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Article: Surface topography as a material parameter.

Jacobs, Tevis D B / Pastewka, Lars

2023 Volume 47, Issue 12, Page(s) 1205–1210

Language	English
Publishing date	2023-01-31
Publishing country	England
Document type	Journal Article ; Review
ZDB-ID	2136359-6
ISSN	1938-1425 ; 0883-7694
ISSN (online)	1938-1425
ISSN	0883-7694
DOI	10.1557/s43577-022-00465-5
Database	MEDical Literature Analysis and Retrieval System OnLINE

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Article ; Online: Why soft contacts are stickier when breaking than when making them.

Sanner, Antoine / Kumar, Nityanshu / Dhinojwala, Ali / Jacobs, Tevis D B / Pastewka, Lars

Science advances

2024 Volume 10, Issue 10, Page(s) eadl1277

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 ... ...

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.
Language	English
Publishing date	2024-03-06
Publishing country	United States
Document type	Journal Article
ZDB-ID	2810933-8
ISSN	2375-2548 ; 2375-2548
ISSN (online)	2375-2548
ISSN	2375-2548
DOI	10.1126/sciadv.adl1277
Database	MEDical Literature Analysis and Retrieval System OnLINE

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Article ; Online: Separating Geometric and Diffusive Contributions to the Surface Nucleation of Dislocations in Nanoparticles.

Ding, Ruikang / Azadehranjbar, Soodabeh / Padilla Espinosa, Ingrid M / Martini, Ashlie / Jacobs, Tevis D B

ACS nano

2024 Volume 18, Issue 5, Page(s) 4170–4179

Abstract: While metal nanoparticles are widely used, their small size makes them mechanically unstable. Extensive prior research has demonstrated that nanoparticles with sizes in the range of 10-50 nm fail by the surface nucleation of dislocations, which is a ... ...

Abstract	While metal nanoparticles are widely used, their small size makes them mechanically unstable. Extensive prior research has demonstrated that nanoparticles with sizes in the range of 10-50 nm fail by the surface nucleation of dislocations, which is a thermally activated process. Two different contributions have been suggested to cause the weakening of smaller particles: first, geometric effects such as increased surface curvature reduce the barrier for dislocation nucleation; second, surface diffusion happens faster on smaller particles, thus accelerating the formation of surface kinks which nucleate dislocations. These two factors are difficult to disentangle. Here we use
Language	English
Publishing date	2024-01-26
Publishing country	United States
Document type	Journal Article
ISSN	1936-086X
ISSN (online)	1936-086X
DOI	10.1021/acsnano.3c09026
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Article: Atomistic Simulations of the Elastic Compression of Platinum Nanoparticles.

Padilla Espinosa, Ingrid M / Jacobs, Tevis D B / Martini, Ashlie

Nanoscale research letters

2022 Volume 17, Issue 1, Page(s) 96

Abstract: The elastic behavior of nanoparticles depends strongly on particle shape, size, and crystallographic orientation. Many prior investigations have characterized the elastic modulus of nanoscale particles using experiments or simulations; however their ... ...

Abstract	The elastic behavior of nanoparticles depends strongly on particle shape, size, and crystallographic orientation. Many prior investigations have characterized the elastic modulus of nanoscale particles using experiments or simulations; however their reported values vary widely depending on the methods for measurement and calculation. To understand these discrepancies, we used classical molecular dynamics simulation to model the compression of platinum nanoparticles with two different polyhedral shapes and a range of sizes from 4 to 20 nm, loaded in two different crystal orientations. Multiple standard methods were used to calculate the elastic modulus from stress-vs-strain data for each nanoparticle. The magnitudes and particle-size dependence of the resulting moduli varied with calculation method and, even for larger nanoparticles where bulk-like behavior may be expected, the effective elastic modulus depended strongly on shape and orientation. Analysis of per-atom stress distributions indicated that the shape- and orientation-dependence arise due to stress triaxiality and inhomogeneity across the particle. When the effective elastic modulus was recalculated using a representative volume element in the center of a large nanoparticle, the elastic modulus had the expected value for each orientation and was shape independent. It is only for single-digit nanoparticles that meaningful differences emerged, where even the very center of the particle had a lower modulus due to the effect of the surface. These findings provide better understanding of the elastic properties of nanoparticles and disentangle geometric contributions (such as stress triaxiality and spatial inhomogeneity) from true changes in elastic properties of the nanoscale material.
Language	English
Publishing date	2022-10-03
Publishing country	United States
Document type	Journal Article
ZDB-ID	2253244-4
ISSN	1556-276X ; 1931-7573
ISSN (online)	1556-276X
ISSN	1931-7573
DOI	10.1186/s11671-022-03734-z
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Article ; Online: Size-Dependent Role of Surfaces in the Deformation of Platinum Nanoparticles.

Azadehranjbar, Soodabeh / Ding, Ruikang / Padilla Espinosa, Ingrid M / Martini, Ashlie / Jacobs, Tevis D B

ACS nano

2023 Volume 17, Issue 9, Page(s) 8133–8140

Abstract: The mechanical behavior of nanostructures is known to transition from a Hall-Petch-like "smaller-is-stronger" trend, explained by dislocation starvation, to an inverse Hall-Petch "smaller-is-weaker" trend, typically attributed to the effect of surface ... ...

Abstract	The mechanical behavior of nanostructures is known to transition from a Hall-Petch-like "smaller-is-stronger" trend, explained by dislocation starvation, to an inverse Hall-Petch "smaller-is-weaker" trend, typically attributed to the effect of surface diffusion. Yet recent work on platinum nanowires demonstrated the persistence of the smaller-is-stronger behavior down to few-nanometer diameters. Here, we used in situ nanomechanical testing inside of a transmission electron microscope (TEM) to study the strength and deformation mechanisms of platinum nanoparticles, revealing the prominent and size-dependent role of surfaces. For larger particles with diameters from 41 nm down to approximately 9 nm, deformation was predominantly displacive yet still showed the smaller-is-weaker trend, suggesting a key role of surface curvature on dislocation nucleation. For particles below 9 nm, the weakening saturated to a constant value and particles deformed homogeneously, with shape recovery after load removal. Our high-resolution TEM videos revealed the role of surface atom migration in shape change during and after loading. During compression, the deformation was accommodated by atomic motion from lower-energy facets to higher-energy facets, which may indicate that it was governed by a confined-geometry equilibration; when the compression was removed, atom migration was reversed, and the original stress-free equilibrium shape was recovered.
Language	English
Publishing date	2023-04-26
Publishing country	United States
Document type	Journal Article
ISSN	1936-086X
ISSN (online)	1936-086X
DOI	10.1021/acsnano.2c11457
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Article ; Online: Evaluation of Force Fields for Molecular Dynamics Simulations of Platinum in Bulk and Nanoparticle Forms.

Padilla Espinosa, Ingrid M / Jacobs, Tevis D B / Martini, Ashlie

Journal of chemical theory and computation

2021 Volume 17, Issue 7, Page(s) 4486–4498

Abstract: Understanding the size- and shape-dependent properties of platinum nanoparticles is critical for enabling the design of nanoparticle-based applications with optimal and potentially tunable functionality. Toward this goal, we evaluated nine different ... ...

Abstract	Understanding the size- and shape-dependent properties of platinum nanoparticles is critical for enabling the design of nanoparticle-based applications with optimal and potentially tunable functionality. Toward this goal, we evaluated nine different empirical potentials with the purpose of accurately modeling faceted platinum nanoparticles using molecular dynamics simulation. First, the potentials were evaluated by computing bulk and surface properties-surface energy, lattice constant, stiffness constants, and the equation of state-and comparing these to prior experimental measurements and quantum mechanics calculations. Then, the potentials were assessed in terms of the stability of cubic and icosahedral nanoparticles with faces in the {100} and {111} planes, respectively. Although none of the force fields predicts all the evaluated properties with perfect accuracy, one potential-the embedded atom method formalism with a specific parameter set-was identified as best able to model platinum in both bulk and nanoparticle forms.
Language	English
Publishing date	2021-06-01
Publishing country	United States
Document type	Journal Article
ISSN	1549-9626
ISSN (online)	1549-9626
DOI	10.1021/acs.jctc.1c00434
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Article ; Online: Origin of Pressure-Dependent Adhesion in Nanoscale Contacts.

Baker, Andrew J / Vishnubhotla, Sai Bharadwaj / Chen, Rimei / Martini, Ashlie / Jacobs, Tevis D B

Nano letters

2022 Volume 22, Issue 14, Page(s) 5954–5960

Abstract: The adhesion between nanoscale components has been shown to increase with applied load, contradicting well-established mechanics models. Here, we ... ...

Abstract	The adhesion between nanoscale components has been shown to increase with applied load, contradicting well-established mechanics models. Here, we use
MeSH term(s)	Adhesives ; Physical Phenomena
Chemical Substances	Adhesives
Language	English
Publishing date	2022-07-06
Publishing country	United States
Document type	Journal Article ; Research Support, U.S. Gov't, Non-P.H.S.
ISSN	1530-6992
ISSN (online)	1530-6992
DOI	10.1021/acs.nanolett.2c02016
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Article ; Online: Dependence of adhesive friction on surface roughness and elastic modulus.

Maksuta, Daniel / Dalvi, Siddhesh / Gujrati, Abhijeet / Pastewka, Lars / Jacobs, Tevis D B / Dhinojwala, Ali

Soft matter

2022 Volume 18, Issue 31, Page(s) 5843–5849

Abstract: Friction is one of the leading causes of energy loss in moving parts, and understanding how roughness affects friction is of utmost importance. From creating surfaces with high friction to prevent slip and movement, to creating surfaces with low friction ...

Abstract	Friction is one of the leading causes of energy loss in moving parts, and understanding how roughness affects friction is of utmost importance. From creating surfaces with high friction to prevent slip and movement, to creating surfaces with low friction to minimize energy loss, roughness plays a key role. By measuring shear stresses of crosslinked elastomers on three rough surfaces of similar surface chemistry across nearly six decades of sliding velocity, we demonstrate the dominant role of adhesive frictional dissipation. Furthermore, while it was previously known that roughness-induced oscillations affected the viscoelastic dissipation, we show that these oscillations also control the molecular detachment process and the resulting adhesive dissipation. This contrasts with typical models of friction, where only the amount of contact area and the strength of interfacial bonding govern the adhesive dissipation. Finally, we show that all the data can be collapsed onto a universal curve when the shear stress is scaled by the square root of elastic modulus and the velocity is scaled by a critical velocity at which the system exhibits macroscopic buckling instabilities. Taken together, these results suggest a design principle broadly applicable to frictional systems ranging from tires to soft robotics.
Language	English
Publishing date	2022-08-10
Publishing country	England
Document type	Journal Article
ZDB-ID	2191476-X
ISSN	1744-6848 ; 1744-683X
ISSN (online)	1744-6848
ISSN	1744-683X
DOI	10.1039/d2sm00163b
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Article ; Online: Surface Area and Local Curvature: Why Roughness Improves the Bioactivity of Neural Implants.

Ding, Ruikang / Miller, Nathaniel C / Woeppel, Kevin M / Cui, Xinyan T / Jacobs, Tevis D B

Langmuir : the ACS journal of surfaces and colloids

2022 Volume 38, Issue 24, Page(s) 7512–7521

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 ... ...

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.
MeSH term(s)	Coated Materials, Biocompatible/chemistry ; Nanoparticles/chemistry ; Surface Properties ; Titanium/chemistry
Chemical Substances	Coated Materials, Biocompatible ; Titanium (D1JT611TNE)
Language	English
Publishing date	2022-06-09
Publishing country	United States
Document type	Journal Article ; Research Support, N.I.H., Extramural ; Research Support, U.S. Gov't, Non-P.H.S.
ZDB-ID	2005937-1
ISSN	1520-5827 ; 0743-7463
ISSN (online)	1520-5827
ISSN	0743-7463
DOI	10.1021/acs.langmuir.2c00473
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Book ; Online: The surface-topography challenge

Jacobs, Tevis D. B. / Miller, Nathaniel / Müser, Martin H. / Pastewka, Lars

Problem definition

2022

Abstract: We present to the community a surface-definition problem, whose solution we consider to be critical for the proper description of contacts between nominally flat surfaces [1,2]. In 2015, M\"user and Dapp issued the Contact Mechanics Challenge, which ... ...

Abstract	We present to the community a surface-definition problem, whose solution we consider to be critical for the proper description of contacts between nominally flat surfaces [1,2]. In 2015, M\"user and Dapp issued the Contact Mechanics Challenge, which provided complete topography data for a fictional surface and asked theorists and modelers to compute the expected contact parameters for such a surface. This effort was a success, but exposed one glaring flaw in the community's understanding of the nature of contact: these models require as input a complete description of surface topography, which is rarely or never available for real-world surfaces [3-6]. The present challenge is to experimentalists: we will send you samples of two materials (one smoother and one rougher); you determine the surface topography of these materials. We call on you to measure such surfaces however you wish, using contact-based techniques, light scattering, microscopy, or other techniques. Examples of quantities of interest are: root-mean-square (RMS) parameters; the power spectral density (PSD); or the autocorrelation function (ACF). For the material, we have chosen chromium nitride, a wear- and corrosion-resistant coating used in industrial applications including automotive components, cutting tools, and die-casting. To participate, simply go to: https://contact.engineering/challenge to provide your shipping address and other information, then samples will be shipped out to you. The only requirement of participation is that your raw topography measurements are deposited on the free contact.engineering web app to facilitate data sharing. The purpose of this challenge is for our community to move towards: (a) better agreement on how to describe the multi-scale topography of experimental surfaces; and (b) better understanding of how to apply the well-developed models and theories to real-world surfaces. Comment: 5 pages, 0 figures
Keywords	Condensed Matter - Materials Science
Subject code	670
Publishing date	2022-06-27
Publishing country	us
Document type	Book ; Online
Database	BASE - Bielefeld Academic Search Engine (life sciences selection)

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