Ms. Lisa Murray
School of Materials Engineering
BS Materials Engineering, Iowa State University
Graduation: Summer 2015
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Project: Characterization of Shear Banding in a Structured Fluid
Shear banding phenomena have been theorized to occur in concentrated magnesium oxide suspensions stabilized with a poly(acrylic acid)-based comb-polymer. The evolution of the polymer-induced particle microstructure over time results in stress overshoots, which are observed in shear start-up tests. Two particle size distributions are explored: a narrow distribution of 0.5 - 40 microns and a wide distribution of 0.5 to 400 microns. Smaller particle sizes evoke a greater overshoot magnitude while the wide size distribution yielded multiple overshoots with varied peak magnitudes. Based on the overshoots of shear start-ups and the shear-resistance demonstrated in creep tests, two particle microstructures are proposed to form during shear based on adsorbed polymer-polymer interactions. The narrow size distribution suspension is theorized to create polymer-entangled particle networks while the wide distribution follows evidence of hydrocluster formation. Varying concentration of comb-polymer also impacts the entanglement of the comb-polymer side chains through diminishing the affects of particle networks. This work has been published in the Journal of Applied Polymer Science (doi: 10.1002/app.40429).
In addition to shear banding, Lisa conducts research on other on-going rheology projects. Her current focus is on the flow behavior of free polymer chains in cementitious suspensions for analysis of chain aggregation and polymer-particle interactions under shear. For this work Lisa supervises Emily Soltys, an undergraduate research assistant.
Research on lignin-based polymer additives for cements is currently underway with an emphasis on viscosity reduction and the influence of polymer structure on suspension processing. This project is in collaboration with Prof. Newell Washburn and Chetali Gupta at Carnegie Mellon University.
Further research endeavors include the characterization of polymer-grafted silica nanoparticles and the construction of an ultrasonic speckle velocimetry (USV) rheometer system. Guidence for the USV system is given by Prof. Sebastein Manneville at ENS-Lyon, France.
Lisa graduated in 2011 from Iowa State University with a BS in Materials Engineering, specializing in electronic materials and polymers, and minoring in Latin. During her undergraduate years Lisa interned twice at 3M, working with TEM tomography and X-ray micro-CT materials properties analysis. She then spent a year at Johns Hopkins University researching semiconducting polymer nanoparticles and entered Purdue as a materials engineering PhD student in August 2012. One of Lisa’s greatest achievements is being an NSF fellowship recipient and she enjoys being involved with professional organizations and campus groups, including the Women in Engineering Mentoring Program, MSE Graduate Student Safety Committee, and the Purdue Salsa Dancing Club.