Rheological properties of silicone-surfactant-based wormlike micellar solution

Abstract

One of the major drawbacks of ionic-surfactant-based wormlike micelles (WLMs) is their poor low-temperature stability, which severely limits their application. Generally, an ionic surfactant with a linear C12–C16 alkyl chain has a Krafft point around or above room temperature. Therefore, there is a demand for ionic-surfactant-based WLMs with greater lowtemperature stability. Silicone surfactants have flexible hydrophobic chain structures. Hence, they are expected to be suitable candidates for WLMs that can be stable at low temperatures. Sodium trimethylsilyl tetra(dimethylsiloxane) decyl sulfate (Si5C10SO4Na) and benzyltrimethylammonium chloride (BTAC) were used as surfactant and electrolyte, respectively, to obtain the WLM system with desired properties. No precipitation of surfactant crystals was observed in the WLM system obtained in this study when temperature was decreased to as low as 0 °C, indicating excellent low-temperature stability. Steady rheological measurements on the viscous solutions show shear thinning corresponding nearly to a power law relation (viscosity ∝ [shear rate]−1). Zero shear viscosity (η0) increased with increase in R, reaching a maximum at around R = 0.3 and decreasing thereafter. Oscillatory shear measurements for the viscoelastic samples, formed around the maximum-viscosity composition, show that the storage modulus (G′) and the loss modulus (G′′), with respect to the oscillation frequency (ω), cross each other and fit the Maxwell model very well in the low-ω region. The normalized Cole-Cole plot of G′′ / G′′max against G′ / G′′max was obtained as a semicircle centered at G′ / G′′max = 1, as is typical for WLM systems.