Friction between Polymer Brushes in Good Solvent Conditions: Steady-State Sliding versus Transient Behavior
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Bibliographic record
Abstract
Previous molecular dynamics simulations of friction between polymer brushes in relative sliding motion [Kreer, T.; Müser, M. H.; Binder, K.; Klein, J. Langmuir 2001, 17, 7804] are extended beyond steady-state conditions. We study two different protocols: (i) stop and return and (ii) stop and go. In protocol (i), the relative, lateral motion between the two surfaces is stopped abruptly and reimposed opposite to the initial direction after the system could relax for some time. Protocol (ii) is similar except that the sliding direction is maintained. In the constant-velocity steady state, the average lateral extension l c of the polymers is found to be a power law of the sliding velocity v, namely, l c ∝ v 0.3 . When the sliding direction is inverted, a shear stress maximum is observed after the two walls have slid a relative distance of 2 l c . This maximum occurs when the average inclination of the polymers is 90°, and it is accompanied by brush swelling. In protocol (ii), no brush swelling is found and shear stress maxima are absent in the itinerant stages of the go phase, with the exception of large v . We conclude that dissipation mechanisms for oscillatory shear are similar to those for constant-velocity sliding if the driving amplitude 𝒜 distinctly exceeds 2 l c . Moreover, enhanced loss at 𝒜 ≈ 2 l c is not necessarily related to stick−slip motion.
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Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
Machine scores (provisional)
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Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
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