Rheology, Structure, and Dynamics of Langmuir films

这是一笔赠款，用于支持基于新设计的界面流变仪的开发和应用，该设计具有更高的灵敏度和更快的动态响应。此外，它的开放式结构允许使用布鲁斯特角度显微镜和吸收二色性等光学方法同时获取结构测量结果。研究表明，大多数由复杂材料(脂肪酸、聚合物和脂类)组成的界面在受到流动影响时会以高度非线性的方式响应。这一行为的证据包括最近在P.I.实验室进行的测量，显示了在各种长度尺度上流动引起的界面微结构的变化。宏观上，这些分子和中尺度的变形和取向在二维上表现为剪切变稀粘度和第一正应力。然而，目前对非牛顿界面流变学与分子和微观结构机制之间的联系知之甚少。将获得力学流变性数据以及分子水平的响应，以建立结构-性能本构关系。提出的界面流变仪的设计属于受控应力仪器的范畴。施加的应力是使用磁场梯度产生的，该磁场梯度使驻留在朗缪尔薄膜表面的棒流动。该仪器既可以进行蠕变柔量测试，也可以进行动态振荡测试，从而获得薄膜的线性和非线性粘弹性特性。使用朗缪尔槽作为测量平台，可以在测量过程中确定所需的薄膜热力学条件。计划研究各种复杂的流体界面，包括：(1)许多相中的脂肪酸单分子层，包括液体凝聚相和固相；(2)聚合物溶液单分子层，其中聚合物是刚性的、类似于二维液晶的毛状杆状材料；以及(3)液体膨胀、凝聚和两相状态的脂单分子层。

This is a grant to support the development and application an interfacial rheometer based on a new design that offers increased sensitivity and a faster dynamic response. Furthermore, its open architecture allows for the simultaneous acquisition of structural measurements using optical methods such as Brewster angle microscopy and absorptive dichroism. It is demonstrated that most interfaces comprised of complex materials (fatty acids, polymers, and lipids) respond in a highly nonlinear manner when subjected to flow. The evidence of this behavior includes recent measurements performed in the laboratory of the P.I. showing flow induced changes in interfacial microstructure on a variety of length scales. Macroscopically, these molecular and mesoscale deformations and orientations are manifested as shear thinning viscosities and first normal stresses in two dimensions. However, at the present time, very little is known about the connection of non-Newtonian interfacial rheology and molecular and microstructural mechanisms. Mechanical rheological data will be acquired, along with molecular level responses, to establish structure-property constitutive relationships. The proposed design of an interfacial rheometer is of the class of controlled stress instruments. The applied stress is generated using magnetic field gradients that subject a rod residing at the surface of a Langmuir films to flow. Both creep compliance and dynamic oscillatory testing will be possible with the instrument so that the linear and nonlinear viscoelastic properties of the films can be obtained. The use of a Langmuir trough as the platform for the measurements will make it possible to establish the desired thermodynamic condition of the film during the measurements. It is planned to study a variety of complex fluid interfaces including: (1) fatty acid monolayers in a number of phases including liquid condensed and solid phases, (2) polymer solution monolayers where the polymers are rigid, hairy rod materials that resemble two-dimensional liquid crystals, and (3) lipid monolayers in the liquid expanded, condensed and two phase states.