Working with scientists at the National Institutes of Standards and Technology Center for Neutron Research and the Institute Laue Langevin, Grenoble France, we have developed instruments for the measurement of microstructure under steady and dynamic shear flow. Unique instruments capable of probing the 1,2 plane of shear flow are now available for the general user community. Read more about this instrument and watch the published instructional video at JOVE, Gurnon et al. 2014, and a C&EN article about neutrons, as well as an explanatory video about neutron scattering in general featuring Sir Patrick Stewart from the European Spallation Source.
Working with scientists at Genentech and the National Institutes of Standards and Technology Center for Neutron Research, we are measuring the properties of mAbs in concentrated solution using neutron, light, Cryo-TEM, rheology and allied methods. The sketch is from Dr. Rob Dimeo, the director of the NIST Center for neutron research, a talented scientific illustrator, who captured the recent award lecture of Dr. Doug Godfrin at the ACNS 2016.
Wormlike Micelles are self-assembled surfactant mesophases with viscoelasticity and special nonlinear rheological properties. We study the thermodynamics and rheology of these complex fluids using advanced rheological, neutron scattering techniques, cryo-TEM, light scattering, and allied methods. WLMs are broadly used in the consumer products (e.g. shampoo) as well as drag reducing agents and importantly, in oil recovery. Learn more about our research on branching in WLMs in a recent COCIS review here.
Ionic Liquids: Self-Assembly and Colloidal Dispersion
Ionic liquids are room temperature salts with special properties, such as low volatility and high thermal stability that make them attractive for a broad range of uses from lubricants to green solvents and CO2 capture medium. Our research focuses on measuring, understanding and predicting the self-assembly of surfactants and block copolymers as well as the dispersion of nanoparticles and colloids in ionic liquids. We use characterization tools such as neutron scattering, light scattering, TEM, ITC, etc… and study model systems both at equilibrium and under flow. We use theories and simulations based molecular dynamics to understand these measurements and make predictions. You can read more about our current work on ionic liquids here.
Shear Thickening Colloidal Dispersions
Shear Thickening Colloidal Dispersions are fascinating field-responsive or “smart” materials that are of great scientific curiosity as well as significant technological importance. We use advanced rheo-optic and neutron scattering methods combined with rheology to understand shear thickening at a fundamental level. This understanding is translated to practice through the development of advanced body armor, puncture resistant medical gloves, space suits, concussion resistant protective equipment for football (US patents #7,226,878; 7,498,276; 7,825,045 and numerous recent filings), as well as on our company’s web site http://www.stf-technologies.com/. A recent review article with Prof. John Brady on shear thickening is here, and you can read more about this Colloidal Suspension Rheology.
How do Colloidal Gels form and Flow?
Colloidal Dispersions form gels due to interparticle attractions. Our studies on model, thermoreversible colloidal gels using neutron and light scattering, rheology and simulations have established the gel state diagram for the adhesive hard spheres. This was shown by simulation to correspond to rigidity percolation. We have also established the effect of gravity on setting the minimum stable gel concentration, and have established differences between colloidal gels, glasses, and phase separated gelling systems. These viscoelastic materials show interesting flow behavior that has been recently probed by rheo-SANS. We are now exploring the role of particle shape on gel dynamical arrest.
Bioinspired Polymer Materials
From the development of intricate surface topography (i.e. superadhesion of gecko’s feet) to triggered self healing of material damage, nature has demonstrated remarkable material design and properties. Our research focuses on the development of bio-inspired polymer materials which include (1) material wrinkling/buckling on elastomers and (2) self-healing polymer systems capable of regenerating functionality after material damage.
Foods such as ketchup, some paints and inks, and concentrated colloidal pastes and slurries often show a time-dependent rheology known as thixotropy. It is defined as: “the continuous decrease of viscosity with time when flow is applied to a sample that has been previously at reset and the subsequent recovery of viscosity in time when the flow is discontinued.” This time-dependent rheology arises because flow can induce reversible and irreversible structural changes in dispersions. The analysis of flow effects on microstructure and rheology remains one of the challenging problems in colloid science. The microstructural changes due to flow are quite complex and not fully understood. Our NSF funded research with Prof. Antony Beris has as a goal the development of a new thermodynamically consistent model for thixotropic suspension rheology. Read more about thixotropy in a recent review article in Advances in Colloid and Interface Science.