Department of Physical-Chemistry, Institute of Chemistry, University of Campinas, Campinas, P.O. Box 6154, 13084-862, SP, Brazil.
J Colloid Interface Sci. 2010 May 15;345(2):351-9. doi: 10.1016/j.jcis.2010.01.086. Epub 2010 Feb 4.
The effect of hydrophobic and hydrophilic co-solutes on the rheological properties of wormlike micelles of cetyltrimethylammonium bromide (CTAB) and sodium salicylate (NaSal) or sodium bromide (NaBr) was investigated. Monomeric (ethanol, 2-propanol, benzene and benzylic alcohol) and polymeric species (poly(ethylene oxide), poly(vinyl alcohol) and poly(propylene oxide), respectively PEO, PVA and PPO) of varying molecular weight were studied in order to assess the effect of co-solute 'length' on the interactions with the wormlike micelles. Rheological properties were characterised by the plateau modulus G(0) and the relaxation time τ(R) obtained from fits to the Maxwell model, and by the zero-shear viscosity η(0). The rheological properties were unaltered by the addition of all hydrophilic solutes (up to 20 mM). With hydrophobic co-solutes instead, both η(0) and τ(R) decreased considerably, while G(0) was unaffected. The effects were particularly remarkable with PPO for concentrations as low as 5 mM (ca. 0.3 g L(-1)), and τ(R) was seen to follow an exponential decrease with polymer M(w). The effect of the aromatic solutes (benzene and benzyl alcohol) on the rheology was highly dependent on the counterions used to induce micellar growth (Sal(-) or Br(-)), revealing a different type of interaction. Surprisingly, small-angle neutron scattering and Cryo-TEM measurements showed that the drastic changes observed in the rheology were not correlated to any visible structural change. Therefore the strong decrease in viscosity and relaxation time are to be attributed to other mechanisms than micellar break-up or rod-to-sphere transition.
研究了疏水和亲水共溶剂对十六烷基三甲基溴化铵（CTAB）和水杨酸钠（NaSal）或溴化钠（NaBr）蠕虫状胶束流变性的影响。研究了不同分子量的单体（乙醇、2-丙醇、苯和苄醇）和聚合物（聚（环氧乙烷）、聚（聚乙烯醇）和聚（环氧丙烷），分别为 PEO、PVA 和 PPO），以评估共溶剂“长度”对与蠕虫状胶束相互作用的影响。流变性质通过从 Maxwell 模型拟合得到的平台模量 G(0)和弛豫时间 τ(R)以及零剪切粘度 η(0)来表征。添加所有亲水性溶剂（高达 20 mM）都不会改变流变性质。相反，对于疏水性共溶剂，η(0)和 τ(R)都大大降低，而 G(0)不受影响。用低浓度的 PPO（约 0.3 g L(-1)）甚至 5 mM 就可以观察到特别显著的效果，并且 τ(R)与聚合物 M(w)呈指数下降关系。芳香族溶剂（苯和苄醇）对流变学的影响高度依赖于用于诱导胶束生长的反离子（Sal(-)或 Br(-)），这揭示了不同类型的相互作用。令人惊讶的是，小角中子散射和低温透射电子显微镜测量表明，在流变学中观察到的剧烈变化与任何可见的结构变化无关。因此，粘度和弛豫时间的强烈下降归因于除胶束破裂或棒状到球状转变之外的其他机制。
