MRI: Colloidal Characterization Capability through Combined DLS-ACS Analysis

St. Cloud State University, Saint Cloud MN

Investigators

Abstract

Technical This award from the Major Research Instrumentation Program funds the establishment of an integrated particle property distribution measurements system on a single ferronematic sample. Colloid dynamics are particularly complex when strong interactions amongst the suspended particles can overwhelm the fluctuation-dissipation and thermalization. This problem is prominently manifest in ferrofluids where long range magnetic dipole interactions can lead to gradual agglomeration and loss of desirable colloidal characteristics. A particular class of ferrofluids known as ferronematics, where specially fabricated ferromagnetic nano-particles are suspended in liquid crystal host matrices, is gaining increasing popularity due to their strong magneto-optical response. Long term stability of ferronematics depend on the incorporation of surfactants that support sufficient electric charge or steric effects to counteract the inter-particle magnetic attraction. Proper dynamical representation of ferronematics requires that the mathematical dynamical equation be modified to incorporate the inter-particle forces and be averaged over the entire ensemble of particle physical, magnetic, and electric properties. Dynamic light scattering with zeta-potential capability is used to determine particle size and surface charge and then that information is fed forward to the ac susceptibility measurement with swept frequency capability that characterizes particle magnetics as a function of its physical dimension. The combined distributions are then used to develop and validate advanced dynamical models and to evaluate colloid stability against agglomeration and sedimentation. Non Technical As the science and technology of nanoparticles evolve, various classes of liquid suspended nanoparticles (colloids) are proving to be of particular importance to science, engineering, and environmental applications. Understanding the critical nanoparticle parameters that differentiate dispersed suspension from sedimentation or agglomeration will lead to superior classes of engineered materials such as ferrofluids, nano-drug delivery agents, and biofuels, as well as improved environmental understanding of hydrologic flows in oceans and lakes. This award from the Major Research Instrumentation program funds the establishment of a complementary pair of characterization instruments. The first tool determines particle size and surface charge distributions using Dynamic Light Scattering (DLS). That information is then fed forward to a magnetic measurement, AC Susceptibility (ACS), that utilizes the same colloid sample and characterizes the particle magnetization distribution and magnetic switching behavior. DLS will also be used for studying hydrologic sedimentation research such as dynamics density and turbidity flows. In addition to colloidal research, several undergraduate classes in the departments of chemistry, physics, and atmospheric and hydrological sciences will incorporate these characterization techniques in their instructional laboratories.