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Studying Large Amplitude Oscillatory Shear Response of Soft Materials
Published on: April 25, 2019
Viscoelasticity of a nonionic lamellar phase
B Medronho1, Maria G Miguel, U Olsson
1Physical Chemistry 1, Center of Chemistry and Chemical Engineering, Lund University, Box 124, 22100 Lund, Sweden. Bruno.Medronho@fkem1.lu.se
Langmuir : the ACS Journal of Surfaces and Colloids
|April 19, 2007
Summary
This study reveals that the elasticity of nonionic lamellar phases is linked to screw dislocations, which decrease with rising temperature. These dislocations may also explain the "onion" texture observed under shear flow.
Area of Science:
- Materials Science
- Soft Matter Physics
- Physical Chemistry
Background:
- Nonionic lamellar phases exhibit complex viscoelastic properties.
- Understanding the relationship between molecular structure and macroscopic behavior is crucial.
Purpose of the Study:
- To investigate the linear viscoelastic properties of a nonionic lamellar phase.
- To determine the temperature dependence of these properties and their underlying mechanisms.
Main Methods:
- Small-amplitude oscillatory measurements were performed over a frequency range of 0.5-5 Hz.
- 2H Nuclear Magnetic Resonance (NMR) experimentation was utilized.
Main Results:
- A solid-like elastic response was observed across the studied temperature range (42–20 °C).
- Elastic modulus increased significantly with decreasing temperature, attributed to screw dislocations.
- Screw dislocation density was found to decrease with increasing temperature.
- A shear-induced "onion" texture formed at lower temperatures, potentially due to dislocation instability.
- A random mesh phase was identified at lower temperatures via 2H NMR.
Conclusions:
- The elasticity of the nonionic lamellar phase is primarily governed by screw dislocations connecting layers.
- Temperature significantly influences the density of these dislocations and the material's viscoelasticity.
- Shear flow can induce structural changes like the "onion" texture, possibly related to dislocation dynamics.
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