Rheological and structural properties of aqueous solutions of a hydrophobically modified polyelectrolyte and its unmodified analogue |
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Authors: | Kenneth D Knudsen Anna-Lena Kjøniksen |
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Institution: | a Department of Physics, Institute for Energy Technology, N-2027 Kjeller, Norway b Department of Chemistry, University of Oslo, P.O. Box 1033, Blindern, N-0315 Oslo, Norway |
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Abstract: | Rheological methods and small angle neutron scattering (SANS) were used in the characterization of dilute and semidilute aqueous solutions, both with and without added salt, of anionic poly(vinyl alcohol) (PVA−) and its hydrophobically modified analogue (HM-PVA−). The rheological measurements showed that the concentration induced viscosification effect and elastic responses are considerably stronger for solutions of HM-PVA− than in solutions of the unmodified polyelectrolyte. Over the considered polymer concentration domain, the solutions of PVA− exhibit virtually Newtonian behavior, whereas strong shear thinning effects are observed in the HM-PVA− solutions. The SANS results for HM-PVA− solutions reveal a pronounced peak in the plot of scattering intensity versus scattering wavevector q at intermediate q values and the position of the maximum scales with polymer concentration as qmax∼c0.28±0.02. This peak is suppressed in solutions of the unmodified polyelectrolyte and merely a shoulder in the scattering curve appears. Additionally, an “upturn” in the scattered intensity is observed at small q values and the magnitude of this effect depends on polymer concentration, hydrophobicity and salt addition. At large q values, the SANS results from HM-PVA− solutions suggest morphological changes, from rod-like chains to a network of semiflexible chains, as the polyelectrolyte concentration increases. |
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Keywords: | Hydrophobically modified polyelectrolyte Association SANS Rheology |
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