Upoma Marufa Akter, He Ziwen, Tran Huy, Sivells Tiara, Cyran Jenée D, Pack Min Young
Department of Mechanical Engineering, Baylor University, Waco 76798, Texas, United States.
Department of Chemistry, Boise State University, Boise 83725, Idaho, United States.
Langmuir. 2024 Sep 17;40(37):19377-19387. doi: 10.1021/acs.langmuir.4c01533. Epub 2024 Sep 3.
In many commercial applications, polymer-dye interactions are frequently encountered from food to wastewater treatment, and while shear rheology has been well characterized, the extensional properties are not well known. The extensional viscosity η and relaxation time λ are the extensional rheological parameters that provide valuable insights into how aqueous polymers respond during deformation, and this study investigated the effect of dyes on the extensional rheology of three different aqueous polymer solutions (e.g., anionic, cationic, and neutral) paired with two different dye salts (e.g., anionic and cationic) using drop pinch-off experiments. We have found that the influence of dyes on the pinch-off dynamics is complex but generally leads to a decrease in, for example, the apparent extensional relaxation time. We have utilized the dripping-onto-substrate method to probe the uniaxial deformation of widely used polymers such as xanthan gum (XG), poly(diallyldimethylammonium chloride) (PDADMAC), and poly(ethylene oxide) (PEO) as the anionic, cationic, and neutral polymers, respectively, paired with either fluorescein (Fl) or methylene blue (MB) as the anionic and cationic dyes, respectively. Polymer-dye pairs with opposite charges (e.g., XG-MB and PDADMAC-Fl) displayed a pronounced decrease in pinch-off times, but even PEO, which is a neutral polymer, resulted in decreased pinch-off times, which was restored by the addition of NaCl. The pinch-off times for the Boger fluid (mixture of poly(ethylene glycol) and PEO), however, were surprisingly uninfluenced by dyes. These results showed that not only did the small addition of dyes strongly decrease the polymer relaxation times, but the relative importance of the dye salts on the polymer pinch-off dynamics was also different from that of pure salts such as NaCl.
在许多商业应用中，从食品到废水处理，聚合物与染料的相互作用屡见不鲜。虽然剪切流变学已得到充分表征，但其拉伸性能却鲜为人知。拉伸粘度η和松弛时间λ是拉伸流变参数，能为水性聚合物在变形过程中的响应提供有价值的见解。本研究通过液滴 pinch-off 实验，研究了染料对三种不同水性聚合物溶液（即阴离子型、阳离子型和中性）与两种不同染料盐（即阴离子型和阳离子型）的拉伸流变学的影响。我们发现，染料对 pinch-off 动力学的影响很复杂，但通常会导致例如表观拉伸松弛时间的减少。我们利用液滴滴落在基底上的方法，分别研究了广泛使用的聚合物（如黄原胶（XG）、聚二烯丙基二甲基氯化铵（PDADMAC）和聚环氧乙烷（PEO），分别作为阴离子型、阳离子型和中性聚合物）与荧光素（Fl）或亚甲基蓝（MB）（分别作为阴离子型和阳离子型染料）的单轴变形。带相反电荷的聚合物 - 染料对（如 XG - MB 和 PDADMAC - Fl）的 pinch-off 时间显著减少，但即使是中性聚合物 PEO，也导致 pinch-off 时间减少，而添加 NaCl 可使其恢复。然而，博格流体（聚乙二醇和 PEO 的混合物）的 pinch-off 时间出人意料地不受染料影响。这些结果表明，不仅少量染料的添加会显著降低聚合物的松弛时间，而且染料盐对聚合物 pinch-off 动力学的相对重要性也与 NaCl 等纯盐不同。
