Magnetic Needle Viscometer for Langmuir Monolayers

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• 作者：Junqi Ding ; Heidi E. Warriner ; Joseph A. Zasadzinski ; and Daniel K. Schwartz
• 刊名：Langmuir
• 出版年：2002
• 出版时间：April 2, 2002
• 年：2002
• 卷：18
• 期：7
• 页码：2800 - 2806
• 全文大小：294K
• 年卷期：v.18,no.7(April 2, 2002)
• ISSN：1520-5827

文摘

We have built a magnetic needle viscometer capable of measuring the surface shear viscosity of Langmuirmonolayers at constant surface pressure or molecular area. A Langmuir trough with dual symmetricalcompression/expansion barriers is positioned between two electromagnetic coils that create a homogeneousmagnetic field gradient. The gradient drives a Teflon-encapsulated magnetic needle floating on the monolayeralong the surface to a terminal velocity. A channel created by two glass plates centers the needle andminimizes drift. The ratio of monolayer surface shear viscosity at a given composition, temperature, surfacepressure, and so forth to a reference surface shear viscosity is determined by taking the appropriate ratioof the limiting velocities of the magnetic needle for a given applied force. The monolayer viscometer wascalibrated using thin films of silicone oil of known viscosity. We demonstrate the utility of the viscometerby showing that the shear viscosity of saturated dipalmitoylphosphatidylcholine is strongly dependent ontemperature and surface pressure and correlates with the liquid expanded to liquid condensed phasetransition.