Materials Science and Engineering , The Dow Chemical Company , Building 1702 , Midland , Michigan 48674 , United States.
Langmuir. 2018 Sep 18;34(37):10993-11002. doi: 10.1021/acs.langmuir.8b01711. Epub 2018 Sep 6.
Hydrophobically modified ethoxylated urethane (HEUR) thickeners are widely used as rheology modifiers for waterborne paints. Although the rheology of HEUR solutions in water is fairly well-understood, their impact on the rheology of waterborne latex/pigment suspensions (formulated paints) is more complicated. We study the shear rheology of model HEUR/latex/TiO suspensions in water and investigate the dependence of both oscillatory and steady shear behaviors on the strength of the HEUR hydrophobes. We observe that in both oscillatory and steady shear experiments, rheological curves could be shifted onto a single master curve, demonstrating a "time-hydrophobe superposition". We also note that the oscillatory shear behavior exhibits a power-law spectrum of relaxation times, unlike the single-Maxwellian behavior of pure HEUR solutions. On the basis of these results and earlier experimental and theoretical findings, we propose that the rheology of the HEUR-thickened latex/TiO suspensions is mainly determined by the transient network of HEUR-bridged latex particles, with a broad distribution of the characteristic lifetimes of the bridge. The model is found to be in good qualitative and semiquantitative agreement with the experiments for both steady shear and oscillatory shear.
疏水改性乙氧基化聚氨酯（HEUR）增稠剂被广泛用作水性涂料的流变改性剂。尽管 HEUR 在水中的流变性已经得到了很好的理解，但它们对水性乳胶/颜料悬浮液（配制涂料）的流变性的影响更加复杂。我们研究了模型 HEUR/乳胶/TiO 悬浮液在水中的剪切流变性，并研究了振荡和稳态剪切行为对 HEUR 疏水基团强度的依赖性。我们观察到，在振荡和稳态剪切实验中，流变曲线可以叠加到单个主曲线上，表现出“时间-疏水基团叠加”。我们还注意到，与纯 HEUR 溶液的单一麦克斯韦尔行为不同，振荡剪切行为表现出松弛时间的幂律谱。基于这些结果以及早期的实验和理论发现，我们提出 HEUR 增稠乳胶/TiO 悬浮液的流变性主要由 HEUR 桥连乳胶颗粒的瞬态网络决定，桥的特征寿命分布较宽。该模型在稳态剪切和振荡剪切实验中都得到了很好的定性和半定量的验证。
