The multiscale self-assembly of atoms, molecules, and particles is the origin of all physical mesoscopic matter. The spatial organization, symmetry, and physical properties of the assembled structures are determined by thermodynamic characteristics of their building blocks. Colloidal particles are emerging as models for understanding governing principles of directed-assembly and non-equilibrium response of advanced materials. Here, I will present the concept of using external field driven interactions to direct the assembly and spatial migration of colloids.

Poly(N-isopropylacrylamide) (PNIPAM) is a well-known thermo-sensitive polymer that exhibits a low critical solution temperature (LCST) at around 305 K in aqueous solutions. The coil-to-globule transition of PNIPAM can be induced by a small temperature variation (1~2 K) accompanied by abrupt conformational changes. The LCST behavior of PNIPAM has been attracting research interests for several decades because of its implication in a number of living phenomena, especially on protein folding and DNA packing.