Control of Anisotropic Reinforcement Particles for New Families of Bioinspired Materials

Randall Erb
ETH Zurich
Monday, April 2, 2012
Duke University | 2201 Hudson Hall | 10am

Recently, we have found an ultra-high magnetic response in stiff anisotropic platelet particles by adsorbing nominal amounts of magnetite nanoparticles onto the surface of the metal oxide. This modification allows for the remote control of particle orientation and spatial positioning under magnetic fields only an order of magnitude larger than the Earth’s magnetic field. This level of control, among numerous exciting possibilities, can lead to the positioning of particle reinforcement in manmade materials that mimics the structures found in natural systems such as seashells or mammalian bone.

We have developed an energy model for these particle suspensions that explain this ultrahigh response and suggest the key parameters essential in these systems. To help validate these parameters, we consider an idealized system and analyze the dynamic response of isolated platelets under magnetic fields. We find that using theoretical Perrin friction factors, originally developed to describe rotational drag for anisotropic molecules, we can precisely predict the interplay between magnetic, viscous and gravitational torques on these particles. We extend our model to describe the alignment of the platelets second major axis under rotating magnetic fields. We have found a relationship between the viscosity of the suspension and the critical frequency required to change from ‘rolling’ to ‘fully-aligned’ modes.

Finally, we use these techniques to create a family of advanced materials exhibiting 3-d reinforcements, spatial gradients, and various deliberate alignments. These composites exhibit the 3-D reinforced biological structures predicted to have enhanced material properties, such as higher stiffness and ‘wear-free’ characteristics. We also will briefly highlight the possibility of using these systems in swellable materials to produce anisotropic and directed
swelling.