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Dynamic Compressibility of Poly (Vinyl Acetate) and Its Relation to Free Volume
This study measured the bulk compliance of poly (vinyl acetate) under varying conditions. Results showed differences in limiting compliances, suggesting complex contributing processes beyond free volume theory.
Area of Science:
- Polymer Science
- Materials Science
- Rheology
Background:
- Poly (vinyl acetate) (PVAc) exhibits complex viscoelastic behavior.
- Understanding bulk compliance is crucial for material characterization.
- Previous studies often focused on limited pressure or temperature ranges.
Purpose of the Study:
- To measure the dynamic compressibility of poly (vinyl acetate) across a wide range of frequencies, temperatures, and static hydrostatic stresses.
- To investigate the influence of static pressure on the viscoelastic properties of PVAc.
- To compare experimental findings with predictions from free volume theory.
Main Methods:
- Dynamic compressibility measurements using piezoelectric transducers in a noncompliant cavity.
- Testing frequencies from 50 to 1,000 Hz.
- Temperature range: 0 to 100 °C; Pressure range: 0 to 981 bars.
- Data reduction using WLF (Williams-Landel-Ferry) equations extended for pressure.
Main Results:
- Observed an inflection in storage compliance and a maximum in loss compliance within the tested temperature range, indicating a dispersion region.
- Successfully extended WLF equations to include static pressure effects.
- Found a larger difference between limiting compliances (zero and infinite frequencies) than predicted by the free volume concept using the determined dT/dP shift.
Conclusions:
- The free volume concept, even when extended for pressure, does not fully explain the observed viscoelastic behavior of poly (vinyl acetate).
- Additional physical or chemical processes likely contribute to the discrepancy in limiting compliances.
- Further investigation into these contributing processes is warranted for a comprehensive understanding of PVAc rheology.
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