Thermal-induced simultaneous liquid-liquid phase separation and liquid-solid transition in aqueous polyurethane dispersions

Samy A. Madbouly, Joshua U. Otaigbe, Ajaya K. Nanda, Douglas A. Wicks

Research output: Contribution to journalArticle

30 Citations (Scopus)

Abstract

Thermal-induced simultaneous phase separation and liquid-solid transition (gelation) in waterborne polyurethane dispersions has been detected morphologically and rheologically. The viscoelastic material functions, such as dynamic shear moduli, G′ and G″ complex shear viscosity, η* and loss tangent, tan δ were found to be very sensitive to the structure evolution during the gelation process and the subsequent formation of a fractal polymer gel. At the onset temperature of the gelation process, an abrupt increase in G′, G″ and η* (several orders of magnitude) was observed during the dynamic temperature ramps (2 °C/min heating-rate) over a wide range of angular frequency. The temperature dependencies of G′, G″ and tan δ were found to be frequency independent at the gel-point, Tgel, providing a fingerprint for determining Tgel of the dispersions. Furthermore, a dramatic increase in zero-shear viscosity, η0 (v-shape) was observed at T=T gel and found to be in good agreement with the value obtained from the tan δ versus T data. As expected, the time-temperature-superposition principle was found to be only valid for temperatures lower than the T gel; the principle failed at T≥70 °C. The morphology of the dispersions at 70 °C for 2 h showed for 36, 38 and 40 wt% formation of a network structure having a unique periodicity and phase connectivity. A lower critical solution temperature (LCST) phase diagram was estimated based on the different morphologies of the dispersions. The coexistence of liquid-liquid and liquid-solid transitions at the same temperature range confirmed the complex behavior of the polyurethane dispersions, pointing to the need for a new theory that explicitly takes this special behavior into account.

Original languageEnglish (US)
Pages (from-to)10897-10907
Number of pages11
JournalPolymer
Volume46
Issue number24
DOIs
StatePublished - Nov 21 2005

Fingerprint

Polyurethanes
Dispersions
Phase separation
Liquids
Gelation
Gels
Shear viscosity
Temperature
Hot Temperature
Heating rate
Fractals
Phase diagrams
Polymers
Elastic moduli

All Science Journal Classification (ASJC) codes

  • Organic Chemistry
  • Polymers and Plastics
  • Materials Chemistry

Cite this

Madbouly, Samy A. ; Otaigbe, Joshua U. ; Nanda, Ajaya K. ; Wicks, Douglas A. / Thermal-induced simultaneous liquid-liquid phase separation and liquid-solid transition in aqueous polyurethane dispersions. In: Polymer. 2005 ; Vol. 46, No. 24. pp. 10897-10907.
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Thermal-induced simultaneous liquid-liquid phase separation and liquid-solid transition in aqueous polyurethane dispersions. / Madbouly, Samy A.; Otaigbe, Joshua U.; Nanda, Ajaya K.; Wicks, Douglas A.

In: Polymer, Vol. 46, No. 24, 21.11.2005, p. 10897-10907.

Research output: Contribution to journalArticle

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