Dynamics of self-propelling magnetic colloids
Mon, Mar 10
2:00 PM — 3:15 PM
Steinman Hall 160 - Lecture Hall
The ChE Department would like to welcome Ubaldo Cordova-FigueroaAbstract:
As the synthesis of machinery and tools on the size of macromolecules or colloidal particles become more important, plenty of fundamental questions must be answered in order to govern and control this spatial dimension. Energy at nano- or micro-scales can be harnessed more intelligently and used to power these machines without the need of external stimuli. In the last decade, multiple pioneer studies have shown that asymmetric chemical reactions at the surface of a microparticle immersed in a fluid can induce self-propulsion. These 'active' colloidal particles exhibit a ballistic motion that becomes diffusive at long times. In addition, it has been found that pairs of these particles interact with each other in a Coulomb-like fashion. Another important challenge is control over the directionality of these ‘motors’, which is commonly achieved using magnetic fields. Magnetic colloids interact via dipole-dipole interactions and form aggregates of various sizes and lengths. It is well understood that by enhancing diffusion, in this case by self-propulsion, the time scale for particle interactions is reduced such that aggregates are formed faster in attractive colloidal suspensions. It is unclear, however, the effect of self-propulsion of magnetic particles, particularly at very high propulsion speeds, to cluster size formation in relation to the applied magnetic field and strength of interparticle interactions. In this work, we develop a simple colloidal model consisting of a monodisperse suspension of self-propelling magnetic particles immersed in a Newtonian fluid subject to a constant external magnetic field. First, the diffusion and mean velocity of a self-propelling magnetic colloid will be discussed as preamble to understand the effect of multi-particle interactions. Using Brownian dynamics simulation, we interrogate the suspension over time by measuring cluster properties, such as mean effective size and number of clusters. All these properties are then compared for various particle speeds, magnetic field strengths, and dipolar coupling constants. Our goal is to develop a deep understanding of these systems as potential dynamic units that could be used in applications, such as self-healing materials, drug and cargo delivery, sensors, and lab-in-a-chip devices.
Dr. Ubaldo M. Córdova-Figueroa completed his BS degree in Chemical Engineering at the University of Puerto Rico at Mayagüez (UPRM) in 2003. That same year, he went to Pasadena, CA to pursue a MS and PhD in Chemical Engineering at the California Institute of Technology. Under Prof. John F. Brady’s advisement, he studied recent experiments showing catalytically driven propulsion at nano- and micro-scales appearing as a possible mechanism for the transport of colloidal particles. During his PhD work, he also devoted time to study macro- and microrheology of colloidal suspensions using Brownian dynamics simulations and propulsion mechanisms at low Reynolds number flow. This experience gave him the opportunity to become an expert in colloidal transport, the exploitation of chemical reactions, and in the use of analytical and computational methods. Nevertheless, the most important outcome of this stage in his life was the sudden deep and genuine interest in transport phenomena and colloidal hydrodynamics and the need to teach others what he was learning. In 2008 he obtained his PhD and returned to UPRM where he is now an Associate Professor in Chemical Engineering. In 2011, he was awarded the prestigious NSF CAREER award, and in 2013 as Distinguished Professor in Chemical Engineering. His research experience includes the authoring of peer-reviewed articles in Physics Review Letters, Soft Matter, Journal of Fluid Mechanics, Advanced Functional Materials, and Nature Chemistry. His research group considers a wide range of topics in transport phenomena and colloidal physics with special attention to propulsion mechanisms at low Reynolds numbers.