The structure and rheological properties of concentrated lamellar systems of ethoxylated alcohol (CmEn)-water binary mixtures were investigated. It was found that in the linear viscoelastic region the shapes of the storage and the loss modulus vs. frequency curves are specific to and characteristic of the lamellar system. The storage modulus increases slightly and the loss modulus goes through a minimum with increasing frequency. The sample is mainly elastic throughout the whole investigated frequency range. The surfactant type, concentration and temperature have a strong influence on the frequency-dependent viscoelastic properties. The structure becomes more elastic with decreasing temperature and tan δ goes through a minimum with increasing surfactant concentration. The effect of the surfactant type (value of m and n) was investigated only in a narrow range of m and n, because when the ethoxylation number or the Hydrophobic carbon chain length changes the boundaries of the lamellar mesophase in the phase diagram also change and it becomes impossible to produce a lamellar phase at the same concentration and within the same temperature range as in the case of the system with Synperonic A7. Nevertheless it was found that tan δ depends both on the hydrophobic chain length and on the ethoxylation number. The storage and loss moduli were also found to be sensitive to structural changes in the sample, such as the ordering of lamellae with increasing concentration, or the melting of the carbon chains of the surfactants with increasing temperature. The high-shear viscosity showed a much weaker dependence on the surfactant type and concentration; it was mainly dependent on the temperature and applied shear rate.
|Number of pages||7|
|Specialist publication||Tenside, Surfactants, Detergents|
|Publication status||Published - Dec 1 1999|
ASJC Scopus subject areas
- Chemical Engineering(all)
- Condensed Matter Physics