Bu Huaitian, Naess Stine N, Beheshti Neda, Zhu Kaizheng, Knudsen Kenneth D, Kjøniksen Anna-Lena, Elgsaeter Arnljot, Nyström Bo
Department of Chemistry, University of Oslo, N-0315 Oslo, Norway.
Langmuir. 2006 Oct 10;22(21):9023-9. doi: 10.1021/la0608664.
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.
本文报道了添加β-环糊精（β-CD）或羟丙基-β-环糊精（HP-β-CD）以及温度对羟乙基纤维素（HEC）及其疏水改性类似物（HM-HEC）半稀溶液的热力学、流变学和结构特征的影响。差示扫描量热法（DSC）测量表明，在HEC和HM-HEC溶液中高浓度时，β-CD存在热诱导的晶体熔融转变。在水溶液中未观察到HP-β-CD的转变。粘度结果表明，在共溶质浓度为2 mM时，β-CD单元穿入HM-HEC（C16基团）的疏水尾部形成柱状结构。这种排列在包裹疏水链方面比HP-β-CD单元实现的单体疏水失活更有效。在共溶质浓度高于8 mM时，任何一种共溶质的疏水相互作用都不会进一步解耦。对HM-HEC/β-CD混合物进行的小角中子散射（SANS）实验表明，添加β-CD后，HM-HEC/D₂O溶液中的大规模缔合结构减少，并且在添加2 mM β-CD时观察到有趣的温度效应。在高β-CD浓度和低温下，大的β-CD簇或微晶的形成在HEC和HM-HEC网络中产生交联，导致粘度提高几个数量级。这种强烈的温度效应在SANS探测的结构特征中未体现出来。
