Effects of β-cyclodextrin and β-cyclodextrin polymer addition and temperature on the modulation of hydrophobic interactions in aqueous solutions of two hydrophobically modified biopolymers

Abstract

Novel information about the effects of temperature and addition of hydroxypropyl-β-cyclodextrin (HP-β-CD) or a charged β-cyclodextrin polymer (poly(β-CDN +)) on the rheological features of aqueous solutions of hydrophobically modified hydroxyethylcellulose (HM-HEC) and hydrophobically modified dextran (HM-dextran) is given. The viscosity results for the HM-HEC/poly(β-CDN +) system demonstrated that the addition of this cosolute sets up bridges between adjacent polymer chains, which lead to a strong enhancement of the viscosity. Furthermore, a shear thickening effect is registered at fairly high shear rates, and this feature is influenced by temperature. On the other hand, addition of HP-β-CD monomers to the system generates decoupling of associations via inclusion complex formation with the polymer hydrophobic tails. For the HM-dextran solutions, the interaction with the cosolutes is weak and only a slight increase of the viscosity by addition of poly(β-CDN +) is observed. In contrast to the HM-HEC solutions, addition of HP-β-CD monomers to the aqueous solutions of HM-dextran deactivates the intramolecular hydrophobic associations and thereby the compact coil structure expands and this leads to viscosity enhancement. Elevated temperature induces higher chain mobility and the formation of weaker network associations. The bridges formed in the HM-HEC/poly(β-CDN +) system are especially sensitive to temperature changes.