The AnnaLab Website

From the CCFE Website: CFE faculty Anna and Walker have intitated a new project to quantify the interfacial aspects of dispersants used to treat oil spills in marine environments. A three year project will characterize the impact of components of dispersants on model oil-water systems.

The project is funded through the  Consortium for the Molecular Engineering of Dispersant Systems (C-MEDS) awarded to Tulane University.

Our paper entitled “Interfacial Dynamics and Rheology of Polymer-Grafted Nanoparticles at Air-Water and Xylene-Water interfaces,” by N.J. Alvarez, S.L. Anna, T. Saigal, R.D. Tilton, and L.M. Walker, was published in Langmuir, 28 (2012) 8052 – 8063.

Dynamics of polymer grafted nanoparticles adsorbing at oil/water and air/water interfaces are characterized along with mechanics of the resulting particle‐laden interfaces.

Abstract: Particle-stabilized emulsions and foams offer a number of advantages over traditional surfactant-stabilized systems, most notably a greater stability against coalescence and coarsening. Nanoparticles are often less effective than micrometer-scale colloidal particles as stabilizers, but nanoparticles grafted with polymers can be particularly effective emulsifiers, stabilizing emulsions for long times at very low concentrations. In this work, we characterize the long-time and dynamic interfacial tension reduction by polymer-grafted nanoparticles adsorbing from suspension and the corresponding dilatational moduli for both xylene–water and air–water interfaces. The dilatational moduli at both types of interfaces are measured by a forced sinusoidal oscillation of the interface. Surface tension measurements at the air–water interface are interpreted with the aid of independent ellipsometry measurements of surface excess concentrations. The results suggest that the ability of polymer-grafted nanoparticles to produce significant surface and interfacial tension reductions and dilatational moduli at very low surface coverage is a key factor underlying their ability to stabilize Pickering emulsions at extremely low concentrations.

Our paper entitled “Tuning Bubbly Structures in Microchannels,” by S.M. Vuong and S.L. Anna, was published in Biomicrofluidics, Special Issue on Multiphase Microfluidics, Guest Ed. Saif Khan, 6 (2012) 022004.

Bubble shapes and structures organized in terms of volume fraction and bubble size

Abstract: Foams have many useful applications that arise from the structure and size distribution of the bubbles within them. Microfluidics allows for the rapid formation of uniform bubbles, where bubble size and volume fraction are functions of the input gas pressure, liquid flow rate, and device geometry. After formation, the microchannel confines the bubbles and determines the resulting foam structure. Bubbly structures can vary from a single row (“dripping”), to multiple rows (“alternating”), to densely packed bubbles (“bamboo” and dry foams). We show that each configuration arises in a distinct region of the operating space defined by bubble volume and volume fraction. We describe the boundaries between these regions using geometric arguments and show that the boundaries are functions of the channel aspect ratio. We compare these geometric arguments with foam structures observed in experiments using flow-focusing, T-junction, and co-flow designs to generate nitrogen bubbles in surfactant-stabilized water and water droplets in surfactant-stabilized oil. The outcome of this work is a set of design parameters that can be used to achieve desired foam structures as a function of device geometry and experimental control parameters.

Anthony Kotula was one of 10 students selected to present a talk in the Langmuir Student Awards session at the 86th ACS Colloid and Surface Science Symposium.  The conference will be held at Johns Hopkins University in Baltimore, MD, June 10-13. 2012.  Anthony’s talk is entitled “Dynamics of adsorption of particles to fluid-fluid interfaces in a microchannel”.  Congratulations to Anthony!

Shelley L. Anna was selected as an Honorable Mention of a Carnegie Science Award in the category of Emerging Female Scientist.  This award will be celebrated during the 16th Annual Carnegie Science Awards, to be held May 11, 2012.

Professor Shelley Anna was appointed the Russell V. Trader Career Faculty Fellow effective November 1, 2011, for two years. Faculty Career Development Chairs are term professorships of one to three years that recognize outstanding young faculty in the college and give them the freedom to engage in creative ventures that are not readily supported by traditional granting agencies. Through their work, these young educators raise the level of performance of all around them and bring honor to the institution.

Note: Russell Trader attended Carnegie Institute of Technology c. 1920 and studied Machine Construction in the College of Industries, the forerunner of Mechanical Engineering. Upon the death of his wife, Rachael, in 2000, Carnegie Mellon University received funds to establish the Russell V. Trader Career Faculty Fund in Mechanical Engineering as a lasting memorial to Russell Trader. The principal of this fund is used to provide faculty support through research, fellowships and equipment funding.