Davidson Michael L, Laufer Liat, Gottlieb Moshe, Walker Lynn M
Department of Chemical Engineering, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, United States.
Department of Chemical Engineering, Ben-Gurion University of the Negev, Beer-Sheva 84105, Israel.
Langmuir. 2020 Jul 7;36(26):7227-7235. doi: 10.1021/acs.langmuir.0c00477. Epub 2020 Jun 25.
The connection between block copolymer architecture and adsorption at fluid/fluid interfaces is poorly understood. We characterize the interfacial properties of a well-defined series of polyethylene oxide/polydimethyl siloxane (PDMS) diblock and BAB triblock copolymers at the dodecane/water interface. They are oil-soluble and quite flexible because of their hydrophobic PDMS block. Rather than relying on equilibrium interfacial measurements for which it is difficult to mitigate experimental uncertainty during adsorption, we combine measurements of steady-state adsorption, dilatational rheology, and adsorption/desorption dynamics. Steady-state interfacial pressure is insensitive to interfacial curvature and mostly agrees with theory. Adsorption does not occur in the diffusive limit as is the case for many aqueous, small-molecule surfactants. Dilatational rheology reveals differences in behavior between the diblocks and triblocks, and all interfaces possess elasticities below the thermodynamic limit. Desorption dynamics show that material exchange between the interface and the neighboring fluid occurs too slowly to relax dilatational stresses. The mechanism of relaxation occurs at the interface, likely from the reorientation of adsorbed chains.
嵌段共聚物结构与在流体/流体界面吸附之间的联系目前还知之甚少。我们对一系列定义明确的聚环氧乙烷/聚二甲基硅氧烷（PDMS）二嵌段和BAB三嵌段共聚物在十二烷/水界面的界面性质进行了表征。由于其疏水的PDMS嵌段，它们是油溶性的且相当柔韧。我们没有依赖于平衡界面测量（在吸附过程中难以减轻实验不确定性），而是结合了稳态吸附、拉伸流变学以及吸附/解吸动力学的测量。稳态界面压力对界面曲率不敏感，并且大多与理论相符。吸附并不像许多水性小分子表面活性剂那样发生在扩散极限情况。拉伸流变学揭示了二嵌段和三嵌段之间行为的差异，并且所有界面的弹性都低于热力学极限。解吸动力学表明，界面与相邻流体之间的物质交换发生得太慢，无法松弛拉伸应力。松弛机制发生在界面处，可能是由于吸附链的重新取向。
