Rheological Monitoring of Polyacrylamide Gelation: Importance of Cross-Link Density and Temperature
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Bibliographic record
Abstract
Dynamic shear oscillation measurements at small strains are used to characterize the polymerization process in situ and the viscoelastic properties of cross-linked polyacrylamide hydrogels. Hydrogels are synthesized by free-radical redox polymerization of acrylamide (8 wt %) for different concentrations of cross-linker, N,N ‘-methylenebis(acrylamide) (BIS), at different temperatures. Both elastic modulus G ‘ and viscous modulus G ‘ ‘ are measured in real time during the gelation which takes place directly between parallel rheometer plates. The elastic modulus G ‘ remains constant with frequency, G ‘ ( ω ) ≈ cte, and is significantly larger than G ‘ ‘ ( ω ), characteristic of a well-developed cross-linked polymer network. Temperature scanning of the elastic modulus shows that G ‘ ( T ) is a linear relationship with a proportionality value that depends on the polymerization temperature T pol . This observation is in agreement with the classical theory of rubberlike elasticity, i.e ., G ‘ = n e RT where n e is the active network links density. The results confirm that the final G ‘ and G ‘ ‘ are sensitive to the cross-linker concentration as well as the polymerization temperature. Moreover, G ‘ follows a linear progression over a large range of BIS concentration. For a given acrylamide monomer concentration, there exists an optimal bis(acrylamide) cross-linker concentration and an optimal polymerization temperature which give rise to an “ideal” hydrogel, i.e., exhibiting a maximal elasticity.
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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 it