(271a) Directing Colloidal Self-Assembly
In this talk, I will discuss the use of directing electric and magnetic fields to circumvent kinetic bottle necks during colloidal self-assembly. A useful model system has been suspensions of superparamagnetic colloids. In a strong, steady magnetic field, paramagnetic colloids form system-spanning, kinetically arrested networks similar to a gel. From this state, it is possible to phase separate and condense the suspension by toggling the external field . In its evolution towards the equilibrium state, the suspension undergoes a Rayleigh-Plateau instability for a range of field strengths and toggle frequencies . The particles initially chain together to form a percolated network that coarsens diffusively. With time, the surface of the growing domains in the network become unstable. The amplitude of the waves eventually reaches a critical value and the columns pinch off and condense into ellipsoidal structures.
A key advantage of directed self-assembly in toggled fields is the relatively large range of field-strengths, analogous to effective temperatures, that lead to phase separation. Our results demonstrate how kinetic barriers to a colloidal phase transition are subverted through measured, periodic variation of driving forces while retaining the strengths of a â??bottom-upâ? self-assembly process.
 Swan, J. W. et al., Proc. Natl. Acad. Sci. U. S. A. 2012, 109, 16023â??16028.
 Swan, J. W.; Bauer, J. L.; Liu, Y.; Furst, E. M. Soft Matter 2014, 10, 1102â??1109.