Mechanochemistry:  The Mechanical Activation of Covalent Bonds

Beyer, Martin K.; Clausen-Schaumann, Hauke

doi:10.1021/cr030697h

Cited by 1,061 publications

(738 citation statements)

References 376 publications

(650 reference statements)

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“…Therefore, by activating each component of this composite deliberately and looking at the changes in the reaction kinetics, we may be able to clarify the origin of the kinetic barrier. Mechanical ball milling, which is regarded as an effective way to reduce particle size, increase surface area, create defects on crystalline boundaries, and activate chemical bonds, [37] was applied to activate the reactants Mg(NH 2 ) 2 The morphologies of the activated and nonactivated reactants together with those of the as-prepared Samples I (NA) and I (NN) are exhibited in Figure 1. As displayed in Figure 1 a and b, both particle sizes of the activated Mg(NH 2 ) 2 and LiH can be reduced to less than 200 nm, but the aggregation of those small particles gives an appearance of larger particles with a size of 0.5-2 mm.…”

Section: Resultsmentioning

confidence: 99%

Solid-Solid Heterogeneous Catalysis: The Role of Potassium in Promoting the Dehydrogenation of the Mg(NH₂)₂/2 LiH Composite

et al. 2013

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Considerable efforts have been devoted to the catalytic modification of hydrogen storage materials. The K‐modified Mg(NH2)2/2 LiH composite is a typical model for such studies. In this work, we analyze the origin of the kinetic barrier in the first step of the dehydrogenation and investigate how K catalyzes this heterogeneous solid‐state reaction. Our results indicate that the interface reaction of Mg(NH2)2 and LiH is the main source of the kinetic barrier at the early stage of the dehydrogenation for the intensively ball‐milled Mg(NH2)2/2 LiH sample. K can effectively activate Mg(NH2)2 as well as promote LiH to participate in the dehydrogenation. Three K species of KH, K2Mg(NH2)4, and Li3K(NH2)4 likely transform circularly in the dehydrogenation (KH↔K2Mg(NH2)4↔KLi3(NH2)4), which creates a more energy‐favorable pathway and thus leads to the overall kinetic enhancement. This catalytic role of K in the amide/hydride system is different from the conventional catalysis of transition metals in the alanate system.

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Section: Resultsmentioning

confidence: 99%

Solid-Solid Heterogeneous Catalysis: The Role of Potassium in Promoting the Dehydrogenation of the Mg(NH₂)₂/2 LiH Composite

et al. 2013

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“…The localized and well-adhered pattern of the graphene-residue accumulation on the indenter suggests that an interfacial interaction much stronger than vdW forces, such as of covalent nature, may possibly be active at the interface. Previously, such mechanically-activated covalent bond formations have been observed in atomic force microscopy (AFM) experiments [23,24,25].…”

Section: ) Amentioning

confidence: 98%

Strain Shielding from Mechanically Activated Covalent Bond Formation during Nanoindentation of Graphene Delays the Onset of Failure

Kumar

Parks

2015

Nano Lett.

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Mechanical failure of an ideal crystal is dictated either by an elastic instability or a soft-mode instability. Previous interpretations of nano-indentation experiments on suspended graphene sheets [1,2], however, indicate an anomaly: the inferred strain in the graphene sheet directly beneath the diamond indenter at the measured failure load is anomalously large compared to the fracture strains predicted by both soft-mode and acoustic analyses. Through multi-scale modeling combining the results of continuum, atomistic, and quantum calculations; and analysis of experiments, we identify a strain-shielding effect initiated by mechanochemical interactions at the graphene-indenter interface as the operative mechanism responsible for this anomaly. Transmission electron micrographs (TEM) and a molecular model of the diamond indenter's tip suggest that the tip surface contains facets comprising crystallographic {111} and {100} planes. Ab initio and molecular dynamics (MD) simulations confirm that a covalent bond (weld) formation between graphene and the crystallographic {111} and {100} facets on the indenter's surface can be induced by compressive contact stresses of the order achieved in nano-indentation tests. Finite element analysis (FEA) and MD simulations of nano-indentation reveal that the shear stiction provided by the induced covalent bonding restricts relative slip of the graphene sheet at its contact with the indenter, thus initiating a local strain-shielding effect. As a result, subsequent to stress-induced bonding at the graphene-indenter interface, the spatial variation of continuing incremental strain is substantially redistributed, locally shielding the region directly beneath the indenter by limiting the buildup of strain while imparting deformation to the surrounding regions. The extent of strain shielding is governed by strength of the shear stiction, which depends upon the level of hydrogen saturation at the indenter's surface. We show that, at intermediate levels of hydrogen saturation, the strain-shielding effect can enable the graphene to support experimentally-determined fracture loads and displacements without prematurely reaching locally limiting states of stress and deformation.Keywords: Graphene, ideal strength, lattice stability, nano-indentation, mechanochemistry, strain-shielding. Lee, et al. [1] measured the fracture strength of graphene using nano-indentation experiments and reported an unprecedentedly high intrinsic strength, measuring orders of magnitude greater than those of conventional materials. The nano-indentation involves instrumented indentation of a suspended graphene sheet by a nanoscale diamond indenter up to the point of failure. However, the local stress and strain beneath the indenter are not directly measurable in such nano-indentation experiments; instead, the indentation load (F ) as a function of indentation depth (u z | r=0 ) during the course of indentation is recorded. Finite Elements Analysis (FEA) based on an appropriate constitutive description of graphe...

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“…During the last half a century or so, the importance of the elastic and dissipative properties of biomolecules has been widely recognized in the life sciences community, and a number of excellent reviews have been published (see, e.g., (1)(2)(3), to cite only a few). Here, we speak not only about such naturally evident aspects as, say, muscle proteins, molecular motors, and the conversion of an external stress into a biochemical signal and its transmission, but also about the much more general influence of the applied force on virtually all characteristics of life, including mechanically induced phase transitions and mechanical activation (or deactivation) of biochemical reactions.…”

Section: Introductionmentioning

confidence: 99%

Can Dissipative Properties of Single Molecules Be Extracted from a Force Spectroscopy Experiment?

Benedetti

Gazizova

Kulik

et al. 2016

Biophysical Journal

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We performed dynamic force spectroscopy of single dextran and titin I27 molecules using small-amplitude and low-frequency (40-240 Hz) dithering of an atomic force microscope tip excited by a sine wave voltage fed onto the tip-carrying piezo. We show that for such low-frequency dithering experiments, recorded phase information can be unambiguously interpreted within the framework of a transparent theoretical model that starts from a well-known partial differential equation to describe the dithering of an atomic force microscope cantilever and a single molecule attached to its end system, uses an appropriate set of initial and boundary conditions, and does not exploit any implicit suggestions. We conclude that the observed phase (dissipation) signal is due completely to the dissipation related to the dithering of the cantilever itself (i.e., to the change of boundary conditions in the course of stretching). For both cases, only the upper bound of the dissipation of a single molecule has been established as not exceeding 3,10 À7 kg=s. We compare our results with previously reported measurements of the viscoelastic properties of single molecules, and we emphasize that extreme caution must be taken in distinguishing between the dissipation related to the stretched molecule and the dissipation that originates from the viscous damping of the dithered cantilever. We also present the results of an amplitude channel data analysis, which reveal that the typical values of the spring constant of a I27 molecule at the moment of module unfolding are equal to 451:5 mN=m, and the typical values of the spring constant of dextran at the moment of chair-boat transition are equal to 30 À 50 mN=m.

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Mechanochemistry: The Mechanical Activation of Covalent Bonds

Cited by 1,061 publications

References 376 publications

Solid-Solid Heterogeneous Catalysis: The Role of Potassium in Promoting the Dehydrogenation of the Mg(NH₂)₂/2 LiH Composite

Solid-Solid Heterogeneous Catalysis: The Role of Potassium in Promoting the Dehydrogenation of the Mg(NH₂)₂/2 LiH Composite

Strain Shielding from Mechanically Activated Covalent Bond Formation during Nanoindentation of Graphene Delays the Onset of Failure

Can Dissipative Properties of Single Molecules Be Extracted from a Force Spectroscopy Experiment?

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Mechanochemistry: The Mechanical Activation of Covalent Bonds

Cited by 1,061 publications

References 376 publications

Solid-Solid Heterogeneous Catalysis: The Role of Potassium in Promoting the Dehydrogenation of the Mg(NH2)2/2 LiH Composite

Solid-Solid Heterogeneous Catalysis: The Role of Potassium in Promoting the Dehydrogenation of the Mg(NH2)2/2 LiH Composite

Strain Shielding from Mechanically Activated Covalent Bond Formation during Nanoindentation of Graphene Delays the Onset of Failure

Can Dissipative Properties of Single Molecules Be Extracted from a Force Spectroscopy Experiment?

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Product

Resources

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Solid-Solid Heterogeneous Catalysis: The Role of Potassium in Promoting the Dehydrogenation of the Mg(NH₂)₂/2 LiH Composite

Solid-Solid Heterogeneous Catalysis: The Role of Potassium in Promoting the Dehydrogenation of the Mg(NH₂)₂/2 LiH Composite