• 한국윤활학회:학술대회논문집
• /
• 한국윤활학회 2002년도 proceedings of the second asia international conference on tribology
• /
• pp.63-64
• /
• 2002

In a micro-scale contact, surface forces such as capillary force and van der Waals Interaction significantly Influence the contact between asperities of rough surfaces. Little is, however, known about the variation of these surface forces as a function of chemical property of the surface (hydrophilicity), relative humidity and deformation of asperities In the real area of contact. A better understanding of these surface forces is of great necessity in order to find an optimal solution for reducing friction and adhesion of micro surfaces. We proposed an effective method to analyze capillary and van der Waals forces In nano-scale contact. In this method, Winklerian foundation model was employed to analyze the contact of rough surfaces that were obtained from atomic force microscopy (AFM) height Images. Self-mated contact of diamond-like-carbon (DLC) coatings was analyzed, as an example, by the proposed model. It was shown that the capillary force was significantly influenced by relative humidify and wet angle of the DLC surface. The deformation of asperities to a critical magnitude by external loading led to a considerable increase of both capillary and van der Waals forces.

• 대한기계학회논문집A
• /
• 제26권10호
• /
• pp.2180-2186
• /
• 2002

In a micro-scale contact, capillary force and van der Waals interaction significantly influence the contact between asperities of rough surfaces. Little is, however, known about the variation of these surface forces as a function of chemical property of the surface (wet angle), relative humidity and deformation of asperities in the real area of contact. A better understanding of these surface forces is of great necessity in order to find a solution for reducing friction and adhesion of micro surfaces. The objective of this study is to investigate the surface forces in micro-scale rough surface contact. We proposed an effective method to analyze capillary and van der Waals forces in micro-scale contact. In this method, Winkler spring model was employed to analyze the contact of rough surfaces that were obtained from atomic force microscopy (AFM) height images. Self-mated contact of DLC(diamond like carbon) coatings was analyzed, as an example, by the proposed model. It was shown that the capillary force was significantly influenced by relative humidity and wet angle of the DLC surface. The deformation of asperities to a critical magnitude by external loading led to a considerable increase of both capillary and van der Waals forces.

• 한국진공학회:학술대회논문집
• /
• 한국진공학회 2011년도 제40회 동계학술대회 초록집
• /
• pp.449-449
• /
• 2011

We reported the direct effect of intrinsic surface energy of dry adhesive material to the Van der Waals and capillary forces contributions of the total adhesion force in an artificial gecko-inspired adhesion system. To mimic the gecko foot we fabricated tilted nanohairy structures using both lithography and ion beam treatment. The nanohairy structures were replicated from Si wafer mold using UV curable polymeric materials. The control of nanohairs slanting angles was based on the uniform linear argon ion irradiation to the nanohairy polymeric surface. The surface energy was studied utilizing subsequent conventional oxygen ion treatment on the nanohairy structures which resulted in gradient surface energy. Our shear adhesion test results were found in good agreement with the accepted Van der Waals and capillary forces theory in the gecko adhesion system. Surface energy would give a direct impact to the effective Hamaker constant in Van der Waals force and the filling angle (${\varphi}$) of water meniscus in capillary force contributions of gecko inspired adhesion system. With the increasing surface energy, the effective Hamaker constant also increased but the filling angle decreased, resulting in a competition between the two forces. Using a simple mathematical model, we compared our experimental results to show the quantitative contributions of Van der Waals and capillary forces in a single adhesion system on both hydrophobic and hydrophilic surfaces. We found that the Van der Waals force contributes about 82.75% and 89.97% to the total adhesion force on hydrophilic and hydrophobic test surfaces, respectively, while the remaining contribution was occupied by capillary force. We also showed that it is possible to design ultrahigh dry adhesive with adhesion strength of more than 10 times higher than apparent gecko adhesion force by controlling the surface energy and the slanting angle induced-contact line of dry adhesive the materials.

• 한국소음진동공학회논문집
• /
• 제20권9호
• /
• pp.805-815
• /
• 2010

This paper studies the influence of internal moving fluid and flow-induced structural instability of multi-wall carbon nanotubes conveying fluid. Detailed results are demonstrated for the variation of natural frequencies with flow velocity, and the flow-induced divergence and flutter instability characteristics of multi-wall carbon nanotubes conveying fluid and modelled as a thin-walled beam are investigated. Effects of various boundary conditions, Van der Waals forces, and non-classical transverse shear and rotary inertia are incorporated in this study. The governing equations and three different boundary conditions are derived through Hamilton's principle. Numerical analysis is performed by using extended Galerkin's method which enables us to obtain more exact solutions compared with conventional Galerkin's method. This paper also presents the comparison between the characteristics of single-wall and multi-wall carbon nanotubes considering the effect of van der Waals forces. Variations of critical flow velocity for different boundary conditions of two-wall carbon nanotubes are investigated and pertinent conclusion is outlined.

• 접착 및 계면
• /
• 제24권3호
• /
• pp.100-104
• /
• 2023

본 Van der Waals heterostructure 기반의 트랜지스터의 경우 표면에 불포화 결함(dangling bond) 없이 Van der Waals 힘으로만 결합되어 있어 우수한 전자특성을 보이기 때문에 최근 많이 연구되고 있다. 하지만, 트랜지스터에 사용되는 2차원 물질들은 대부분 스카치테이프(mechanical exfoliation) 방법을 기반으로 하는 기초 연구에 머물러 있다. 그렇기 때문에 이를 발전시키기 위해 반데르발스 수직이종접합 전계효과 트랜지스터를 제작하는 데 사용되는 모든 소재를 CVD (chemical vapor deposition)에서 성장된 소재를 사용하였다. 전극으로는 CVD로 성장된 그래핀을 포토리소그래피 공정을 통해 패터닝하여 사용하였으며, CVD로 성장된 MoSe₂를 픽업/전사하는 방식으로, 둘 사이의 반데르발스 이종접합 전계효과 트랜지스터를 제작하였다. 본 연구에서는 이를 통해 제작된 소자의 특성을 보았으며 MoSe₂의 결함 유무에 따라 트랜지스터의 특성에 변화가 있음을 확인하였다.

• 한국생산제조학회지
• /
• 제18권4호
• /
• pp.369-374
• /
• 2009

In micro/nano-scale contacts in MEMS and NEMS, capillary and van der Waals forces generated around contacting micro-asperities significantly influence the performance of concerning device as they are closely related to adhesion and stiction of interacting surfaces. In this regard, it is of prime importance to accurately estimate the magnitude of surface forces so that an optimal solution for reducing friction and adhesion of micro/nano-surfaces may be obtained We introduced an effective method to calculate these surface forces based on topography information obtained from an atomic force microscope. This method was used to calculate surface forces generated in the contact interface formed between diamond-like carbon coating and $Si_3N_4$ ball. This method is shown to effectively demonstrate the influence of capillary force in the contact area, especially in humid atmosphere.

• 한국소음진동공학회:학술대회논문집
• /
• 한국소음진동공학회 2005년도 추계학술대회논문집
• /
• pp.702-707
• /
• 2005

The equations of motion of the structure, which is a small scale cantilever beam considering electrostatic force, squeeze film damping and van der Waals force are obtained employing Galerkin's method based on Euler beam theory. The influence of each force is investigated fur changing the size of a small scale cantilever beam which assumed uniform shape. Also the forces which are affected by the required size of a small scale cantilever beam for manufacturing are forecasted.

• 약학회지
• /
• 제24권2호
• /
• pp.135-141
• /
• 1980

The crystal and molecular structure of 2-methyl-3-(N-trimethyl ammonium)phenol iodide, $C_{10}H_{16}NOI, was determined by X-ray diffraction method. The compound crystallizes in the orthorhombic space group $P_{na2}_{1}$ with a=13.327(3), b=12.496(3), C=7.227(2)A and Z=4. A total of 489 independent observed reflections were collected by the automated Four-circle diffractometer and was solved by heavy atom method and refined by anisotropic block-diagonal least-squares method to the R value of 0.04. The benzene ring is slightly distorted from regular hexagon. The I atom and 2-methyl-3-(N-trimethyl ammonium)phenol group is held together by van der Waals forces in the crystal. Intermolecular hydrogen bond is of the type O-H....I with the length 3.35.angs.. Apart from the hydrogen bonding system the molecules are held together by van der Waals forces in the crystal.

• Advances in nano research
• /
• 제6권2호
• /
• pp.135-145
• /
• 2018

This work represents the study of the vibration response of the double walled carbon nanotubes (DWCNT) for various boundary conditions. The inner and outer carbon nanotubes are modeled as two individual Euler-Bernoulli's elastic beams interacting each other by Van der waals force. Differential transform method (DTM) is used as a numerical method to solve the governing differential equations and associated boundary conditions. The influence of Winkler elastic medium on vibration frequency is also examined and results are interpreted. MATLAB is used as a tool for solving the governing differential equations. The fundamental natural frequencies are validating with those available in literature and observed a good agreement between them.

• Advances in nano research
• /
• 제9권2호
• /
• pp.69-82
• /
• 2020

In this paper, a new explicit analytical formula is derived for the critical buckling load of Double Walled Carbon Nanotubes (DWCNTs) embedded in Winkler elastic medium without taking into account the effects of the nonlocal parameter, which indicates the effects of the surrounding elastic matrix combined with the intertube Van der Waals (VdW) forces. Furthermore, we present a model which predicts that the critical axial buckling load embedded in Winkler, Pasternak or Kerr elastic medium under axial compression using the nonlocal Donnell shell theory, this model takes into account the effects of internal small length scale and the VdW interactions between the inner and outer nanotubes. The present model predicts that the critical axial buckling load of embedded DWCNTs is greater than that without medium under identical conditions and parameters. We can conclude that the embedded DWCNTs are less susceptible to axial buckling than those without medium.