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 machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| 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) | 0.001 | 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 source (direct Gemma or distilled Codex), 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".