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Abstract Extensional flow properties of polymer solutions in volatile solvents govern many industrially-relevant coating processes, but existing instrumentation lacks the environment necessary to control evaporation. To mitigate evaporation during dripping-onto-substrate (DoS) extensional rheology measurements, we developed a chamber to enclose the sample in an environment saturated with solvent vapor. We validated the evaporation-controlled DoS device by measuring a model high molecular weight polyethylene oxide (PEO) in various organic solvents both inside and outside of the chamber. Evaporation substantially increased the extensional relaxation time$$\lambda _{E}$$ for PEO in volatile solvents like dichloromethane and chloroform. PEO/chloroform solutions displayed an over 20-fold increase in$$\lambda _{E}$$ due to the formation of an evaporation-induced surface film; evaporation studies confirmed surface features and skin formation reminiscent of buckling instabilities commonly observed in drying polymer solutions. Finally, the relaxation times of semi-dilute PEO/chloroform solutions were measured with environmental control, where$$\lambda _{E}$$ scaled with concentration by the exponent$$m=0.62$$ . These measurements validate the evaporation-controlled DoS environment, and confirm that chloroform is a good solvent for PEO, with a Flory exponent of$$\nu =0.54$$ . Our results are the first to control evaporation during DoS extensional rheology, and provide guidelines establishing when environmental control is necessary to obtain accurate rheological parameters.
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On the thermogravimetric analysis of polymers: Polyethylene oxide powder and nanofibers
Abstract Thermogravimetric analysis of polyethylene oxide (powder and nanofibers obtained by force spinning water or chloroform solutions of polyethylene oxide) was studied using different theoretical models such as Friedman and Flynn‐Wall‐Ozawa. A semiempirical approach for estimating the “sigmoid activation energy” from the thermal degradation was suggested and confirmed by the experimental data on PEO powder and nanofibers' mats. The equation allowed for calculating a “sigmoid activation energy” from a single thermogram using a single heating rate without requiring any model for the actual complex set of chemical reactions involved in the thermal degradation process. For PEO (powder and nanofibers obtained from water solutions), the “sigmoid activation energy” increased as the heating rate was increased. The sigmoid activation energy for PEO mats obtained from chloroform solutions exhibited a small decrease as the heating rate was increased. Thermograms' derivatives were fitted to determine the coordinates of the inflection points. The “sigmoid activation energy” was compared to the activation energy determined from the Flynn‐Wall‐Ozawa model. Similarities between the thermal degradation of polyethylene oxide powder and of the nanofibers obtained from water solutions were discussed. Significant differences between the sigmoid activation energies of the mats obtained from water and chloroform solutions were reported.
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- Award ID(s):
- 2122178
- PAR ID:
- 10447336
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Journal of Applied Polymer Science
- Volume:
- 139
- Issue:
- 18
- ISSN:
- 0021-8995
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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