How do we characterize complex materials and interfaces for better material design?

The study of complex materials and characterization of their mechanical properties has a long history, with the modern founding of the term “rheology,” dating to 1929. At its core, rheology looks to understand what internal mechanisms dictate a materials response to deformation. In the Christopher lab, we focus on developing novel rheological, microscopy, microfluidic, and simulation methods to better understand the mechanisms that control viscoelasticity of high interface systems, biofilms, and colloidal suspensions. We apply what we learn to improve the utility and better control these materials for commercial product development, medical treatment, and advanced manufacturing. Today, I will give a general overview of several projects my lab has tackled in my time at Texas Tech, 

• It has long been known that liquid interfaces with adhered particles have distinct interfacial viscoelasticity that impacts the bulk properties of Pickering emulsions. In my lab we have developed various experimental and simulation techniques to understand how particles adsorb to an interface, interparticle forces affect interfacial microstructure, and microstructure impacts interfacial viscoelasticity. Our results provide means to engineer emulsion properties in a controlled and predictable way.
• Biofilm, communities of bacteria embedded in a self-secreted hydrogel, impact disease and industry. The viscoelasticity of these systems impacts their efficacy and/or ease of removal. Using both interfacial and microrheology, we have characterized the development of P. Aeruginosa biofilms in a range of conditions to understand the relationships between interface, environment, and biology on their mechanical properties. We show here how it is possible to use rheology to understand biological functionality and engineer viscoelasticity of these materials.
• 3D printing of colloidal suspensions has applications in ceramics, energetics, and industrial manufacturing. However, development of inks for these applications is severely limited by a lack of understanding in how changes to ink composition affect printability and end use properties. Studying model systems, we have shown that there are in fact robust means to use basic rheological tests to predict ink’s printability. Furthermore, we have shown how printing parameters can be used to modify end use properties of inks without changing composition.

Dr. Christopher is the associate chair of graduate studies and a professor in the Department of Mechanical Engineering at Texas Tech University, where he has worked since 2011. He received a BS in Mechanical Engineering (2002) and a BA in Film (2003) from Columbia University. He attended Carnegie Mellon and graduated with a PhD in Mechanical engineering and a MS in Chemical Engineering in 2008. Afterwards, he spent 2 years in the Polymers Division of the National Institute of Standards and Technology as a NRC Postdoc. His research focuses on studying the rheology and flow of complex fluids and interfaces through uniquely developed microfluidics, rheology, and computational tools. Since beginning work at Texas Tech, he has been named a Whitacre Research Fellow and won the TA Distinguished Young Rheologist award.