On the one hand, microrheology has been a powerful tool since the mid-80's for characterizing 3D viscoelastic materials. On the other hand, the study of soft interfaces has identified several poorly characterized complex systems including low-surface-viscosity Langmuir films and spatially heterogeneous Langmuir films. This proposal represents a merger between these two ideas: we propose to characterize the rheological properties of interfaces, taking into account their full complexity, including adjacent 3D materials, microscopic spatial heterogeneities and nonlinear effects. We will develop and enhance a two-particle surface microrheology, and provide this way new characterizations of these soft interfaces.
Using this method, our research objectives include:  measuring very low surface viscosities achieved by spreading surfactants (DpPC) at an air/water interface and which are so low that they have not been measured by other techniques. Then, turning to monolayers of proteins (beta-lactoglobulin), we will further extend this technique to viscoelastic membranes and measure surface elasticities.  Focusing on heterogeneous monolayers with complex properties. Under surface pressure, surfactants form heterogeneous structures such as liquid expanded and liquid condensed phases to which we will apply our technique to measure length-scale dependent surface viscosities. We will finally measure the flow field and extend a 3D model by Levine and Lubensky to capture the most important features of the rheology of this spatially heterogeneous films. If successful, the model will be able to account for differences between the 1-particle and 2-particle measurements, in other words, reconciling the local and global rheological behavior of the interface.
This project provides benchmark experiments on heterogeneous flat layers paving the way for further studies of more complex systems such as cell plasma membranes which present heterogeneous surfaces and curvature.
Call for proposal
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