-tribotester. Results showed that at both nano- and micro-scales, the modified Si (100) surfaces exhibited enhanced friction behavior when compared to bare Si (100) surfaces. The improved nano-friction behavior of the modified surfaces was attributed to their lower intrinsic adhesion and reduced real area of contact. In the case of nano-patterns, the physical (geometrical) reduction in contact area contributed in decreasing their friction. At micro-scale, wear was observed in the test samples (except in the case of SAMs), which influenced their friction behavior. Further, as a novel bio-mimetic approach for tribological application at micro-scale, the surface topography of natural leaves of Lotus and Colocasia were replicated by capillary force lithography using two different molding techniques. Interestingly, these bio-mimetically engineered surfaces exhibited superior micro-friction behavior. Indeed, this could be the first bio-mimetic approach of creating effective tribological materials by the direct replication of natural surfaces.</P>

Photolithographic Silicon Patterns with Z-DOL(perfluoropolyether, PFPE) Coating as Tribological Surfaces for Miniaturized Devices

R. Arvind Singh,Duc-Cuong Pham,Eui-Sung Yoon 한국트라이볼로지학회 2008 KSTLE International Journal Vol.9 No.1/2

Silicon micro-patterns were fabricated on Si(100) wafers using photolithography and DRIE (Deep Reactive Ion Etching) fabrication techniques. The patterned shapes included micro-pillars and micro-channels. After the fabrication of the patterns, the patterned surfaces were chemically modified by coating Z-DOL(perfluoropolyether, PFPE) thin films. The surfaces were then evaluated for their micro-friction behavior in comparison with those of bare Si(100) flat, Z-DOL coated Si(100) flat and uncoated Si patterns. Experimental results showed that the chemically treated(Z-DOL coated) patterned surfaces exhibited the lowest values of coefiicient of friction when compared to the rest of the test materials. The results indicate that a combination of both the topographical and chemical modification is very effective in reducing the friction property. Combined surface treatments such as these could be useful for tribological applications in miniaturized devices such as Micro/Nano-Electro-Mechanical-Systems(MEMS/NEMS).

Friction Mechanisms of Silicon Wafer and Silicon Wafer Coated with Diamond-like Carbon Film and Two Monolayers

Singh R. Arvind,Yoon Eui-Sung,Han Hung-Gu,Kong Ho-Sung The Korean Society of Mechanical Engineers 2006 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.20 No.6

The friction behaviour of Si-wafer, diamond-like carbon (DLC) and two self-assembled monolayers (SAMs) namely dimethyldichlorosilane (DMDC) and diphenyl-dichlorosilane (DPDC) coated on Si-wafer was studied under loading conditions in milli-newton (mN) range. Experiments were performed using a ball-on-flat type reciprocating micro-tribo tester. Glass balls with various radii 0.25 mm, 0.5 mm and 1 mm were used. The applied normal load was in the range of 1.5 mN to 4.8 mN. Results showed that the friction increased with the applied normal load in the case of all the test materials. It was also observed that friction was affected by the ball size. Friction increased with the increase in the ball size in the case of Si-wafer. The SAMs also showed a similar trend, but had lower values of friction than those of Si-wafer In-terestingly, for DLC it was observed that friction decreased with the increase in the ball size. This distinct difference in the behavior of friction in DLC was attributed to the difference in the operating mechanism. It was observed that Si-wafer and DLC exhibited wear, whereas wear was absent in the SAMs. Observations showed that solid-solid adhesion was dominant in Si-wafer, while plowing in DLC. The wear in these two materials significantly Influenced their friction. In the case of SAMs their friction behaviour was largely influenced by the nature of their molecular chains.

Friction Mechanisms of Silicon Wafer and Silicon Wafer Coated with Diamond-like Carbon Film and Two Monolayers

R. Arvind Singh,Eui-Sung Yoon,Hung-Gu Han,Hosung Kong 대한기계학회 2006 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.20 No.6

The friction behaviour of Si-wafer, diamond-like carbon (DLC) and two self-assembled monolayers (SAMs) namely dimethyldichlorosilane (DMDC) and diphenyl-dichlorosilane (DPDC) coated on Si-wafer was studied under loading conditions in milli-newton (mN) range. Experiments were performed using a ball-an-flat type reciprocating micro-tribo tester. Glass balls with various radii 0.25 ㎜, 0.5 ㎜ and 1 ㎜ were used. The applied normal load was in the range of 1.5 mN to 4.8 mN. Results showed that the friction increased with the applied normal load in the case of all the test materials. It was also observed that friction was affected by the ball size. Friction increased with the increase in the ball size in the case of Si-wafer. The SAMs also showed a similar trend, but had lower values of friction than those of Si-wafer. Interestingly, for DLC it was observed that friction decreased with the increase in the ball size. This distinct difference in the behavior of friction in DLC was attributed to the difference in the operating mechanism. It was observed that Si-wafer and DLC exhibited wear, whereas wear was absent in the SAMs. Observations showed that solid-solid adhesion was dominant in Si-wafer, while plowing in DLC. The wear in these two materials significantly influenced their friction. In the case of SAMs their friction behaviour was largely influenced by the nature of their molecular chains.

Biomimetics in Tribology - Recent Developments

R. Arvind Singh,윤의성 한국물리학회 2008 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.52 No.3

The study and simulation of biological systems for desired properties is popularly known as ``Biomimetics''. Such an approach involves the transformation of the underlying principles discovered in nature into man-made technology. In recent times, biomimetics has become popular in the fields of materials science and engineering. It is being applied in diverse areas ranging from micro/nano-electronics to structural engineering and is now rapidly emerging in the field of tribology. Tribology is a multi-disciplinary and multi-scale study of adhesion, friction, and wear phenomena between contacting surfaces. The present article provides examples of bio-inspired topics and recent developments related to tribology. It covers the details of bio-inspired polymeric surfaces that exhibit low/high adhesion and of the friction properties at micro/nanoscales. Some examples of bio-inspired inventions that have already become technological solutions and of bio-materials that are guiding researchers to fabricate excellent wear resistant materials are discussed in this article.

Application of Biomimetic Surfaces for MEMS Tribology

R. Arvind Singh,Duc-Cuong Pham,Eui-Sung Yoon 대한기계학회 2008 대한기계학회 춘추학술대회 Vol.2008 No.11

“Biomimetics” is the study and simulation of biological systems with desired properties. In recent times, biomimetic surfaces have emerged as novel solutions for tribological applications in micro-electromechanical systems (MEMS). These biomimetic surfaces are attractive for MEMS application as they exhibit low adhesion/friction and wear properties at small-scales. In this paper, we present some of the examples of biomimetic surfaces that have potential application in small-scale devices.