1
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Sanner A, Kumar N, Dhinojwala A, Jacobs TDB, Pastewka L. Why soft contacts are stickier when breaking than when making them. SCIENCE ADVANCES 2024; 10:eadl1277. [PMID: 38446897 PMCID: PMC10917342 DOI: 10.1126/sciadv.adl1277] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/29/2023] [Accepted: 01/30/2024] [Indexed: 03/08/2024]
Abstract
Soft solids are sticky. They attract each other and spontaneously form a large area of contact. Their force of attraction is higher when separating than when forming contact, a phenomenon known as adhesion hysteresis. The common explanation for this hysteresis is viscoelastic energy dissipation or contact aging. Here, we use experiments and simulations to show that it emerges even for perfectly elastic solids. Pinning by surface roughness triggers the stick-slip motion of the contact line, dissipating energy. We derive a simple and general parameter-free equation that quantitatively describes contact formation in the presence of roughness. Our results highlight the crucial role of surface roughness and present a fundamental shift in our understanding of soft adhesion.
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Affiliation(s)
- Antoine Sanner
- Department of Microsystems Engineering (IMTEK), University of Freiburg, Georges-Köhler-Allee 103, 79110 Freiburg, Germany
- Cluster of Excellence livMatS, Freiburg Center for Interactive Materials and Bioinspired Technologies, University of Freiburg, Georges-Köhler-Allee 105, 79110 Freiburg, Germany
- Institute for Building Materials, ETH Zurich, Zurich 8093, Switzerland
| | - Nityanshu Kumar
- School of Polymer Science and Polymer Engineering, The University of Akron, Akron, OH 44325, USA
- Science & Technology Division, Corning Incorporated, Corning, NY 14831, USA
| | - Ali Dhinojwala
- School of Polymer Science and Polymer Engineering, The University of Akron, Akron, OH 44325, USA
| | - Tevis D. B. Jacobs
- Department of Mechanical Engineering and Materials Science, University of Pittsburgh, 3700 O’Hara Street, Pittsburgh, PA 15261, USA
| | - Lars Pastewka
- Department of Microsystems Engineering (IMTEK), University of Freiburg, Georges-Köhler-Allee 103, 79110 Freiburg, Germany
- Cluster of Excellence livMatS, Freiburg Center for Interactive Materials and Bioinspired Technologies, University of Freiburg, Georges-Köhler-Allee 105, 79110 Freiburg, Germany
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2
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Yan C, Guan D, Wang Y, Lai PY, Chen HY, Tong P. Avalanches and Extreme Value Statistics of a Mesoscale Moving Contact Line. PHYSICAL REVIEW LETTERS 2024; 132:084003. [PMID: 38457705 DOI: 10.1103/physrevlett.132.084003] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/21/2023] [Revised: 11/13/2023] [Accepted: 01/16/2024] [Indexed: 03/10/2024]
Abstract
We report direct atomic force microscopy measurements of pinning-depinning dynamics of a circular moving contact line (CL) over the rough surface of a micron-sized vertical hanging glass fiber, which intersects a liquid-air interface. The measured capillary force acting on the CL exhibits sawtoothlike fluctuations, with a linear accumulation of force of slope k (stick) followed by a sharp release of force δf, which is proportional to the CL slip length. From a thorough analysis of a large volume of the stick-slip events, we find that the local maximal force F_{c} needed for CL depinning follows the extreme value statistics and the measured δf follows the avalanche dynamics with a power law distribution in good agreement with the Alessandro-Beatrice-Bertotti-Montorsi (ABBM) model. The experiment provides an accurate statistical description of the CL dynamics at mesoscale, which has important implications to a common class of problems involving stick-slip motion in a random defect or roughness landscape.
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Affiliation(s)
- Caishan Yan
- Department of Physics, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong
| | - Dongshi Guan
- State Key Laboratory of Nonlinear Mechanics, Institute of Mechanics, Chinese Academy of Sciences, Beijing 100190, China
- School of Engineering Science, University of Chinese Academy of Sciences, Beijing 100049, China
| | - Yin Wang
- Department of Physics, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong
| | - Pik-Yin Lai
- Department of Physics and Center for Complex Systems, National Central University, Taoyuan City 320, Taiwan
- Physics Division, National Center for Theoretical Sciences, Taipei 10617, Taiwan
| | - Hsuan-Yi Chen
- Department of Physics and Center for Complex Systems, National Central University, Taoyuan City 320, Taiwan
- Physics Division, National Center for Theoretical Sciences, Taipei 10617, Taiwan
| | - Penger Tong
- Department of Physics, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong
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3
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Singh K, Paliwal N, Kasamias K. Surface roughness characterization using representative elementary area (REA) analysis. Sci Rep 2024; 14:1785. [PMID: 38245565 PMCID: PMC10799896 DOI: 10.1038/s41598-024-52329-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2023] [Accepted: 01/17/2024] [Indexed: 01/22/2024] Open
Abstract
We proposed the Representative Elementary Area (REA) analysis method and illustrated how it is needed to evaluate representative roughness parameters of surfaces. We used mean height (Sa) roughness to study how its variations converge to a steady state as we expanded the area of investigation (AOI) using combined scan tiles obtained through Confocal Laser Scanning Microscopy. We tested quartz and glass surfaces, subjecting them to various levels of polishing with grit sizes ranging between # 60 and #1200. The scan tiles revealed a multiscale roughness texture characterized by the dominance of valleys over peaks, lacking a fractal nature. REA analysis revealed Sa variations converged to a steady state as AOI increased, highlighting the necessity of the proposed method. The steady-state Sa, denoted as [Formula: see text], followed an inverse power law with polishing grit size, with its exponent dependent on the material hardness. The REA length representing [Formula: see text] of glass surfaces, followed another inverse power law with polishing grit size and an indeterminate relationship for quartz surfaces. The multiscale characteristics and convergence to steady state were also evident in skewness, kurtosis, and autocorrelation length (Sal) parameters. Sal increased to a maximum value before decreasing linearly as AOI was linearly increased. The maximum Sal, termed as [Formula: see text], exhibited a linear relationship with REA. In the absence of REA analysis, the magnitude of uncertainty depended on the polishing grit size. Finely polished surfaces exhibited a 10-20% variability, which increased to up to 70% relative to the steady-state Sa with coarser polishing.
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Affiliation(s)
- Kuldeep Singh
- Department of Earth Sciences, Kent State University, 325 S. Lincoln St., Kent, OH, 44242, USA.
| | - Nitin Paliwal
- Department of Earth Sciences, Kent State University, 325 S. Lincoln St., Kent, OH, 44242, USA
| | - Konstantinos Kasamias
- Department of Earth Sciences, Kent State University, 325 S. Lincoln St., Kent, OH, 44242, USA
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4
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Peng L, Hsu CC, Xiao C, Bonn D, Weber B. Controlling Macroscopic Friction through Interfacial Siloxane Bonding. PHYSICAL REVIEW LETTERS 2023; 131:226201. [PMID: 38101386 DOI: 10.1103/physrevlett.131.226201] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/24/2023] [Accepted: 10/12/2023] [Indexed: 12/17/2023]
Abstract
Controlling macroscopic friction is crucial for numerous natural and industrial applications, ranging from forecasting earthquakes to miniaturizing semiconductor devices, but predicting and manipulating friction phenomena remains a challenge due to the unknown relationship between nanoscale and macroscopic friction. Here, we show experimentally that dry friction at multiasperity Si-on-Si interfaces is dominated by the formation of interfacial siloxane (Si─O─Si) bonds, the density of which can be precisely regulated by exposing plasma-cleaned silicon surfaces to dry nitrogen. Our results show how the bond density can be used to quantitatively understand and control the macroscopic friction. Our findings establish a unique connection between the molecular scale at which adhesion occurs, and the friction coefficient that is the key macroscopic parameter for industrial and natural tribology challenges.
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Affiliation(s)
- Liang Peng
- Van der Waals-Zeeman Institute, Institute of Physics, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands
| | - Chao-Chun Hsu
- Van't Hoff Institute for Molecular Sciences, University of Amsterdam, 1098 XH Amsterdam, The Netherlands
| | - Chen Xiao
- Van der Waals-Zeeman Institute, Institute of Physics, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands
- Advanced Research Center for Nanolithography (ARCNL), Science Park 106, 1098 XG Amsterdam, The Netherlands
| | - Daniel Bonn
- Van der Waals-Zeeman Institute, Institute of Physics, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands
| | - Bart Weber
- Van der Waals-Zeeman Institute, Institute of Physics, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands
- Advanced Research Center for Nanolithography (ARCNL), Science Park 106, 1098 XG Amsterdam, The Netherlands
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5
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Sinkhonde D. Employing spatial, hybrid and amplitude roughness parameters for unveiling the surface roughness features of mineral and organic admixtures. Heliyon 2023; 9:e20539. [PMID: 37842609 PMCID: PMC10568350 DOI: 10.1016/j.heliyon.2023.e20539] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2023] [Revised: 07/26/2023] [Accepted: 09/22/2023] [Indexed: 10/17/2023] Open
Abstract
Scanning electron microscopy (SEM) permits to evaluate the surface morphology and surface roughness of pozzolans and admixtures. The field of mineral and organic admixtures has considerable interest in using SEM. However, several challenges are encountered which hamper the precision of quantitative roughness evaluation of mineral and organic admixtures using SEM and these challenges are usually bypassed in literature. In this research, surface roughness properties of pozzolans and admixtures were analysed from six perspectives: spatial parameters, hybrid parameters, amplitude parameters, surface roughness profiles, bearing ratio curves (BRCs) and amplitude density functions (ADFs). The generated roughness characteristics provided detailed information of roughness properties of the pozzolans and admixtures in a time efficient and cost effective way, which is usually very hard to achieve using experimental works. The comparisons of the obtained roughness data for the specimens showed considerable agreement with the roughness profiles and verified the interpretation of the established roughness profiles. Using the ADFs and BRCs for evaluating heights of the roughness profiles provided significant data encapsulated in the shapes of ADFs and BRCs. Moreover, the interpretation of the transformed logarithmic profiles seemed to have nearly retained similar meanings with the conventional profiles, although their scrutiny was observed to be complex. With brand new discussions on spatial, hybrid and amplitude parameters of mineral and organic admixtures, this research is a step forward in characterisation of roughness parameters of mineral and organic admixtures. This study expands the characterisation of pozzolans and admixtures, highlighting significant parameters to be considered in the application of mineral and organic admixtures.
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Affiliation(s)
- David Sinkhonde
- Department of Civil and Construction Engineering, Pan African University Institute for Basic Sciences, Technology and Innovation, Nairobi, Kenya
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6
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Fallah Tafti M, Aghamollaei H, Moosazadeh Moghaddam M, Jadidi K, Faghihi S. An inspired microenvironment of cell replicas to induce stem cells into keratocyte-like dendritic cells for corneal regeneration. Sci Rep 2023; 13:15012. [PMID: 37696883 PMCID: PMC10495344 DOI: 10.1038/s41598-023-42359-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2023] [Accepted: 09/08/2023] [Indexed: 09/13/2023] Open
Abstract
Corneal stromal disorders due to the loss of keratocytes can affect visual impairment and blindness. Corneal cell therapy is a promising therapeutic strategy for healing corneal tissue or even enhancing corneal function upon advanced disorders, however, the sources of corneal keratocytes are limited for clinical applications. Here, the capacity of cell-imprinted substrates fabricated by molding human keratocyte templates to induce differentiation of human adipose-derived stem cells (hADSCs) into keratocytes, is presented. Keratocytes are isolated from human corneal stroma and grown to transmit their ECM architecture and cell-like topographies to a PDMS substrate. The hADSCs are then seeded on cell-imprinted substrates and their differentiation to keratocytes in DMEM/F12 (with and without chemical factors) are evaluated by real-time PCR and immunocytochemistry. The mesenchymal stem cells grown on patterned substrates present gene and protein expression profiles similar to corneal keratocytes. In contrast, a negligible expression of myofibroblast marker in the hADSCs cultivated on the imprinted substrates, is observed. Microscopic analysis reveals dendritic morphology and ellipsoid nuclei similar to primary keratocytes. Overall, it is demonstrated that biomimetic imprinted substrates would be a sufficient driver to solely direct the stem cell fate toward target cells which is a significant achievement toward corneal regeneration.
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Affiliation(s)
- Mahsa Fallah Tafti
- Stem Cell and Regenerative Medicine Group, National Institute of Genetic Engineering and Biotechnology, 14965/161, Tehran, Iran
| | - Hossein Aghamollaei
- Chemical Injuries Research Center, Systems Biology and Poisonings Institute, Baqiyatallah University of Medical Sciences, Tehran, Iran
| | - Mehrdad Moosazadeh Moghaddam
- Tissue Engineering and Regenerative Medicine Research Center, Baqiyatallah University of Medical Sciences, Tehran, Iran
| | - Khosrow Jadidi
- Vision Health Research Center, Semnan University of Medical Sciences, Semnan, 1435916471, Iran.
| | - Shahab Faghihi
- Stem Cell and Regenerative Medicine Group, National Institute of Genetic Engineering and Biotechnology, 14965/161, Tehran, Iran.
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7
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Wang J, Sun H, Jia W, Song Y, Quan P, Fang L, Liu C. Construction of Imatinib Controlled Release Film-Forming System Based on Drug Ion-Pair and Oligomeric Ionic Liquids for the Long Local Therapy of Cutaneous Melanoma. AAPS PharmSciTech 2023; 24:87. [PMID: 36964446 DOI: 10.1208/s12249-023-02546-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/08/2023] [Accepted: 02/14/2023] [Indexed: 03/26/2023] Open
Abstract
An imatinib controlled release film-forming system (FFS) was developed based on the drug ion-pair and newly designed oligomeric ionic liquids (OILs) for the topical therapy of cutaneous melanoma, which avoided the systemic side-effect of oral administration and maintained a long local therapy effect. The OILs significantly improved the drug release capacity about 1.5-fold, and the formability and stability of FFSs (verified by AFM/PLM). The in vivo anti-tumor efficacy studies in melanoma tumor bearing mice showed that compared with the oral capsules, the topical application of the optimized imatinib FFS significantly (p < 0.01) increased tumor inhibition rate (67.54 ± 2.72%) and the amount of apoptotic cells. As confirmed by FT-IR and NMR, the partial protonation of OILs were demonstrated to have high hydrogen bond forming capacity, thus showing low polarity and good biocompatibility. More importantly, based on 13C-NMR study, OILs demonstrated higher hydrogen bond forming capacity, and formed bridge between drug ion-pair (O-H of counter-ion) and PVA (O-H), increased the molecular mobility of PVA, thus maintaining a long drug release capacity. Therefore, an imatinib FFS was developed with good therapeutic effect and the effect of drug ion-pair and OILs on increasing the drug skin retention and controlled release of imatinib FFS for topical therapy was clarified at the molecular level, which provided a safe and effective way for the treatment of cutaneous melanoma.
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Affiliation(s)
- Junzhu Wang
- Department of Pharmaceutical Sciences, Shenyang Pharmaceutical University, 103 Wenhua Road, Shenyang, 110016, Liaoning, China
| | - Han Sun
- Department of Pharmaceutical Sciences, Shenyang Pharmaceutical University, 103 Wenhua Road, Shenyang, 110016, Liaoning, China
| | - Wenxuan Jia
- Department of Pharmaceutical Sciences, Shenyang Pharmaceutical University, 103 Wenhua Road, Shenyang, 110016, Liaoning, China
| | - Yilin Song
- Department of Pharmaceutical Sciences, Shenyang Pharmaceutical University, 103 Wenhua Road, Shenyang, 110016, Liaoning, China
| | - Peng Quan
- Department of Pharmaceutical Sciences, Shenyang Pharmaceutical University, 103 Wenhua Road, Shenyang, 110016, Liaoning, China
| | - Liang Fang
- Department of Pharmaceutical Sciences, Shenyang Pharmaceutical University, 103 Wenhua Road, Shenyang, 110016, Liaoning, China
| | - Chao Liu
- Department of Pharmaceutical Sciences, Shenyang Pharmaceutical University, 103 Wenhua Road, Shenyang, 110016, Liaoning, China.
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8
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Sheglov DV, Rogilo DI, Fedina LI, Sitnikov SV, Sysoev EV, Latyshev AV. Bottom-Up Generated Height Gauges for Silicon-Based Nanometrology. ACS APPLIED MATERIALS & INTERFACES 2023; 15:12511-12523. [PMID: 36808946 DOI: 10.1021/acsami.2c20154] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/18/2023]
Abstract
Steady progress in integrated circuit design has forced basic metrology to adopt silicon lattice parameter as a secondary realization of the SI meter that lacks convenient physical gauges for precise surface measurements at a nanoscale. To employ this fundamental shift in nanoscience and nanotechnology, we propose a set of self-organized silicon surface morphologies as a gauge for height measurements within the whole nanoscale (0.3-100 nm) range. Using 2 nm sharp atomic force microscopy (AFM) probes, we have measured the roughness of wide (up to 230 μm in diameter) singular terraces and the height of monatomic steps on the step-bunched and amphitheater-like Si(111) surfaces. For both types of self-organized surface morphology, the root-mean-square terrace roughness exceeds 70 pm but has a little effect on step height measurements having 10 pm accuracy for AFM technique in air. We implement a step-free 230-μm-wide singular terrace as a reference mirror in an optical interferometer to reduce the systematic error of height measurements from >5 nm to about 0.12 nm, which allows visualizing 136-pm-high monatomic steps on the Si(001) surface. Then, using a "pit-patterned" extremely wide terrace with dense but counted monatomic steps in a pit wall, we have optically measured mean Si(111) interplanar spacing (313.8 ± 0.4 pm) that agrees well with the most precise metrological data (313.56 pm). This opens up avenues for the creation of silicon-based height gauges using bottom-up approaches and advances optical interferometry among techniques for metrology-grade nanoscale height measurements.
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Affiliation(s)
- Dmitry V Sheglov
- Rzhanov Institute of Semiconductor Physics SB RAS, Lavrentiev aven. 13, Novosibirsk 630090, Russia
| | - Dmitry I Rogilo
- Rzhanov Institute of Semiconductor Physics SB RAS, Lavrentiev aven. 13, Novosibirsk 630090, Russia
| | - Liudmila I Fedina
- Rzhanov Institute of Semiconductor Physics SB RAS, Lavrentiev aven. 13, Novosibirsk 630090, Russia
| | - Sergey V Sitnikov
- Rzhanov Institute of Semiconductor Physics SB RAS, Lavrentiev aven. 13, Novosibirsk 630090, Russia
| | - Evgeny V Sysoev
- Technological Design Institute of Scientific Instrument Engineering SB RAS, Russkaya str. 41, Novosibirsk 630058, Russia
| | - Alexander V Latyshev
- Rzhanov Institute of Semiconductor Physics SB RAS, Lavrentiev aven. 13, Novosibirsk 630090, Russia
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9
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Jacobs TDB, Pastewka L. Surface topography as a material parameter. MRS BULLETIN 2023; 47:1205-1210. [PMID: 36846501 PMCID: PMC9947057 DOI: 10.1557/s43577-022-00465-5] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Accepted: 12/05/2022] [Indexed: 06/18/2023]
Abstract
ABSTRACT Materials science is about understanding the relationship between a material's structure and its properties-in the sphere of mechanical behavior, this includes elastic modulus, yield strength, and other bulk properties. We show in this issue that, analogously, a material's surface structure governs its surface properties-such as adhesion, friction, and surface stiffness. For bulk materials, microstructure is a critical component of structure; for surfaces, the structure is governed largely by surface topography. The articles in this issue cover the latest understanding of these structure-property connections for surfaces. This includes both the theoretical basis for how properties depend on topography, as well as the latest understanding of how surface topography emerges, how to measure and understand topography-dependent properties, and how to engineer surfaces to improve performance. The present article frames the importance of surface topography and its effect on properties; it also outlines some of the critical knowledge gaps that impede progress toward optimally performing surfaces.
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Affiliation(s)
- Tevis D. B. Jacobs
- Department of Mechanical Engineering and Materials Science, University of Pittsburgh, Pittsburgh, USA
| | - Lars Pastewka
- Department of Microsystems Engineering, University of Freiburg, Freiburg, Germany
- Cluster of Excellence livMatS, Freiburg Center for Interactive Materials and Bioinspired Technologies, University of Freiburg, Freiburg, Germany
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10
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Müser MH, Nicola L. Modeling the surface topography dependence of friction, adhesion, and contact compliance. MRS BULLETIN 2023; 47:1221-1228. [PMID: 36846502 PMCID: PMC9947065 DOI: 10.1557/s43577-022-00468-2] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Accepted: 11/28/2022] [Indexed: 06/18/2023]
Abstract
The small-scale topography of surfaces critically affects the contact area of solids and thus the forces acting between them. Although this has long been known, only recent advances made it possible to reliably model interfacial forces and related quantities for surfaces with multiscale roughness. This article sketches both recent and traditional approaches to their mechanics, while addressing the relevance of nonlinearity and nonlocality arising in soft- and hard-matter contacts.
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Affiliation(s)
- Martin H. Müser
- Department of Materials Science and Engineering, Saarland University, Saarbrücken, Germany
| | - Lucia Nicola
- Department of Industrial Engineering, University of Padua, Padua, Italy
- Department of Materials Engineering, Delft University of Technology, Delft, The Netherlands
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11
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Gao L, Zhong X, Chen J, Zhang Y, Liu J, Zhang B. Optimizing the electronic structure of Fe-doped Co3O4 supported Ru catalyst via metal-support interaction boosting oxygen evolution reaction and hydrogen evolution reaction. CHINESE CHEM LETT 2022. [DOI: 10.1016/j.cclet.2022.108085] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
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12
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Jetti YS, Ostoja-Starzewski M. Elastic contact of random surfaces with fractal and Hurst effects. Proc Math Phys Eng Sci 2022. [DOI: 10.1098/rspa.2022.0384] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
Most of the recent research on random surface contact mechanics has been on self-affine surfaces. In such models, the fractal dimension (which represents the ‘roughness’) and the Hurst parameter (which represents the ‘spatial memory’) are linearly dependent. In this study, we investigate the non-adhesive, frictionless contact between elastic solids with non-self-affine manifolds. In particular, we use Cauchy and Dagum covariance functions, which can decouple the fractal and Hurst effects, to describe the height distribution of the random surfaces. A numerical model based on the Boussinesq point load fundamental solutions is employed along with the discrete convolution FFT method to perform the contact analysis. We investigate the true contact area evolution under increasing load for surfaces with a wide range of fractal and Hurst parameters. It is observed that the contact area evolution at light loads is almost independent of the Hurst parameter and non-monotonically dependent on the fractal dimension. By contrast, previous studies predicted the contact evolution to be weakly dependent on the Hurst parameter and the fractal dimension. The curvature of the plots of the slope of the contact area evolution is found to depend on the fractal dimension, contrary to previous studies, which predicted either convexity or concavity.
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Affiliation(s)
- Yaswanth Sai Jetti
- Department of Mechanical Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA
| | - Martin Ostoja-Starzewski
- Department of Mechanical Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA
- Institute for Condensed Matter Theory and Beckman Institute, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA
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13
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Palecek AM, Garner AM, Klittich MR, Stark AY, Scherger JD, Bernard C, Niewiarowski PH, Dhinojwala A. An investigation of gecko attachment on wet and rough substrates leads to the application of surface roughness power spectral density analysis. Sci Rep 2022; 12:11556. [PMID: 35798824 PMCID: PMC9262901 DOI: 10.1038/s41598-022-15698-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2021] [Accepted: 06/28/2022] [Indexed: 11/18/2022] Open
Abstract
The roughness and wettability of surfaces exploited by free-ranging geckos can be highly variable and attachment to these substrates is context dependent (e.g., presence or absence of surface water). Although previous studies focus on the effect of these variables on attachment independently, geckos encounter a variety of conditions in their natural environment simultaneously. Here, we measured maximum shear load of geckos in air and when their toes were submerged underwater on substrates that varied in both surface roughness and wettability. Gecko attachment was greater in water than in air on smooth and rough hydrophobic substrates, and attachment to rough hydrophilic substrates did not differ when tested in air or water. Attachment varied considerably with surface roughness and characterization revealed that routine measurements of root mean square height can misrepresent the complexity of roughness, especially when measured with single instruments. We used surface roughness power spectra to characterize substrate surface roughness and examined the relationship between gecko attachment performance across the power spectra. This comparison suggests that roughness wavelengths less than 70 nm predominantly dictate gecko attachment. This study highlights the complexity of attachment in natural conditions and the need for comprehensive surface characterization when studying biological adhesive system performance.
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Affiliation(s)
- Amanda M Palecek
- Gecko Adhesion Research Group, The University of Akron, Akron, OH, USA. .,Department of Biology, The University of Akron, Akron, OH, USA. .,Department of Biological Sciences, Clemson University, Clemson, SC, USA.
| | - Austin M Garner
- Gecko Adhesion Research Group, The University of Akron, Akron, OH, USA.,Integrated Bioscience Program, The University of Akron, Akron, OH, USA.,Department of Biology, The University of Akron, Akron, OH, USA.,Department of Biology, Villanova University, Villanova, PA, USA
| | - Mena R Klittich
- Gecko Adhesion Research Group, The University of Akron, Akron, OH, USA.,Department of Polymer Science, The University of Akron, Akron, OH, USA.,Avery Dennison, Oegstgeest, The Netherlands
| | - Alyssa Y Stark
- Gecko Adhesion Research Group, The University of Akron, Akron, OH, USA.,Integrated Bioscience Program, The University of Akron, Akron, OH, USA.,Department of Biology, The University of Akron, Akron, OH, USA.,Department of Biology, Villanova University, Villanova, PA, USA
| | - Jacob D Scherger
- Department of Polymer Science, The University of Akron, Akron, OH, USA
| | - Craig Bernard
- Gecko Adhesion Research Group, The University of Akron, Akron, OH, USA.,Department of Biology, The University of Akron, Akron, OH, USA
| | - Peter H Niewiarowski
- Gecko Adhesion Research Group, The University of Akron, Akron, OH, USA.,Integrated Bioscience Program, The University of Akron, Akron, OH, USA.,Department of Biology, The University of Akron, Akron, OH, USA
| | - Ali Dhinojwala
- Gecko Adhesion Research Group, The University of Akron, Akron, OH, USA.,Integrated Bioscience Program, The University of Akron, Akron, OH, USA.,Department of Polymer Science, The University of Akron, Akron, OH, USA
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14
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Ding R, Miller NC, Woeppel KM, Cui XT, Jacobs TDB. Surface Area and Local Curvature: Why Roughness Improves the Bioactivity of Neural Implants. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2022; 38:7512-7521. [PMID: 35678760 PMCID: PMC10080668 DOI: 10.1021/acs.langmuir.2c00473] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/15/2023]
Abstract
While roughening the surface of neural implants has been shown to significantly improve their performance, the mechanism for this improvement is not understood, preventing systematic optimization of surfaces. Specifically, prior work has shown that the cellular response to a surface can be significantly enhanced by coating the implant surface with inorganic nanoparticles and neuroadhesion protein L1, and this improvement occurs even when the surface chemistry is identical between the nanoparticle-coated and uncoated electrodes, suggesting the critical importance of surface topography. Here, we use transmission electron microscopy to characterize the topography of bare and nanoparticle-coated implants across 7 orders of magnitude in size, from the device scale to the atomic scale. The results reveal multiscale roughness, which cannot be adequately described using conventional roughness parameters. Indeed, the topography is nearly identical between the two samples at the smallest scales and also at the largest scales but vastly different in the intermediate scales, especially in the range of 5-100 nm. Using a multiscale topography analysis, we show that the coating causes a 76% increase in the available surface area for contact and an order-of-magnitude increase in local surface curvature at characteristic sizes corresponding to specific biological structures. These are correlated with a 75% increase in bound proteins on the surface and a 134% increase in neurite outgrowth. The present investigation presents a framework for analyzing the scale-dependent topography of medical device-relevant surfaces, and suggests the most critical size scales that determine the biological response to implanted materials.
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Affiliation(s)
- Ruikang Ding
- Mechanical Engineering & Materials Science, University of Pittsburgh, 3700 O'Hara St., Benedum Hall Room 636, Pittsburgh, Pennsylvania 15261, United States
| | - Nathaniel C Miller
- Mechanical Engineering & Materials Science, University of Pittsburgh, 3700 O'Hara St., Benedum Hall Room 636, Pittsburgh, Pennsylvania 15261, United States
| | - Kevin M Woeppel
- Bioengineering, University of Pittsburgh, 5057 Biomedical Science Tower 3, 3501 Fifth Ave, Pittsburgh, Pennsylvania 15260, United States
- Center for the Neural Basis of Cognition, 4400 Fifth Ave, Suite 115, Pittsburgh, Pennsylvania 15213, United States
| | - Xinyan T Cui
- Bioengineering, University of Pittsburgh, 5057 Biomedical Science Tower 3, 3501 Fifth Ave, Pittsburgh, Pennsylvania 15260, United States
- Center for the Neural Basis of Cognition, 4400 Fifth Ave, Suite 115, Pittsburgh, Pennsylvania 15213, United States
- McGowan Institute for Regenerative Medicine, Pittsburgh, Pennsylvania 15213, United States
| | - Tevis D B Jacobs
- Mechanical Engineering & Materials Science, University of Pittsburgh, 3700 O'Hara St., Benedum Hall Room 636, Pittsburgh, Pennsylvania 15261, United States
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15
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Abstract
It has been shown experimentally that boundary friction is proportional to load (commonly known as Amontons’ law) for more than 500 years, and the fact that it holds true over many scales (from microns to kilometres, and from nano-Newtons to Mega-Newtons) and for materials which deform both elastically and plastically has been the subject of much research, in order to more fully understand its wide applicability (and also to find any deviations from the law). Attempts to explain and understand Amontons’ law recognise that real surfaces are rough; as such, many researchers have studied the contact of rough surfaces under both elastic and plastic deformation conditions. As the focus on energy efficiency is ever increasing, machines are now being used with lower-viscosity lubricants, operating at higher loads and temperatures, such that the oil films separating the moving surfaces are becoming thinner, and there is a greater chance of mixed/boundary lubrication occurring. Because mixed/boundary lubrication occurs when the two moving rough surfaces come into contact, it is thought timely to review this topic and the current state of the theoretical and experimental understanding of rough-surface contact for the prediction of friction in the mixed/boundary lubrication regime.
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16
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Affiliation(s)
- Guido Raos
- Department of Chemistry, Materials and Chemical Engineering “G. Natta”, Politecnico di Milano, Via L. Mancinelli 7, I-20131 Milano, Italy
| | - Bruno Zappone
- Consiglio Nazionale delle Ricerche - Istituto di Nanotecnologia (CNR-Nanotec), Via P. Bucci, 33/C, 87036 Rende (CS), Italy
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17
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Beaulieu C, Vidal D, Yari B, Chaouki J, Bertrand F. Impact of surface roughness on heat transfer through spherical particle packed beds. Chem Eng Sci 2021. [DOI: 10.1016/j.ces.2020.116256] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
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18
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Ultrananocrystalline Diamond Nanowires: Fabrication, Characterization, and Sensor Applications. MATERIALS 2021; 14:ma14030661. [PMID: 33572648 PMCID: PMC7867003 DOI: 10.3390/ma14030661] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 01/03/2021] [Revised: 01/26/2021] [Accepted: 01/28/2021] [Indexed: 11/17/2022]
Abstract
The aim of this review is to provide a survey of the recent advances and the main remaining challenges related to the ultrananocrystalline diamond (UNCD) nanowires and other nanostructures which exhibit excellent capability as the core components for many diverse novel sensing devices, due to the unique material properties and geometry advantages. The boron or nitrogen doping introduced in the gas phase during deposition promotes p-type or n-type conductivity. With the establishment of the UNCD nanofabrication techniques, more and more nanostructure-based devices are being explored in measuring basic physical and chemical parameters via classic and quantum methods, as exemplified by gas sensors, ultraviolet photodetectors, piezoresistance effect-based devices, biological applications and biosensors, and nitrogen-vacancy color center-based magnetic field quantum sensors. Highlighted finally are some of the remaining challenges and the future outlook in this area.
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19
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Duman AN. Grain analysis of atomic force microscopy images via persistent homology. Ultramicroscopy 2020; 220:113176. [PMID: 33249346 DOI: 10.1016/j.ultramic.2020.113176] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2020] [Revised: 10/26/2020] [Accepted: 11/13/2020] [Indexed: 11/27/2022]
Abstract
Atomic force microscopy (AFM) is an established technique in nanoscale grain analysis due to its accuracy in producing 3-dimensional images. Even though height threshold and watershed algorithms are commonly used to determine the grain size and number of grains, they mostly require image processing that result in the change of topographical features of the surface that generates misleading conclusions. In this study, we use persistent homology, a method of representing topological features, to obtain more accurate information about the granular surfaces from unprocessed AFM images than the conventional methods. The method is also useful as a robust alternative to common parameters describing the topography of the AFM images. Most of these parameters such as arithmetic roughness and root-mean-squared roughness are represented by a single number which results in uncertainty in characterization of different surfaces. Persistent homology provides more precise summary about surface properties than a single parameter.
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Affiliation(s)
- Ali Nabi Duman
- Department of Mathematics and Statistics, King Fahd University of Petroleum and Minerals, Dhahran, Saudi Arabia.
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20
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Sahli R, Prot A, Wang A, Müser MH, Piovarči M, Didyk P, Bennewitz R. Tactile perception of randomly rough surfaces. Sci Rep 2020; 10:15800. [PMID: 32978470 PMCID: PMC7519105 DOI: 10.1038/s41598-020-72890-y] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2020] [Accepted: 09/08/2020] [Indexed: 11/09/2022] Open
Abstract
Most everyday surfaces are randomly rough and self-similar on sufficiently small scales. We investigated the tactile perception of randomly rough surfaces using 3D-printed samples, where the topographic structure and the statistical properties of scale-dependent roughness were varied independently. We found that the tactile perception of similarity between surfaces was dominated by the statistical micro-scale roughness rather than by their topographic resemblance. Participants were able to notice differences in the Hurst roughness exponent of 0.2, or a difference in surface curvature of 0.8 \documentclass[12pt]{minimal}
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\begin{document}$$\hbox {mm}^{-1}$$\end{document}mm-1 for surfaces with curvatures between 1 and 3 \documentclass[12pt]{minimal}
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\begin{document}$$\hbox {mm}^{-1}$$\end{document}mm-1. In contrast, visual perception of similarity between color-coded images of the surface height was dominated by their topographic resemblance. We conclude that vibration cues from roughness at the length scale of the finger ridge distance distract the participants from including the topography into the judgement of similarity. The interaction between surface asperities and fingertip skin led to higher friction for higher micro-scale roughness. Individual friction data allowed us to construct a psychometric curve which relates similarity decisions to differences in friction. Participants noticed differences in the friction coefficient as small as 0.035 for samples with friction coefficients between 0.34 and 0.45.
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Affiliation(s)
- Riad Sahli
- INM - Leibniz Institute for New Materials, 66123, Saarbrücken, Germany
| | - Aubin Prot
- INM - Leibniz Institute for New Materials, 66123, Saarbrücken, Germany.,Department of Physics, Saarland University, 66123, Saarbrücken, Germany
| | - Anle Wang
- Department of Materials Science and Engineering, Saarland University, 66123, Saarbrücken, Germany
| | - Martin H Müser
- INM - Leibniz Institute for New Materials, 66123, Saarbrücken, Germany.,Department of Materials Science and Engineering, Saarland University, 66123, Saarbrücken, Germany
| | - Michal Piovarči
- Cluster of Excellence (MMCI), Saarland Informatics Campus, 66123, Saarbrücken, Germany.,Università della Svizzera italiana, 6900, Lugano, Switzerland
| | - Piotr Didyk
- Cluster of Excellence (MMCI), Saarland Informatics Campus, 66123, Saarbrücken, Germany.,Università della Svizzera italiana, 6900, Lugano, Switzerland
| | - Roland Bennewitz
- INM - Leibniz Institute for New Materials, 66123, Saarbrücken, Germany. .,Department of Physics, Saarland University, 66123, Saarbrücken, Germany.
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21
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Petrova D, Sharma DK, Vacha M, Bonn D, Brouwer AM, Weber B. Ageing of Polymer Frictional Interfaces: The Role of Quantity and Quality of Contact. ACS APPLIED MATERIALS & INTERFACES 2020; 12:9890-9895. [PMID: 32024365 PMCID: PMC7049987 DOI: 10.1021/acsami.9b19125] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/27/2019] [Accepted: 02/04/2020] [Indexed: 05/06/2023]
Abstract
When two objects are in contact, the force necessary for one to start sliding over the other is larger than the force necessary to keep the sliding motion going. This difference between static and dynamic friction is thought to result from a reduction in the area of real contact upon the onset of slip. Here, we resolve the structure in the area of contact on the molecular scale by means of environment-sensitive molecular rotors using (super-resolution) fluorescence microscopy and fluorescence lifetime imaging. We demonstrate that the macroscopic friction force is not only controlled by the area of real contact but also controlled by the "quality" of that area of real contact, which determines the friction per unit contact area. We show that the latter is affected by the local density of the contacting surfaces, a parameter that can be expected to change in time at any interface that involves glassy, amorphous materials.
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Affiliation(s)
- D. Petrova
- van
‘t Hoff Institute for Molecular Sciences, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, Netherlands
| | - D. K. Sharma
- Department
of Materials Science and Engineering, Tokyo
Institute of Technology, Ookayama 2-12-1-S8-44, Meguro-ku, 152-8552 Tokyo, Japan
| | - M. Vacha
- Department
of Materials Science and Engineering, Tokyo
Institute of Technology, Ookayama 2-12-1-S8-44, Meguro-ku, 152-8552 Tokyo, Japan
| | - D. Bonn
- Van
der Waals-Zeeman Institute, IoP, University
of Amsterdam, Science Park 904, 1098XH Amsterdam, The Netherlands
| | - A. M. Brouwer
- van
‘t Hoff Institute for Molecular Sciences, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, Netherlands
| | - B. Weber
- Van
der Waals-Zeeman Institute, IoP, University
of Amsterdam, Science Park 904, 1098XH Amsterdam, The Netherlands
- Advanced
Research Center for Nanolithography (ARCNL), Science Park 110, 1098 XG Amsterdam, Netherlands
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22
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Hinkle AR, Nöhring WG, Leute R, Junge T, Pastewka L. The emergence of small-scale self-affine surface roughness from deformation. SCIENCE ADVANCES 2020; 6:eaax0847. [PMID: 32110722 PMCID: PMC7021500 DOI: 10.1126/sciadv.aax0847] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/20/2019] [Accepted: 11/26/2019] [Indexed: 05/14/2023]
Abstract
Most natural and man-made surfaces appear to be rough on many length scales. There is presently no unifying theory of the origin of roughness or the self-affine nature of surface topography. One likely contributor to the formation of roughness is deformation, which underlies many processes that shape surfaces such as machining, fracture, and wear. Using molecular dynamics, we simulate the biaxial compression of single-crystal Au, the high-entropy alloy Ni36.67Co30Fe16.67Ti16.67, and amorphous Cu50Zr50 and show that even surfaces of homogeneous materials develop a self-affine structure. By characterizing subsurface deformation, we connect the self-affinity of the surface to the spatial correlation of deformation events occurring within the bulk and present scaling relations for the evolution of roughness with strain. These results open routes toward interpreting and engineering roughness profiles.
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Affiliation(s)
- Adam R. Hinkle
- Material, Physical and Chemical Sciences Center, Sandia National Laboratories, Albuquerque, NM 87123, USA
- Institute for Applied Materials, Karlsruhe Institute of Technology, 76131 Karlsruhe, Germany
| | - Wolfram G. Nöhring
- Department of Microsystems Engineering, University of Freiburg, 79110 Freiburg, Germany
| | - Richard Leute
- Department of Microsystems Engineering, University of Freiburg, 79110 Freiburg, Germany
| | - Till Junge
- Department of Mechanical Engineering, École Polytechnique Fédérale de Lausanne, 1015 Lausanne, Switzerland
| | - Lars Pastewka
- Institute for Applied Materials, Karlsruhe Institute of Technology, 76131 Karlsruhe, Germany
- Department of Microsystems Engineering, University of Freiburg, 79110 Freiburg, Germany
- Freiburg Materials Research Center, University of Freiburg, 79104 Freiburg, Germany
- Cluster of Excellence livMatS, University of Freiburg, 79110 Freiburg, Germany
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23
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Dalvi S, Gujrati A, Khanal SR, Pastewka L, Dhinojwala A, Jacobs TDB. Linking energy loss in soft adhesion to surface roughness. Proc Natl Acad Sci U S A 2019; 116:25484-25490. [PMID: 31772024 PMCID: PMC6925979 DOI: 10.1073/pnas.1913126116] [Citation(s) in RCA: 26] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
A mechanistic understanding of adhesion in soft materials is critical in the fields of transportation (tires, gaskets, and seals), biomaterials, microcontact printing, and soft robotics. Measurements have long demonstrated that the apparent work of adhesion coming into contact is consistently lower than the intrinsic work of adhesion for the materials, and that there is adhesion hysteresis during separation, commonly explained by viscoelastic dissipation. Still lacking is a quantitative experimentally validated link between adhesion and measured topography. Here, we used in situ measurements of contact size to investigate the adhesion behavior of soft elastic polydimethylsiloxane hemispheres (modulus ranging from 0.7 to 10 MPa) on 4 different polycrystalline diamond substrates with topography characterized across 8 orders of magnitude, including down to the angstrom scale. The results show that the reduction in apparent work of adhesion is equal to the energy required to achieve conformal contact. Further, the energy loss during contact and removal is equal to the product of the intrinsic work of adhesion and the true contact area. These findings provide a simple mechanism to quantitatively link the widely observed adhesion hysteresis to roughness rather than viscoelastic dissipation.
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Affiliation(s)
- Siddhesh Dalvi
- Department of Polymer Science, The University of Akron, Akron, OH 44325
| | - Abhijeet Gujrati
- Department of Mechanical Engineering and Materials Science, University of Pittsburgh, Pittsburgh, PA 15261
| | - Subarna R Khanal
- Department of Mechanical Engineering and Materials Science, University of Pittsburgh, Pittsburgh, PA 15261
| | - Lars Pastewka
- Department of Microsystems Engineering, University of Freiburg, 79110 Freiburg, Germany
| | - Ali Dhinojwala
- Department of Polymer Science, The University of Akron, Akron, OH 44325;
| | - Tevis D B Jacobs
- Department of Mechanical Engineering and Materials Science, University of Pittsburgh, Pittsburgh, PA 15261;
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24
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Monti JM, McGuiggan PM, Robbins MO. Effect of Roughness and Elasticity on Interactions between Charged Colloidal Spheres. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2019; 35:15948-15959. [PMID: 31574219 DOI: 10.1021/acs.langmuir.9b02161] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
The effects of realistic roughness and elasticity on the interactions between charged silica spheres are studied as a function of surface potential, screening length, interfacial energy, and roughness. The repulsive force Frep that must be overcome to bring charged spheres into contact is relatively insensitive to elasticity unless spheres are hundreds of times softer than silica. Frep is also insensitive to roughness and interfacial energy. In contrast, roughness has a large effect on the binding energy of spheres and the force Fsep to separate them. Both are lowered by 1 to 2 orders of magnitude by the measured surface roughness of less than 1 nm on 1 μm silica spheres. The reason is that interactions between rigid spheres are dominated by the highest surface peaks rather than the entire spherical surface. Elasticity can increase the pull-off force of rough spheres by a factor of 2 or more because additional surface area can be brought into contact. The implications of these results for shear-thickening transitions are discussed.
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Affiliation(s)
- Joseph M Monti
- Department of Physics and Astronomy , Johns Hopkins University , Baltimore , MD 21218 , United States
| | - Patricia M McGuiggan
- Department of Materials Science and Engineering , Johns Hopkins University , Baltimore , MD 21218 , United States
| | - Mark O Robbins
- Department of Physics and Astronomy , Johns Hopkins University , Baltimore , MD 21218 , United States
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25
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Niewiarowski PH, Dhinojwala A, Garner AM. A Physical Model Approach to Gecko Adhesion Opportunity and Constraint: How Rough Could It Be? Integr Comp Biol 2019; 59:203-213. [PMID: 31065674 DOI: 10.1093/icb/icz029] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
It has been nearly 20 years since Autumn and colleagues established the central role of van der Waals intermolecular forces in how geckos stick. Much has been discovered about the structure and function of fibrillar adhesives in geckos and other taxa, and substantial success has been achieved in translating natural models into bioinspired synthetic adhesives. Nevertheless, synthetics still cannot match the multidimensional performance observed in the natural gecko system that is simultaneously robust to dirt and water, resilient over thousands of cycles, and purportedly competent on surfaces that are rough at drastically different length scales. Apparent insensitivity of adhesion to variability in roughness is particularly interesting from both a theoretical and applied perspective. Progress on understanding the extent to which and the basis of how the gecko adhesive system is robust to variation in roughness is impeded by the complexity of quantifying roughness of natural surfaces and a dearth of data on free-ranging gecko substrate use. Here we review the main challenges in characterizing rough surfaces as they relate to collecting relevant estimates of variation in gecko adhesive performance across different substrates in their natural habitats. In response to these challenges, we propose a practical protocol (borrowing from thermal biophysical ecological methods) that will enable researchers to design detailed studies of structure-function relationships of the gecko fibrillar system. Employing such an approach will help provide specific hypotheses about how adhesive pad structure translates into a capacity for robust gecko adhesion across large variation in substrate roughness. Preliminary data we present on this approach suggest its promise in advancing the study of how geckos deal with roughness variation. We argue and outline how such data can help advance development of design parameters to improve bioinspired adhesives based on the gecko fibrillar system.
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Affiliation(s)
- Peter H Niewiarowski
- Integrated Bioscience Program, Department of Biology, University of Akron, Akron, OH 44325, USA
| | - Ali Dhinojwala
- Integrated Bioscience Program, Department of Biology, University of Akron, Akron, OH 44325, USA.,Department of Polymer Science, University of Akron, Akron, OH 44325, USA
| | - Austin M Garner
- Integrated Bioscience Program, Department of Biology, University of Akron, Akron, OH 44325, USA
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26
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Łojkowski M, Walheim S, Jokubauskas P, Schimmel T, Święszkowski W. Tuning the Wettability of a Thin Polymer Film by Gradually Changing the Geometry of Nanoscale Pore Edges. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2019; 35:5987-5996. [PMID: 30946782 DOI: 10.1021/acs.langmuir.9b00467] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
Controlling wetting of solids by liquids attracts attention because of its scientific and technological importance. In this paper, the wettability of a highly uniform porous poly(methyl methacrylate) film on a silicon substrate containing a high density of randomly distributed self-similar pores was gradually tuned by changing the shape of nanometric crownlike structures around the pores. Fine-tuning the topography of these thin films was performed by isothermal annealing. The equilibrium contact angle of a water droplet placed on the surface of the films could be varied from 72 to 102°. The contact angle changes were assumed to be a consequence of changes in surface topography in the nanoscale. A simple method of a quantitative description of the change of the topography of these films was developed. Critical dimensions of these films were determined in horizontal and vertical directions relative to the surface plane. The slope coefficient (SC) describing how sharp the structures are, is defined as the ratio between the critical dimensions: the root-mean-square roughness σ and the autocorrelation length ξ. For SC > 0.08, the contact angle increased proportionally to the value of SC, whereas for SC < 0.08, the contact angle proportionally decreased. At the highest SC values, the contact angles were 6-10% higher than those predicted for flat porous surfaces using the Cassie-Baxter equation. We suggest that this discrepancy is due to the capillary tension caused by the submicron-scale undulation of the triple line, which was found to be proportional to the height of the crownlike pore edges and the value of SC. The same effect is responsible for the linear dependence of the contact angle on the SC value.
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Affiliation(s)
- Maciej Łojkowski
- Faculty of Materials Science and Engineering , Warsaw University of Technology , Wołoska 141 , 02-507 Warsaw , Poland
| | - Stefan Walheim
- Institute of Nanotechnology (INT), Karlsruhe Institute of Technology (KIT) , Hermann-von-Helmholtz-Platz 1 , Eggenstein-Leopoldshafen , 76344 Baden-Württemberg, DE , Germany
- Institute of Applied Physics , Karlsruhe Institute of Technology (KIT) , Wolfgang-Gaede-Straße 1 , Karlsruhe , 76131 DE , Germany
| | - Petras Jokubauskas
- Faculty of Geology, Institute of Geochemistry, Mineralogy and Petrology , University of Warsaw , Żwirki i Wigury 93 , 02-089 Warsaw , Poland
| | - Thomas Schimmel
- Institute of Nanotechnology (INT), Karlsruhe Institute of Technology (KIT) , Hermann-von-Helmholtz-Platz 1 , Eggenstein-Leopoldshafen , 76344 Baden-Württemberg, DE , Germany
- Institute of Applied Physics , Karlsruhe Institute of Technology (KIT) , Wolfgang-Gaede-Straße 1 , Karlsruhe , 76131 DE , Germany
| | - Wojciech Święszkowski
- Faculty of Materials Science and Engineering , Warsaw University of Technology , Wołoska 141 , 02-507 Warsaw , Poland
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27
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Higham TE, Russell AP, Niewiarowski PH, Wright A, Speck T. The Ecomechanics of Gecko Adhesion: Natural Surface Topography, Evolution, and Biomimetics. Integr Comp Biol 2019; 59:148-167. [DOI: 10.1093/icb/icz013] [Citation(s) in RCA: 36] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
Abstract
The study of gecko adhesion is necessarily interdisciplinary due to the hierarchical nature of the adhesive system and the complexity of interactions between the animals and their habitats. In nature, geckos move on a wide range of surfaces including soft sand dunes, trees, and rocks, but much of the research over the past two decades has focused on their adhesive performance on artificial surfaces. Exploring the complex interactions between geckos and their natural habitats will reveal aspects of the adhesive system that can be applied to biomimetic research, such as the factors that facilitate movement on dirty and rough surfaces with varying microtopography. Additionally, contrasting suites of constraints and topographies are found on rocks and plants, likely driving differences in locomotion and morphology. Our overarching goals are to bring to light several aspects of ecology that are important for gecko–habitat interactions, and to propose a framework for how they can inspire material scientists and functional ecologists. We also present new data on surface roughness and topography of a variety of surfaces, and adhesive performance of Phelsuma geckos on surfaces of varying roughness. We address the following key questions: (1) why and how should ecology be incorporated into the study of gecko adhesion? (2) What topographical features of rocks and plants likely drive adhesive performance? (3) How can ecological studies inform material science research? Recent advances in surface replication techniques that eliminate confounding factors among surface types facilitate the ability to address some of these questions. We pinpoint gaps in our understanding and identify key initiatives that should be adopted as we move forward. Most importantly, fine details of locomotor microhabitat use of both diurnal and nocturnal geckos are needed.
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Affiliation(s)
- Timothy E Higham
- Department of Evolution, Ecology, and Organismal Biology, University of California, Riverside, CA 92506, USA
| | - Anthony P Russell
- Department of Biological Sciences, University of Calgary, Calgary, Alberta, Canada T2N 1N4
| | - Peter H Niewiarowski
- Department of Biology and Integrated Bioscience Program, University of Akron, Akron, OH 44325, USA
| | - Amber Wright
- Department of Biology, University of Hawaii at Manoa, Honolulu, HI 96822, USA
| | - Thomas Speck
- Plant Biomechanics Group and Botanic Garden, University of Freiburg, 79085 Freiburg, Germany
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28
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Weber B, Suhina T, Brouwer AM, Bonn D. Frictional weakening of slip interfaces. SCIENCE ADVANCES 2019; 5:eaav7603. [PMID: 30972367 PMCID: PMC6450692 DOI: 10.1126/sciadv.aav7603] [Citation(s) in RCA: 17] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/17/2018] [Accepted: 02/11/2019] [Indexed: 05/22/2023]
Abstract
When two objects are in contact, the force necessary to overcome friction is larger than the force necessary to keep sliding motion going. This difference between static and dynamic friction is usually attributed to the growth of the area of real contact between rough surfaces in time when the system is at rest. We directly measure the area of real contact and show that it actually increases during macroscopic slip, despite the fact that dynamic friction is smaller than static friction. This signals a decrease in the interfacial shear strength, the friction per unit contact area, which is due to a mechanical weakening of the asperities. This provides a novel explanation for stick-slip phenomena in, e.g., earthquakes.
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Affiliation(s)
- B. Weber
- Van der Waals–Zeeman Institute, Institute of Physics, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, Netherlands
- Advanced Research Center for Nanolithography (ARCNL), Science Park 110, 1098 XG Amsterdam, Netherlands
- Corresponding author. (B.W); (D.B.)
| | - T. Suhina
- Van der Waals–Zeeman Institute, Institute of Physics, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, Netherlands
- Van’t Hoff Institute for Molecular Sciences, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, Netherlands
| | - A. M. Brouwer
- Van’t Hoff Institute for Molecular Sciences, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, Netherlands
| | - D. Bonn
- Van der Waals–Zeeman Institute, Institute of Physics, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, Netherlands
- Corresponding author. (B.W); (D.B.)
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