Beheshti Neda, Bu Huaitian, Zhu Kaizheng, Kjøniksen Anna-Lena, Knudsen Kenneth D, Pamies Ramón, Hernandez Cifre José G, García de la Torre José, Nyström Bo
Department of Chemistry, University of Oslo, P.O. Box 1033, Blindern, N-0315 Oslo, Norway.
J Phys Chem B. 2006 Apr 6;110(13):6601-8. doi: 10.1021/jp056828v.
The formation of associative networks in semidilute aqueous solutions of hydrophobically modified hydroxyethylcellulose (HM-HEC) is dependent on intermolecular hydrophobic interactions. Addition of hydroxypropyl-beta-cyclodextrin (HP-beta-CD) monomers to the system provides decoupling of these associations via inclusion complex formation with the polymer hydrophobic tails. Results from viscosity, polymer NMR self-diffusion, and dynamic light scattering (DLS) measurements show that the hydrophobic interactions in HM-HEC solutions are effectively suppressed when the level of HP-beta-CD addition increases. Small-angle neutron scattering (SANS) results reveal that the large-scale association complexes in HM-HEC solutions are strongly diminished when the concentration of HP-beta-CD rises. The time correlation data obtained from the DLS experiments unveiled the existence of two relaxation modes: one single exponential at short times followed by a stretched exponential at longer times. The fast mode is always diffusive, whereas the slow mode exhibits progressively stronger wavevector dependence as the intensity of the hydrophobic interactions increases. This feature, as well as the accompanying drop of the stretched exponential beta as the HP-beta-CD concentration decreases, is attributed to enhanced hydrophobic interactions and can be well rationalized in the framework of the coupling model of Ngai.
在疏水改性羟乙基纤维素（HM-HEC）的半稀释水溶液中，缔合网络的形成取决于分子间的疏水相互作用。向该体系中添加羟丙基-β-环糊精（HP-β-CD）单体，通过与聚合物疏水链段形成包合物，使这些缔合作用解耦。粘度、聚合物核磁共振自扩散以及动态光散射（DLS）测量结果表明，随着HP-β-CD添加量的增加，HM-HEC溶液中的疏水相互作用得到有效抑制。小角中子散射（SANS）结果显示，当HP-β-CD浓度升高时，HM-HEC溶液中的大规模缔合复合物会显著减少。从DLS实验获得的时间关联数据揭示了两种弛豫模式的存在：短时间内为单指数形式，较长时间后为拉伸指数形式。快速模式始终是扩散性的，而随着疏水相互作用强度的增加，慢速模式表现出逐渐增强的波矢依赖性。随着HP-β-CD浓度降低，拉伸指数β随之下降，这一特征以及上述现象均归因于疏水相互作用的增强，并且可以在Ngai的耦合模型框架内得到很好的解释。
