Linear Rheology of Entangled Six-Arm and Eight-Arm Polybutadienes
Bibliographic record
Abstract
Relaxation dynamics of various model entangled six-arm (A 3 - A -A 3 ) and eight-arm (A 3 - A -A 2 - A -A 3 ) polybutadiene melts are investigated using low-amplitude oscillatory shear and time-dependent step strain measurements. The frequency (time) and temperature range covered in these experiments are sufficiently broad to characterize the entire liquid-state relaxation spectrum of the materials. Several new findings about multiarm polymer dynamics are reported. First, the mean segmental relaxation time of multiarm polymers is a function of crossbar ( A ) molecular weight and polymer architecture. Second, for polymers with fixed arm (A) molecular weight, but variable crossbar molecular weight, terminal relaxation time (λ) and limiting shear viscosity (η 0 ) scale quite strongly with crossbar molecular weight M b (λ ∼ M b ∼6.8-7, η 0 ∼ M b ∼8 ). When the crossbar tube length is renormalized by dilution of relaxed arms and the relaxation time and viscosity are rescaled to remove the inherent M b dependence of segmental scale properties, these scaling exponents become closer to values expected for crossbar reptation in a dilated tube. Finally, relaxation dynamics of eight-arm A 3 - A -A 2 - A -A 3 polybutadienes are found to be quite different from those of six-arm A 3 - A -A 3 polymers with comparable arm molecular weight. Specifically, the slowest relaxation mode in well-entangled eight-arm polymers appears to be dominated by Rouse-like fluctuation effects, which blur the transition from high-frequency arm to terminal backbone relaxation.
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How this classification was reachedexpand
Full frame distilled prediction
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)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one teacher head, not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".