Wantke Klaus-Dieter, Fruhner Horst
Max-Planck-Institute of Colloids and Interface, Am Mühlenberg 1, Golm/Potsdam, D-14476, Germany
J Colloid Interface Sci. 2001 May 15;237(2):185-199. doi: 10.1006/jcis.2001.7455.
A new version of the oscillating bubble method enables us to determine the dilational modulus of fluid surfaces in the frequency range 1 Hz</=f</=500 Hz. The frequency behavior of this complex modulus exhibits the influence of various physical effects which requires explanation in the framework of an appropriate theoretical model. For the evaluation of our measurements a theoretical modulus is used which includes compositional and intrinsic viscous effects. The compositional effects are described by the established model of dynamic surface tension. However, a modified interpretation is required to explain the values of the involved parameters which deviate strongly from the values calculated using equilibrium data. In addition, several experiments demonstrate the influence of an intrinsic surface dilational viscosity. This can be interpreted as the effect of molecular exchange at the surface in a nonequilibrium state. For the investigation of such processes we have compared the surface dilational moduli of solutions of alkyldimethylphosphine oxides with various chain lengths. The theoretical model was tested using these experimental results. It was possible to determine the parameters of the model. The parameters characterize the elastic and viscous properties of the surface as well as molecular exchange processes between surface and bulk. Their values mark scales for the influence of compositional effects, intrinsic effects, and molecular kinetics on the dilational properties of the surface. Copyright 2001 Academic Press.
一种新的振荡气泡法使我们能够在1Hz≤f≤500Hz的频率范围内测定流体表面的扩张模量。这种复模量的频率行为展现了各种物理效应的影响，这需要在合适的理论模型框架内进行解释。为了评估我们的测量结果，使用了一种理论模量，它包括成分效应和固有粘性效应。成分效应由已确立的动态表面张力模型描述。然而，需要一种修正的解释来解释所涉及参数的值，这些值与使用平衡数据计算出的值有很大偏差。此外，一些实验证明了固有表面扩张粘度的影响。这可以解释为非平衡状态下表面分子交换的效应。为了研究此类过程，我们比较了不同链长的烷基二甲基氧化膦溶液的表面扩张模量。利用这些实验结果对理论模型进行了检验。有可能确定模型的参数。这些参数表征了表面的弹性和粘性特性以及表面与本体之间的分子交换过程。它们的值标志着成分效应、固有效应和分子动力学对表面扩张特性影响的尺度。版权所有2001年学术出版社。
