Alonso Coralie, Zasadzinski Joseph A
Department of Chemical Engineering, University of California, Santa Barbara, California 93106-5080, USA.
J Phys Chem B. 2006 Nov 9;110(44):22185-91. doi: 10.1021/jp055870n.
The two-dimensional surface shear viscosity, eta, of fatty acid monolayers of different chain lengths, measured using a simple magnetic needle viscometer, strongly correlates with the molecular organization in condensed phases and the absolute temperature. eta can increase by orders of magnitude at phase boundaries associated with tilted to untilted molecular order, providing the underlying order is semicrystalline. Hence, untilted, long-range ordered CS phases are the most viscous films. However, despite being untilted, the LS rotator phase is less viscous than certain laterally ordered tilted phases, suggesting a decrease of the van der Waals interactions due to molecular rotation. In certain regions of the L2 phase, eta reaches a maximum before the L2-LS transition, an anomalous behavior correlated with the change in the lattice symmetry of the headgroup. Surface shear viscosity, even when measured with a macroscopic probe, is particularly sensitive to the microscopic organization of monolayers.
使用简单磁针粘度计测量的不同链长脂肪酸单分子层的二维表面剪切粘度η，与凝聚相中的分子组织和绝对温度密切相关。在与分子排列从倾斜到非倾斜相关的相界处，η可增加几个数量级，前提是底层排列为半结晶状态。因此，非倾斜的、长程有序的CS相是粘性最大的薄膜。然而，尽管LS旋转相是非倾斜的，但它的粘性比某些横向有序的倾斜相要小，这表明由于分子旋转，范德华相互作用减弱。在L2相的某些区域，η在L2-LS转变之前达到最大值，这种异常行为与头基晶格对称性的变化有关。表面剪切粘度，即使是用宏观探针测量，也对单分子层的微观组织特别敏感。
