Paper Number
VP85
Session
Pre-recorded Flash Presentations (virtual)
Title
Fast flows on linear and branched wormlike micelles
Presentation Date and Time
All Week (Asynchronous) Any Time
Track / Room
Pre-recorded Presentation / Virtual
Authors
- Tonti, Manuela (University of Naples Federico II)
- Costanzo, Salvatore (University of Naples Federico II, Chemical, Materials and Industrial Production Engineering)
- Ianniruberto, Giovanni (Federico II University, Department of Chemical, Materials and Production Engineering)
- Grizzuti, Nino (University of Naples Federico II, Chemical, Materials and Industrial Production Engineering)
- Pasquino, Rossana (University of Naples Federico II, Chemical, Materials and Industrial Production Engineering)
Author and Affiliation Lines
Manuela Tonti, Salvatore Costanzo, Giovanni Ianniruberto, Nino Grizzuti and Rossana Pasquino
Chemical, Materials and Industrial Production Engineering, University of Naples Federico II, Naples 80125, Italy
Speaker / Presenter
Pasquino, Rossana
Keywords
experimental methods; flow-induced instabilities; micelles; non-Newtonian fluids; surfactants
Text of Abstract
Surfactant molecules assemble in water into supramolecular aggregates, referred to as micelles. The micellar morphology can be tuned by changing some parameters in the system (i.e. salinity, pH, and temperature). The most efficient way to induce morphological and/or structural changes is adding complex salts. The latter can penetrate the micellar core, affecting the effective size of the surfactant molecules, thus inducing a morphological transition from spherical micelles into elongated ones, linear or branched, entangled or unentangled. We report shear startup data on solutions of entangled linear and branched wormlike micelles, differing in concentration and type of two binding aromatic sodium salts. The surfactant molecule is Cetylpiridinium Chloride, at fixed concentration (100mM). Sodium Salycilate and Diclofenac Sodium are used as binding salts, at different concentrations (40-70mM). We proved that the type of salt and its packing effectiveness at the micellar interface are crucial for the dynamics of the wormlike micelles. More specifically, we found that linear wormlike micelles behave similarly to ordinary polymers in fast shear flows, exhibiting pronounced overshoots as well as tiny undershoots in transient shear viscosity, before approaching the steady state. The analogy is emphasized by successfully comparing data with predictions of a constitutive equation, recently adopted for ordinary entangled polymers. Concerning the branched structure, the experimental results in start-up flow strongly depend on the type of salt. In specific cases, the surfactant solutions show flow instabilities and strain hardening. A possible mechanism for the onset of these singularities is proposed.