在相反电荷表面活性剂存在下阳离子瓜尔胶水溶液流变行为

合成了阳离子瓜尔胶(CG)，研究了其水溶液在十二烷基硫酸钠(SDS)存在下的流变行为．测定结果表明，随SDS浓度的增加，溶液零切黏度增加了3个数量级以上．小幅振荡剪切实验结果表明模量几乎和SDS浓度无关，但是驰豫时间则随着SDS浓度增加而迅速增加．因此，SDS的加入将会使交联点的强度增加，但是不会改变交联点密度．SDS对CG流变行为的影响可以用两阶段模型加以描述．在SDS存在下CG水溶液流变行为主要受到由SDS胶束形成的交联点的控制．根据Arrhenius公式得到的瓜儿胶水溶液的流动活化能在将SDS分子疏水尾端从胶束移到水相之中所需能量是一致的.

Rheological Behavior of Aqueous Solutions of Cationic Guar in Presence of Oppositely Charged Surfactant

The cationic guar (CG) is synthesized and the rheological behavior of aqueous solutions of CG in the presence of sodium dodecyl sulfate (SDS) is studied in detail. The steady viscosity measurements show that the zero shear viscosity enhancement can be almost 3 orders of magnitude as the concentration of SDS increases from 0 to 0.043%. The gel-like formation is observed as the concentration of SDS is greater than 0.016%. The oscillatory rheological measurements of CG solutions in the presence of SDS show that the crossover modulus is almost independent of the concentration of SDS whereas the apparent relaxation time increases swiftly upon increasing the concentration of SDS. The experimental results indicate that the strength rather than the number of the cross-links is greatly affected bySDS molecules. The mechanism concerning the effect of SDS upon the rheology of CG solutions can be coined by the two-stage model. Before the formation of cross-links at the critical concentration, the electrostatic interaction between SDS and cationic site of CG chains plays a key role and the SDS molecules bind to CG chains through the electrostatic interaction. After the formation of cross-links at the concentration greater than the critical concentration, the cooperative hydrophobic interaction become dominant and SDS molecules bind to the cross-links through the hydrophobic interaction. The rheological behavior of aqueous solutions of CG in the presence of SDS is chiefly determined by the micelle-like cross-links between CG chains. In fact, the flow activation energy of CG solution, obtained from the temperature dependence of the apparent relaxation time, falls in the range of transferring a hydrophobic tail of SDS from the micelle to an aqueous environment.