Substituent effects on the mechanochemical response of zinc dialkyldithiophosphate

Zhang, Jie; Ewen, James P.; Spikes, H. A.

doi:10.1039/d2me00049k

Cited by 7 publications

(15 citation statements)

References 86 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Δ V * is sometimes interpreted as volume change that occurs when the transition state is formed from the reactants. 96 In our simulations, as well as previous experiments of ZDDP tribofilm growth, 8,10,54 Δ V * is positive, indicating that the volume of the transition state is larger than the reactants, confirming that the rate-determining step involves bond breaking. 91 We use shear stress, τ , in eqn (1) rather than normal stress, σ .…”

Section: Resultssupporting

confidence: 86%

“…Previous experimental studies of mechanochemical tribofilm growth have treated the activation volume as a temperature-independent reaction constant; however, these studies considered a much smaller temperature range than the present study. 8–10,54,91 In our recent NEMD study of trialkyl phophate mechanochemical decomposition, we also observed that the activation volume increased with increasing temperature. 46 This was partially explained through a reduction in the elastic modulus of the α-Fe(110) slabs.…”

Section: Resultsmentioning

confidence: 66%

“…This percentage range is consistent with previous NEMD simulations using trialkyl phosphates (4%), 46 while experiments using ZDDPs with different alkyl substituent showed somewhat larger percentages (7–17%). 54…”

Section: Resultsmentioning

confidence: 99%

See 2 more Smart Citations

Effects of surface chemistry on the mechanochemical decomposition of tricresyl phosphate

Ogbomo,

Bhuiyan,

Latorre

et al. 2024

Phys. Chem. Chem. Phys.

Self Cite

View full text Add to dashboard Cite

show abstract

Section: Resultssupporting

confidence: 86%

Section: Resultsmentioning

confidence: 66%

See 1 more Smart Citation

Effects of surface chemistry on the mechanochemical decomposition of tricresyl phosphate

Ogbomo,

Bhuiyan,

Latorre

et al. 2024

Phys. Chem. Chem. Phys.

Self Cite

View full text Add to dashboard Cite

show abstract

“…It has recently been found that the activation energy and pre-exponential factors for the rate of mechanochemical decomposition of a well-known lubricant additive, zinc dialkyl dithiophosphate (ZPPD), are in uenced by changing the nature of the function groups that surround the core of the additive [27]. In particular, it has been found that the activation energy for the reaction is accompanied by a corresponding change in the pre-exponential factor, , such that the activation energy varies linearly with .…”

Section: Compensation Effects In Stress-modi Ed Processesmentioning

confidence: 99%

An Analysis of Shear-Dependent Mechanochemical Reaction Kinetics

Rana,

Hopper,

Sidoroff

et al. 2024

Preprint

View full text Add to dashboard Cite

The variation in the rate of a tribochemical reaction is calculated as a function of combined normal and shear stresses using Evans-Polanyi perturbation theory. The effect of perturbations such as stresses is obtained using transition-state theory from their influence on the equilibrium constant between the initial- and transition-state structures using the molar Gibbs free energy change. An advantage of this approach is it capability of calculating the effect of several perturbations, such as combined normal and shear stresses. Two effects have been identified. The first is that the effective activation volume contains contributions from both the normal and shear stresses. More importantly, the analysis predicts that the asymptote of this plot at zero stress is not equal to the thermal reaction rate; there is a change in the inherent tribochemical reaction rate that depends on velocity. This prediction is shown to be true for the shear-induced decomposition of ethyl thiolate species adsorbed on a Cu(100) single crystal substrate where this effect contributes to about two orders of magnitude increase in the reaction rate. This indicates that tribochemical reactions can be influenced by either just normal stresses or a combination of normal and shear stresses, but that the latter contribution is much larger. It is predicted that there is a linear relationship between the activation energy and the logarithm of the pr-exponential factor of this asymptotic rate constant, known as a compensation effect in catalysis. While this has not yet been seen for tribochemical reactions on surfaces, it has been found for reactions occurring in sheared fluids.

show abstract

“…This concept is widely used to explain i.e. tribofilm formation and atomic scale wear. − On the other hand, in boundary lubrication, the stress activation volume is interpreted as the volume of boundary layer molecules that are moved at the interface during the thermally activated shear process. ,,− In the remainder of the paper, the stress activation volume is always referred to in the latter meaning. According to eq , the effective energy barrier for discrete processes underlying relative motion of the boundary layer decreases with the product of the stress activation volume and the applied shear stress. ,, For single-asperity contacts, the dependence of the shear stress on sliding velocity can be accurately captured by the Eyring model. ,,,, However, for larger multi-contact interfaces, it remains challenging to connect the theoretical description of boundary lubrication to experimental observations due to limitations in our ability to measure the area of real contact and, thus, the shear stress. , Moreover, there is no direct method available to locally probe the mobility of boundary layers and connect the activation volume to the free volume of the lubricant.…”

Section: Introductionmentioning

confidence: 99%

Molecular Probing of the Stress Activation Volume in Vapor Phase Lubricated Friction

Hsu

Peng

Hsia

et al. 2023

ACS Appl. Mater. Interfaces

View full text Add to dashboard Cite

When two solid objects slide over each other, friction results from the interactions between the asperities of the (invariably rough) surfaces. Lubrication happens when viscous lubricants separate the two surfaces and carry the load such that solid-on-solid contacts are avoided. Yet, even small amounts of low-viscosity lubricants can still significantly lower friction through a process called boundary lubrication. Understanding the origin of the boundary lubricating effect is hampered by challenges in measuring the interfacial properties of lubricants directly between the two surfaces. Here, we use rigidochromic fluorescent probe molecules to measure precisely what happens on a molecular scale during vapor-phase boundary lubrication of a polymer bead-on-glass interface. The probe molecules have a longer fluorescence lifetime in a confined environment, which allows one to measure the area of real contact between rough surfaces and infer the shear stress at the lubricated interfaces. The latter is shown to be proportional to the inverse of the local interfacial free volume determined using the measured fluorescence lifetime. The free volume can then be used in an Eyring-type model as the stress activation volume, allowing to collapse the data of stress as a function of sliding velocity and partial pressure of the vapor phase lubricant. This shows directly that as more boundary lubricant is applied, larger clusters of lubricant molecules become involved in the shear process thereby lowering the friction.

show abstract

Substituent effects on the mechanochemical response of zinc dialkyldithiophosphate

Abstract: Mechanochemistry is known to play a key role in the function of some lubricant additives, such as the tribofilm growth of zinc dialkyldithiophosphate (ZDDP). This raises the intriguing possibility of...

Cited by 7 publications

References 86 publications

Effects of surface chemistry on the mechanochemical decomposition of tricresyl phosphate

Effects of surface chemistry on the mechanochemical decomposition of tricresyl phosphate

An Analysis of Shear-Dependent Mechanochemical Reaction Kinetics

Molecular Probing of the Stress Activation Volume in Vapor Phase Lubricated Friction

Contact Info

Product

Resources

About