title: Characterization of thermally sensitive interactions in aqueous mixtures of hydrophobically modified hydroxyethylcellulose and cyclodextrins.
abstract: Effects of beta-cyclodextrin (beta-CD) or hydroxypropyl-beta-cyclodextrin (HP-beta-CD) addition and temperature on thermodynamic, rheological, and structural features of semidilute solutions of hydroxyethylcellulose (HEC) and its hydrophobically modified analogue (HM-HEC) are reported. Differential scanning calorimetric (DSC) measurements revealed a thermally induced crystal melting transition of beta-CD at high concentrations in solutions of HEC and HM-HEC. No transition with HP-beta-CD was observed in aqueous solution. Viscosity results indicated that at a cosolute concentration of 2 mm, the beta-CD units are threaded onto hydrophobic tails of HM-HEC (C16 groups) to form columnar structures. This arrangement is more effective in the encapsulation of the hydrophobic chains than the monomer hydrophobic deactivation accomplished by the HP-beta-CD units. At cosolute concentrations above 8 mm, no further decoupling of the hydrophobic interactions occurs for any of the cosolutes. Small-angle neutron scattering (SANS) experiments on HM-HEC/beta-CD mixtures suggest that the large-scale association structures in HM-HEC/D(2)O solutions are reduced upon addition of beta-CD, and an interesting temperature effect is observed at 2 mm beta-CD addition. At high beta-CD concentrations and low temperatures, the formation of large beta-CD clusters or crystallites generates cross-links in the HEC and HM-HEC networks, resulting in a viscosity enhancement of several orders of magnitude. This strong temperature effect is not reflected in the structural features probed by SANS.
authors.affiliation: Department of Chemistry, University of Oslo, N-0315 Oslo, Norway.
authors.forename: Huaitian
authors.initials: H
authors.lastname: Bu
authors.forename: Stine N
authors.initials: SN
authors.lastname: Naess
authors.forename: Neda
authors.initials: N
authors.lastname: Beheshti
authors.forename: Kaizheng
authors.initials: K
authors.lastname: Zhu
authors.forename: Kenneth D
authors.initials: KD
authors.lastname: Knudsen
authors.forename: Anna-Lena
authors.initials: AL
authors.lastname: Kjøniksen
authors.forename: Arnljot
authors.initials: A
authors.lastname: Elgsaeter
authors.forename: Bo
authors.initials: B
authors.lastname: Nyström