Dynamic Self Assembled Magnetic Colloids

Thomas Fischer
The University of Bayreuth
Thursday, February 20, 2014
Duke University, Schiciano B | 4:30pm

Technology uses scientific laws for the construction of devices. These devices do not self assemble, but top down principles are used. Specific external, not intrinsic plans, are followed in plants to build the device. Nature uses a different principle. The plan of a biological life form is stored intrinsically. Build up follows the bottom up principle and the object self assembles from its building blocks. Bottom up self assembly can be divided into static and dynamic self assembly. Static self assembled objects adapt their equilibrium structure via relaxation processes from a non equilibrium dispersion of building blocks. Once the equilibrium structure is reached the structure remains in equilibrium incapable of performing work to its surroundings. Static self assembled structures therefore fulfil no active function. Dynamic self assembled structures maintain there structure by feeding from a source of energy and steadily producing entropy that protects the structure from decay. Part of the energy consumed can be used to perform work to the surroundings. Dynamic self assembled structures can fulfil a function and act as machines or motors.

In biology the smallest dynamic self assembled structure with function is called an organelle. Organelles are structures that due to their complexity of interactions and variety of building blocks are too difficult to describe in a rigorous physical sense. Our desire to understand life fails using first principle physics fails for simplest biological organelles. There are two possibilities to overcome such difficulties. One starts to investigate simplest biological objects such as for example viruses. Another approach is, to dynamically self assemble artificial structures with fully understood interactions between its building blocks that perform a simple function.

The present work reports on the dynamic self assembly of dynamic colloidal structures. Magnetic colloidal particles that on a mesoscopic long range scale interact via well understood magnetic dipole interactions are used as building blocks. We show that a suitable mixture of paramagnetic and/or diamagnetic colloids in a dynamic but spatially homogeneous magnetic field leads to the formation of dynamic self assembled structures that may perform simple functions.