Rheology, Structure, and Dynamics of Langmuir films

这是一个赠款，以支持开发和应用一个界面流变仪的基础上，一个新的设计，提供更高的灵敏度和更快的动态响应。 此外，它的开放式架构允许使用光学方法，如布鲁斯特角显微镜和吸收二色性的结构测量的同时采集。 它表明，大多数接口组成的复杂材料（脂肪酸，聚合物和脂质）响应时，受到流动的高度非线性的方式。 这种行为的证据包括最近在P.I.实验室进行的测量。示出了在各种长度尺度上的界面微观结构中的流动引起的变化。 宏观上，这些分子和介观尺度的变形和取向表现为剪切稀化粘度和二维的第一正应力。 然而，在目前的时间，很少有人知道的非牛顿界面流变学和分子和微观结构机制的连接。力学流变数据将被采集，沿着分子水平的响应，以建立结构-性能本构关系。 所提出的界面流变仪的设计属于受控应力仪器类。 所施加的应力是使用磁场梯度产生的，该磁场梯度使位于朗缪尔膜表面的杆流动。 蠕变柔量和动态振荡测试都可以用该仪器进行，从而可以获得薄膜的线性和非线性粘弹性。 使用朗缪尔槽作为用于测量的平台将使得有可能在测量期间建立膜的期望的热力学条件。 计划研究各种复杂的流体界面，包括：（1）脂肪酸单分子层在许多相，包括液体凝聚和固相，（2）聚合物溶液单层，其中聚合物是刚性的，毛棒材料，类似于二维液晶，和（3）脂质单分子层在液体膨胀，凝聚和两相状态。

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.