Dear All, Happy New Year! I am delighted to announce a special seminar by a visiting professor, Prof. Kyu Hyun from Pusan University, Korea. Prof. Hyun is a well-regarded expert in rheology and will be visiting our School for his sabbatical from January until December this year. This is an informal talk, and anyone interested is welcome to attend. The details are as follows. Time/Location: 10:30 - 11:30 AM on Thursday, January 11th , 2024. Room 3059 FRNY. Title: Characterization of Complex Fluids by Dynamic Oscillatory Shear Test Biosketch: Dr. Kyu Hyun is a Professor in the School of Chemical Engineering and the Vice Dean in the College of Engineering at Pusan National University (PNU), South Korea. He earned his BS in Chemical Engineering from Seoul National University (SNU) in 1998, followed by a MS degree in 2000 and a PhD in 2005, both in Chemical Engineering, also from SNU. Dr. Hyun has an extensive academic background, including postdoctoral research at various prestigious institutions, such as the Max-Planck Institute for Polymer, Karlsruhe Institute of Technology, and Deustsches Elektonen-Synchrotron, Germany. He has held several key positions at PNU, including the Head of the School of Chemical and Biomolecular Engineering. Dr. Hyun has made significant contributions to the field of rheology, particularly in nonlinear oscillatory shear tests and complex fluid characterization. His research has been widely recognized, leading to awards such as the 'Distinguished Young Rheologist' from TA Instruments (USA), the Humboldt Fellowship from Alexander von Humboldt Foundation (Germany), and the 'Young Rheologist' Award from the Korean Society of Rheology (KSR). Abstract: Dynamic oscillatory shear tests are common in rheology and have been used to investigate a wide range of soft matter and complex fluids including polymer melts and solutions, block copolymers, biological macromolecules, polyelectrolytes, surfactants, suspensions, emulsions, and beyond. More specifically, small amplitude oscillatory shear (SAOS) tests have become the canonical method for probing the linear viscoelastic properties of these complex fluids because of the firm theoretical background and the ease of implementing suitable test protocols. However, in most processing operations the deformations can be large and rapid: it is therefore the nonlinear material properties that control the system response. A full sample characterization thus requires well-defined nonlinear test protocols. Consequently, there has been a recent renewal of interest in exploiting large amplitude oscillatory shear (LAOS) tests to investigate and quantify the nonlinear viscoelastic behavior of complex fluids. In terms of the experimental input, both LAOS and SAOS require the user to select appropriate ranges of strain amplitude (γ0) and frequency (ω). However, there is a distinct difference in the analysis of experimental output, i.e. the material response. At sufficiently large strain amplitude, the material response will become nonlinear in LAOS tests and the familiar material functions used to quantify the linear behavior in SAOS tests are no longer sufficient. For example, the definitions of the linear viscoelastic moduli G' (ω) and G"(ω) are based inherently on the assumption that the stress response is purely sinusoidal (linear). However, a nonlinear stress response is not a perfect sinusoid, and therefore the viscoelastic moduli are not uniquely defined; other methods are needed for quantifying the nonlinear material response under LAOS deformation. In this presentation, I first summarize the typical nonlinear responses observed with complex fluids under LAOS deformations, then introduce and critically compare several methods that quantify the nonlinear oscillatory stress response. I show that LAOS characterization is a rigorous test for rheological models and advanced quality control. ----------------------------------------------------------------------------------------

You-Yeon Won

Professor

Davidson School of Chemical Engineering Purdue University Forney Hall of Chemical Engineering 480 Stadium Mall Drive West Lafayette, IN 47907-2100 Phone: (765)494-4077 https://engineering.purdue.edu/ChE/People/ptProfile?id=11263

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