Growth Of Wormlike Micelles Research Articles

Prediction of the second critical micelle concentration of aqueous tween and span solutions via CPA EoS: Application of the quantitative theory in growth of wormlike micelles

A new combination of previously established molecular-thermodynamic methods was offered in conjunction with the Cubic Plus Association (CPA) equation of state (EoS) for the assessment of the second critical micelle concentration (SCMC), and curvature parameters in aqueous solutions of non-ionic surfactants encompassing Tween 80, Tween 60, Span 80, and Span 60. This combination will yield a quantifiable examination that adheres to creating the micelles resembling worms, enabling the optimization of critical curvature parameters, as well as the prediction of the SCMC. This previously well-known model is reliant upon theoretical components, including chain conformation, headgroup-steric effects, and interfacial tension pertaining to the energy of micelle-free systems. So, the optimized curvature parameters obtained because of these forces can be used as the input of CPA EoS to independently count the association interactions and predict the SCMC for the first time. For the aforementioned surfactants, the first critical micelle concentration (FCMC) data was previously used to modify five pure parameters of the CPA EoS. Consequently, applying the adjusted parameters, the SCMC of noted aqueous solutions has been predicted reasonably using CPA EoS.

Growth of wormlike micelles in nonionic surfactant solutions: Quantitative theory vs. experiment

Growth of wormlike micelles in nonionic surfactant solutions: Quantitative theory vs. experiment

The influence of concentration and pH on the structure and rheology of cationic surfactant/hydrotrope structured fluids

Abstract In this paper, we show how to tailor the structure and rheology of aqueous solutions of the cationic surfactant cetyltrimethylammonium tosylate, CTAT, by adding a hydrotrope (potassium phthalic acid, PPA) or changing pH. Aqueous solutions of neat CTAT and CTAT/PPA binary mixtures were evaluated under different hydrotrope concentrations and compared with solutions of an analogous surfactant, cetyltrimethylammonium chloride (CTAC). PPA content promotes substantial increases in micellar flexibility and inter-micellar entanglements, resulting in a higher degree of structure in the fluid. Increasing the pH in neat CTAT leads to significant increases in low shear rate viscosities in comparison with CTAT at its original pH, because the OH ions favor surfactant aggregation as well as the growth of worm-like micelles. Nevertheless, increasing the pH in CTAT/PPA mixtures produced a progressive decrease in the low shear rate viscosities. This result is due to the nature of the interactions between CTAT and PPA, as well as to the ionization degree of the functional groups present in PPA. Cryo-TEM and 1 H NMR measurements evidenced, respectively, the microstructural and chemical environmental changes of CTAT upon PPA addition and explain the rheological properties of the CTAT/PPA mixtures as a function of the fluid structure.

A systematic study of equilibrium structure, thermodynamics, and rheology of aqueous CTAB/NaNO 3 wormlike micelles

We present a systematic study of the self-assembly of wormlike micelles (WLMs) comprised of cetyltrimethylammonium bromide (CTAB) and sodium nitrate (NaNO 3) in aqueous solution as a function of CTAB concentration, NaNO 3 concentration, and temperature throughout the dilute and semi-dilute regions of the phase diagram where linear micelles are observed. Combining measurements using isothermal titration calorimetry, rheometry, flow-birefringence, cryo-transmission electron microscopy (cryo-TEM), and small angle neutron scattering (SANS) enables complete characterization of the structure, thermodynamics, and rheology of CTAB/NaNO 3 micelles. The addition of NaNO 3 is found to increase the micellization enthalpy as well as the micellar scission energy, resulting in the elongation and growth of WLMs. We find quantitative agreement between the scission energy determined from rheology and the enthalpy of micellization determined from ITC, as well as for contour lengths extracted from rheology and SANS. At fixed molar ratio of NaNO 3 and CTAB, the solution rheology exhibits scaling consistent with dilute, semi-dilute overlapping, and semi-dilute entangled regimes typically found in polymer solutions, as confirmed by cryo-TEM and SANS. The transition between these scaling regimes coincides with the structural transitions identified by SANS. The results validate the relationship between structural parameters and rheological behavior underlying theories for ionic WLMs.