Hydrogen‐Bond Mediated Structural Evolution and Mechano‐Optical Anisotropy During Drying and Uniaxial Stretching of Poly(Vinyl Alcohol) Films: Effect of Molecular Weight
Bibliographic record
Abstract
ABSTRACT This study presents a systematic investigation of the structural and mechano‐optical evolution of 88% hydrolyzed poly(vinyl alcohol) (PVA) films from solution casting to uniaxial stretching. The effects of molecular weight, drying conditions, and deformation temperature were examined using real‐time birefringence, small‐ and wide‐angle x‐ray scattering (SAXS/WAXS), and calorimetry. Polymer chains adopt a random in‐plane orientation beyond a critical concentration during drying, resulting in optically uniaxial films characterized by positive out‐of‐plane birefringence and near‐zero in‐plane birefringence. Lower drying temperatures, thinner initial film thicknesses, lower solid content, higher air speeds, and higher molecular weight all promoted stronger out‐of‐plane birefringence, reflecting enhanced in‐plane alignment and limited chain relaxation due to early vitrification. In uniaxial stretching, the low‐temperature behavior is governed primarily by hydrogen bonding, with chain entanglement playing a minor role. At higher temperatures (≈130°C), weakened hydrogen bonds and partial melting facilitate chain mobility, resulting in maximum extensibility and orientation, as evidenced by peak strain‐optical constants and four‐point SAXS patterns. These patterns indicate that lamellar rotation and interlamellar shear are key mechanisms for stress dissipation. These findings highlight hydrogen bonding as a critical factor controlling orientation, crystallization, and mechanical anisotropy in PVA, offering insights for tailoring structure–property relationships in hydrogen‐bonded polymers.
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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".