3 years ago

Wormlike Surfactant Micelles with Embedded Polymer Chains

Wormlike Surfactant Micelles with Embedded Polymer Chains
Elena E. Dormidontova, Vyacheslav S. Molchanov, Hari Sharma, Alexander L. Vasiliev, Alexander L. Kwiatkowski, Olga E. Philippova, Anton S. Orekhov
Active use of wormlike micelle (WLM) solutions in a broad range of applications demands control of their viscoelastic properties under different external conditions that can be achieved by using hybrid materials, such as polymer–surfactant complexes. Understanding the properties of such hybrid materials remains a challenge. Using a combination of several experimental techniques with molecular dynamics simulations, we investigate the interaction of poly(4-vinylpyridine) with WLMs of the anionic surfactant potassium oleate. We find that this polymer is solubilized by the micelles at the interface between the tails and headgroups of surfactant, thus screening the hydrophobic polymer backbone from interactions with water while maintaining hydrogen bonding between the pyridine rings and water. By use of SANS with contrast variation, it was shown that the macromolecules associated with the micelles have an expanded coil-like conformation with persistence length 4-fold higher than that of a polymer chain in a good solvent. The rheological behavior of the micellar solutions shows that at low polymer concentrations (regime I) the system maintains high viscoelasticity with the plateau modulus remaining almost unchanged, while the zero-shear viscosity slightly decreases. At higher polymer concentrations (regime II), the viscosity drops by more than 4 orders of magnitude, approaching that of pure solvent. The transition from the I to II regime occurs when the number of added macromolecules is approximately equal to the number of elastically active strands in micellar network. The observed changes are attributed to polymer-induced shortening of WLMs accompanied by loop and branch formation. The saturated polymer–surfactant complex contains about one surfactant per repeat unit of the polymer and represents a best compromise when the WLM retains its general cylindrical geometry (but not the viscoelastic properties) and the polymer maintains an expanded coil-like conformation.

Publisher URL: http://dx.doi.org/10.1021/acs.macromol.7b01500

DOI: 10.1021/acs.macromol.7b01500

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