EAGER: Viability study for interfacial spectroscopy

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When a liquid drop is subjected to an external force, it typically undergoes oscillations in its shape with a frequency that depends on the material properties of the drop. In some naturally occurring and technological processes of interest, drops contain inclusions in their interior. These inclusions, which could be small bubbles or solid particles, can affect the characteristic oscillations of the drop. The goal of this EAGER proposal is to show that by measuring the frequency of drop oscillations, the size, number and locations of such inclusions can be determined. The project will use a combination of theory, numerical computations and experiments to demonstrate the feasibility of this idea, which is called “interfacial spectroscopy.” The results could be useful as a quality control tool in a variety of processing operations involving such materials as inks, paints, and other suspensions or to detect impurities and contaminants in multiphase systems. The project will involve high-school students and undergraduates in the design and implementation of experiments to validate the approach.Natural pulsations of multiphase systems like particle-laden drops exhibit surface waves with intriguing frequency and decay features. Recent studies have shown that slightly deviating frequencies for a few modes form bands akin to fine-structure split in atomic energy levels. It can be shown that such frequency and decay spectra are unique for each internal structure of the multiphase multispecies domains. This suggests the possibility of finding what is inside a complicated opaque liquid from experimentally measured interfacial wave spectra data. This EAGER project will establish the viability and accuracy of this diagnostic technique. The project will concentrate on four specific matters considering particle-laden drops to be the representative of complex systems. First, simulations will demonstrate how frequencies and decay constants of interfacial waves vary with size, number and position of the particles inside a droplet. Secondly, an inversion algorithm will be devised to extract the particulate details from spectral information. Then, the diagnostic procedure will be applied in real experiments to test the capability and the limit of the technology. Fourthly, the uniqueness theorem for inversion will be generalized to see whether more complex structures can be revealed using the approach.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.